Byteman问题：Location Specifiers对List/Map的API操作无效

我尝试用Byteman的Location Specifier监听List/Map的操作，发现一个问题：调用List/Map的API（比如add方法）添加元素时，对应的规则完全没触发；但用赋值运算符=给list变量赋值时，规则能正常触发。我原本预期每次执行list.add这类操作后规则都会触发，但实际没发生，看起来Location逻辑只识别赋值运算符=的操作。

以下是测试代码、Byteman规则及输出截图：

测试代码 #

import java.util.*;  

public class SimpleTest  
    {
         public static void main(String[] args)
         {         
           System.out.println("Java: Entering main");
           for (int i = 1; i <= 1; i++) 
           {
             loopTest(i);
             try
             {
                Thread.sleep(1000);
             }
             catch(InterruptedException e)
             {
                System.out.println(e);
             }  
           }                  
         }
         
         public static void loopTest(int i)
         {
           System.out.println("Java: Iteration " + i);
           Integer a;
           a=new Integer(1);
           a=new Integer(2);
           a=new Integer(3);
           System.out.println("Java: a is " + a);
           
           System.out.println(" *********************** ");
           //创建List  
                     List<String> list=new ArrayList<String>();  
                     //向List添加元素  
                     list.add("Mango");  
                     list.add("Apple");  
                     list.add("Banana");             

                     //用for-each循环遍历List  
                     for(String fruit:list)
                     {  
                      System.out.println("Java: list is" + fruit);                        
                     }  
           
           //重新初始化list
           list=Arrays.asList("foo", "bar");
           
           //用for-each循环遍历新的List  
                     for(String fruit:list)
                     {  
                      System.out.println("Java: list (new) is" + fruit);                       
                     }  
         }
    }

Byteman规则 #

RULE trace main entry
CLASS SimpleTest
METHOD main
AT ENTRY
IF true
DO System.out.println("Byteman detected you are entering main - test")
ENDRULE

RULE catch_SimpleTest.loopTest
CLASS SimpleTest
METHOD loopTest
COMPILE
AT ENTRY
IF true
DO 
 System.out.println("Byteman Enter loopTest - " + $1)
ENDRULE

RULE catch_SimpleTest.loopTest0
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $a 0
IF true
DO 
 System.out.println("Byteman loopTest0: " + $a)
ENDRULE

RULE catch_SimpleTest.loopTest1
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $a 1
IF true
DO 
 System.out.println("Byteman loopTest1: " + $a)
ENDRULE

RULE catch_SimpleTest.loopTest2
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $a 2
IF true
DO 
 System.out.println("Byteman loopTest2: " + $a)
ENDRULE

RULE catch_SimpleTest.loopTest3
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $a 3
IF true
DO 
 System.out.println("Byteman loopTest3: " + $a)
ENDRULE

RULE catch_SimpleTest.loopTestALL
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $a ALL
IF true
DO 
 System.out.println("Byteman loopTestALL: " + $a)
ENDRULE

RULE catch_SimpleTest.loopTestList1
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $list 1
IF true
DO 
 System.out.println("Byteman loopTestList1: " + $list)
ENDRULE

RULE catch_SimpleTest.loopTestList2
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $list 2
IF true
DO 
 System.out.println("Byteman loopTestList2: " + $list)
ENDRULE

RULE catch_SimpleTest.loopTestList3
CLASS SimpleTest
METHOD loopTest
COMPILE
AFTER WRITE $list 3
IF true
DO 
 System.out.println("Byteman loopTestList3: " + $list)
ENDRULE

Byteman输出截图 #

问题解决方法 #

你的规则只监听了变量赋值操作（AFTER WRITE $list），这类Location Specifier仅针对list变量本身的赋值（比如list = new ArrayList()或list = Arrays.asList(...)），而list.add()是调用List对象的方法，修改的是对象内部的状态，并没有改变list变量的引用值，所以不会触发你定义的AFTER WRITE $list规则。

要监听add这类List操作，你需要把规则的目标类改成List的实现类（比如ArrayList），并监听对应的方法：

示例规则1：监听ArrayList的add方法 #

RULE trace ArrayList add operation
CLASS java.util.ArrayList
METHOD add
AT ENTRY
IF true
DO 
 System.out.println("Byteman detected ArrayList.add called with element: " + $1)
ENDRULE

示例规则2：监听所有List实现类的add方法 #

RULE trace List add operation
CLASS java.util.List
METHOD add
AT ENTRY
IF true
DO 
 System.out.println("Byteman detected List.add called with element: " + $1)
ENDRULE

关键说明 #

• AFTER WRITE $var这类Location是监听局部变量/字段的赋值行为，只有当变量的引用被改变时才会触发；
• 要监听对象的方法调用，需要将规则的CLASS指定为方法所在的类（或接口），METHOD指定为目标方法名，用AT ENTRY或AT EXIT来定位方法执行的时机。

修改后，每次调用list.add()时，对应的Byteman规则就会触发。

内容的提问来源于stack exchange，提问作者Asif Ansari