使用JDI监听Java程序运行

转载于：http://liugang594.iteye.com/blog/1397811#bc2311991

Java虚拟机提供了一套用于调试（JVMDI）和监视（JVMPI）的接口，Java5之后统一为JVMTI：http://docs.oracle.com/javase/1.5.0/docs/guide/jvmti/ 。

 

其中JVMDI分为三个部分：JVMDI，JDWP和JDI .http://docs.oracle.com/javase/1.4.2/docs/guide/jpda/architecture.html

 

这篇就是简单的介绍一下怎么使用JDI去监视程序的运行的。

 

首先假设有一个简单的程序：

 package test;

 public class Test {

     public static void main(String[] args) {
         new Thread() {
             @Override
             public void run() {
                 Test test = new Test();
                 while (true) {
                     try {
                         sleep(5000);
                     } catch (InterruptedException e) {
                         e.printStackTrace();
                     }
                     test.printHello();
                 }
             }
         }.start();
     }

     protected void printHello() {
         System.out.println("hello");

     }

 }

 

程序中，每隔五秒种，printHello()方法就会执行一次。

 

如果你希望每次printHell()被执行的时候通知你一下，在不修改代码的情况下，你要怎么办？没办法吧？

 

看看JDI的定义：

 JDI - Java Debug Interface
 Defines a high-level Java language interface which tool developers can easily use to write remote debugger applications.

 

所以首先，我们先以远程调试的方式启动上面的Test类：

 java -Xdebug -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8800 -cp . test.Test

 

大致就是以socket传输的方式调试Test类，调试的连接端口为8800，并且连接过程不挂起。

 

一量启动，就可以看到如下的输出：

 

 Listening for transport dt_socket at address: 8800
 hello
 hello
 hello

 

这样Server被调试端就准备好了，下面就是写监听端了。这里就要用到jdk中提供的JDI接口了。要使用此接口，我们需要在类路径里包含JDK下的tools.jar等包，可以在<JDK>/lib目录下找着。

一、取得连接器

 VirtualMachineManager vmm = Bootstrap.virtualMachineManager();
 List<AttachingConnector> connectors = vmm.attachingConnectors();
 SocketAttachingConnector sac = null;
 for (AttachingConnector ac : connectors) {
     if (ac instanceof SocketAttachingConnector) {
         sac = (SocketAttachingConnector) ac;
         break;
     }
 }
 if (sac == null) {
     System.out.println("JDI error");
     return;
 }

 

二、连接到远程虚拟器

 Map arguments = sac.defaultArguments();
 Connector.Argument hostArg = (Connector.Argument) arguments.get(HOST);
 Connector.Argument portArg = (Connector.Argument) arguments.get(PORT);

 hostArg.setValue("127.0.0.1");
 portArg.setValue(String.valueOf(8800));

 vm = sac.attach(arguments);

 

三、取得要关注的类和方法

 List<ReferenceType> classesByName = vm.classesByName("test.Test");
 if (classesByName == null || classesByName.size() == 0) {
     System.out.println("No class found");
     return;
 }
 ReferenceType rt = classesByName.get(0);
 List<Method> methodsByName = rt.methodsByName("printHello");
 if (methodsByName == null || methodsByName.size() == 0) {
     System.out.println("No method found");
     return;
 }
 Method method = methodsByName.get(0);

 

四、注册监听

 vm.setDebugTraceMode(VirtualMachine.TRACE_EVENTS);
 vm.resume();
 EventRequestManager erm = vm.eventRequestManager();

 MethodEntryRequest methodEntryRequest = erm.createMethodEntryRequest();
 methodEntryRequest.addClassFilter(rt);
 methodEntryRequest.setSuspendPolicy(EventRequest.SUSPEND_NONE);
 methodEntryRequest.enable();

 BreakpointRequest breakpointRequest = erm
         .createBreakpointRequest(method.location());
 breakpointRequest.setSuspendPolicy(EventRequest.SUSPEND_EVENT_THREAD);
 breakpointRequest.enable();

 eventLoop();

 

这里监听每次方法入口的时候，以及在方法上注册一个断点，发一个通知。

 

四、eventLoop()的实现

 private static void eventLoop() throws Exception {
     eventQueue = vm.eventQueue();
     while (true) {
         if (vmExit == true) {
             break;
         }
         eventSet = eventQueue.remove();
         EventIterator eventIterator = eventSet.eventIterator();
         while (eventIterator.hasNext()) {
             Event event = (Event) eventIterator.next();
             execute(event);
         }
     }
 }

 private static void execute(Event event) throws Exception {
     if (event instanceof VMStartEvent) {
         System.out.println("VM started");
         eventSet.resume();
     } else if (event instanceof BreakpointEvent) {
         System.out
                 .println("Reach Method printHello of test.Test");
         eventSet.resume();
     } else if (event instanceof MethodEntryEvent) {
         MethodEntryEvent mee = (MethodEntryEvent) event;
         Method method = mee.method();
         System.out.println(method.name() + " was Entered!");
         eventSet.resume();
     } else if (event instanceof VMDisconnectEvent) {
         vmExit = true;
     } else {
         eventSet.resume();
     }
 }

 

最后看输出：

 [JDI: EventSet: SUSPEND_EVENT_THREAD]
 [JDI: Event: MethodEntryEvent@test.Test:23 in thread Thread-0]
 [JDI: Event: BreakpointEvent@test.Test:23 in thread Thread-0]
 printHello was Entered!
 Reach Method printHello of test.Test
 [JDI: EventSet: SUSPEND_EVENT_THREAD]
 printHello was Entered!
 [JDI: Event: MethodEntryEvent@test.Test:23 in thread Thread-0]
 [JDI: Event: BreakpointEvent@test.Test:23 in thread Thread-0]
 Reach Method printHello of test.Test