我对ASM和字节码操作相当陌生。我的任务相当简单：我告诉我的代理要访问什么类和方法，它测量该方法的执行时间。测量是通过Guava库的Stopwatch类完成的。ASM基本上通过在方法体的开头启动Stopwatch并在方法体的末尾停止它并打印出执行时间来包围方法体。这在一些方法上有效，但在大多数方法上失败了。

这是ASM访问目标方法开头的部分。

package com.agent.agentclasses;


import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.commons.LocalVariablesSorter;
import org.objectweb.asm.Type;

public class ModifierMethodWriter  extends LocalVariablesSorter /*MethodVisitor*/ {
    private int time;
    protected ModifierMethodWriter(int api, int access, String desc, MethodVisitor mv) {
        super(api, access, desc, mv);
    }


    @Override
    public void visitCode() {
        System.out.println("I am @ModifierMethodWriter!");

        /*
        *   Guava - beginning of the method !
        */
        time = newLocal(Type.getObjectType("stopwatch"));


        super.visitMethodInsn(Opcodes.INVOKESTATIC, "com/google/common/base/Stopwatch", "createStarted", "()Lcom/google/common/base/Stopwatch;", false);

        super.visitVarInsn(Opcodes.ASTORE, time);
        super.visitCode();




    }

添加代码到最后！

package com.agent.agentclasses;

import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.commons.AdviceAdapter;

public class AddCodeBeforeReturn extends AdviceAdapter { 
    public AddCodeBeforeReturn(int api, MethodVisitor mv,
             int acc, String name, String desc){

        super(api, mv, acc, name, desc);

    }
    @Override
    protected void onMethodExit(int opcode) {
        /*
        *   Guava - Before return !
        */
        super.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
        super.visitIntInsn(Opcodes.ALOAD, 2);
        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "com/google/common/base/Stopwatch", "stop", "()Lcom/google/common/base/Stopwatch;", false);
        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "com/google/common/base/Stopwatch", "toString", "()Ljava/lang/String;", false);
        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
    }
}

这是我想测试代理的测试类：它是HSQLdb类，我想测量selectAll（）方法的执行时间。

package com.agent.database;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import com.agent.testclasses.*;
public class Database {

    private Connection connection = null;  
    private ResultSet resultSet = null;  
    private Statement statement = null;
    private String createtablestr = " CREATE TABLE IF NOT EXISTS Students(Id int,Name varchar(255));";
    private static int id = 1;

    public String connect() {
        System.out.println("I am in connect!");
        try{
        Class.forName("org.hsqldb.jdbcDriver");
        connection = DriverManager.getConnection("jdbc:hsqldb:file:C:/hsqldb/studentdb", "sa", "");
        if (connection == null)
        {

            return "Error: Connection failed.";
        }
            statement = connection.createStatement();
            statement.executeUpdate(createtablestr);
        }catch(Throwable ex){
            ex.printStackTrace();
        }

        return "Connection succesful!";
    }

    public String insert(Student student){
        connect();  
        try {

            String insertStr = "INSERT INTO Students VALUES ('"+ id +"','"+ student.getName() + "')";
            statement.executeUpdate(insertStr);
            id++;
        }catch(Throwable ex){ex.printStackTrace(); return "Error: Data was not written!";}

        return "Data written succesfully!";
    }   

    public String selectAll() {


        connect();  
        String outputHTML="";
        try{


            resultSet = statement.executeQuery("SELECT * FROM Students");


            while (resultSet.next()) 
            {  
                outputHTML+= "<tr>" + "<td>" + resultSet.getString("Id") + "</td>" + "<td>" + resultSet.getString("Name") + "</td>"  + "</tr>";
            }



            resultSet.close();
            connection.commit();
            connection.close();


        } 
        catch (Throwable e) 
        {
            e.printStackTrace();
        }

        return outputHTML;
   }
}

最后，jvm thorws的例外：

Exception in thread "main" java.lang.VerifyError: Stack map does not match the one at exception handler 85
    Exception Details:
      Location:
        com/agent/database/Database.connect()Ljava/lang/String; @85: astore_2
      Reason:
        Type top (current frame, locals[1]) is not assignable to 'stopwatch' (stack map, locals[1])
      Current Frame:
        bci: @12
        flags: { }
        locals: { 'com/agent/database/Database', top, 'com/google/common/base/Stopwatch' }
        stack: { 'java/lang/Throwable' }
      Stackmap Frame:
        bci: @85
        flags: { }
        locals: { 'com/agent/database/Database', 'stopwatch' }
        stack: { 'java/lang/Throwable' }
      Bytecode:
        0x0000000: b800 2a4d b200 3212 34b6 003a 123c b800
        0x0000010: 4257 2a12 4412 4612 48b8 004e b500 182a
        0x0000020: b400 18c7 0014 1250 b200 3219 02b6 0053
        0x0000030: b600 56b6 003a b02a 2ab4 0018 b900 5e01
        0x0000040: 00b5 001c 2ab4 001c 2ab4 0020 b900 6402
        0x0000050: 0057 a700 084d 2cb6 0067 1269 b200 3219
        0x0000060: 02b6 0053 b600 56b6 003a b0            
      Exception Handler Table:
        bci [12, 38] => handler: 85
        bci [55, 82] => handler: 85
      Stackmap Table:
        append_frame(@55,Object[#88])
        same_locals_1_stack_item_frame(@85,Object[#44])
        same_frame(@90)

        at com.agent.testers.tester1.main(tester1.java:15)

在我看来，ASM在Stopwatch的局部变量表中创建新条目后，jvm试图用我试图定位的方法的局部变量覆盖它（在本例中为selectAll（））。因此：

类型top（当前帧，本地[1]）不能分配给“秒表”（堆栈图，本地[1]）

我不确定这是否是实际问题，但我需要解决它！最后，我的代理应该可以使用任何方法插入。感谢您的所有帮助！谢谢。