java - ASM ByteCode - 异常的 stackTrace

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？

附上代码。这里获取该方法是否正常终止或抛出 一个异常(exception)。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，我们为代码中需要引用的各个点创建一堆标签。然后我们在方法执行周围设置一个 try-catch block 。然后我们调用“try” block 中的代码，如果try block 中抛出异常，执行将跳转到异常在堆栈上的lCatchBlockStart标签处。示例 catch block 调用 e.printStackTrace()。

在本例中我使用了局部变量 1，因为它恰好可用。您可能必须选择其他一些变量 - 当然，您没有将异常存储在变量中，但这样做很常见。

除非您在构建 ClassWriter 时使用 COMPUTE_FRAMES 标志，否则您还必须插入访问Frame() 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);