使用JDI监听Java程序运行

va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