(ecj)Eclipse的Java编译器分析之一——ecj介绍
Java是一个开放的平台，对于除发布编译器/解释器/基础类库之外，该语言的负责机构更多的是制定一系列标准，任何符合标准的厂商产品均可用于市场投放。甚至包括其编译器及解释器。
(比如Hibernate提供了JPA实现；Tomcat实现了Java EE服务器标准，其Servlet容器通过了Java认证；各数据库或中间件厂商也根据JDBC接口开发驱动。说白了，Java基本就是都提供接口，然后让厂商开发实现，因此有时候我会骂，边骂边编码！)
GCC有java编译器，可以看看。
我们主要主要介绍Eclipse自己开发和使用的针对Java的编译器：(ecj) the Eclipse Compiler for Java。Eclipse没有使用JDK自带的编译器，而是自己开发的，ecj也通过了java的验证。
除了Eclipse之外，Tomcat也用到了Ecj，用于动态编译jsp文件。我们安装Tomcat后可在lib文件夹下找到ecj：
现在问题来了：怎么取得ecj源码呢？
别急，我们从tomcat源码中查看一下：
虽然我不熟ant，但我也能知道，Tomcat6.0.37中使用的ecj下载路径是：
http://archive.eclipse.org/eclipse/downloads/drops4/R-4.2.2-201302041200/ecj-4.2.2.jar
这个还是class文件，刚开始我也没辙，不过后来我灵机一动：在ecj后面加个src竟然成了！-_-
http://archive.eclipse.org/eclipse/downloads/drops4/R-4.2.2-201302041200/ecjsrc-4.2.2.jar
下面是我下载好后倒入项目文件后截图：
这个文件报错，不过可以把他删除了看，我先没有删除，因为这个文件是ecj与ant的桥梁。从源码可以看出这个JDTCompilerAdapter是继承自ant的DefaultCompilerAdapter，用于ant的编译器适配器。个人感觉ecj从代码(技术)上并没有耦合任何一个调用者，这里的ant也只是一个适配器，你删除或者留着没有任何影响。Tomcat里也没有使用ant。
我从这里主要是想看看高层怎么调用ecj来编译代码，我们看看关键代码：
private static String compilerClass = "org.eclipse.jdt.internal.compiler.batch.Main"; //$NON-NLS-1$ /**
* Performs a compile using the JDT batch compiler
* @throws BuildException if anything wrong happen during the compilation
* @return boolean true if the compilation is ok, false otherwise
*/
public boolean execute() throws BuildException {
this.attributes.log(AntAdapterMessages.getString("ant.jdtadapter.info.usingJDTCompiler"), Project.MSG_VERBOSE); //$NON-NLS-1$
Commandline cmd = setupJavacCommand(); try {
Class c = Class.forName(compilerClass);
Constructor batchCompilerConstructor =
c.getConstructor(new Class[] {
PrintWriter.class,
PrintWriter.class,
Boolean.TYPE,
Map.class});
Object batchCompilerInstance =
batchCompilerConstructor.newInstance(new Object[] {
new PrintWriter(System.out),
new PrintWriter(System.err),
Boolean.TRUE,
this.customDefaultOptions});
Method compile =
c.getMethod("compile", new Class[] {String[].class}); //$NON-NLS-1$
Object result =
compile.invoke(batchCompilerInstance, new Object[] {
cmd.getArguments()});
final boolean resultValue = ((Boolean) result).booleanValue();
if (!resultValue && this.logFileName != null) {
this.attributes.log(AntAdapterMessages.getString("ant.jdtadapter.error.compilationFailed", this.logFileName)); //$NON-NLS-1$
}
return resultValue;
} catch (ClassNotFoundException cnfe) {
throw new BuildException(AntAdapterMessages.getString("ant.jdtadapter.error.cannotFindJDTCompiler")); //$NON-NLS-1$
} catch (Exception ex) {
throw new BuildException(ex);
}
}
我把代码换了下行，大家看13和26行，可以看出这里使用了
org.eclipse.jdt.internal.compiler.batch.Main#compile(String[])方法来进行编译，我们可以稍微看看：
从源码上来看1664是配置，1684可能是编译，不过我们先不细看。
我们再看看Tomcat怎么使用ecj的，我们查看org.apache.jasper.compiler.JDTCompiler源码(我贴出了源码，不过有点长)：
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/ package org.apache.jasper.compiler; import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.StringTokenizer; import org.apache.jasper.JasperException;
import org.eclipse.jdt.core.compiler.IProblem;
import org.eclipse.jdt.internal.compiler.ClassFile;
import org.eclipse.jdt.internal.compiler.CompilationResult;
import org.eclipse.jdt.internal.compiler.Compiler;
import org.eclipse.jdt.internal.compiler.DefaultErrorHandlingPolicies;
import org.eclipse.jdt.internal.compiler.ICompilerRequestor;
import org.eclipse.jdt.internal.compiler.IErrorHandlingPolicy;
import org.eclipse.jdt.internal.compiler.IProblemFactory;
import org.eclipse.jdt.internal.compiler.classfmt.ClassFileReader;
import org.eclipse.jdt.internal.compiler.env.ICompilationUnit;
import org.eclipse.jdt.internal.compiler.env.INameEnvironment;
import org.eclipse.jdt.internal.compiler.env.NameEnvironmentAnswer;
import org.eclipse.jdt.internal.compiler.impl.CompilerOptions;
import org.eclipse.jdt.internal.compiler.problem.DefaultProblemFactory; /**
* JDT class compiler. This compiler will load source dependencies from the
* context classloader, reducing dramatically disk access during
* the compilation process.
*
* @author Cocoon2
* @author Remy Maucherat
*/
public class JDTCompiler extends org.apache.jasper.compiler.Compiler { /**
* Compile the servlet from .java file to .class file
*/
protected void generateClass(String[] smap)
throws FileNotFoundException, JasperException, Exception { long t1 = 0;
if (log.isDebugEnabled()) {
t1 = System.currentTimeMillis();
} final String sourceFile = ctxt.getServletJavaFileName();
final String outputDir = ctxt.getOptions().getScratchDir().getAbsolutePath();
String packageName = ctxt.getServletPackageName();
final String targetClassName =
((packageName.length() != 0) ? (packageName + ".") : "")
+ ctxt.getServletClassName();
final ClassLoader classLoader = ctxt.getJspLoader();
String[] fileNames = new String[] {sourceFile};
String[] classNames = new String[] {targetClassName};
final ArrayList problemList = new ArrayList(); class CompilationUnit implements ICompilationUnit { String className;
String sourceFile; CompilationUnit(String sourceFile, String className) {
this.className = className;
this.sourceFile = sourceFile;
} public char[] getFileName() {
return sourceFile.toCharArray();
} public char[] getContents() {
char[] result = null;
FileInputStream is = null;
try {
is = new FileInputStream(sourceFile);
Reader reader =
new BufferedReader(new InputStreamReader(is, ctxt.getOptions().getJavaEncoding()));
if (reader != null) {
char[] chars = new char[8192];
StringBuffer buf = new StringBuffer();
int count;
while ((count = reader.read(chars, 0,
chars.length)) > 0) {
buf.append(chars, 0, count);
}
result = new char[buf.length()];
buf.getChars(0, result.length, result, 0);
}
} catch (IOException e) {
log.error("Compilation error", e);
} finally {
if (is != null) {
try {
is.close();
} catch (IOException exc) {
// Ignore
}
}
}
return result;
} public char[] getMainTypeName() {
int dot = className.lastIndexOf('.');
if (dot > 0) {
return className.substring(dot + 1).toCharArray();
}
return className.toCharArray();
} public char[][] getPackageName() {
StringTokenizer izer =
new StringTokenizer(className, ".");
char[][] result = new char[izer.countTokens()-1][];
for (int i = 0; i < result.length; i++) {
String tok = izer.nextToken();
result[i] = tok.toCharArray();
}
return result;
} public boolean ignoreOptionalProblems() {
return false;
}
} final INameEnvironment env = new INameEnvironment() { public NameEnvironmentAnswer
findType(char[][] compoundTypeName) {
String result = "";
String sep = "";
for (int i = 0; i < compoundTypeName.length; i++) {
result += sep;
result += new String(compoundTypeName[i]);
sep = ".";
}
return findType(result);
} public NameEnvironmentAnswer
findType(char[] typeName,
char[][] packageName) {
String result = "";
String sep = "";
for (int i = 0; i < packageName.length; i++) {
result += sep;
result += new String(packageName[i]);
sep = ".";
}
result += sep;
result += new String(typeName);
return findType(result);
} private NameEnvironmentAnswer findType(String className) { InputStream is = null;
try {
if (className.equals(targetClassName)) {
ICompilationUnit compilationUnit =
new CompilationUnit(sourceFile, className);
return
new NameEnvironmentAnswer(compilationUnit, null);
}
String resourceName =
className.replace('.', '/') + ".class";
is = classLoader.getResourceAsStream(resourceName);
if (is != null) {
byte[] classBytes;
byte[] buf = new byte[8192];
ByteArrayOutputStream baos =
new ByteArrayOutputStream(buf.length);
int count;
while ((count = is.read(buf, 0, buf.length)) > 0) {
baos.write(buf, 0, count);
}
baos.flush();
classBytes = baos.toByteArray();
char[] fileName = className.toCharArray();
ClassFileReader classFileReader =
new ClassFileReader(classBytes, fileName,
true);
return
new NameEnvironmentAnswer(classFileReader, null);
}
} catch (IOException exc) {
log.error("Compilation error", exc);
} catch (org.eclipse.jdt.internal.compiler.classfmt.ClassFormatException exc) {
log.error("Compilation error", exc);
} finally {
if (is != null) {
try {
is.close();
} catch (IOException exc) {
// Ignore
}
}
}
return null;
} private boolean isPackage(String result) {
if (result.equals(targetClassName)) {
return false;
}
String resourceName = result.replace('.', '/') + ".class";
InputStream is =
classLoader.getResourceAsStream(resourceName);
return is == null;
} public boolean isPackage(char[][] parentPackageName,
char[] packageName) {
String result = "";
String sep = "";
if (parentPackageName != null) {
for (int i = 0; i < parentPackageName.length; i++) {
result += sep;
String str = new String(parentPackageName[i]);
result += str;
sep = ".";
}
}
String str = new String(packageName);
if (Character.isUpperCase(str.charAt(0))) {
if (!isPackage(result)) {
return false;
}
}
result += sep;
result += str;
return isPackage(result);
} public void cleanup() {
} }; final IErrorHandlingPolicy policy =
DefaultErrorHandlingPolicies.proceedWithAllProblems(); final Map settings = new HashMap();
settings.put(CompilerOptions.OPTION_LineNumberAttribute,
CompilerOptions.GENERATE);
settings.put(CompilerOptions.OPTION_SourceFileAttribute,
CompilerOptions.GENERATE);
settings.put(CompilerOptions.OPTION_ReportDeprecation,
CompilerOptions.IGNORE);
if (ctxt.getOptions().getJavaEncoding() != null) {
settings.put(CompilerOptions.OPTION_Encoding,
ctxt.getOptions().getJavaEncoding());
}
if (ctxt.getOptions().getClassDebugInfo()) {
settings.put(CompilerOptions.OPTION_LocalVariableAttribute,
CompilerOptions.GENERATE);
} // Source JVM
if(ctxt.getOptions().getCompilerSourceVM() != null) {
String opt = ctxt.getOptions().getCompilerSourceVM();
if(opt.equals("1.1")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_1);
} else if(opt.equals("1.2")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_2);
} else if(opt.equals("1.3")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_3);
} else if(opt.equals("1.4")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_4);
} else if(opt.equals("1.5")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_5);
} else if(opt.equals("1.6")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_6);
} else if(opt.equals("1.7")) {
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_7);
} else {
log.warn("Unknown source VM " + opt + " ignored.");
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_5);
}
} else {
// Default to 1.5
settings.put(CompilerOptions.OPTION_Source,
CompilerOptions.VERSION_1_5);
} // Target JVM
if(ctxt.getOptions().getCompilerTargetVM() != null) {
String opt = ctxt.getOptions().getCompilerTargetVM();
if(opt.equals("1.1")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_1);
} else if(opt.equals("1.2")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_2);
} else if(opt.equals("1.3")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_3);
} else if(opt.equals("1.4")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_4);
} else if(opt.equals("1.5")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_5);
settings.put(CompilerOptions.OPTION_Compliance,
CompilerOptions.VERSION_1_5);
} else if(opt.equals("1.6")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_6);
settings.put(CompilerOptions.OPTION_Compliance,
CompilerOptions.VERSION_1_6);
} else if(opt.equals("1.7")) {
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_7);
settings.put(CompilerOptions.OPTION_Compliance,
CompilerOptions.VERSION_1_7);
} else {
log.warn("Unknown target VM " + opt + " ignored.");
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_5);
}
} else {
// Default to 1.5
settings.put(CompilerOptions.OPTION_TargetPlatform,
CompilerOptions.VERSION_1_5);
settings.put(CompilerOptions.OPTION_Compliance,
CompilerOptions.VERSION_1_5);
} final IProblemFactory problemFactory =
new DefaultProblemFactory(Locale.getDefault()); final ICompilerRequestor requestor = new ICompilerRequestor() {
public void acceptResult(CompilationResult result) {
try {
if (result.hasProblems()) {
IProblem[] problems = result.getProblems();
for (int i = 0; i < problems.length; i++) {
IProblem problem = problems[i];
if (problem.isError()) {
String name =
new String(problems[i].getOriginatingFileName());
try {
problemList.add(ErrorDispatcher.createJavacError
(name, pageNodes, new StringBuffer(problem.getMessage()),
problem.getSourceLineNumber(), ctxt));
} catch (JasperException e) {
log.error("Error visiting node", e);
}
}
}
}
if (problemList.isEmpty()) {
ClassFile[] classFiles = result.getClassFiles();
for (int i = 0; i < classFiles.length; i++) {
ClassFile classFile = classFiles[i];
char[][] compoundName =
classFile.getCompoundName();
String className = "";
String sep = "";
for (int j = 0;
j < compoundName.length; j++) {
className += sep;
className += new String(compoundName[j]);
sep = ".";
}
byte[] bytes = classFile.getBytes();
String outFile = outputDir + "/" +
className.replace('.', '/') + ".class";
FileOutputStream fout =
new FileOutputStream(outFile);
BufferedOutputStream bos =
new BufferedOutputStream(fout);
bos.write(bytes);
bos.close();
}
}
} catch (IOException exc) {
log.error("Compilation error", exc);
}
}
}; ICompilationUnit[] compilationUnits =
new ICompilationUnit[classNames.length];
for (int i = 0; i < compilationUnits.length; i++) {
String className = classNames[i];
compilationUnits[i] = new CompilationUnit(fileNames[i], className);
}
Compiler compiler = new Compiler(env,
policy,
settings,
requestor,
problemFactory,
true);
compiler.compile(compilationUnits); if (!ctxt.keepGenerated()) {
File javaFile = new File(ctxt.getServletJavaFileName());
javaFile.delete();
} if (!problemList.isEmpty()) {
JavacErrorDetail[] jeds =
(JavacErrorDetail[]) problemList.toArray(new JavacErrorDetail[0]);
errDispatcher.javacError(jeds);
} if( log.isDebugEnabled() ) {
long t2=System.currentTimeMillis();
log.debug("Compiled " + ctxt.getServletJavaFileName() + " "
+ (t2-t1) + "ms");
} if (ctxt.isPrototypeMode()) {
return;
} // JSR45 Support
if (! options.isSmapSuppressed()) {
SmapUtil.installSmap(smap);
} } }
TomcatAdapter
从427可以知道，Tomcat使用了org.eclipse.jdt.internal.compiler.Compiler#compile(ICompilationUnit[])
当然，在这之前使用了很多代码来进行配置。
第一篇文章就到这里。
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（最后编辑时间2014-01-18 13:59:01）
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