3.6 执行InjectUnitTest.java的test()方法查看InjectTest.class结果
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package com.xyaty.asmdemo;
public class InjectTest {
public InjectTest() {
long var1 = System.currentTimeMillis();
long var3 = System.currentTimeMillis();
System.out.println("execute: " + (var3 - var1) + "ms");
}
public static void main(String[] var0) throws InterruptedException {
long var1 = System.currentTimeMillis();
Thread.sleep(1000L);
long var3 = System.currentTimeMillis();
System.out.println("execute: " + (var3 - var1) + "ms");
}
public void methodA() {
long var1 = System.currentTimeMillis();
System.out.println("methodA");
long var3 = System.currentTimeMillis();
System.out.println("execute: " + (var3 - var1) + "ms");
}
}
发现在每个方法中都加入了
long var1 = System.currentTimeMillis();
和
long var3 = System.currentTimeMillis();
System.out.println("execute: " + (var3 - var1) + "ms");
如果仅仅在main()方法才注入代码，就需要引入自定义注解来标记指定的方法
四、引入自定义注解，标记方法才注入代码
4.1 注解类ASMTest.java，并通过javac编译成ASMTest.class（略）
package com.xyaty.asmdemo;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* DESC :
*/
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.METHOD)
public @interface ASMTest {
}
4.2 在InjectTest.java的main()方法上加上注解@ASMTest，标记此方法，并通过javac生成class
package com.xyaty.asmdemo;
/**
* DESC :
*/
public class InjectTest {
@ASMTest
public static void main(String[] args) throws InterruptedException {
Thread.sleep(1000);
}
public void methodA() {
System.out.println("methodA");
}
}
4.3 在上述MyMethodVisitor的下列方法中加入注解判断
@Override
public AnnotationVisitor visitAnnotation(String descriptor, boolean visible) {
System.out.println("visitAnnotation===>methodName="+getName()+", descriptor="+descriptor);
//如果方法的注解名字是@ASMTest，则给此方法注入代码
if ("Lcom/xyaty/asmdemo/ASMTest;".equals(descriptor)) {
isInject = true;
} else {
isInject = false;
}
return super.visitAnnotation(descriptor, visible);
}
/**
* 进入方法插入内容
*/
@Override
protected void onMethodEnter() {
super.onMethodEnter();
if (!isInject) {
return;
}
}
@Override
protected void onMethodExit(int opcode) {
super.onMethodExit(opcode);
if (!isInject) {
return;
}
}
InjectUnitTest.java完整代码如下：
package com.xyaty.asmdemo;
import org.junit.Test;
import org.objectweb.asm.AnnotationVisitor;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.commons.AdviceAdapter;
import org.objectweb.asm.commons.Method;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
/**
* DESC :
*/
public class InjectUnitTest {
/**
* 单元测试方法，右击test()方法，选择run test()方法即可查看结果
*/
@Test
public void test() {
try {
//读取待插桩的class
FileInputStream fis = new FileInputStream(
new File("src/test/java/com/xyaty/asmdemo/InjectTest.class"));
/**
* 执行分析与插桩
* ClassReader是class字节码的读取与分析引擎
*/
ClassReader classReader = new ClassReader(fis);
// ClassWriter写出器， COMPUTE_FRAMES表示自动计算栈帧和局部变量表的大小
ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
/**
* 执行分析，处理结果写入classWriter， EXPAND_FRAMES表示栈图以扩展格式进行访问
* 执行插桩的代码就在MyClassVisitor中实现
*/
classReader.accept(new MyClassVisitor(Opcodes.ASM9, classWriter), ClassReader.EXPAND_FRAMES);
//获得执行了插桩之后的字节码数据
byte[] bytes = classWriter.toByteArray();
// 重新写入InjectTest.class中（也可以写入到其他class中，InjectTest1.class），完成插桩
FileOutputStream fos = new FileOutputStream(
new File("src/test/java/com/xyaty/asmdemo/InjectTest.class"));
fos.write(bytes);
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
public class MyClassVisitor extends ClassVisitor {
public MyClassVisitor(int api, ClassVisitor classVisitor) {
super(api, classVisitor);
}
@Override
public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
System.out.println("visitMethod==>name="+name);
/**
* 会输出以下方法：
* visitMethod==>name=<init>
* visitMethod==>name=main
*/
MethodVisitor methodVisitor = super.visitMethod(access, name, descriptor, signature, exceptions);
return new MyMethodVisitor(api, methodVisitor, access, name,descriptor);
}
}
/**
* 之所以继承自AdviceAdapter，是因为AdviceAdapter是MethodVisitor的子类，
* AdviceAdapter封装了指令插入方法，更为直观与简单，
* 要使用其中的onMethodEnter和 onMethodExit方法进行字节码插桩，
*
* 继承关系如下：
* AdviceAdapter extends GeneratorAdapter
* GeneratorAdapter extends LocalVariablesSorter
* LocalVariablesSorter extends MethodVisitor
*/
public class MyMethodVisitor extends AdviceAdapter {
long start;
private int startIdentifier;
private boolean isInject = false;//是否注入代码
@Override
public AnnotationVisitor visitAnnotation(String descriptor, boolean visible) {
System.out.println("visitAnnotation===>methodName="+getName()+", descriptor="+descriptor);
//如果方法的注解名字是@ASMTest，则给此方法注入代码
if ("Lcom/xyaty/asmdemo/ASMTest;".equals(descriptor)) {
isInject = true;
} else {
isInject = false;
}
return super.visitAnnotation(descriptor, visible);
}
protected MyMethodVisitor(int api, MethodVisitor methodVisitor, int access, String name, String descriptor) {
super(api, methodVisitor, access, name, descriptor);
}
/**
* 进入方法插入内容
*/
@Override
protected void onMethodEnter() {
super.onMethodEnter();
if (!isInject) {
return;
}
// start = System.currentTimeMillis();
/**
* @Type owner 调用哪个类
* @Method method 调用某个类的静态方法（参数name: 方法名字，descriptor：方法中参数和方法返回值类型）
*/
invokeStatic(Type.getType("Ljava/lang/System;"), new Method("currentTimeMillis", "()J"));
//调用newLocal创建一个long类型的变量，返回一个int类型索引identifier
startIdentifier = newLocal(Type.LONG_TYPE);
//保存到本地变量索引中，用一个本地变量接收上一步执行的结果
storeLocal(startIdentifier);
}
/**
* 在方法结尾插入内容
* @param opcode
*/
@Override
protected void onMethodExit(int opcode) {
super.onMethodExit(opcode);
if (!isInject) {
return;
}
// long end = System.currentTimeMillis();
// System.out.println("execute: "+(end - start)+"ms");
invokeStatic(Type.getType("Ljava/lang/System;"), new Method("currentTimeMillis", "()J"));
//调用newLocal创建一个long类型的变量，返回一个int类型索引identifier
int endIdentifier = newLocal(Type.LONG_TYPE);
//保存到本地变量索引中，用一个本地变量接收上一步执行的结果
storeLocal(endIdentifier);
//获取System的静态字段out,类型为PrintStream
getStatic(Type.getType("Ljava/lang/System;"),
"out", Type.getType("Ljava/io/PrintStream;"));
/**
* "execute: "+(end - start)+"ms"实际是内部创建StringBuilder来拼接
* 源码：NEW java/lang/StringBuilder
* 创建一个对象StringBuilder
*/
newInstance(Type.getType("Ljava/lang/StringBuilder;"));
// dup压入栈顶，让下面的INVOKESPECIAL 知道执行谁的构造方法创建StringBuilder
dup();
/**
* 源码：INVOKESPECIAL java/lang/StringBuilder.<init> ()V
* 创建StringBuilder的构造方法，用init来代替
*/
invokeConstructor(Type.getType("Ljava/lang/StringBuilder;"),
new Method("<init>", "()V"));
visitLdcInsn("execute: ");
/**
* 源码：INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
* 调用append方法
*/
invokeVirtual(Type.getType("Ljava/lang/StringBuilder;"),
new Method("append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;"));
/**
* 对结束时间和开始时间进行减法操作
* LLOAD 3 先加载结束时间
* LLOAD 1 后加载开始时间
* LSUB 执行减法操作
*/
loadLocal(endIdentifier);
loadLocal(startIdentifier);
//执行减法操作，返回long类型
math(SUB, Type.LONG_TYPE);
/**
* 源码：INVOKEVIRTUAL java/lang/StringBuilder.append (J)Ljava/lang/StringBuilder;
* LDC "ms"
*/
invokeVirtual(Type.getType("Ljava/lang/StringBuilder;"),
new Method("append", "(J)Ljava/lang/StringBuilder;"));
//拼接毫秒
visitLdcInsn("ms");
/**
* 源码：
* INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
* INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
* INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
*/
invokeVirtual(Type.getType("Ljava/lang/StringBuilder;"),
new Method("append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;"));
invokeVirtual(Type.getType("Ljava/lang/StringBuilder;"),
new Method("toString", "()Ljava/lang/String;"));
invokeVirtual(Type.getType("Ljava/io/PrintStream;"),
new Method("println", "(Ljava/lang/String;)V"));
}
}
}
再次运行InjectTest.class结果如下，可以看到只有main()方法注入了代码
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package com.xyaty.asmdemo;
public class InjectTest {
public InjectTest() {
}
@ASMTest
public static void main(String[] var0) throws InterruptedException {
long var1 = System.currentTimeMillis();
Thread.sleep(1000L);
long var3 = System.currentTimeMillis();
System.out.println("execute: " + (var3 - var1) + "ms");
}
public void methodA() {
System.out.println("methodA");
}
}
到此结束。
参考文章：
https://blog.csdn.net/zenmela2011/article/details/125586333
https://blog.csdn.net/huangbin123/article/details/123322667
