如何使这个SwingWorker代码可测试

恕我直言，这对于一个匿名类来说很复杂。我的方法是将匿名类重构为如下所示：

public class FileWriterWorker extends SwingWorker<File, Void> {
    private final String location;
    private final Response target;
    private final Object creator;

    public FileWriterWorker(Object creator, String location, Response target) {
        this.creator = creator;
        this.location = location;
        this.target = target;
    }

    @Override
    protected File doInBackground() throws Exception {
        File file = new File("out.txt");
        Writer writer = null;
        try {
            writer = new FileWriter(file);
            creator.write(location, writer);
        }
        finally {
            if (writer != null) {
                writer.close();
            }
        }
        return file;
    }

    @Override
    protected void done() {
        try {
            File file = get();
            target.success(file);
        }
        catch (InterruptedException ex) {
            target.failure(new BackgroundException(ex));
        }
        catch (ExecutionException ex) {
            target.failure(new BackgroundException(ex));
        }
    }

    public interface Response {
        void success(File f);
        void failure(BackgroundException ex);
    }

    public class BackgroundException extends Exception {
        public BackgroundException(Throwable cause) {
            super(cause);
        }
    }
}

这允许独立于GUI测试文件写入功能

然后，变成这样：actionPerformed

public void actionPerformed(ActionEvent e) {
    setEnabled(false);
    Object creator;
    new FileWriterWorker(creator, url.getText(), new FileWriterWorker.Response() {
        @Override
        public void failure(FileWriterWorker.BackgroundException ex) {
            setEnabled(true);
            Throwable bgCause = ex.getCause();
            if (bgCause instanceof InterruptedException) {
                logger.log(Level.INFO, "Thread interupted, process aborting.", bgCause);
                Thread.currentThread().interrupt();
            }
            else if (cause instanceof ExecutionException) {
                Throwable cause = bgCause.getCause() == null ? bgCause : bgCause.getCause();
                logger.log(Level.SEVERE, "An exception occurred that was "
                    + "not supposed to happen.", cause);
                JOptionPane.showMessageDialog(FileInputFrame.this, "Error: "
                    + cause.getClass().getSimpleName() + " "
                    + cause.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
            }
        }

        @Override
        public void success(File f) {
            setEnabled(true);
            JOptionPane.showMessageDialog(FileInputFrame.this,
                "File has been retrieved and saved to:\n"
                + file.getAbsolutePath());
            try {
                Desktop.getDesktop().open(file);
            }
            catch (IOException iOException) {
                logger.log(Level.INFO, "Unable to open file for viewing.", ex);
            }
        }
    }).execute();
}

此外，可以将 的实例分配给变量并独立于 进行测试。FileWriterWorker.ResponseFileWriterWorker

当前的实现将线程问题，UI和文件写入耦合在一起 - 正如您发现的那样，耦合使得很难单独测试各个组件。

这是一个相当长的响应，但它归结为将这三个问题从当前实现中拉出到具有已定义接口的单独类中。

排除应用程序逻辑

首先，将重点放在核心应用程序逻辑上，并将其移动到单独的类/接口中。接口允许更容易的模拟，并使用其他摇摆线程框架。这种分离意味着您可以完全独立于其他关注点来测试应用程序逻辑。

interface FileWriter
{
    void writeFile(File outputFile, String location, Creator creator)
         throws IOException;
    // you could also create your own exception type to avoid the checked exception.

    // a request object allows all the params to be encapsulated in one object.
    // this makes chaining services easier. See later.
    void writeFile(FileWriteRequest writeRequest); 
}

class FileWriteRequest
{
    File outputFile;
    String location;
    Creator creator;
    // constructor, getters etc..
}


class DefualtFileWriter implements FileWriter
{
    // this is basically the code from doInBackground()
    public File writeFile(File outputFile, String location, Creator creator)
       throws IOException 
    {
            Writer writer = null;
            try {
                writer = new FileWriter(outputFile);
                creator.write(location, writer);
            } finally {
                if (writer != null) {
                    writer.close();
                }
            }
            return file;
    }   
    public void writeFile(FileWriterRequest request) {
         writeFile(request.outputFile, request.location, request.creator);
    }
}

分离出用户界面

现在，应用程序逻辑是分开的，然后我们考虑成功和错误处理。这意味着可以在不实际写入文件的情况下测试 UI。特别是，可以测试错误处理，而实际上不需要引发这些错误。在这里，错误非常简单，但通常有些错误可能很难引起。通过分离出错误处理，还有机会重用或替换错误的处理方式。例如，稍后使用JXErrorPane。

interface FileWriterHandler {
     void done();
     void handleFileWritten(File file);
     void handleFileWriteError(Throwable t);
}  

class FileWriterJOptionPaneOpenDesktopHandler implements FileWriterHandler
{
   private JFrame owner;
   private JComponent enableMe;

   public void done() { enableMe.setEnabled(true); }

   public void handleFileWritten(File file) {
       try {
         JOptionPane.showMessageDialog(owner,
                    "File has been retrieved and saved to:\n"
                    + file.getAbsolutePath());
         Desktop.getDesktop().open(file);
       }
       catch (IOException ex) {
           handleDesktopOpenError(ex);
       }
   }

   public void handleDesktopOpenError(IOException ex) {
        logger.log(Level.INFO, "Unable to open file for viewing.", ex);        
   }

   public void handleFileWriteError(Throwable t) {
        if (t instanceof InterruptedException) {
                logger.log(Level.INFO, "Thread interupted, process aborting.", ex);  
                // no point interrupting the EDT thread
        }
       else if (t instanceof ExecutionException) {
           Throwable cause = ex.getCause() == null ? ex : ex.getCause();
           handleGeneralError(cause);
       }
       else
         handleGeneralError(t);
   }

   public void handleGeneralError(Throwable cause) {
        logger.log(Level.SEVERE, "An exception occurred that was "
                    + "not supposed to happen.", cause);
        JOptionPane.showMessageDialog(owner, "Error: "
                    + cause.getClass().getSimpleName() + " "
                    + cause.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
   }
}

分离出线程

最后，我们还可以使用 FileWriterService 分离出线程问题。使用上面的 FileWriteRequest 使编码变得更加简单。

interface FileWriterService
{
   // rather than have separate parms for file writing, it is
   void handleWriteRequest(FileWriteRequest request, FileWriter writer, FileWriterHandler handler);
}

class SwingWorkerFileWriterService 
   implements FileWriterService
{
   void handleWriteRequest(FileWriteRequest request, FileWriter writer, FileWriterHandler handler) {
       Worker worker = new Worker(request, fileWriter, fileWriterHandler);
       worker.execute();
   }

   static class Worker extends SwingWorker<File,Void> {
        // set in constructor
        private FileWriter fileWriter;
        private FileWriterHandler fileWriterHandler;
        private FileWriterRequest fileWriterRequest;

        protected File doInBackground() {
            return fileWriter.writeFile(fileWriterRequest);
        }
        protected void done() {
            fileWriterHandler.done();
            try
            {
                File f = get();
                fileWriterHandler.handleFileWritten(f);
            }
            catch (Exception ex)
            {                   
                // you could also specifically unwrap the ExecutorException here, since that
                // is specific to the service implementation using SwingWorker/Executors.
                fileWriterHandler.handleFileError(ex);
            }
        }
   }

}

系统的每个部分都是可单独测试的 - 应用程序逻辑，表示（成功和错误处理）和线程实现也是一个单独的关注点。

这可能看起来很多接口，但实现主要是从原始代码中剪切和粘贴的。这些接口提供了使这些类可测试所需的分离。

我不是SwingWorker的粉丝，所以把它们放在一个界面后面有助于防止它们产生的混乱。它还允许您使用不同的实现来实现单独的 UI/后台线程。例如，要使用 Spin，您只需要提供 FileWriterService 的新实现。