All In One Examples

Application

Program

package sample;

import java.lang.management.ManagementFactory;
import java.util.Random;
import java.util.concurrent.TimeUnit;

public class Program {
    public static void main(String[] args) throws Exception {
        // 第一步，打印进程 ID
        String nameOfRunningVM = ManagementFactory.getRuntimeMXBean().getName();
        System.out.println(nameOfRunningVM);

        // 第二步，倒计时退出
        int count = 600;
        for (int i = 0; i < count; i++) {
            String info = String.format("|%03d| %s remains %03d seconds", i, nameOfRunningVM, (count - i));
            System.out.println(info);

            Random rand = new Random(System.currentTimeMillis());
            int a = rand.nextInt(10);
            int b = rand.nextInt(10);
            boolean flag = rand.nextBoolean();
            String message;
            if (flag) {
                message = String.format("a + b = %d", HelloWorld.add(a, b));
            }
            else {
                message = String.format("a - b = %d", HelloWorld.sub(a, b));
            }
            System.out.println(message);

            TimeUnit.SECONDS.sleep(1);
        }
    }
}

HelloWorld

package sample;

public class HelloWorld extends Object implements Cloneable {
    public int intValue;
    public String strValue;

    public static int add(int a, int b) {
        return a + b;
    }

    public static int sub(int a, int b) {
        return a - b;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

Agent Jar

define

package lsieun.agent;

import lsieun.instrument.*;
import lsieun.utils.*;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.Instrumentation;

public class LoadTimeAgent {
    public static void premain(String agentArgs, Instrumentation inst) {
        // 第一步，打印信息：agentArgs, inst, classloader, thread
        PrintUtils.printAgentInfo(LoadTimeAgent.class, "Premain-Class", agentArgs, inst);

        // 第二步，指定要修改的类
        String className = "sample.HelloWorld";

        // 第三步，使用 inst：添加 transformer
        ClassFileTransformer transformer = new ASMTransformer(className);
        inst.addTransformer(transformer, false);
    }
}

redefine

package lsieun.agent;

import lsieun.instrument.*;
import lsieun.utils.*;

import java.io.InputStream;
import java.lang.instrument.ClassDefinition;
import java.lang.instrument.Instrumentation;

public class DynamicAgent {
    public static void agentmain(String agentArgs, Instrumentation inst) {
        // 第一步，打印信息：agentArgs, inst, classloader, thread
        PrintUtils.printAgentInfo(DynamicAgent.class, "Agent-Class", agentArgs, inst);

        // 第二步，指定要修改的类
        String className = "sample.HelloWorld";

        // 第三步，使用 inst：进行 redefine 操作
        // ClassFileTransformer transformer = new StackTraceTransformer(className);
        // inst.addTransformer(transformer, true);
        try {
            Class<?> clazz = Class.forName(className);
            if (inst.isModifiableClass(clazz)) {
                String item = String.format("/%s.class", className.replace(".", "/"));
                System.out.println(item);
                InputStream in = LoadTimeAgent.class.getResourceAsStream(item);
                int available = in.available();
                byte[] bytes = new byte[available];
                in.read(bytes);
                ClassDefinition classDefinition = new ClassDefinition(clazz, bytes);
                inst.redefineClasses(classDefinition);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

retransform

package lsieun.agent;

import lsieun.instrument.*;
import lsieun.utils.*;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.Instrumentation;

public class DynamicAgent {
    public static void agentmain(String agentArgs, Instrumentation inst) {
        // 第一步，打印信息：agentArgs, inst, classloader, thread
        PrintUtils.printAgentInfo(DynamicAgent.class, "Agent-Class", agentArgs, inst);

        // 第二步，指定要修改的类
        String className = "sample.HelloWorld";

        // 第三步，使用 inst：进行 re-transform 操作
        ClassFileTransformer transformer = new ASMTransformer(className);
        inst.addTransformer(transformer, true);
        try {
            Class<?> clazz = Class.forName(className);
            if (inst.isModifiableClass(clazz)) {
                inst.retransformClasses(clazz);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            inst.removeTransformer(transformer);
        }
    }
}

Run

	define	redefine	retransform
Interface Add	OK	NO	NO
Field Add	OK	NO	NO
Method Add	OK	NO	NO
Method Remove	OK	NO	NO
Method Body Modify	OK	OK	OK

Interface Add

在 ASMTransformer 当中，修改代码：

ClassVisitor cv = new AddInterfaceVisitor(cw, "java/io/Serializable");

在 define 的情况下，正常运行；在 redefine 和 retransform 的情况下，则出现 UnsupportedOperationException 异常：

java.lang.UnsupportedOperationException: class redefinition failed: attempted to change superclass or interfaces

Field Add

在 ASMTransformer 当中，修改代码：

ClassVisitor cv = new AddFiledVisitor(cw, Opcodes.ACC_PUBLIC, "objValue", "Ljava/lang/Object;");

在 define 的情况下，正常运行；在 redefine 和 retransform 的情况下，则出现 UnsupportedOperationException 异常：

java.lang.UnsupportedOperationException: class redefinition failed: attempted to change the schema (add/remove fields)

Method Add

在 ASMTransformer 当中，修改代码：

ClassVisitor cv = new AddMethodVisitor(cw, Opcodes.ACC_PUBLIC, "mul", "(II)I", null, null) {
    @Override
    protected void generateMethodBody(MethodVisitor mv) {
        mv.visitCode();
        mv.visitVarInsn(Opcodes.ILOAD, 1);
        mv.visitVarInsn(Opcodes.ILOAD, 2);
        mv.visitInsn(Opcodes.IMUL);
        mv.visitInsn(Opcodes.IRETURN);
        mv.visitMaxs(2, 3);
        mv.visitEnd();
    }
};

在 define 的情况下，正常运行；在 redefine 和 retransform 的情况下，则出现 UnsupportedOperationException 异常：

java.lang.UnsupportedOperationException: class redefinition failed: attempted to add a method

Method Remove

在 ASMTransformer 当中，修改代码：

ClassVisitor cv = new RemoveMethodVisitor(cw, "sub", "(II)I");

在 define 的情况下，正常运行；在 redefine 和 retransform 的情况下，则出现 UnsupportedOperationException 异常：

java.lang.UnsupportedOperationException: class redefinition failed: attempted to delete a method

Method Body Modify

在 ASMTransformer 当中，修改代码：

ClassVisitor cv = new PrintMethodParameterVisitor(cw);

在 define 的情况下，正常运行；在 redefine 和 retransform 的情况下，也正常运行。

Stack Trace

将 ASMTransformer 类替换成 StackTraceTransformer 类。

在 define 情况，从下面的输出结果可以看到是 ClassLoader.defineClass() 方法触发的：

$ java -cp ./target/classes/ -javaagent:./target/TheAgent.jar sample.Program

java.lang.Exception: Exception From lsieun.instrument.StackTraceTransformer
        at lsieun.instrument.StackTraceTransformer.transform(StackTraceTransformer.java:23)
        at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
        at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        at sample.Program.main(Program.java:25)

在 redefine 情况，从下面的输出结果可以看到是 InstrumentationImpl.redefineClasses() 方法触发的：

java.lang.Exception: Exception From lsieun.instrument.StackTraceTransformer
        at lsieun.instrument.StackTraceTransformer.transform(StackTraceTransformer.java:23)
        at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
        at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
        at sun.instrument.InstrumentationImpl.redefineClasses0(Native Method)
        at sun.instrument.InstrumentationImpl.redefineClasses(InstrumentationImpl.java:170)
        at lsieun.agent.DynamicAgent.agentmain(DynamicAgent.java:32)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
        at sun.instrument.InstrumentationImpl.loadClassAndCallAgentmain(InstrumentationImpl.java:411)

在 retransform 情况，从下面的输出结果可以看到是 InstrumentationImpl.retransformClasses() 方法触发的：

java.lang.Exception: Exception From lsieun.instrument.StackTraceTransformer
        at lsieun.instrument.StackTraceTransformer.transform(StackTraceTransformer.java:23)
        at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
        at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
        at sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
        at sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:144)
        at lsieun.agent.DynamicAgent.agentmain(DynamicAgent.java:42)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
        at sun.instrument.InstrumentationImpl.loadClassAndCallAgentmain(InstrumentationImpl.java:411)