ClassLoader源码
最近找工作，面试网易和微策略，都问到了ClassLoader这个东西，看来应该是比较重要的，所以在这总结一下，嗯，类源码有点长，慢慢看吧。
翻译一下，不当之处欢迎指正。
/**
* A class loader is an object that is responsible for loading classes. The 翻译：ClassLoader是一个用于加载类的对象。它是一个抽象类。
* class <tt>ClassLoader</tt> is an abstract class. Given the <a 给出一个类的二进制名称，它能够定位并且产生用于构造类的数据。
* href="#name">binary name</a> of a class, a class loader should attempt to 一个典型的策略就是将名称转换为文件名，然后从文件系统中读取类文件。
* locate or generate data that constitutes a definition for the class. A
* typical strategy is to transform the name into a file name and then read a
* "class file" of that name from a file system.
*
* <p> Every {@link Class <tt>Class</tt>} object contains a {@link 每个对象都包含了一个相应类加载器的引用，可以通过getClassLoader()
* Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined 获取这个引用。
* it.
*
* <p> <tt>Class</tt> objects for array classes are not created by class 数组类的类对象不是类加载器创造的，而是java运行时要求自动创造的。
* loaders, but are created automatically as required by the Java runtime. 数组类的类加载器，和它的元素类型的类加载器一样，通过getClassLoader()
* The class loader for an array class, as returned by {@link 返回；如果元素类型是一个泛型，那么这个数组类就没有类加载器。
* Class#getClassLoader()} is the same as the class loader for its element
* type; if the element type is a primitive type, then the array class has no
* class loader.
*
* <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to 实现了ClassLoader子类的应用是为了扩展一些行为，这些行为
* extend the manner in which the Java virtual machine dynamically loads 能够使java虚拟机动态加载类。
* classes.
*
* <p> Class loaders may typically be used by security managers to indicate 类加载器经常被用来安全领域的安全管理。（这地方翻译不够精确，使用*号mark一下，
* security domains. 后面使用*缘由与此处相同）
*
* <p> The <tt>ClassLoader</tt> class uses a delegation model to search for ClassLoader使用了一个代理模型来寻找类和资源。
* classes and resources. Each instance of <tt>ClassLoader</tt> has an 每个ClassLoader的实例都有一个相关的父类加载器。
* associated parent class loader. When requested to find a class or 当要求找到一个类或者资源的时候，ClassLoader的实例将会使用代理先寻找父类的类和资源，
* resource, a <tt>ClassLoader</tt> instance will delegate the search for the 然后找到这个类本身的类和资源。java虚拟机内嵌的类加载器，被称作
* class or resource to its parent class loader before attempting to find the 类加载器引导程序，虽然它本身没有父类但是它可能会充当某一个类加载器实例的父类。（*）
* class or resource itself. The virtual machine's built-in class loader,
* called the "bootstrap class loader", does not itself have a parent but may
* serve as the parent of a <tt>ClassLoader</tt> instance.
*
* <p> Class loaders that support concurrent loading of classes are known as 支持并发式加载类的类加载器最广为人知的是,类加载器的并行能力和要求
* <em>parallel capable</em> class loaders and are required to register 在它们的类初始化的时候，通过调用registerAsParallelCapable()方法来注册类加载器本身。
* themselves at their class initialization time by invoking the
* {@link
* #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
* method. Note that the <tt>ClassLoader</tt> class is registered as parallel 需要注意的是ClassLoader这个类默认被注册为拥有并发能力。
* capable by default. However, its subclasses still need to register themselves 然而，如果要保证ClassLoader的子类具有并发能力的话仍然需要注册它们
* if they are parallel capable. <br> 本身。
* In environments in which the delegation model is not strictly 在代理模式不是严格分级的环境下，
* hierarchical, class loaders need to be parallel capable, otherwise class 类加载器需要具有并发能力，否则类加载可能会造成死锁，
* loading can lead to deadlocks because the loader lock is held for the 因为loader lock在类加载过程期间一直被持有。
* duration of the class loading process (see {@link #loadClass
* <tt>loadClass</tt>} methods).
*
* <p> Normally, the Java virtual machine loads classes from the local file 通常的话，java虚拟机以一种平台相关的方式从本地文件系统
* system in a platform-dependent manner. For example, on UNIX systems, the 中加载类。例如，在unix系统上，虚拟机将会从CLSSPATH环境变量
* virtual machine loads classes from the directory defined by the 定义的目录下加载类。
* <tt>CLASSPATH</tt> environment variable.
*
* <p> However, some classes may not originate from a file; they may originate 然而，一些类可能原本不是来自文件；它们可能来自于
* from other sources, such as the network, or they could be constructed by an 其它的一些资源，例如网络，或者它们能够通过一个应用来构造。
* application. The method {@link #defineClass(String, byte[], int, int) defineClass(String ,byte[],int,int)方法将一个数组的字节
* <tt>defineClass</tt>} converts an array of bytes into an instance of class 转换成一个类的实例。这个新的类实例可以使用newInstance()方法来创建。
* <tt>Class</tt>. Instances of this newly defined class can be created using
* {@link Class#newInstance <tt>Class.newInstance</tt>}.
*
* <p> The methods and constructors of objects created by a class loader may 对象的方法和构造器通过类加载器来创建，可能会涉及到其它的类。
* reference other classes. To determine the class(es) referred to, the Java 为了确定所涉及到的类，java虚拟机调用原本创建类的类加载器的loadclass()
* virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of 方法。
* the class loader that originally created the class.
*
* <p> For example, an application could create a network class loader to 例如，一个应用可能会创建一个网络类加载器来从服务器上下载类文件。
* download class files from a server. Sample code might look like: 样例代码像这样子：
*
* <blockquote><pre>
* ClassLoader loader = new NetworkClassLoader(host, port);
* Object main = loader.loadClass("Main", true).newInstance();
* . . .
* </pre></blockquote>
*
* <p> The network class loader subclass must define the methods {@link 这个网络类加载器的子类必须定义findClass()方法
* #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class 和loadClassData()方法用来从网络中加载类。
* from the network. Once it has downloaded the bytes that make up the class, 一旦它下载完了组成类的字节，它就会使用defineClass()
* it should use the method {@link #defineClass <tt>defineClass</tt>} to 方法来创建一个类的实例。一个简单的实现是：
* create a class instance. A sample implementation is:
*
* <blockquote><pre>
* class NetworkClassLoader extends ClassLoader {
* String host;
* int port;
*
* public Class findClass(String name) {
* byte[] b = loadClassData(name);
* return defineClass(name, b, 0, b.length);
* }
*
* private byte[] loadClassData(String name) {
* // load the class data from the connection
* . . .
* }
* }
* </pre></blockquote>
*
* <h3> <a name="name">Binary names</a> </h3>
*
* <p> Any class name provided as a {@link String} parameter to methods in
* <tt>ClassLoader</tt> must be a binary name as defined by
* <cite>The Java™ Language Specification</cite>.
*
* <p> Examples of valid class names include:
* <blockquote><pre>
* "java.lang.String"
* "javax.swing.JSpinner$DefaultEditor"
* "java.security.KeyStore$Builder$FileBuilder$1"
* "java.net.URLClassLoader$3$1"
* </pre></blockquote>
*
* @see #resolveClass(Class)
* @since 1.0
*/
public abstract class ClassLoader {
private static native void registerNatives();
static {
registerNatives();
}
// The parent class loader for delegation
// Note: VM hardcoded the offset of this field, thus all new fields
// must be added *after* it.
private final ClassLoader parent;
/**
* Encapsulates the set of parallel capable loader types.
*/
private static class ParallelLoaders {
private ParallelLoaders() {}
// the set of parallel capable loader types
private static final Set<Class<? extends ClassLoader>> loaderTypes =
Collections.newSetFromMap(
new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
static {
synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
}
/**
* Registers the given class loader type as parallel capabale.
* Returns {@code true} is successfully registered; {@code false} if
* loader's super class is not registered.
*/
static boolean register(Class<? extends ClassLoader> c) {
synchronized (loaderTypes) {
if (loaderTypes.contains(c.getSuperclass())) {
// register the class loader as parallel capable
// if and only if all of its super classes are.
// Note: given current classloading sequence, if
// the immediate super class is parallel capable,
// all the super classes higher up must be too.
loaderTypes.add(c);
return true;
} else {
return false;
}
}
}
/**
* Returns {@code true} if the given class loader type is
* registered as parallel capable.
*/
static boolean isRegistered(Class<? extends ClassLoader> c) {
synchronized (loaderTypes) {
return loaderTypes.contains(c);
}
}
}
// Maps class name to the corresponding lock object when the current
// class loader is parallel capable.
// Note: VM also uses this field to decide if the current class loader
// is parallel capable and the appropriate lock object for class loading.
private final ConcurrentHashMap<String, Object> parallelLockMap;
// Hashtable that maps packages to certs
private final Map <String, Certificate[]> package2certs;
// Shared among all packages with unsigned classes
private static final Certificate[] nocerts = new Certificate[0];
// The classes loaded by this class loader. The only purpose of this table
// is to keep the classes from being GC'ed until the loader is GC'ed.
private final Vector<Class<?>> classes = new Vector<>();
// The "default" domain. Set as the default ProtectionDomain on newly
// created classes.
private final ProtectionDomain defaultDomain =
new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
null, this, null);
// The initiating protection domains for all classes loaded by this loader
private final Set<ProtectionDomain> domains;
// Invoked by the VM to record every loaded class with this loader.
void addClass(Class<?> c) {
classes.addElement(c);
}
// The packages defined in this class loader. Each package name is mapped
// to its corresponding Package object.
// @GuardedBy("itself")
private final HashMap<String, Package> packages = new HashMap<>();
private static Void checkCreateClassLoader() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkCreateClassLoader();
}
return null;
}
private ClassLoader(Void unused, ClassLoader parent) {
this.parent = parent;
if (ParallelLoaders.isRegistered(this.getClass())) {
parallelLockMap = new ConcurrentHashMap<>();
package2certs = new ConcurrentHashMap<>();
domains =
Collections.synchronizedSet(new HashSet<ProtectionDomain>());
assertionLock = new Object();
} else {
// no finer-grained lock; lock on the classloader instance
parallelLockMap = null;
package2certs = new Hashtable<>();
domains = new HashSet<>();
assertionLock = this;
}
}
/**
* Creates a new class loader using the specified parent class loader for
* delegation.
*
* <p> If there is a security manager, its {@link
* SecurityManager#checkCreateClassLoader()
* <tt>checkCreateClassLoader</tt>} method is invoked. This may result in
* a security exception. </p>
*
* @param parent
* The parent class loader
*
* @throws SecurityException
* If a security manager exists and its
* <tt>checkCreateClassLoader</tt> method doesn't allow creation
* of a new class loader.
*
* @since 1.2
*/
protected ClassLoader(ClassLoader parent) {
this(checkCreateClassLoader(), parent);
}
/**
* Creates a new class loader using the <tt>ClassLoader</tt> returned by
* the method {@link #getSystemClassLoader()
* <tt>getSystemClassLoader()</tt>} as the parent class loader.
*
* <p> If there is a security manager, its {@link
* SecurityManager#checkCreateClassLoader()
* <tt>checkCreateClassLoader</tt>} method is invoked. This may result in
* a security exception. </p>
*
* @throws SecurityException
* If a security manager exists and its
* <tt>checkCreateClassLoader</tt> method doesn't allow creation
* of a new class loader.
*/
protected ClassLoader() {
this(checkCreateClassLoader(), getSystemClassLoader());
}
// -- Class --
/**
* Loads the class with the specified <a href="#name">binary name</a>.
* This method searches for classes in the same manner as the {@link
* #loadClass(String, boolean)} method. It is invoked by the Java virtual
* machine to resolve class references. Invoking this method is equivalent
* to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
* false)</tt>}.
*
* @param name
* The <a href="#name">binary name</a> of the class
*
* @return The resulting <tt>Class</tt> object
*
* @throws ClassNotFoundException
* If the class was not found
*/
public Class<?> loadClass(String name) throws ClassNotFoundException {
return loadClass(name, false);
}
/**
* Loads the class with the specified <a href="#name">binary name</a>. The
* default implementation of this method searches for classes in the
* following order:
*
* <ol>
*
* <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
* has already been loaded. </p></li>
*
* <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
* on the parent class loader. If the parent is <tt>null</tt> the class
* loader built-in to the virtual machine is used, instead. </p></li>
*
* <li><p> Invoke the {@link #findClass(String)} method to find the
* class. </p></li>
*
* </ol>
*
* <p> If the class was found using the above steps, and the
* <tt>resolve</tt> flag is true, this method will then invoke the {@link
* #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
*
* <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
* #findClass(String)}, rather than this method. </p>
*
* <p> Unless overridden, this method synchronizes on the result of
* {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
* during the entire class loading process.
*
* @param name
* The <a href="#name">binary name</a> of the class
*
* @param resolve
* If <tt>true</tt> then resolve the class
*
* @return The resulting <tt>Class</tt> object
*
* @throws ClassNotFoundException
* If the class could not be found
*/
protected Class<?> loadClass(String name, boolean resolve)
throws ClassNotFoundException
{
synchronized (getClassLoadingLock(name)) {
// First, check if the class has already been loaded
Class<?> c = findLoadedClass(name);
if (c == null) {
long t0 = System.nanoTime();
try {
if (parent != null) {
c = parent.loadClass(name, false);
} else {
c = findBootstrapClassOrNull(name);
}
} catch (ClassNotFoundException e) {
// ClassNotFoundException thrown if class not found
// from the non-null parent class loader
}
if (c == null) {
// If still not found, then invoke findClass in order
// to find the class.
long t1 = System.nanoTime();
c = findClass(name);
// this is the defining class loader; record the stats
sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
sun.misc.PerfCounter.getFindClasses().increment();
}
}
if (resolve) {
resolveClass(c);
}
return c;
}
}
/**
* Returns the lock object for class loading operations.
* For backward compatibility, the default implementation of this method
* behaves as follows. If this ClassLoader object is registered as
* parallel capable, the method returns a dedicated object associated
* with the specified class name. Otherwise, the method returns this
* ClassLoader object.
*
* @param className
* The name of the to-be-loaded class
*
* @return the lock for class loading operations
*
* @throws NullPointerException
* If registered as parallel capable and <tt>className</tt> is null
*
* @see #loadClass(String, boolean)
*
* @since 1.7
*/
protected Object getClassLoadingLock(String className) {
Object lock = this;
if (parallelLockMap != null) {
Object newLock = new Object();
lock = parallelLockMap.putIfAbsent(className, newLock);
if (lock == null) {
lock = newLock;
}
}
return lock;
}
// This method is invoked by the virtual machine to load a class.
private Class<?> loadClassInternal(String name)
throws ClassNotFoundException
{
// For backward compatibility, explicitly lock on 'this' when
// the current class loader is not parallel capable.
if (parallelLockMap == null) {
synchronized (this) {
return loadClass(name);
}
} else {
return loadClass(name);
}
}
// Invoked by the VM after loading class with this loader.
private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
if (ReflectUtil.isNonPublicProxyClass(cls)) {
for (Class<?> intf: cls.getInterfaces()) {
checkPackageAccess(intf, pd);
}
return;
}
final String name = cls.getName();
final int i = name.lastIndexOf('.');
if (i != -1) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
sm.checkPackageAccess(name.substring(0, i));
return null;
}
}, new AccessControlContext(new ProtectionDomain[] {pd}));
}
}
domains.add(pd);
}
/**
* Finds the class with the specified <a href="#name">binary name</a>.
* This method should be overridden by class loader implementations that
* follow the delegation model for loading classes, and will be invoked by
* the {@link #loadClass <tt>loadClass</tt>} method after checking the
* parent class loader for the requested class. The default implementation
* throws a <tt>ClassNotFoundException</tt>.
*
* @param name
* The <a href="#name">binary name</a> of the class
*
* @return The resulting <tt>Class</tt> object
*
* @throws ClassNotFoundException
* If the class could not be found
*
* @since 1.2
*/
protected Class<?> findClass(String name) throws ClassNotFoundException {
throw new ClassNotFoundException(name);
}
/**
* Converts an array of bytes into an instance of class <tt>Class</tt>.
* Before the <tt>Class</tt> can be used it must be resolved. This method
* is deprecated in favor of the version that takes a <a
* href="#name">binary name</a> as its first argument, and is more secure.
*
* @param b
* The bytes that make up the class data. The bytes in positions
* <tt>off</tt> through <tt>off+len-1</tt> should have the format
* of a valid class file as defined by
* <cite>The Java™ Virtual Machine Specification</cite>.
*
* @param off
* The start offset in <tt>b</tt> of the class data
*
* @param len
* The length of the class data
*
* @return The <tt>Class</tt> object that was created from the specified
* class data
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws IndexOutOfBoundsException
* If either <tt>off</tt> or <tt>len</tt> is negative, or if
* <tt>off+len</tt> is greater than <tt>b.length</tt>.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class, or if an attempt is made
* to define a class in a package with a fully-qualified name
* that starts with "{@code java.}".
*
* @see #loadClass(String, boolean)
* @see #resolveClass(Class)
*
* @deprecated Replaced by {@link #defineClass(String, byte[], int, int)
* defineClass(String, byte[], int, int)}
*/
@Deprecated
protected final Class<?> defineClass(byte[] b, int off, int len)
throws ClassFormatError
{
return defineClass(null, b, off, len, null);
}
/**
* Converts an array of bytes into an instance of class <tt>Class</tt>.
* Before the <tt>Class</tt> can be used it must be resolved.
*
* <p> This method assigns a default {@link java.security.ProtectionDomain
* <tt>ProtectionDomain</tt>} to the newly defined class. The
* <tt>ProtectionDomain</tt> is effectively granted the same set of
* permissions returned when {@link
* java.security.Policy#getPermissions(java.security.CodeSource)
* <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
* is invoked. The default domain is created on the first invocation of
* {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
* and re-used on subsequent invocations.
*
* <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
* the {@link #defineClass(String, byte[], int, int,
* java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
* <tt>ProtectionDomain</tt> as one of its arguments. </p>
*
* @param name
* The expected <a href="#name">binary name</a> of the class, or
* <tt>null</tt> if not known
*
* @param b
* The bytes that make up the class data. The bytes in positions
* <tt>off</tt> through <tt>off+len-1</tt> should have the format
* of a valid class file as defined by
* <cite>The Java™ Virtual Machine Specification</cite>.
*
* @param off
* The start offset in <tt>b</tt> of the class data
*
* @param len
* The length of the class data
*
* @return The <tt>Class</tt> object that was created from the specified
* class data.
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws IndexOutOfBoundsException
* If either <tt>off</tt> or <tt>len</tt> is negative, or if
* <tt>off+len</tt> is greater than <tt>b.length</tt>.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class (which is unsigned), or if
* <tt>name</tt> begins with "<tt>java.</tt>".
*
* @see #loadClass(String, boolean)
* @see #resolveClass(Class)
* @see java.security.CodeSource
* @see java.security.SecureClassLoader
*
* @since 1.1
*/
protected final Class<?> defineClass(String name, byte[] b, int off, int len)
throws ClassFormatError
{
return defineClass(name, b, off, len, null);
}
/* Determine protection domain, and check that:
- not define java.* class,
- signer of this class matches signers for the rest of the classes in
package.
*/
private ProtectionDomain preDefineClass(String name,
ProtectionDomain pd)
{
if (!checkName(name))
throw new NoClassDefFoundError("IllegalName: " + name);
if ((name != null) && name.startsWith("java.")) {
throw new SecurityException
("Prohibited package name: " +
name.substring(0, name.lastIndexOf('.')));
}
if (pd == null) {
pd = defaultDomain;
}
if (name != null) checkCerts(name, pd.getCodeSource());
return pd;
}
private String defineClassSourceLocation(ProtectionDomain pd)
{
CodeSource cs = pd.getCodeSource();
String source = null;
if (cs != null && cs.getLocation() != null) {
source = cs.getLocation().toString();
}
return source;
}
private void postDefineClass(Class<?> c, ProtectionDomain pd)
{
if (pd.getCodeSource() != null) {
Certificate certs[] = pd.getCodeSource().getCertificates();
if (certs != null)
setSigners(c, certs);
}
}
/**
* Converts an array of bytes into an instance of class <tt>Class</tt>,
* with an optional <tt>ProtectionDomain</tt>. If the domain is
* <tt>null</tt>, then a default domain will be assigned to the class as
* specified in the documentation for {@link #defineClass(String, byte[],
* int, int)}. Before the class can be used it must be resolved.
*
* <p> The first class defined in a package determines the exact set of
* certificates that all subsequent classes defined in that package must
* contain. The set of certificates for a class is obtained from the
* {@link java.security.CodeSource <tt>CodeSource</tt>} within the
* <tt>ProtectionDomain</tt> of the class. Any classes added to that
* package must contain the same set of certificates or a
* <tt>SecurityException</tt> will be thrown. Note that if
* <tt>name</tt> is <tt>null</tt>, this check is not performed.
* You should always pass in the <a href="#name">binary name</a> of the
* class you are defining as well as the bytes. This ensures that the
* class you are defining is indeed the class you think it is.
*
* <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
* all classes in the "<tt>java.*</tt> packages can only be defined by the
* bootstrap class loader. If <tt>name</tt> is not <tt>null</tt>, it
* must be equal to the <a href="#name">binary name</a> of the class
* specified by the byte array "<tt>b</tt>", otherwise a {@link
* NoClassDefFoundError <tt>NoClassDefFoundError</tt>} will be thrown. </p>
*
* @param name
* The expected <a href="#name">binary name</a> of the class, or
* <tt>null</tt> if not known
*
* @param b
* The bytes that make up the class data. The bytes in positions
* <tt>off</tt> through <tt>off+len-1</tt> should have the format
* of a valid class file as defined by
* <cite>The Java™ Virtual Machine Specification</cite>.
*
* @param off
* The start offset in <tt>b</tt> of the class data
*
* @param len
* The length of the class data
*
* @param protectionDomain
* The ProtectionDomain of the class
*
* @return The <tt>Class</tt> object created from the data,
* and optional <tt>ProtectionDomain</tt>.
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws NoClassDefFoundError
* If <tt>name</tt> is not equal to the <a href="#name">binary
* name</a> of the class specified by <tt>b</tt>
*
* @throws IndexOutOfBoundsException
* If either <tt>off</tt> or <tt>len</tt> is negative, or if
* <tt>off+len</tt> is greater than <tt>b.length</tt>.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class, or if <tt>name</tt> begins with
* "<tt>java.</tt>".
*/
protected final Class<?> defineClass(String name, byte[] b, int off, int len,
ProtectionDomain protectionDomain)
throws ClassFormatError
{
protectionDomain = preDefineClass(name, protectionDomain);
String source = defineClassSourceLocation(protectionDomain);
Class<?> c = defineClass1(name, b, off, len, protectionDomain, source);
postDefineClass(c, protectionDomain);
return c;
}
/**
* Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
* into an instance of class <tt>Class</tt>,
* with an optional <tt>ProtectionDomain</tt>. If the domain is
* <tt>null</tt>, then a default domain will be assigned to the class as
* specified in the documentation for {@link #defineClass(String, byte[],
* int, int)}. Before the class can be used it must be resolved.
*
* <p>The rules about the first class defined in a package determining the
* set of certificates for the package, and the restrictions on class names
* are identical to those specified in the documentation for {@link
* #defineClass(String, byte[], int, int, ProtectionDomain)}.
*
* <p> An invocation of this method of the form
* <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
* <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
* result as the statements
*
*<p> <tt>
* ...<br>
* byte[] temp = new byte[bBuffer.{@link
* java.nio.ByteBuffer#remaining remaining}()];<br>
* bBuffer.{@link java.nio.ByteBuffer#get(byte[])
* get}(temp);<br>
* return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
* cl.defineClass}(name, temp, 0,
* temp.length, pd);<br>
* </tt></p>
*
* @param name
* The expected <a href="#name">binary name</a>. of the class, or
* <tt>null</tt> if not known
*
* @param b
* The bytes that make up the class data. The bytes from positions
* <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
* </tt> should have the format of a valid class file as defined by
* <cite>The Java™ Virtual Machine Specification</cite>.
*
* @param protectionDomain
* The ProtectionDomain of the class, or <tt>null</tt>.
*
* @return The <tt>Class</tt> object created from the data,
* and optional <tt>ProtectionDomain</tt>.
*
* @throws ClassFormatError
* If the data did not contain a valid class.
*
* @throws NoClassDefFoundError
* If <tt>name</tt> is not equal to the <a href="#name">binary
* name</a> of the class specified by <tt>b</tt>
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class, or if <tt>name</tt> begins with
* "<tt>java.</tt>".
*
* @see #defineClass(String, byte[], int, int, ProtectionDomain)
*
* @since 1.5
*/
protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
ProtectionDomain protectionDomain)
throws ClassFormatError
{
int len = b.remaining();
// Use byte[] if not a direct ByteBufer:
if (!b.isDirect()) {
if (b.hasArray()) {
return defineClass(name, b.array(),
b.position() + b.arrayOffset(), len,
protectionDomain);
} else {
// no array, or read-only array
byte[] tb = new byte[len];
b.get(tb); // get bytes out of byte buffer.
return defineClass(name, tb, 0, len, protectionDomain);
}
}
protectionDomain = preDefineClass(name, protectionDomain);
String source = defineClassSourceLocation(protectionDomain);
Class<?> c = defineClass2(name, b, b.position(), len, protectionDomain, source);
postDefineClass(c, protectionDomain);
return c;
}
private native Class<?> defineClass0(String name, byte[] b, int off, int len,
ProtectionDomain pd);
private native Class<?> defineClass1(String name, byte[] b, int off, int len,
ProtectionDomain pd, String source);
private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
int off, int len, ProtectionDomain pd,
String source);
// true if the name is null or has the potential to be a valid binary name
private boolean checkName(String name) {
if ((name == null) || (name.length() == 0))
return true;
if ((name.indexOf('/') != -1)
|| (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
return false;
return true;
}
private void checkCerts(String name, CodeSource cs) {
int i = name.lastIndexOf('.');
String pname = (i == -1) ? "" : name.substring(0, i);
Certificate[] certs = null;
if (cs != null) {
certs = cs.getCertificates();
}
Certificate[] pcerts = null;
if (parallelLockMap == null) {
synchronized (this) {
pcerts = package2certs.get(pname);
if (pcerts == null) {
package2certs.put(pname, (certs == null? nocerts:certs));
}
}
} else {
pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
putIfAbsent(pname, (certs == null? nocerts:certs));
}
if (pcerts != null && !compareCerts(pcerts, certs)) {
throw new SecurityException("class \""+ name +
"\"'s signer information does not match signer information of other classes in the same package");
}
}
/**
* check to make sure the certs for the new class (certs) are the same as
* the certs for the first class inserted in the package (pcerts)
*/
private boolean compareCerts(Certificate[] pcerts,
Certificate[] certs)
{
// certs can be null, indicating no certs.
if ((certs == null) || (certs.length == 0)) {
return pcerts.length == 0;
}
// the length must be the same at this point
if (certs.length != pcerts.length)
return false;
// go through and make sure all the certs in one array
// are in the other and vice-versa.
boolean match;
for (int i = 0; i < certs.length; i++) {
match = false;
for (int j = 0; j < pcerts.length; j++) {
if (certs[i].equals(pcerts[j])) {
match = true;
break;
}
}
if (!match) return false;
}
// now do the same for pcerts
for (int i = 0; i < pcerts.length; i++) {
match = false;
for (int j = 0; j < certs.length; j++) {
if (pcerts[i].equals(certs[j])) {
match = true;
break;
}
}
if (!match) return false;
}
return true;
}
/**
* Links the specified class. This (misleadingly named) method may be
* used by a class loader to link a class. If the class <tt>c</tt> has
* already been linked, then this method simply returns. Otherwise, the
* class is linked as described in the "Execution" chapter of
* <cite>The Java™ Language Specification</cite>.
*
* @param c
* The class to link
*
* @throws NullPointerException
* If <tt>c</tt> is <tt>null</tt>.
*
* @see #defineClass(String, byte[], int, int)
*/
protected final void resolveClass(Class<?> c) {
resolveClass0(c);
}
private native void resolveClass0(Class<?> c);
/**
* Finds a class with the specified <a href="#name">binary name</a>,
* loading it if necessary.
*
* <p> This method loads the class through the system class loader (see
* {@link #getSystemClassLoader()}). The <tt>Class</tt> object returned
* might have more than one <tt>ClassLoader</tt> associated with it.
* Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
* because most class loaders need to override just {@link
* #findClass(String)}. </p>
*
* @param name
* The <a href="#name">binary name</a> of the class
*
* @return The <tt>Class</tt> object for the specified <tt>name</tt>
*
* @throws ClassNotFoundException
* If the class could not be found
*
* @see #ClassLoader(ClassLoader)
* @see #getParent()
*/
protected final Class<?> findSystemClass(String name)
throws ClassNotFoundException
{
ClassLoader system = getSystemClassLoader();
if (system == null) {
if (!checkName(name))
throw new ClassNotFoundException(name);
Class<?> cls = findBootstrapClass(name);
if (cls == null) {
throw new ClassNotFoundException(name);
}
return cls;
}
return system.loadClass(name);
}
/**
* Returns a class loaded by the bootstrap class loader;
* or return null if not found.
*/
private Class<?> findBootstrapClassOrNull(String name)
{
if (!checkName(name)) return null;
return findBootstrapClass(name);
}
// return null if not found
private native Class<?> findBootstrapClass(String name);
/**
* Returns the class with the given <a href="#name">binary name</a> if this
* loader has been recorded by the Java virtual machine as an initiating
* loader of a class with that <a href="#name">binary name</a>. Otherwise
* <tt>null</tt> is returned.
*
* @param name
* The <a href="#name">binary name</a> of the class
*
* @return The <tt>Class</tt> object, or <tt>null</tt> if the class has
* not been loaded
*
* @since 1.1
*/
protected final Class<?> findLoadedClass(String name) {
if (!checkName(name))
return null;
return findLoadedClass0(name);
}
private native final Class<?> findLoadedClass0(String name);
/**
* Sets the signers of a class. This should be invoked after defining a
* class.
*
* @param c
* The <tt>Class</tt> object
*
* @param signers
* The signers for the class
*
* @since 1.1
*/
protected final void setSigners(Class<?> c, Object[] signers) {
c.setSigners(signers);
}
// -- Resource --
/**
* Finds the resource with the given name. A resource is some data
* (images, audio, text, etc) that can be accessed by class code in a way
* that is independent of the location of the code.
*
* <p> The name of a resource is a '<tt>/</tt>'-separated path name that
* identifies the resource.
*
* <p> This method will first search the parent class loader for the
* resource; if the parent is <tt>null</tt> the path of the class loader
* built-in to the virtual machine is searched. That failing, this method
* will invoke {@link #findResource(String)} to find the resource. </p>
*
* @apiNote When overriding this method it is recommended that an
* implementation ensures that any delegation is consistent with the {@link
* #getResources(java.lang.String) getResources(String)} method.
*
* @param name
* The resource name
*
* @return A <tt>URL</tt> object for reading the resource, or
* <tt>null</tt> if the resource could not be found or the invoker
* doesn't have adequate privileges to get the resource.
*
* @since 1.1
*/
public URL getResource(String name) {
URL url;
if (parent != null) {
url = parent.getResource(name);
} else {
url = getBootstrapResource(name);
}
if (url == null) {
url = findResource(name);
}
return url;
}
/**
* Finds all the resources with the given name. A resource is some data
* (images, audio, text, etc) that can be accessed by class code in a way
* that is independent of the location of the code.
*
* <p>The name of a resource is a <tt>/</tt>-separated path name that
* identifies the resource.
*
* <p> The search order is described in the documentation for {@link
* #getResource(String)}. </p>
*
* @apiNote When overriding this method it is recommended that an
* implementation ensures that any delegation is consistent with the {@link
* #getResource(java.lang.String) getResource(String)} method. This should
* ensure that the first element returned by the Enumeration's
* {@code nextElement} method is the same resource that the
* {@code getResource(String)} method would return.
*
* @param name
* The resource name
*
* @return An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
* the resource. If no resources could be found, the enumeration
* will be empty. Resources that the class loader doesn't have
* access to will not be in the enumeration.
*
* @throws IOException
* If I/O errors occur
*
* @see #findResources(String)
*
* @since 1.2
*/
public Enumeration<URL> getResources(String name) throws IOException {
@SuppressWarnings("unchecked")
Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
if (parent != null) {
tmp[0] = parent.getResources(name);
} else {
tmp[0] = getBootstrapResources(name);
}
tmp[1] = findResources(name);
return new CompoundEnumeration<>(tmp);
}
/**
* Finds the resource with the given name. Class loader implementations
* should override this method to specify where to find resources.
*
* @param name
* The resource name
*
* @return A <tt>URL</tt> object for reading the resource, or
* <tt>null</tt> if the resource could not be found
*
* @since 1.2
*/
protected URL findResource(String name) {
return null;
}
/**
* Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
* representing all the resources with the given name. Class loader
* implementations should override this method to specify where to load
* resources from.
*
* @param name
* The resource name
*
* @return An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
* the resources
*
* @throws IOException
* If I/O errors occur
*
* @since 1.2
*/
protected Enumeration<URL> findResources(String name) throws IOException {
return java.util.Collections.emptyEnumeration();
}
/**
* Registers the caller as parallel capable.
* The registration succeeds if and only if all of the following
* conditions are met:
* <ol>
* <li> no instance of the caller has been created</li>
* <li> all of the super classes (except class Object) of the caller are
* registered as parallel capable</li>
* </ol>
* <p>Note that once a class loader is registered as parallel capable, there
* is no way to change it back.</p>
*
* @return true if the caller is successfully registered as
* parallel capable and false if otherwise.
*
* @since 1.7
*/
@CallerSensitive
protected static boolean registerAsParallelCapable() {
Class<? extends ClassLoader> callerClass =
Reflection.getCallerClass().asSubclass(ClassLoader.class);
return ParallelLoaders.register(callerClass);
}
/**
* Find a resource of the specified name from the search path used to load
* classes. This method locates the resource through the system class
* loader (see {@link #getSystemClassLoader()}).
*
* @param name
* The resource name
*
* @return A {@link java.net.URL <tt>URL</tt>} object for reading the
* resource, or <tt>null</tt> if the resource could not be found
*
* @since 1.1
*/
public static URL getSystemResource(String name) {
ClassLoader system = getSystemClassLoader();
if (system == null) {
return getBootstrapResource(name);
}
return system.getResource(name);
}
/**
* Finds all resources of the specified name from the search path used to
* load classes. The resources thus found are returned as an
* {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
* java.net.URL <tt>URL</tt>} objects.
*
* <p> The search order is described in the documentation for {@link
* #getSystemResource(String)}. </p>
*
* @param name
* The resource name
*
* @return An enumeration of resource {@link java.net.URL <tt>URL</tt>}
* objects
*
* @throws IOException
* If I/O errors occur
* @since 1.2
*/
public static Enumeration<URL> getSystemResources(String name)
throws IOException
{
ClassLoader system = getSystemClassLoader();
if (system == null) {
return getBootstrapResources(name);
}
return system.getResources(name);
}
/**
* Find resources from the VM's built-in classloader.
*/
private static URL getBootstrapResource(String name) {
URLClassPath ucp = getBootstrapClassPath();
Resource res = ucp.getResource(name);
return res != null ? res.getURL() : null;
}
/**
* Find resources from the VM's built-in classloader.
*/
private static Enumeration<URL> getBootstrapResources(String name)
throws IOException
{
final Enumeration<Resource> e =
getBootstrapClassPath().getResources(name);
return new Enumeration<URL> () {
public URL nextElement() {
return e.nextElement().getURL();
}
public boolean hasMoreElements() {
return e.hasMoreElements();
}
};
}
// Returns the URLClassPath that is used for finding system resources.
static URLClassPath getBootstrapClassPath() {
return sun.misc.Launcher.getBootstrapClassPath();
}
/**
* Returns an input stream for reading the specified resource.
*
* <p> The search order is described in the documentation for {@link
* #getResource(String)}. </p>
*
* @param name
* The resource name
*
* @return An input stream for reading the resource, or <tt>null</tt>
* if the resource could not be found
*
* @since 1.1
*/
public InputStream getResourceAsStream(String name) {
URL url = getResource(name);
try {
return url != null ? url.openStream() : null;
} catch (IOException e) {
return null;
}
}
/**
* Open for reading, a resource of the specified name from the search path
* used to load classes. This method locates the resource through the
* system class loader (see {@link #getSystemClassLoader()}).
*
* @param name
* The resource name
*
* @return An input stream for reading the resource, or <tt>null</tt>
* if the resource could not be found
*
* @since 1.1
*/
public static InputStream getSystemResourceAsStream(String name) {
URL url = getSystemResource(name);
try {
return url != null ? url.openStream() : null;
} catch (IOException e) {
return null;
}
}
// -- Hierarchy --
/**
* Returns the parent class loader for delegation. Some implementations may
* use <tt>null</tt> to represent the bootstrap class loader. This method
* will return <tt>null</tt> in such implementations if this class loader's
* parent is the bootstrap class loader.
*
* <p> If a security manager is present, and the invoker's class loader is
* not <tt>null</tt> and is not an ancestor of this class loader, then this
* method invokes the security manager's {@link
* SecurityManager#checkPermission(java.security.Permission)
* <tt>checkPermission</tt>} method with a {@link
* RuntimePermission#RuntimePermission(String)
* <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
* access to the parent class loader is permitted. If not, a
* <tt>SecurityException</tt> will be thrown. </p>
*
* @return The parent <tt>ClassLoader</tt>
*
* @throws SecurityException
* If a security manager exists and its <tt>checkPermission</tt>
* method doesn't allow access to this class loader's parent class
* loader.
*
* @since 1.2
*/
@CallerSensitive
public final ClassLoader getParent() {
if (parent == null)
return null;
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
// Check access to the parent class loader
// If the caller's class loader is same as this class loader,
// permission check is performed.
checkClassLoaderPermission(parent, Reflection.getCallerClass());
}
return parent;
}
/**
* Returns the system class loader for delegation. This is the default
* delegation parent for new <tt>ClassLoader</tt> instances, and is
* typically the class loader used to start the application.
*
* <p> This method is first invoked early in the runtime's startup
* sequence, at which point it creates the system class loader and sets it
* as the context class loader of the invoking <tt>Thread</tt>.
*
* <p> The default system class loader is an implementation-dependent
* instance of this class.
*
* <p> If the system property "<tt>java.system.class.loader</tt>" is defined
* when this method is first invoked then the value of that property is
* taken to be the name of a class that will be returned as the system
* class loader. The class is loaded using the default system class loader
* and must define a public constructor that takes a single parameter of
* type <tt>ClassLoader</tt> which is used as the delegation parent. An
* instance is then created using this constructor with the default system
* class loader as the parameter. The resulting class loader is defined
* to be the system class loader.
*
* <p> If a security manager is present, and the invoker's class loader is
* not <tt>null</tt> and the invoker's class loader is not the same as or
* an ancestor of the system class loader, then this method invokes the
* security manager's {@link
* SecurityManager#checkPermission(java.security.Permission)
* <tt>checkPermission</tt>} method with a {@link
* RuntimePermission#RuntimePermission(String)
* <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
* access to the system class loader. If not, a
* <tt>SecurityException</tt> will be thrown. </p>
*
* @return The system <tt>ClassLoader</tt> for delegation, or
* <tt>null</tt> if none
*
* @throws SecurityException
* If a security manager exists and its <tt>checkPermission</tt>
* method doesn't allow access to the system class loader.
*
* @throws IllegalStateException
* If invoked recursively during the construction of the class
* loader specified by the "<tt>java.system.class.loader</tt>"
* property.
*
* @throws Error
* If the system property "<tt>java.system.class.loader</tt>"
* is defined but the named class could not be loaded, the
* provider class does not define the required constructor, or an
* exception is thrown by that constructor when it is invoked. The
* underlying cause of the error can be retrieved via the
* {@link Throwable#getCause()} method.
*
* @revised 1.4
*/
@CallerSensitive
public static ClassLoader getSystemClassLoader() {
initSystemClassLoader();
if (scl == null) {
return null;
}
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkClassLoaderPermission(scl, Reflection.getCallerClass());
}
return scl;
}
private static synchronized void initSystemClassLoader() {
if (!sclSet) {
if (scl != null)
throw new IllegalStateException("recursive invocation");
sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
if (l != null) {
Throwable oops = null;
scl = l.getClassLoader();
try {
scl = AccessController.doPrivileged(
new SystemClassLoaderAction(scl));
} catch (PrivilegedActionException pae) {
oops = pae.getCause();
if (oops instanceof InvocationTargetException) {
oops = oops.getCause();
}
}
if (oops != null) {
if (oops instanceof Error) {
throw (Error) oops;
} else {
// wrap the exception
throw new Error(oops);
}
}
}
sclSet = true;
}
}
// Returns true if the specified class loader can be found in this class
// loader's delegation chain.
boolean isAncestor(ClassLoader cl) {
ClassLoader acl = this;
do {
acl = acl.parent;
if (cl == acl) {
return true;
}
} while (acl != null);
return false;
}
// Tests if class loader access requires "getClassLoader" permission
// check. A class loader 'from' can access class loader 'to' if
// class loader 'from' is same as class loader 'to' or an ancestor
// of 'to'. The class loader in a system domain can access
// any class loader.
private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
ClassLoader to)
{
if (from == to)
return false;
if (from == null)
return false;
return !to.isAncestor(from);
}
// Returns the class's class loader, or null if none.
static ClassLoader getClassLoader(Class<?> caller) {
// This can be null if the VM is requesting it
if (caller == null) {
return null;
}
// Circumvent security check since this is package-private
return caller.getClassLoader0();
}
/*
* Checks RuntimePermission("getClassLoader") permission
* if caller's class loader is not null and caller's class loader
* is not the same as or an ancestor of the given cl argument.
*/
static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
// caller can be null if the VM is requesting it
ClassLoader ccl = getClassLoader(caller);
if (needsClassLoaderPermissionCheck(ccl, cl)) {
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
}
}
}
// The class loader for the system
// @GuardedBy("ClassLoader.class")
private static ClassLoader scl;
// Set to true once the system class loader has been set
// @GuardedBy("ClassLoader.class")
private static boolean sclSet;
// -- Package --
/**
* Defines a package by name in this <tt>ClassLoader</tt>. This allows
* class loaders to define the packages for their classes. Packages must
* be created before the class is defined, and package names must be
* unique within a class loader and cannot be redefined or changed once
* created.
*
* @param name
* The package name
*
* @param specTitle
* The specification title
*
* @param specVersion
* The specification version
*
* @param specVendor
* The specification vendor
*
* @param implTitle
* The implementation title
*
* @param implVersion
* The implementation version
*
* @param implVendor
* The implementation vendor
*
* @param sealBase
* If not <tt>null</tt>, then this package is sealed with
* respect to the given code source {@link java.net.URL
* <tt>URL</tt>} object. Otherwise, the package is not sealed.
*
* @return The newly defined <tt>Package</tt> object
*
* @throws IllegalArgumentException
* If package name duplicates an existing package either in this
* class loader or one of its ancestors
*
* @since 1.2
*/
protected Package definePackage(String name, String specTitle,
String specVersion, String specVendor,
String implTitle, String implVersion,
String implVendor, URL sealBase)
throws IllegalArgumentException
{
synchronized (packages) {
Package pkg = getPackage(name);
if (pkg != null) {
throw new IllegalArgumentException(name);
}
pkg = new Package(name, specTitle, specVersion, specVendor,
implTitle, implVersion, implVendor,
sealBase, this);
packages.put(name, pkg);
return pkg;
}
}
/**
* Returns a <tt>Package</tt> that has been defined by this class loader
* or any of its ancestors.
*
* @param name
* The package name
*
* @return The <tt>Package</tt> corresponding to the given name, or
* <tt>null</tt> if not found
*
* @since 1.2
*/
protected Package getPackage(String name) {
Package pkg;
synchronized (packages) {
pkg = packages.get(name);
}
if (pkg == null) {
if (parent != null) {
pkg = parent.getPackage(name);
} else {
pkg = Package.getSystemPackage(name);
}
if (pkg != null) {
synchronized (packages) {
Package pkg2 = packages.get(name);
if (pkg2 == null) {
packages.put(name, pkg);
} else {
pkg = pkg2;
}
}
}
}
return pkg;
}
/**
* Returns all of the <tt>Packages</tt> defined by this class loader and
* its ancestors.
*
* @return The array of <tt>Package</tt> objects defined by this
* <tt>ClassLoader</tt>
*
* @since 1.2
*/
protected Package[] getPackages() {
Map<String, Package> map;
synchronized (packages) {
map = new HashMap<>(packages);
}
Package[] pkgs;
if (parent != null) {
pkgs = parent.getPackages();
} else {
pkgs = Package.getSystemPackages();
}
if (pkgs != null) {
for (int i = 0; i < pkgs.length; i++) {
String pkgName = pkgs[i].getName();
if (map.get(pkgName) == null) {
map.put(pkgName, pkgs[i]);
}
}
}
return map.values().toArray(new Package[map.size()]);
}
// -- Native library access --
/**
* Returns the absolute path name of a native library. The VM invokes this
* method to locate the native libraries that belong to classes loaded with
* this class loader. If this method returns <tt>null</tt>, the VM
* searches the library along the path specified as the
* "<tt>java.library.path</tt>" property.
*
* @param libname
* The library name
*
* @return The absolute path of the native library
*
* @see System#loadLibrary(String)
* @see System#mapLibraryName(String)
*
* @since 1.2
*/
protected String findLibrary(String libname) {
return null;
}
/**
* The inner class NativeLibrary denotes a loaded native library instance.
* Every classloader contains a vector of loaded native libraries in the
* private field <tt>nativeLibraries</tt>. The native libraries loaded
* into the system are entered into the <tt>systemNativeLibraries</tt>
* vector.
*
* <p> Every native library requires a particular version of JNI. This is
* denoted by the private <tt>jniVersion</tt> field. This field is set by
* the VM when it loads the library, and used by the VM to pass the correct
* version of JNI to the native methods. </p>
*
* @see ClassLoader
* @since 1.2
*/
static class NativeLibrary {
// opaque handle to native library, used in native code.
long handle;
// the version of JNI environment the native library requires.
private int jniVersion;
// the class from which the library is loaded, also indicates
// the loader this native library belongs.
private final Class<?> fromClass;
// the canonicalized name of the native library.
// or static library name
String name;
// Indicates if the native library is linked into the VM
boolean isBuiltin;
// Indicates if the native library is loaded
boolean loaded;
native void load(String name, boolean isBuiltin);
native long find(String name);
native void unload(String name, boolean isBuiltin);
static native String findBuiltinLib(String name);
public NativeLibrary(Class<?> fromClass, String name, boolean isBuiltin) {
this.name = name;
this.fromClass = fromClass;
this.isBuiltin = isBuiltin;
}
protected void finalize() {
synchronized (loadedLibraryNames) {
if (fromClass.getClassLoader() != null && loaded) {
/* remove the native library name */
int size = loadedLibraryNames.size();
for (int i = 0; i < size; i++) {
if (name.equals(loadedLibraryNames.elementAt(i))) {
loadedLibraryNames.removeElementAt(i);
break;
}
}
/* unload the library. */
ClassLoader.nativeLibraryContext.push(this);
try {
unload(name, isBuiltin);
} finally {
ClassLoader.nativeLibraryContext.pop();
}
}
}
}
// Invoked in the VM to determine the context class in
// JNI_Load/JNI_Unload
static Class<?> getFromClass() {
return ClassLoader.nativeLibraryContext.peek().fromClass;
}
}
// All native library names we've loaded.
private static Vector<String> loadedLibraryNames = new Vector<>();
// Native libraries belonging to system classes.
private static Vector<NativeLibrary> systemNativeLibraries
= new Vector<>();
// Native libraries associated with the class loader.
private Vector<NativeLibrary> nativeLibraries = new Vector<>();
// native libraries being loaded/unloaded.
private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();
// The paths searched for libraries
private static String usr_paths[];
private static String sys_paths[];
private static String[] initializePath(String propname) {
String ldpath = System.getProperty(propname, "");
String ps = File.pathSeparator;
int ldlen = ldpath.length();
int i, j, n;
// Count the separators in the path
i = ldpath.indexOf(ps);
n = 0;
while (i >= 0) {
n++;
i = ldpath.indexOf(ps, i + 1);
}
// allocate the array of paths - n :'s = n + 1 path elements
String[] paths = new String[n + 1];
// Fill the array with paths from the ldpath
n = i = 0;
j = ldpath.indexOf(ps);
while (j >= 0) {
if (j - i > 0) {
paths[n++] = ldpath.substring(i, j);
} else if (j - i == 0) {
paths[n++] = ".";
}
i = j + 1;
j = ldpath.indexOf(ps, i);
}
paths[n] = ldpath.substring(i, ldlen);
return paths;
}
// Invoked in the java.lang.Runtime class to implement load and loadLibrary.
static void loadLibrary(Class<?> fromClass, String name,
boolean isAbsolute) {
ClassLoader loader =
(fromClass == null) ? null : fromClass.getClassLoader();
if (sys_paths == null) {
usr_paths = initializePath("java.library.path");
sys_paths = initializePath("sun.boot.library.path");
}
if (isAbsolute) {
if (loadLibrary0(fromClass, new File(name))) {
return;
}
throw new UnsatisfiedLinkError("Can't load library: " + name);
}
if (loader != null) {
String libfilename = loader.findLibrary(name);
if (libfilename != null) {
File libfile = new File(libfilename);
if (!libfile.isAbsolute()) {
throw new UnsatisfiedLinkError(
"ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
}
if (loadLibrary0(fromClass, libfile)) {
return;
}
throw new UnsatisfiedLinkError("Can't load " + libfilename);
}
}
for (int i = 0 ; i < sys_paths.length ; i++) {
File libfile = new File(sys_paths[i], System.mapLibraryName(name));
if (loadLibrary0(fromClass, libfile)) {
return;
}
libfile = ClassLoaderHelper.mapAlternativeName(libfile);
if (libfile != null && loadLibrary0(fromClass, libfile)) {
return;
}
}
if (loader != null) {
for (int i = 0 ; i < usr_paths.length ; i++) {
File libfile = new File(usr_paths[i],
System.mapLibraryName(name));
if (loadLibrary0(fromClass, libfile)) {
return;
}
libfile = ClassLoaderHelper.mapAlternativeName(libfile);
if (libfile != null && loadLibrary0(fromClass, libfile)) {
return;
}
}
}
// Oops, it failed
throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
}
private static boolean loadLibrary0(Class<?> fromClass, final File file) {
// Check to see if we're attempting to access a static library
String name = NativeLibrary.findBuiltinLib(file.getName());
boolean isBuiltin = (name != null);
if (!isBuiltin) {
boolean exists = AccessController.doPrivileged(
new PrivilegedAction<Object>() {
public Object run() {
return file.exists() ? Boolean.TRUE : null;
}})
!= null;
if (!exists) {
return false;
}
try {
name = file.getCanonicalPath();
} catch (IOException e) {
return false;
}
}
ClassLoader loader =
(fromClass == null) ? null : fromClass.getClassLoader();
Vector<NativeLibrary> libs =
loader != null ? loader.nativeLibraries : systemNativeLibraries;
synchronized (libs) {
int size = libs.size();
for (int i = 0; i < size; i++) {
NativeLibrary lib = libs.elementAt(i);
if (name.equals(lib.name)) {
return true;
}
}
synchronized (loadedLibraryNames) {
if (loadedLibraryNames.contains(name)) {
throw new UnsatisfiedLinkError
("Native Library " +
name +
" already loaded in another classloader");
}
/* If the library is being loaded (must be by the same thread,
* because Runtime.load and Runtime.loadLibrary are
* synchronous). The reason is can occur is that the JNI_OnLoad
* function can cause another loadLibrary invocation.
*
* Thus we can use a static stack to hold the list of libraries
* we are loading.
*
* If there is a pending load operation for the library, we
* immediately return success; otherwise, we raise
* UnsatisfiedLinkError.
*/
int n = nativeLibraryContext.size();
for (int i = 0; i < n; i++) {
NativeLibrary lib = nativeLibraryContext.elementAt(i);
if (name.equals(lib.name)) {
if (loader == lib.fromClass.getClassLoader()) {
return true;
} else {
throw new UnsatisfiedLinkError
("Native Library " +
name +
" is being loaded in another classloader");
}
}
}
NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
nativeLibraryContext.push(lib);
try {
lib.load(name, isBuiltin);
} finally {
nativeLibraryContext.pop();
}
if (lib.loaded) {
loadedLibraryNames.addElement(name);
libs.addElement(lib);
return true;
}
return false;
}
}
}
// Invoked in the VM class linking code.
static long findNative(ClassLoader loader, String name) {
Vector<NativeLibrary> libs =
loader != null ? loader.nativeLibraries : systemNativeLibraries;
synchronized (libs) {
int size = libs.size();
for (int i = 0; i < size; i++) {
NativeLibrary lib = libs.elementAt(i);
long entry = lib.find(name);
if (entry != 0)
return entry;
}
}
return 0;
}
// -- Assertion management --
final Object assertionLock;
// The default toggle for assertion checking.
// @GuardedBy("assertionLock")
private boolean defaultAssertionStatus = false;
// Maps String packageName to Boolean package default assertion status Note
// that the default package is placed under a null map key. If this field
// is null then we are delegating assertion status queries to the VM, i.e.,
// none of this ClassLoader's assertion status modification methods have
// been invoked.
// @GuardedBy("assertionLock")
private Map<String, Boolean> packageAssertionStatus = null;
// Maps String fullyQualifiedClassName to Boolean assertionStatus If this
// field is null then we are delegating assertion status queries to the VM,
// i.e., none of this ClassLoader's assertion status modification methods
// have been invoked.
// @GuardedBy("assertionLock")
Map<String, Boolean> classAssertionStatus = null;
/**
* Sets the default assertion status for this class loader. This setting
* determines whether classes loaded by this class loader and initialized
* in the future will have assertions enabled or disabled by default.
* This setting may be overridden on a per-package or per-class basis by
* invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
* #setClassAssertionStatus(String, boolean)}.
*
* @param enabled
* <tt>true</tt> if classes loaded by this class loader will
* henceforth have assertions enabled by default, <tt>false</tt>
* if they will have assertions disabled by default.
*
* @since 1.4
*/
public void setDefaultAssertionStatus(boolean enabled) {
synchronized (assertionLock) {
if (classAssertionStatus == null)
initializeJavaAssertionMaps();
defaultAssertionStatus = enabled;
}
}
/**
* Sets the package default assertion status for the named package. The
* package default assertion status determines the assertion status for
* classes initialized in the future that belong to the named package or
* any of its "subpackages".
*
* <p> A subpackage of a package named p is any package whose name begins
* with "<tt>p.</tt>". For example, <tt>javax.swing.text</tt> is a
* subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
* <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
*
* <p> In the event that multiple package defaults apply to a given class,
* the package default pertaining to the most specific package takes
* precedence over the others. For example, if <tt>javax.lang</tt> and
* <tt>javax.lang.reflect</tt> both have package defaults associated with
* them, the latter package default applies to classes in
* <tt>javax.lang.reflect</tt>.
*
* <p> Package defaults take precedence over the class loader's default
* assertion status, and may be overridden on a per-class basis by invoking
* {@link #setClassAssertionStatus(String, boolean)}. </p>
*
* @param packageName
* The name of the package whose package default assertion status
* is to be set. A <tt>null</tt> value indicates the unnamed
* package that is "current"
* (see section 7.4.2 of
* <cite>The Java™ Language Specification</cite>.)
*
* @param enabled
* <tt>true</tt> if classes loaded by this classloader and
* belonging to the named package or any of its subpackages will
* have assertions enabled by default, <tt>false</tt> if they will
* have assertions disabled by default.
*
* @since 1.4
*/
public void setPackageAssertionStatus(String packageName,
boolean enabled) {
synchronized (assertionLock) {
if (packageAssertionStatus == null)
initializeJavaAssertionMaps();
packageAssertionStatus.put(packageName, enabled);
}
}
/**
* Sets the desired assertion status for the named top-level class in this
* class loader and any nested classes contained therein. This setting
* takes precedence over the class loader's default assertion status, and
* over any applicable per-package default. This method has no effect if
* the named class has already been initialized. (Once a class is
* initialized, its assertion status cannot change.)
*
* <p> If the named class is not a top-level class, this invocation will
* have no effect on the actual assertion status of any class. </p>
*
* @param className
* The fully qualified class name of the top-level class whose
* assertion status is to be set.
*
* @param enabled
* <tt>true</tt> if the named class is to have assertions
* enabled when (and if) it is initialized, <tt>false</tt> if the
* class is to have assertions disabled.
*
* @since 1.4
*/
public void setClassAssertionStatus(String className, boolean enabled) {
synchronized (assertionLock) {
if (classAssertionStatus == null)
initializeJavaAssertionMaps();
classAssertionStatus.put(className, enabled);
}
}
/**
* Sets the default assertion status for this class loader to
* <tt>false</tt> and discards any package defaults or class assertion
* status settings associated with the class loader. This method is
* provided so that class loaders can be made to ignore any command line or
* persistent assertion status settings and "start with a clean slate."
*
* @since 1.4
*/
public void clearAssertionStatus() {
/*
* Whether or not "Java assertion maps" are initialized, set
* them to empty maps, effectively ignoring any present settings.
*/
synchronized (assertionLock) {
classAssertionStatus = new HashMap<>();
packageAssertionStatus = new HashMap<>();
defaultAssertionStatus = false;
}
}
/**
* Returns the assertion status that would be assigned to the specified
* class if it were to be initialized at the time this method is invoked.
* If the named class has had its assertion status set, the most recent
* setting will be returned; otherwise, if any package default assertion
* status pertains to this class, the most recent setting for the most
* specific pertinent package default assertion status is returned;
* otherwise, this class loader's default assertion status is returned.
* </p>
*
* @param className
* The fully qualified class name of the class whose desired
* assertion status is being queried.
*
* @return The desired assertion status of the specified class.
*
* @see #setClassAssertionStatus(String, boolean)
* @see #setPackageAssertionStatus(String, boolean)
* @see #setDefaultAssertionStatus(boolean)
*
* @since 1.4
*/
boolean desiredAssertionStatus(String className) {
synchronized (assertionLock) {
// assert classAssertionStatus != null;
// assert packageAssertionStatus != null;
// Check for a class entry
Boolean result = classAssertionStatus.get(className);
if (result != null)
return result.booleanValue();
// Check for most specific package entry
int dotIndex = className.lastIndexOf(".");
if (dotIndex < 0) { // default package
result = packageAssertionStatus.get(null);
if (result != null)
return result.booleanValue();
}
while(dotIndex > 0) {
className = className.substring(0, dotIndex);
result = packageAssertionStatus.get(className);
if (result != null)
return result.booleanValue();
dotIndex = className.lastIndexOf(".", dotIndex-1);
}
// Return the classloader default
return defaultAssertionStatus;
}
}
// Set up the assertions with information provided by the VM.
// Note: Should only be called inside a synchronized block
private void initializeJavaAssertionMaps() {
// assert Thread.holdsLock(assertionLock);
classAssertionStatus = new HashMap<>();
packageAssertionStatus = new HashMap<>();
AssertionStatusDirectives directives = retrieveDirectives();
for(int i = 0; i < directives.classes.length; i++)
classAssertionStatus.put(directives.classes[i],
directives.classEnabled[i]);
for(int i = 0; i < directives.packages.length; i++)
packageAssertionStatus.put(directives.packages[i],
directives.packageEnabled[i]);
defaultAssertionStatus = directives.deflt;
}
// Retrieves the assertion directives from the VM.
private static native AssertionStatusDirectives retrieveDirectives();
}
class SystemClassLoaderAction
implements PrivilegedExceptionAction<ClassLoader> {
private ClassLoader parent;
SystemClassLoaderAction(ClassLoader parent) {
this.parent = parent;
}
public ClassLoader run() throws Exception {
String cls = System.getProperty("java.system.class.loader");
if (cls == null) {
return parent;
}
Constructor<?> ctor = Class.forName(cls, true, parent)
.getDeclaredConstructor(new Class<?>[] { ClassLoader.class });
ClassLoader sys = (ClassLoader) ctor.newInstance(
new Object[] { parent });
Thread.currentThread().setContextClassLoader(sys);
return sys;
}
}
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