java - 如何捕获事件调度线程 (EDT) 异常？

Question

我正在使用一个名为 MyExceptionHandler 的类，它实现了 Thread.UncaughtExceptionHandler 来处理我项目中的正常异常。

据我了解，此类无法捕获 EDT 异常，因此我尝试在 main() 方法中使用它来处理 EDT 异常:

public static void main( final String[] args ) {
    Thread.setDefaultUncaughtExceptionHandler( new MyExceptionHandler() );  // Handle normal exceptions
    System.setProperty( "sun.awt.exception.handler",MyExceptionHandler.class.getName());  // Handle EDT exceptions
    SwingUtilities.invokeLater(new Runnable() {  // Execute some code in the EDT. 
        public void run() {
            JFrame myFrame = new JFrame();
             myFrame.setVisible( true );
        }
    });
}

但直到现在它还没有工作。例如，在初始化 JFrame 时，我从构造函数中的捆绑文件加载其标签，如下所示:

setTitle( bundle.getString( "MyJFrame.title" ) );

我从捆绑文件中删除了 key MyJFrame.title 以测试异常处理程序，但它不起作用!异常通常打印在日志中。

我在这里做错了吗？

Answer 1

EDT 异常处理程序不使用 Thread.UncaughtExceptionHandler。相反，它调用具有以下签名的方法:

public void handle(Throwable thrown);

将它添加到 MyExceptionHandler，它应该可以工作。

这方面的“文档”可以在 EventDispatchThread 中找到，它是 java.awt 中的一个包私有(private)类。从 handleException() 那里引用 javadoc:

/**
 * Handles an exception thrown in the event-dispatch thread.
 *
 * <p> If the system property "sun.awt.exception.handler" is defined, then
 * when this method is invoked it will attempt to do the following:
 *
 * <ol>
 * <li> Load the class named by the value of that property, using the
 *      current thread's context class loader,
 * <li> Instantiate that class using its zero-argument constructor,
 * <li> Find the resulting handler object's <tt>public void handle</tt>
 *      method, which should take a single argument of type
 *      <tt>Throwable</tt>, and
 * <li> Invoke the handler's <tt>handle</tt> method, passing it the
 *      <tt>thrown</tt> argument that was passed to this method.
 * </ol>
 *
 * If any of the first three steps fail then this method will return
 * <tt>false</tt> and all following invocations of this method will return
 * <tt>false</tt> immediately.  An exception thrown by the handler object's
 * <tt>handle</tt> will be caught, and will cause this method to return
 * <tt>false</tt>.  If the handler's <tt>handle</tt> method is successfully
 * invoked, then this method will return <tt>true</tt>.  This method will
 * never throw any sort of exception.
 *
 * <p> <i>Note:</i> This method is a temporary hack to work around the
 * absence of a real API that provides the ability to replace the
 * event-dispatch thread.  The magic "sun.awt.exception.handler" property
 * <i>will be removed</i> in a future release.
 */

Sun 究竟是如何期望你找到这个的，我不知道。

这是一个在 EDT 内外捕获异常的完整示例:

import javax.swing.SwingUtilities;

public class Test {
  public static class ExceptionHandler
                                   implements Thread.UncaughtExceptionHandler {

    public void handle(Throwable thrown) {
      // for EDT exceptions
      handleException(Thread.currentThread().getName(), thrown);
    }

    public void uncaughtException(Thread thread, Throwable thrown) {
      // for other uncaught exceptions
      handleException(thread.getName(), thrown);
    }

    protected void handleException(String tname, Throwable thrown) {
      System.err.println("Exception on " + tname);
      thrown.printStackTrace();
    }
  }

  public static void main(String[] args) {
    Thread.setDefaultUncaughtExceptionHandler(new ExceptionHandler());
    System.setProperty("sun.awt.exception.handler",
                       ExceptionHandler.class.getName());

    // cause an exception on the EDT
    SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        ((Object) null).toString();        
      }
    });

    // cause an exception off the EDT
    ((Object) null).toString();
  }
}

应该可以的。