Question

我正在使用java Instrumentation和ASM ByteCode Library来开发Javaagent。如何获取方法抛出的运行时异常？

附上守则。这里得到的方法是正常终止还是抛出一个例外。但无法检索异常。如何检索异常？

 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

这是一个简单的例子。首先，我们为需要引用的代码中的变量点创建一组标签。然后我们围绕方法执行建立一个try-catch块。然后我们在“try”块中调用代码，如果在try块中抛出异常，执行将跳转到lCatchBlockStart标签，堆栈上有异常。示例catch块调用e.printStackTrace（）。

我在本例中使用了本地变量1，因为它恰好可用。您可能必须选择其他变量 - 当然，您没有将异常存储在变量中，但这样做很常见。

除非在构造ClassWriter时使用COMPUTE_FRAMES标志，否则还必须插入visitFrame（）调用。

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);

ASM ByteCode - 异常的stackTrace

1 个答案: