准备

我们引入asm相关的依赖

  1. <dependency>
  2.             <groupId>org.ow2.asm</groupId>
  3.             <artifactId>asm</artifactId>
  4.             <version>7.2</version>
  5.         </dependency>
  6.         <dependency>
  7.             <groupId>org.ow2.asm</groupId>
  8.             <artifactId>asm-commons</artifactId>
  9.             <version>7.2</version>
  10.         </dependency>
  11.         <dependency>
  12.             <groupId>org.ow2.asm</groupId>
  13.             <artifactId>asm-util</artifactId>
  14.             <version>7.2</version>
  15.         </dependency>

先往代码里插入一句话

假定我们要在代码入口处插入如下语句

  1. System.out.println("hello, i come in ...");

我们先看一下对应的asm代码
image.png
此时，我们就可以照抄写好的代码了

  1. package com.deer.agent.sandbox;
  3. import org.objectweb.asm.*;
  5. import java.lang.instrument.ClassFileTransformer;
  6. import java.lang.instrument.IllegalClassFormatException;
  7. import java.security.ProtectionDomain;
  9. public class AgentClazzTransformer implements ClassFileTransformer {
  10.     @Override
  11.     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
  12.         if(className!=null && className.startsWith("com/deer/base/service")){
  13.             System.out.println("I can see you ...."+className);
  14.             //
  15.             ClassReader cr = new ClassReader(classfileBuffer);
  16.             ClassWriter cw = new ClassWriter(cr,ClassWriter.COMPUTE_FRAMES|ClassWriter.COMPUTE_MAXS);
  17.             cr.accept(new ClassVisitor(Opcodes.ASM7) {
  18.                 @Override
  19.                 public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
  20.                     System.out.println("name: "+name +",descriptor: "+descriptor+",signature: "+signature);
  21.                     MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);
  22.                     mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
  23.                     mv.visitLdcInsn("hello, i come in ...");
  24.                     mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
  25.                     return mv;
  26.                 }
  27.             },ClassWriter.COMPUTE_MAXS);
  29.             return cw.toByteArray();
  30.         }
  32.         return classfileBuffer;
  34.     }
  35. }

我们访问页面后结果如下
image.png
多次重复访问后如下
image.png

为什么没有按照预期执行

我们看上述截图，需要打印输出到console控制台的，没有输出，在方法访问的时候，加个日志，结果只执行了一遍构造函数的逻辑（），这是怎么了？

跳过构造函数

  1. package com.deer.agent.sandbox;
  3. import org.objectweb.asm.*;
  5. import java.lang.instrument.ClassFileTransformer;
  6. import java.lang.instrument.IllegalClassFormatException;
  7. import java.security.ProtectionDomain;
  9. public class AgentClazzTransformer implements ClassFileTransformer {
  10.     @Override
  11.     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
  12.         if(className!=null && className.startsWith("com/deer/base/service")){
  13.             System.out.println("I can see you ...."+className);
  14.             //
  15.             ClassReader cr = new ClassReader(classfileBuffer);
  16.             ClassWriter cw = new ClassWriter(cr,ClassWriter.COMPUTE_FRAMES|ClassWriter.COMPUTE_MAXS);
  17.             cr.accept(new ClassVisitor(Opcodes.ASM7) {
  18.                 @Override
  19.                 public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
  20.                     System.out.println("name: "+name +",descriptor: "+descriptor+",signature: "+signature);
  21.                     MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);
  22.                     //普通构造函数和静态构造函数
  23.                     if(name.equals("<init>") || name.equals("<clinit>")){
  24.                         return  mv;
  25.                     }
  26.                     mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
  27.                     mv.visitLdcInsn("hello, i come in ...");
  28.                     mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
  29.                     return mv;
  30.                 }
  31.             },ClassWriter.COMPUTE_MAXS);
  33.             return cw.toByteArray();
  34.         }
  36.         return classfileBuffer;
  38.     }
  39. }

image.png

计算方法耗时

  1. package com.deer.agent.sandbox;
  3. import org.objectweb.asm.*;
  5. import java.lang.instrument.ClassFileTransformer;
  6. import java.lang.instrument.IllegalClassFormatException;
  7. import java.security.ProtectionDomain;
  9. public class AgentClazzTransformer implements ClassFileTransformer {
  10.     @Override
  11.     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
  12.         if(className!=null && className.startsWith("com/deer/base/service")){
  13.             System.out.println("I can see you ...."+className);
  14.             //
  15.             ClassReader cr = new ClassReader(classfileBuffer);
  16.             ClassWriter cw = new ClassWriter(cr,ClassWriter.COMPUTE_FRAMES|ClassWriter.COMPUTE_MAXS);
  17.             cr.accept(new ClassVisitor(Opcodes.ASM7) {
  18.                 @Override
  19.                 public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
  20.                     System.out.println("name: "+name +",descriptor: "+descriptor+",signature: "+signature);
  21.                     long start = System.nanoTime();
  22.                     MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);
  23.                     //普通构造函数和静态构造函数
  24.                     if(name.equals("<init>") || name.equals("<clinit>")){
  25.                         return  mv;
  26.                     }
  27.                     long delta = System.nanoTime()-start;
  28.                     System.out.println("cost...."+delta);
  29.                     mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
  30.                     mv.visitLdcInsn("hello, i come in ...");
  31.                     mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
  32.                     return mv;
  33.                 }
  34.             },ClassWriter.COMPUTE_MAXS);
  36.             return cw.toByteArray();
  37.         }
  39.         return classfileBuffer;
  41.     }
  42. }

image.png

完成预期

我们观察以上输出结果，和预期相差比较远，但是思路和方向是对的，我们可以进一步进行思路整理，这里给每个类添加了一个字段ASM_TIME_COST，用于记录当前类的名字（方便打印信息）。同时记录每个方法的名字，以及执行时间。我们需要学习相关MethodVisitor的使用方法。完整代码如下

  1. package com.deer.agent.sandbox;
  3. import org.objectweb.asm.ClassReader;
  4. import org.objectweb.asm.ClassWriter;
  6. import java.lang.instrument.ClassFileTransformer;
  7. import java.lang.instrument.IllegalClassFormatException;
  8. import java.security.ProtectionDomain;
  10. public class AgentClazzTransformer implements ClassFileTransformer {
  11.     @Override
  12.     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
  13.         ClassReader cr = new ClassReader(classfileBuffer);
  14.         ClassWriter cw = new ClassWriter(cr,ClassWriter.COMPUTE_MAXS);
  15.         TimeCoster timeCoster = new TimeCoster(cw);
  16.         cr.accept(timeCoster,ClassReader.EXPAND_FRAMES);
  17.         return cw.toByteArray();
  18.     }
  19. }
  1. package com.deer.agent.sandbox;
  3. import org.objectweb.asm.*;
  4. import org.objectweb.asm.commons.AnalyzerAdapter;
  5. import org.objectweb.asm.commons.LocalVariablesSorter;
  7. public class TimeCoster extends ClassVisitor implements Opcodes {
  9.     private String clazzName;
  10.     private String methodName;
  11.     private boolean isInterface;
  12.     private boolean isPresent = false;
  14.     private String filedName = "ASM_TIME_COST";
  16.     public TimeCoster(ClassVisitor classVisitor) {
  17.         super(ASM7, classVisitor);
  18.     }
  20.     @Override
  21.     public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
  22.         super.visit(version, access, name, signature, superName, interfaces);
  23.         clazzName = name;
  24.         isInterface = (access & ACC_INTERFACE) != 0;
  25.     }
  27.     @Override
  28.     public FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value) {
  29.         if (name.equals(filedName)) {
  30.             isPresent = true;
  31.         }
  32.         return super.visitField(access, name, descriptor, signature, value);
  34.     }
  36.     @Override
  37.     public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
  38.         MethodVisitor mv = cv.visitMethod(access, name, descriptor, signature, exceptions);
  39.         //跳过java原生相关的类
  40.         if (!clazzName.startsWith("com/deer/base")
  41.         ) {
  42.             return mv;
  43.         }
  44.         if (!isInterface && mv != null && !name.equals("<init>") && !name.equals("<clinit>")) {
  46.             methodName = name;
  47.             TimerMethod timerMethod = new TimerMethod(mv);
  48.             timerMethod.aa = new AnalyzerAdapter(clazzName, access, name, descriptor, timerMethod);
  49.             timerMethod.lvs = new LocalVariablesSorter(access, descriptor, timerMethod.aa);
  50.             return timerMethod.lvs;
  51.         }
  52.         return mv;
  53.     }
  55.     @Override
  56.     public void visitEnd() {
  57.         if (!isInterface) {
  58.             FieldVisitor fv = cv.visitField(Opcodes.ACC_PUBLIC + Opcodes.ACC_STATIC + Opcodes.ACC_FINAL, filedName, "Ljava/lang/String;", null, clazzName);
  59.             if (fv != null) {
  60.                 fv.visitEnd();
  61.             }
  62.         }
  63.         super.visitEnd();
  64.     }
  66.     class TimerMethod extends MethodVisitor {
  67.         public LocalVariablesSorter lvs;
  68.         public AnalyzerAdapter aa;
  69.         private int time;
  70.         private int maxStack;
  72.         public TimerMethod(MethodVisitor methodVisitor) {
  73.             super(ASM7, methodVisitor);
  74.         }
  76.         @Override
  77.         public void visitCode() {
  78.             super.visitCode();
  79.             mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);
  80.             time = lvs.newLocal(Type.LONG_TYPE);
  81.             mv.visitVarInsn(LSTORE, time);
  82.             maxStack = 4;
  83.         }
  85.         @Override
  86.         public void visitInsn(int opcode) {
  87.             if (((opcode >= IRETURN && opcode <= RETURN) || opcode == ATHROW) && !isPresent) {
  88.                 mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);
  89.                 mv.visitVarInsn(LLOAD, time);
  90.                 mv.visitInsn(LSUB);
  91.                 mv.visitVarInsn(LSTORE, time);
  93.                 mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
  95.                 mv.visitTypeInsn(NEW, "java/lang/StringBuilder");
  96.                 mv.visitInsn(DUP);
  97.                 mv.visitMethodInsn(INVOKESPECIAL, "java/lang/StringBuilder", "<init>", "()V", false);
  98.                 mv.visitFieldInsn(GETSTATIC, clazzName, filedName, "Ljava/lang/String;");
  99.                 mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);
  101.                 mv.visitLdcInsn("  " + methodName + ":");
  102.                 mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);
  104.                 mv.visitVarInsn(LLOAD, time);
  105.                 mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(J)Ljava/lang/StringBuilder;", false);
  106.                 mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false);
  107.                 mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
  109.                 maxStack = Math.max(aa.stack.size() + 4, maxStack);
  110.             }
  111.             super.visitInsn(opcode);
  112.         }
  114.         @Override
  115.         public void visitMaxs(int maxStack, int maxLocals) {
  116.             super.visitMaxs(Math.max(maxStack, this.maxStack), maxLocals);
  117.         }
  118.     }
  119. }