[PT선생님][104]com.sun.jdi.request.AccessWatchpointRequest 알아보기

com.sun.jdi.request.AccessWatchpointRequest 클래스는 Java Debug Interface (JDI)의 일부입니다
이 클래스는 디버깅을 위해 액세스 워치포인트를 설정하는 데 사용됩니다.

액세스 워치포인트는 특정 필드의 값을 검사하고 필드의 값을 읽거나 쓸 때마다 발생하는 이벤트입니다
따라서 이 클래스를 사용하면 애플리케이션에서 특정 필드의 값을 계속 모니터링하면서 필드의 값이 변경될 때마다 이벤트를 발생시킬 수 있습니다.

AccessWatchpointRequest 클래스는 다음과 같은 메서드를 포함합니다.

- addThreadFilter(): 액세스 워치포인트를 활성화할 스레드를 지정합니다.
- addClassFilter(): 액세스 워치포인트를 설정할 클래스를 지정합니다.
- addInstanceFilter(): 액세스 워치포인트를 설정할 인스턴스를 지정합니다.
- addFieldFilter(): 액세스 워치포인트를 설정할 필드를 지정합니다.
- enable(): 액세스 워치포인트를 활성화합니다.
- disable(): 액세스 워치포인트를 비활성화합니다.

다음은 AccessWatchpointRequest의 예제 코드입니다.

 

VirtualMachine vm = ...;
ReferenceType clazz = vm.classesByName("com.example.ClassName").get(0);
Field field = clazz.fieldByName("fieldName");
AccessWatchpointRequest watchpointRequest = vm.eventRequestManager().createAccessWatchpointRequest(field);
watchpointRequest.setSuspendPolicy(EventRequest.SUSPEND_ALL);
watchpointRequest.enable();

이 예제에서는 ClassName 클래스의 fieldName 필드를 모니터링하고 필드의 값이 변경될 때마다 모든 스레드를 중지시킵니다.
`com.sun.jdi.request.AccessWatchpointRequest` 클래스는 JVM에서 모니터링 할 필드의 변경을 추적하기 위한 이벤트를 생성하는 데 사용됩니다
이 클래스는 `com.sun.jdi.request.EventRequest` 클래스의 하위 클래스입니다.

`AccessWatchpointRequest` 객체를 만들면 이벤트가 발생할 필드와 클래스의 식별자를 지정할 수 있습니다
이벤트가 발생하면 JVM은 `com.sun.jdi.event.AccessWatchpointEvent` 객체를 생성하고, 이벤트를 처리하기 위해 `com.sun.jdi.event.EventSet` 객체에 묶어서 `com.sun.jdi.event.EventQueue`에 추가합니다.

`AccessWatchpointRequest` 클래스의 생성자는 다음과 같습니다.

AccessWatchpointRequest AccessWatchpointRequest.addFieldWatch(String fieldName)
AccessWatchpointRequest AccessWatchpointRequest.addFieldWatch(String fieldName, String declaringClass)

첫 번째 생성자는 모니터링 할 필드의 이름만 지정하고, 두 번째 생성자는 필드가 속한 클래스의 이름도 함께 지정합니다
이벤트가 발생하면 JVM은 `AccessWatchpointRequest` 객체의 `isEnabled()` 메소드가 true를 반환하는지 확인하고, true를 반환하면 `AccessWatchpointEvent` 객체가 생성됩니다.

다음은 `AccessWatchpointRequest` 클래스를 사용한 예제 코드입니다.

 

import com.sun.jdi.*;
import com.sun.jdi.connect.*;
import com.sun.jdi.event.*;
import com.sun.jdi.request.*;

import java.util.*;

public class AccessWatchpointExample {
    public static void main(String[] args) throws Exception {
        // Attach to a running JVM with the specified process ID.
        VirtualMachine vm = VirtualMachine.attach(args[0]);

        // Create a reference to the com.example.Employee class.
        ReferenceType employeeType = vm.classesByName("com.example.Employee").get(0);

        // Create a new access watchpoint request for the "salary" field of the Employee class.
        AccessWatchpointRequest request = vm.eventRequestManager().createAccessWatchpointRequest(employeeType.fieldByName("salary"));

        // Enable the access watchpoint request.
        request.enable();

        // Resume the VM to start processing events.
        vm.resume();

        // Wait for an access watchpoint event to occur.
        EventSet eventSet = vm.eventQueue().remove();

        // Get the access watchpoint event from the event set.
        AccessWatchpointEvent event = (AccessWatchpointEvent) eventSet.iterator().next();

        // Print some information about the event.
        System.out.println("Access watchpoint event:");
        System.out.println("Field: " + event.field().name());
        System.out.println("Object: " + event.object().toString());
        System.out.println("Thread: " + event.thread().name());

        // Disconnect from the VM.
        vm.dispose();
    }
}

이 예제 코드에서는 `AccessWatchpointRequest` 클래스를 사용하여 `com.example.Employee` 클래스의 `salary` 필드를 모니터링합니다
이벤트가 발생하면 이벤트 정보를 출력합니다
이 코드는 디버거 도구나 프로파일링 도구 등에서 유용하게 사용될 수 있습니다.