ASM ByteCode - 異常的堆棧跟蹤

Question

我正在使用Java Instrumentation和ASM ByteCode庫來開發Javaagent。 如何獲得由方法拋出的運行時異常？

附代碼。這裏得到方法是否正常終止或拋出 例外。但無法檢索異常。如何檢索異常？

package com.abc.agent.servlet; 

import org.objectweb.asm.Label; 
import org.objectweb.asm.MethodVisitor; 
import org.objectweb.asm.Opcodes; 
import org.objectweb.asm.Type; 

import com.abc.agent.matcher.HttpServletMethodMatcher; 

public class AbcServletMethodVisitorAdapter extends MethodVisitor { 
    private String methodName; 
    private String className; 
    private String description; 
    private boolean doMethodMatch; 
    private int opcode = -1; 

public AbcServletMethodVisitorAdapter(MethodVisitor mv , String methodName , String description , String className) { 
    super(Opcodes.ASM4, mv); 
    this.methodName = methodName; 
    this.className = className; 
    this.description = description; 
    this.doMethodMatch = false; 
} 

public void visitCode() { 
    super.visitCode(); 
    if(methodName.equals("<clinit>") || methodName.equals("<init>")) 
     return; 
    HttpServletMethodMatcher httpServletMethodMatcher = new HttpServletMethodMatcher(className , methodName , description); 
    this.doMethodMatch = httpServletMethodMatcher.isHttpServletMatch(); 
    if(this.doMethodMatch){ 
     mv.visitVarInsn(Opcodes.ALOAD, 0); 
     mv.visitVarInsn(Opcodes.ALOAD, 1); 
     mv.visitLdcInsn(this.className); 
     mv.visitLdcInsn(this.methodName); 
     mv.visitLdcInsn(this.description); 
     mv.visitMethodInsn(Opcodes.INVOKESTATIC, "com/abc/agent/trace/RootTracer", "httpServletDoMethodBegin", "(Ljava/lang/Object;Ljavax/servlet/http/HttpServletRequest;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)V"); 
     mv.visitCode(); 
    } 
    else // Other Methods defined in the HttpServlet... 
    { 
     mv.visitLdcInsn(this.className); 
     mv.visitLdcInsn(this.methodName); 
     mv.visitLdcInsn(this.description); 
     mv.visitMethodInsn(Opcodes.INVOKESTATIC, "com/abc/agent/trace/RootTracer", "httpServletOtherMethodBegin", "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)V"); 
     mv.visitCode(); 
    } 
} 

public void visitMaxs(int maxStack, int maxLocals) { 
    super.visitMaxs(maxStack + 4, maxLocals); 
    } 

public void visitInsn(int opcode) { 
    if(methodName.equals("<clinit>") || methodName.equals("<init>")){ 
     // Do nothing.... 
    } 
    else{ 
     if ((opcode >= Opcodes.IRETURN && opcode <= Opcodes.RETURN) || opcode == Opcodes.ATHROW) { 
      this.opcode = opcode; 
      mv.visitLdcInsn(this.className); 
      mv.visitLdcInsn(this.methodName); 
      mv.visitLdcInsn(this.description); 
      mv.visitLdcInsn(this.opcode); 
      if(this.doMethodMatch) { 
       mv.visitMethodInsn(Opcodes.INVOKESTATIC, "com/abc/agent/trace/RootTracer", "httpServletDoMethodEnd", "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;I)V"); 
      } 
      else{ 
       mv.visitMethodInsn(Opcodes.INVOKESTATIC, "com/abc/agent/trace/RootTracer", "httpServletOtherMethodEnd", "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;I)V"); 
      } 
     } 
    } 
    mv.visitInsn(opcode); 
} 
} 

Answer 1

這是一個簡單的例子。首先，我們爲需要參考的代碼中的變量點創建一堆標籤。然後我們圍繞方法執行建立一個try-catch塊。然後我們調用「try」塊中的代碼，並且如果在try塊中引發異常，則執行將跳轉到lCatchBlockStart標籤，但堆棧中的例外。示例catch塊調用e.printStackTrace（）。

我在本例中使用了局部變量編號1，因爲它碰巧可用。您可能需要選擇一些其他的變量 - 當然你不有存儲在一個變量的例外，但它是相當普遍這樣做。

除非在構建ClassWriter時使用COMPUTE_FRAMES標誌，否則還必須插入visitFrame（）調用。

Label lTryBlockStart = new Label(); 
Label lTryBlockEnd = new Label(); 
Label lCatchBlockStart = new Label(); 
Label lCatchBlockEnd = new Label(); 
// set up try-catch block for RuntimeException 
mv.visitTryCatchBlock(lTryBlockStart, lTryBlockEnd, lCatchBlockStart, "java/lang/RuntimeException"); 
mv.visitLabel(lTryBlockStart); 
// code to call the method goes here 
mv.visitLabel(lTryBlockEnd); 
mv.visitJumpInsn(GOTO, lCatchBlockEnd); // when here, no exception was thrown, so skip exception handler 

// exception handler starts here, with RuntimeException stored on the stack 
mv.visitLabel(lCatchBlockStart); 
mv.visitVarInsn(ASTORE, 1); // store the RuntimeException in local variable 1 
// here we could for example do e.printStackTrace() 
mv.visitVarInsn(ALOAD, 1); // load it 
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/RuntimeException", "printStackTrace", "()V"); 

// exception handler ends here: 
mv.visitLabel(lCatchBlockEnd);