BTrace 问题辅助排查工具使用手册

　　BTrace是调试神器，可以通过自己编写的脚本，获取应用的一切调用信息。而不需要重启应用！

Btrace 项目源码信息（你行你上~）

项目地址：http://github.com/btraceio/btrace

但是应用下载地址是: https://github.com/btraceio/btrace/releases   （因为一般你并不想编译这些代码）

小白的打开姿势，操作步骤：

　　1. 打开 jvisualVm 工具;
　　2. 加载 BTrace 工具, 先把 插件中心地址更改掉: https://visualvm.github.io/uc/8u131/updates.xml.gz ;
　　3. 连接到想要 trace 的服务器, 如本地 tomcat;
　　4. 右击tomcat进程，> Trace application...
　　5. 写debug程序，样例如下:(在IDE中编写)

　　6. 直接使用 brace监控： btrace <pid> BtraceScript.java

来个例子：（拦截 spring 的 doService 方法）

/* BTrace Script Template */

import com.sun.btrace.AnyType;
import com.sun.btrace.BTraceUtils;
import com.sun.btrace.annotations.BTrace;
import com.sun.btrace.annotations.Duration;
import com.sun.btrace.annotations.Kind;
import com.sun.btrace.annotations.Location;
import com.sun.btrace.annotations.OnMethod;
import com.sun.btrace.annotations.ProbeClassName;
import com.sun.btrace.annotations.ProbeMethodName;

import static com.sun.btrace.BTraceUtils.currentThread;
import static com.sun.btrace.BTraceUtils.probeLine;
import static com.sun.btrace.BTraceUtils.threadId;

@BTrace
public class TracingScript {
    /* put your code here */
    @OnMethod(
            clazz = "/org.springframework.servlet.+/",
            method = "/doService.*/",
            location = @Location(Kind.RETURN)
    )
    public static void traceExecute(AnyType[] args, @ProbeClassName String name, @ProbeMethodName String method, @Duration long time) {
        long durationTime = time/1000000;
        if(durationTime > 0){
            String output = name + "." + method + "#" + probeLine() + " cost: " + durationTime + "ms, ThreadId:" + threadId(currentThread());
            BTraceUtils.println(output);
            // 打印整体参数
            BTraceUtils.printArray(args);
            // 调用应用的各字段进行反射调用
            BTraceUtils.printFields(args[1]);
            BTraceUtils.printFields(args[2]);
            BTraceUtils.println("over...");
            // 结束符
            BTraceUtils.println("");
        }
    }
}

在IDE中编写时，需要导入 pom.xml 如下：

        <!-- https://mvnrepository.com/artifact/com.sun.tools.btrace/btrace-agent -->
        <dependency>
            <groupId>com.sun.tools.btrace</groupId>
            <artifactId>btrace-agent</artifactId>
            <version>1.1.3</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.sun.tools.btrace/btrace-boot -->
        <dependency>
            <groupId>com.sun.tools.btrace</groupId>
            <artifactId>btrace-boot</artifactId>
            <version>1.1.3</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.sun.tools.btrace/btrace-client -->
        <dependency>
            <groupId>com.sun.tools.btrace</groupId>
            <artifactId>btrace-client</artifactId>
            <version>1.1.3</version>
        </dependency>

2. 拦截方法定义,也说是 @OnMethod 注解的作用
　　Btrace使用@OnMethod注解定义需要分析的方法入口，在@OnMethod注解中，需要指定class、method以及location等，class表明需要监控的类，method表明需要监控的方法!

@OnMethod(
            clazz = "/org.springframework.servlet.+/",
            method = "/doService.*/",
            location = @Location(Kind.RETURN)
    )

　　1. 正则表达式定位（全匹配是正则的一种特例）

　　　　可以用表达式，批量定义需要监控的类与方法。正则表达式需要写在两个 "/" 中间。
　　　　通过在拦截函数的定义里注入@ProbeClassName String probeClass, @ProbeMethodName String probeMethod 参数，告诉脚本实际匹配到的类和方法名。
　　2. 按接口，父类，Annotation定位

　　比如我想匹配所有的Filter类，在接口或基类的名称前面，加个+ 就行

@OnMethod(clazz="+com.vip.demo.Filter", method="doFilter")

　　也可以按类或方法上的annotaiton匹配，也就是注解匹配，前面加上@就行

@OnMethod(clazz="@javax.jws.WebService", method="@javax.jws.WebMethod")

　　3. 构造方法匹配  <init>

@OnMethod(clazz="java.net.ServerSocket", method="<init>")

　　4. 静态内部类的写法，在类与内部类之间加上"$"

@OnMethod(clazz="com.vip.MyServer$MyInnerClass", method="hello")

3. 拦截时机， 即@Location注解的作用

// Location 的定义
/**
 * This annotation specifies a particular "location" within a
 * traced/probed java method for BTrace probe specifications.
 *
 * @author A. Sundararajan
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Location {
    /**
     * Kind of the location.
     *
     * @see Kind
     */
    Kind value() default Kind.ENTRY;

    /**
     * Specifies where do want to probe with
     * respect to the location of interest.
     *
     * @see Where
     */
    Where where() default Where.BEFORE;

    /**
     * Specifies the fully qualified class name for
     * certain kind of probe locations.
     *
     * <p>
     * <h3>Since 1.3.11</h3>
     * The specification can contain references to user arguments.
     * These references are using Ant style substitution patterns.
     * If a reference is not resolvable the whole probe point will be effectively disabled.
     * <br>
     * <pre>
     * {@code @OnMethod(clazz = "MyClass", method = "myMethod", location = @Location(clazz = "${package}.OtherClass"))}
     * </pre>
     * </p>
     */
    String clazz() default "";

    /**
     * Specifies the method name for
     * certain kind of probe locations.
     *
     * <p>
     * <h3>Since 1.3.11</h3>
     * The specification can contain references to user arguments.
     * These references are using Ant style substitution patterns.
     * If a reference is not resolvable the whole probe point will be effectively disabled.
     * <br>
     * <pre>
     * {@code @OnMethod(clazz = "MyClass", method = "myMethod", location = @Location(clazz = "OtherClass", method = "${method}"))}
     * </pre>
     * </p>
     */
    String method() default "";

    /**
     * Specifies the field name for Kind.FIELD_SET
     * and Kind.FIELD_GET probes.
     *
     * @see Kind#FIELD_GET
     * @see Kind#FIELD_SET
     *
     * <p>
     * <h3>Since 1.3.11</h3>
     * The specification can contain references to user arguments.
     * These references are using Ant style substitution patterns.
     * If a reference is not resolvable the whole probe point will be effectively disabled.
     * <br>
     * <pre>
     * {@code @OnMethod(clazz = "MyClass", method = "myMethod", location = @Location(clazz = "OtherClass", field = "${field}"))}
     * </pre>
     * </p>
     */
    String field() default "";

    /**
     * Specifies field or method type for
     * certain kind of probe locations. The type
     * is specified like in Java source - except
     * the method or field name and parameter names
     * are not included.
     *
     * <p>
     * <h3>Since 1.3.11</h3>
     * The specification can contain references to user arguments.
     * These references are using Ant style substitution patterns.
     * If a reference is not resolvable the whole probe point will be effectively disabled.
     * <br>
     * <pre>
     * {@code @OnMethod(clazz = "MyClass", method = "myMethod", location = @Location(clazz = "OtherClass", type = "${ret} ()"))}
     * </pre>
     * </p>
     */
    String type() default "";

    /**
     * Specifies the line number for Kind.LINE probes.
     *
     * @see Kind#LINE
     */
    int line() default 0;
}

// Kind 的定义
public enum Kind {
    /**
     * <h2>Array element load</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@code type[]} - the array instance</li>
     *   <li>{@link int int} - array index</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain Return} - the return value of the method call (only for {@linkplain Where#AFTER})</li>
     * </ul>
     */
    ARRAY_GET,

    /**
     * <h2>Array element store</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@code type[]} - the array instance</li>
     *   <li>{@link int int} - array index</li>
     *   <li>{@link java.lang.Object Object} - new value</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     * </ul>
     */
    ARRAY_SET,

    /**
     * <h2>Method call</h2>
     * <p>
     * The order and number of unannotated parameters (if provided) must
     * fully match the called method signature. Instead of specific parameter
     * types one can use {@linkplain AnyType} to match any type.
     * <p>
     * If the only unannotated parameter is of type {@link AnyType AnyType[]}
     * it will contain the called method parameters in the order defined by
     * its signature.
     *
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain TargetInstance} - the target instance of the method call
     *       or null if the method is static</li>
     *   <li>{@linkplain TargetMethodOrField} - the name of the method which is called</li>
     *   <li>{@linkplain Return} - the return value of the method call (only for {@linkplain Where#AFTER})</li>
     *   <li>{@linkplain Duration} - the method call duration in nanoseconds (only for {@linkplain Where#AFTER}</li>
     * </ul>
     */
    CALL,

    /**
     * <h2>Exception catch</h2>
     *
     * <p>
     * The order and number of unannotated parameters (if provided) must
     * fully match the probed method signature. Instead of specific parameter
     * types one can use {@linkplain AnyType} to match any type.
     * <p>
     * If the only unannotated parameter is of type {@link AnyType AnyType[]}
     * it will contain the probed method parameters in the order defined by
     * its signature.
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain TargetInstance} - the caught {@linkplain Throwable} (@since 1.3.11)</li>
     * </ul>
     */
    CATCH,

    /**
     * <h2>Checkcast</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.String String} - type to cast to</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain TargetInstance} - the casted instance ({@linkplain AnyType})</li>
     * </ul>
     */
    CHECKCAST,

    /**
     * <h2>Method entry</h2>
     * <p>
     * The order and number of unannotated parameters (if provided) must
     * fully match the probed method signature. Instead of specific parameter
     * types one can use {@linkplain AnyType} to match any type.
     * <p>
     * If the only unannotated parameter is of type {@link AnyType AnyType[]}
     * it will contain the probed method parameters in the order defined by
     * its signature.
     *
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     * </ul>
     */
    ENTRY,

    /**
     * <h2>"return" because of no-catch</h2>
     *
     * <p>
     * The order and number of unannotated parameters (if provided) must
     * fully match the probed method signature. Instead of specific parameter
     * types one can use {@linkplain AnyType} to match any type.
     * <p>
     * If the only unannotated parameter is of type {@link AnyType AnyType[]}
     * it will contain the probed method parameters in the order defined by
     * its signature.
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain Duration} - the method call duration in nanoseconds (only for {@linkplain Where#AFTER}</li>
     *   <li>{@linkplain TargetInstance} - the {@linkplain Throwable} instance (@since 1.3.11)</li>
     * </ul>
     */
    ERROR,

    /**
     * <h2>Getting a field value</h2>
     *
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain TargetInstance} - the field owner instance or null
     *       if the field is static</li>
     *   <li>{@linkplain TargetMethodOrField} - the name of the method which is called</li>
     *   <li>{@linkplain Return} - the return value of the method call (only for {@linkplain Where#AFTER})</li>
     * </ul>
     */
    FIELD_GET,

    /**
     * <h2>Setting a field value</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.Object Object} - new field value</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that field is static</li>
     *   <li>{@linkplain TargetInstance} - the field owner instance or null
     *       if the field is static</li>
     *   <li>{@linkplain TargetMethodOrField} - the name of the method which is called</li>
     * </ul>
     */
    FIELD_SET,

    /**
     * <h2>instanceof check</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.String String} - type to check against</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain TargetInstance} - the checked instance ({@linkplain AnyType})</li>
     * </ul>
     */
    INSTANCEOF,

    /**
     * <h2>Source line number</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link int int} - line number</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     * </ul>
     */
    LINE,

    /**
     * <h2>New object created</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.String String} - object type name</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain Return} - the return value of the method call (only for {@linkplain Where#AFTER})</li>
     * </ul>
     */
    NEW,

    /**
     * <h2>New array created</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.String String} - array type name</li>
     *   <li>{@link int int} - number of dimensions</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain Return} - the return value of the method call (only for {@linkplain Where#AFTER})</li>
     * </ul>
     */
    NEWARRAY,

    /**
     * <h2>Return from method</h2>
     * <p>
     * The order and number of unannotated probe handler parameters (if provided)
     * must fully match the probed method signature. Instead of specific parameter
     * types one can use {@linkplain AnyType} to match any type.
     * <p>
     * If the only unannotated parameter is of type {@link AnyType AnyType[]}
     * it will contain the probed method parameters in the order defined by
     * its signature.
     *
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain Return} - the return value of the method call (only for {@linkplain Where#AFTER})</li>
     *   <li>{@linkplain Duration} - the method call duration in nanoseconds (only for {@linkplain Where#AFTER}</li>
     * </ul>
     */
    RETURN,

    /**
     * <h2>Entry into a synchronized block</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.Object Object} - lock object</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     * </ul>
     */
    SYNC_ENTRY,

    /**
     * <h2>Exit from a synchronized block</h2>
     *
     * <h3>Unannotated probe handler parameters:</h3>
     * <ol>
     *   <li>{@link java.lang.Object Object} - lock object</li>
     * </ol>
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     * </ul>
     */
    SYNC_EXIT,

    /**
     * <h2>Throwing an exception</h2>
     *
     * <p>
     * The order and number of unannotated parameters (if provided) must
     * fully match the probed method signature. Instead of specific parameter
     * types one can use {@linkplain AnyType} to match any type.
     * <p>
     * If the only unannotated parameter is of type {@link AnyType AnyType[]}
     * it will contain the probed method parameters in the order defined by
     * its signature.
     * <h3>Allowed probe handler parameter annotations:</h3>
     * <ul>
     *   <li>{@linkplain ProbeClassName} - the name of the enclosing class</li>
     *   <li>{@linkplain ProbeMethodName} - the name of the enclosing method</li>
     *   <li>{@linkplain Self} - the instance enclosing the declaring method or null
     *       if that method is static</li>
     *   <li>{@linkplain TargetInstance} - the thrown exception (@since 1.3.11)</li>
     * </ul>
     */
    THROW
};

　　Location 主要属性有 value 和 where, 而 value 则是几个常用的定义点！

　　定义Btrace对方法的拦截位置，通过@Location注解指定，默认为Kind.ENTRY。可以为同一个函数的不同的Location，分别定义多个拦截函数。
　　1. Kind.Entry与Kind.Return
　　　　Kind.ENTRY：在进入方法时，调用Btrace脚本
　　　　Kind.RETURN：方法执行完时，调用Btrace脚本，只有把拦截位置定义为Kind.RETURN，才能获取方法的返回结果@Return和执行时间@Duration
　　　　duration的单位是纳秒，要除以 1,000,000 才是毫秒。
　　2. Kind.Error, Kind.Throw和 Kind.Catch
　　　　异常抛出(Throw)，异常被捕获(Catch)，异常没被捕获被抛出函数之外(Error)，主要用于对某些异常情况的跟踪。
　　　　在拦截函数的参数定义里注入一个Throwable的参数，代表异常。
　　3. Kind.Call与Kind.Line
　　　　Kind.CALL：分析方法中调用其它方法的执行情况，比如在execute方法中，想获取add方法的执行耗时，必须把where设置成Where.AFTER.
　　　　Kind.LINE：通过设置line，可以监控代码是否执行到指定的位置.
　　下例定义监控bind()函数里调用的所有其他函数:

　　　　@OnMethod(clazz = "java.net.ServerSocket", method = "bind", location = @Location(value = Kind.CALL, clazz = "/.*/", method = "/.*/", where = Where.AFTER))
　　　　public static void onBind(@Self Object self, @TargetInstance Object instance, @TargetMethodOrField String method, @Duration long duration)

　　所调用的类及方法名所注入到@TargetInstance与 @TargetMethodOrField中。

　　下例监控代码是否到达了Socket类的第363行。

　　　　@OnMethod(clazz = "java.net.ServerSocket", location = @Location(value = Kind.LINE, line = 363))

4. 如何使用Btrace定位问题

　　1. 打印this，参数 与 返回值

　　@OnMethod(clazz = "java.io.File", method = "createTempFile", location = @Location(value = Kind.RETURN))
　　public static void o(@Self Object self, String prefix, String suffix, @Return AnyType result)

　　如果想打印它们，首先按顺序定义用@Self 注释的this， 完整的参数列表，以及用@Return 注释的返回值。

　　需要打印哪个就定义哪个，不需要的就不要定义。但定义一定要按顺序，比如参数列表不能跑到返回值的后面。

　　Self：
　　　　如果是静态函数， self为空。
　　　　前面提到，如果上述使用了非JDK的类，命令行里要指定classpath。不过，如前所述，因为BTrace里不允许调用类的方法，所以定义具体类很多时候也没意 思，所以self定义为Object就够了。
　　　　参数数列表要么不要定义，要定义就要定义完整，否则BTrace无法处理不同参数的同名函数。
　　　　用AnyType来定义任意类型的参数，类似于 Object 。
　　2. 方法执行时，查看对象的实例属性值
　　　　再次强调，为了保证性能不受影响，Btrace不允许调用任何实例方法。
　　　　比如不能调用getter方法（怕在getter里有复杂的计算），只会通过直接反射来读取属性名。
　　　　又比如，除了JDK类，其他类toString时只会打印其类名＋System.IdentityHashCode。
　　　　println, printArray，都按上面的规律进行，所以只能打打基本类型。
　　　　如果想打印一个Object的属性，用printFields()来反射。
　　　　如果只想反射某个属性，参照下面打印Port属性的写法。从性能考虑，应把field用静态变量缓存起来。
　　注意JDK类与非JDK类的区别：

import java.lang.reflect.Field;
//JDK的类这样写就行
private static Field fdFiled = field("java.io,FileInputStream", "fd");
//非JDK的类，要给出ClassLoader，否则ClassNotFound
private static Field portField = field(classForName("com.vip.demo.MyObject", contextClassLoader()), "port");
public static void onChannelRead(@Self Object self) {
    println("port:" + getInt(portField, self));
}

　　3.TLS，拦截函数间的通信机制

　　如果要多个拦截函数之间要通信，可以使用@TLS定义 ThreadLocal的变量来共享

@TLS
private static int port = -1;
@OnMethod(clazz = "java.net.ServerSocket", method = "<init>")
public static void onServerSocket(int p){
    port = p;
}
@OnMethod(clazz = "java.net.ServerSocket", method = "bind")
public static void onBind(){
  println("server socket at " + port);
}

　　4. 谁调用了这个函数(原理：拦截到方法后，把堆栈打出来)

@OnMethod(clazz = "java.lang.System", method = "gc")
public static void onSystemGC() {
    println("entered System.gc()");
    jstack();
}

　　5. 统计方法的调用次数，且每隔1分钟打印调用次数

@Export static AtomicLong counter = new AtomicLong();
@OnMethod(class="com.**.MyObject",method="add")
public static void run(){
    counter.getAndIncrement();
}
@OnTimer(1000*60)
public static void run(){
    BTraceUtils.println("count: " + connter.get());
    counter.set(0);
}

5. linux 上使用 btrace!
　　1. 下载压btrace缩包： wget https://github.com/btraceio/btrace/releases/download/v1.3.11.3/btrace-bin-1.3.11.3.zip ；
　　2. 解压: unzip btrace-bin-1.3.11.3.zip -d btrace-bin-1.3.11.3；
　　3. cd btrace-bin-1.3.11.3, ./btrace <pid> TracingScript.java, 就可以看效果了；
　　4. 修改脚本以解决问题；

　　5. 通过反射机制，可以很方法的得到当前实例的属性值；

        //print one field
        Field oneFiled = BTraceUtils.field("com.xx.test", "name");
        BTraceUtils.println("print one field: " + BTraceUtils.get(oneFiled, args[0]));

　　6. BTraceUtils.printFields(args[1]); 调用封装好的打印复杂对象；

            // 调用应用的各字段进行反射调用
            BTraceUtils.printFields(args[1]);

　　注意： btrace 是字节码注入，是可能导致jvm退出的，所以，应尽量先在测试环境验证ok后，再到线上调用，或者把注入的类范围尽量的缩小，而非大的正则匹配如: clazz="/com.xxx.*/", method="/.*/"，就会导致大量的变更，影响性能也提高了运行风险！

　　快速定位你的线上问题！

　　最后，附上几个调试过程的几个经验之坑：

　　　　1. BTRACE_HOME 的设置，在 /etc/profile.d/btraceenv.sh 中设置即可； 如果不想设置BTRACE_HOME, 可以直接切换到btrace的bin目录操作即可；

　　　　2. 使用 JVisualVm 可以运行的trace代码，不代表使用命令行也运行，最好都使用命令行验证下脚本；

　　　　3. JVisualVm 及一些jdk环境，支持 unsafe=true, 而在其他环境则不一定允许； JVisualVm 中如果去除 unsafe=true, 则有些函数会受限制；

　　　　4. btrace 脚本如果正常情况无法运行如： btrace 7311 TracingScriptTemplate.java， 则可以切换到debug模式查看： btrace -v 7311 TracingScriptTemplate.java，这里面会出现很多btrace的调试日志，如果不想看这些日志，可以直接过滤掉： btrace -v 7311 TracingScriptTemplate.java | grep -v "DEBUG: "；

　　　　5. 借助IDE编写的Trace脚本，可以直接运行，即 trace 脚本可包含package包名，也可以没有包名；但文件必须要以.java结尾（没有试过其他小语种），否则编译时会报错；

　　　　6. 代码中如果本身就使用了一些开发脚本，如springboot的开发组件 spring-boot-devtools ， 则可能导致 btrace 脚本无法注入， 最好先去掉这些组件再上线；

最后，再附一个完整的链路监控的 script 供参考：

/* BTrace Script Template */

import com.sun.btrace.AnyType;
import com.sun.btrace.BTraceUtils;
import com.sun.btrace.annotations.*;

import static com.sun.btrace.BTraceUtils.currentThread;
import static com.sun.btrace.BTraceUtils.probeLine;
import static com.sun.btrace.BTraceUtils.threadId;

@BTrace
public class TracingScript {

    private static final String clazzForTracePattern = "/com.alipay.common.event.tbnotify.adapter.+/";
    private static final String methodForTracePattern = "/.*/";

    @OnMethod(
            clazz = clazzForTracePattern,
            method = methodForTracePattern,
            location = @Location(Kind.ENTRY)
    )
    public static void traceExecuteEnter(AnyType[] args, @ProbeClassName String name, @ProbeMethodName String method) {
        String output = "enter in: " + name + "." + method + "#" + probeLine() + ", ThreadId:" + threadId(currentThread());
        BTraceUtils.println(output);
        // 打印整体参数
        BTraceUtils.printArray(args);
        // 调用应用的各字段进行反射调用
        printPerFields(args);
        BTraceUtils.println("enter over...");
        // 结束符
        BTraceUtils.println("");
    }

    @OnMethod(
            clazz = clazzForTracePattern,
            method = methodForTracePattern,
            location = @Location(Kind.RETURN)
    )
    public static void traceExecuteReturn(AnyType[] args, @ProbeClassName String name, @ProbeMethodName String method, @Return AnyType result, @Duration long time) {
        long durationTime = time/1000000;
        if(durationTime > 0){
            String output = "return from: " + name + "." + method + "#" + probeLine() + " cost: " + durationTime + "ms, ThreadId:" + threadId(currentThread());
            BTraceUtils.println(output);
            // 打印整体参数
            BTraceUtils.printArray(args);
            printPerFields(args);
            BTraceUtils.printFields(result);
            BTraceUtils.println("return over...");
            // 结束符
            BTraceUtils.println("");
        }
    }

    // -----------------------------------------------------
    // =================  以下为捕获异常代码  ================
    // -----------------------------------------------------
    @TLS
    private static Throwable currentException;

    @OnMethod(
            clazz = "java.lang.Throwable",
            method = "<init>"
    )
    public static void onthrow(@Self Throwable self) {
        currentException = self;
    }

    @OnMethod(
            clazz = "java.lang.Throwable",
            method = "<init>"
    )
    public static void onthrow1(@Self Throwable self, String s) {
        currentException = self;
    }

    @OnMethod(
            clazz = "java.lang.Throwable",
            method = "<init>"
    )
    public static void onthrow1(@Self Throwable self, String s, Throwable cause) {
        currentException = self;
    }

    @OnMethod(
            clazz = "java.lang.Throwable",
            method = "<init>"
    )
    public static void onthrow2(@Self Throwable self, Throwable cause) {
        currentException = self;
    }

    @OnMethod(
            clazz = "java.lang.Throwable",
            method = "<init>",
            location = @Location(Kind.RETURN)
    )
    public static void onThrownReturn() {
        if (currentException != null) {
            BTraceUtils.jstack(currentException);
            BTraceUtils.print("<--------------->");
            currentException = null;
        }
    }

    private static void printPerFields(AnyType[] args) {
        // 调用应用的各字段进行反射调用
        if(args.length > 0) {
            BTraceUtils.printFields(args[0]);
        }
        if(args.length >= 2) {
            BTraceUtils.printFields(args[1]);
        }
        if(args.length >= 3) {
            BTraceUtils.printFields(args[2]);
        }
    }

}