Java 在从 swingworker 调用的类中捕获异常

Question

好吧，我有这个代码：

SwingWorker<Void,Void> worker = new SwingWorker<Void, Void>() {
   @Override
   public Void doInBackground() {
       Connection checker = new Connection();
       do{
           checker.checkConnection();
       }while(true);
   }}

方法如下

checkConnection()

public void checkConnection(){
do{
    try{
        URL url = new URL("http://www.google.com");
        URLConnection uc = url.openConnection();
        BufferedReader br = new BufferedReader(new InputStreamReader(uc.getInputStream()));
        String line;
        while ((line = br.readLine()) != null) {
                    System.out.println("You're connected");
        }
        online = true;
    }catch(Exception noConnessione){
        System.out.println("No connection..."); 
        System.out.println("I'm going to try again in 30s...");
        robot.delay(30000);
        online = false;
    }
}while(online == false);}

好吧，如果没有连接，它就不会进入 catch 块，但如果我在没有 swingworker 的情况下使用相同的代码，它就会进入。

我绝对需要swingworker，我该如何解决这个问题？

Answer 1

似乎工作正常

import javax.swing.SwingWorker;
import java.net.URL;
import java.net.URLConnection;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Simple {

  public static void main(String [] arg) {
    System.out.println("Starting worker");
    SwingWorker<Void,Void> worker = new SwingWorker<Void, Void>() {
      @Override
      public Void doInBackground() {
        Connection checker = new Connection();
        do{
          System.out.println("Running routine test");
          checker.checkConnection();
        }while(true);
      }
    };
    worker.execute();
    while(true);
  }
}

class Connection {
  boolean online = false;
  public void checkConnection() {
    System.out.println("Check connection loop");
    while(online == false) {
      try{
        URL url = new URL("http://yyy.google.com");
        URLConnection uc = url.openConnection();
        BufferedReader br = new BufferedReader(new InputStreamReader(uc.getInputStream()));
        String line;
        while ((line = br.readLine()) != null) {
                    System.out.println("You're connected");
        }
        online = true;
      }catch(Exception noConnessione){
        online = false;
      }
      if(online == false) {
        try {
          System.out.println("No connection...");
          System.out.println("I'm going to try again in 3s...");
          System.out.flush();
          Thread.sleep(3000);
        } catch(InterruptedException ex) {
          System.out.println("I was awaken");
        }
      }
    }
  }
}

执行如下

> javac Simple.java
> java Simple
Starting worker
Running routine test
Check connection loop
No connection...
I'm going to try again in 3s...
No connection...
I'm going to try again in 3s...
No connection...
I'm going to try again in 3s...
No connection...
I'm going to try again in 3s...
No connection...
I'm going to try again in 3s...

Answer 2

看起来有一个未捕获的异常/错误正在中止doInBackground 方法。这个异常会被 Swingworker 静默捕获，并且仅在调用 get 方法时报告。

get 方法将阻塞，直到 SwingWorker 终止，这在上面的代码中不打算出现（永远循环）。所以调用应该是被覆盖的donemethod内的模式：

SwingWorker<Void,Void> worker = new SwingWorker<Void, Void>() {
    @Override
    public Void doInBackground() throws Exception {
        ...
    }
    @Override
    public void done() {
        try {
            get();
        } catch (InterruptedException | ExecutionException ex) {
            ex.printStackTrace();
            // TODO
        }
    }
};

但请注意done 在事件调度线程上执行！

替代方案，将doInBackground 的全部内容放在 try-catch 中：

    @Override
    public Void doInBackground() throws Exception {
        try {
            ...
        } catch (Throwable ex) {
            ex.printStackTrace();
            throw ex;
        }
    }

不是解决方案，但应该有助于找到错误，因此希望是解决方案