为什么要使用SwingWorker

在swing开发中，如果一个应用程序，执行一些任务，需要大量的时间来完成，比如下载一个大文件或执行一个复杂的数据库查询。

我们假设这些任务是由用户使用一个按钮触发的。在单线程应用程序，用户单击按钮，进入计算的过程，然后等待任务完成之前，所有的事件都在主线程EDT线程进行。

但如果某些任务耗时很长，用户将甚至不能在中途取消任务，应用程序必须响应只有当长任务完成。不幸的是，许多应用程序显着这样的行为和用户感到沮丧，程序仿佛卡死一样。

多线程可以解决这个问题。它使应用程序能够在不同的线程上执行长任务，但多线程带来一个问题，如果需要实时和主线程EDT进行数据交换，该怎么办？我们知道所有的Swing对象都只有一个线程处理，EDT事件调度线程，这导致一个问题：我们不能在EDT事件分派线程以外的其他线程共享对象的对象。

 

SwingWorker

SwingWorker是一个抽象类，java将它包装好，供方便调用，下面的例子使用字符串对象来通知应用程序。

提供了两个泛型参数。第一个代表返回的对象类型。另一个代表了通知（更新）应用程序的信息的类型，并在下面的例子中高亮显示。

public class MyBlankWorker extends SwingWorker
      
        {  @Override  protected Integer doInBackground() throws Exception {    // Start    publish("Start");    setProgress(1);        // More work was done    publish("More work was done");    setProgress(10);    // Complete    publish("Complete");    setProgress(100);    return 1;  }    @Override  protected void process(List< String> chunks) {    // Messages received from the doInBackground() (when invoking the publish() method)  }}
      

通过setprogress() 设置0和100之间的整数。doinbackground() 用于漫长任务执行。此方法不是由事件调度线程调用的，而是由另一个线程（称为工作线程）。我们可以用publish()方法和/或setprogress()更新进度。调用两个方法都会对事件调度线程的创建新任务，它是工作线程和事件调度线程的线程之间的单向桥。

doinbackground()中调用publish()方法和/或setprogress()必须防止大量的任务发送给事件调度线程，引发洪水事件。

注意：publish()从工作线程调用，而process()由事件调度线程EDT调用。

举例：

输入:

publish("a"); publish("b", "c"); publish("d", "e", "f");

结果就是:

process("a", "b", "c", "d", "e", "f") 最后是一个文件全文检索的异步查询例子，查询某目录下所有的txt文件

import java.io.File;import java.util.ArrayList;import java.util.List;import javax.swing.JTextArea;import javax.swing.SwingWorker;import org.apache.commons.io.FileUtils;import org.apache.commons.io.filefilter.SuffixFileFilter;import org.apache.commons.io.filefilter.TrueFileFilter;import org.apache.commons.lang.StringUtils;/** * Searches the text files under the given directory and counts the number of instances a given word is found in these * file. *  * @author Albert Attard */public class SearchForWordWorker extends SwingWorker
      
        {  private static void failIfInterrupted() throws InterruptedException {    if (Thread.currentThread().isInterrupted()) {      throw new InterruptedException("Interrupted while searching files");    }  }  /** The word that is searched */  private final String word;  /** The directory under which the search occurs. All text files found under the given directory are searched. */  private final File directory;  /** The text area where messages are written. */  private final JTextArea messagesTextArea;  /**   * Creates an instance of the worker   *    * @param word   *          The word to search   * @param directory   *          the directory under which the search will occur. All text files found under the given directory are   *          searched   * @param messagesTextArea   *          The text area where messages are written   */  public SearchForWordWorker(final String word, final File directory, final JTextArea messagesTextArea) {    this.word = word;    this.directory = directory;    this.messagesTextArea = messagesTextArea;  }  @Override  protected Integer doInBackground() throws Exception {    // The number of instances the word is found    int matches = 0;    /*     * List all text files under the given directory using the Apache IO library. This process cannot be interrupted     * (stopped through cancellation). That is why we are checking right after the process whether it was interrupted or     * not.     */    publish("Listing all text files under the directory: " + directory);    final List
       
         textFiles = new ArrayList<>(FileUtils.listFiles(directory, new SuffixFileFilter(".txt"),        TrueFileFilter.TRUE));    SearchForWordWorker.failIfInterrupted();    publish("Found " + textFiles.size() + " text files under the directory: " + directory);    for (int i = 0, size = textFiles.size(); i < size; i++) {      /*       * In order to respond to the cancellations, we need to check whether this thread (the worker thread) was       * interrupted or not. If the thread was interrupted, then we simply throw an InterruptedException to indicate       * that the worker thread was cancelled.       */      SearchForWordWorker.failIfInterrupted();      // Update the status and indicate which file is being searched.      final File file = textFiles.get(i);      publish("Searching file: " + file);      /*       * Read the file content into a string, and count the matches using the Apache common IO and Lang libraries       * respectively.       */      final String text = FileUtils.readFileToString(file);      matches += StringUtils.countMatches(text, word);      Thread.sleep(20);      // Update the progress      setProgress((i + 1) * 100 / size);    }    // Return the number of matches found    return matches;  }  @Override  protected void process(final List
        
          chunks) {    // Updates the messages text area    for (final String string : chunks) {      messagesTextArea.append(string);      messagesTextArea.append("\n");    }  }}
        
       
      

JFrame UI类如下

package com.javacreed.examples.swing.worker.part3;import java.awt.GridBagConstraints;import java.awt.GridBagLayout;import java.awt.Insets;import java.awt.event.ActionEvent;import java.beans.PropertyChangeEvent;import java.beans.PropertyChangeListener;import java.io.File;import javax.swing.AbstractAction;import javax.swing.Action;import javax.swing.JButton;import javax.swing.JFileChooser;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JProgressBar;import javax.swing.JScrollPane;import javax.swing.JTextArea;import javax.swing.JTextField;import javax.swing.SwingWorker.StateValue;public class Application extends JFrame {  /**  */  private static final long serialVersionUID = -8668818312732181049L;  private Action searchCancelAction;  private Action browseAction;  private JTextField wordTextField;  private JTextField directoryPathTextField;  private JTextArea messagesTextArea;  private JProgressBar searchProgressBar;  private SearchForWordWorker searchWorker;  public Application() {    initActions();    initComponents();  }  private void cancel() {    searchWorker.cancel(true);  }  private void initActions() {    browseAction = new AbstractAction("Browse") {      private static final long serialVersionUID = 4669650683189592364L;      @Override      public void actionPerformed(final ActionEvent e) {        final File dir = new File(directoryPathTextField.getText()).getAbsoluteFile();        final JFileChooser fileChooser = new JFileChooser(dir.getParentFile());        fileChooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);        final int option = fileChooser.showOpenDialog(Application.this);        if (option == JFileChooser.APPROVE_OPTION) {          final File selected = fileChooser.getSelectedFile();          directoryPathTextField.setText(selected.getAbsolutePath());        }      }    };    searchCancelAction = new AbstractAction("Search") {      private static final long serialVersionUID = 4669650683189592364L;      @Override      public void actionPerformed(final ActionEvent e) {        if (searchWorker == null) {          search();        } else {          cancel();        }      }    };  }  private void initComponents() {    setLayout(new GridBagLayout());    GridBagConstraints constraints = new GridBagConstraints();    constraints.gridx = 0;    constraints.gridy = 0;    constraints.insets = new Insets(2, 2, 2, 2);    add(new JLabel("Word: "), constraints);    wordTextField = new JTextField();    wordTextField.setText("Hello");    constraints = new GridBagConstraints();    constraints.gridx = 1;    constraints.gridy = 0;    constraints.gridwidth = 2;    constraints.insets = new Insets(2, 2, 2, 2);    constraints.weightx = 1;    constraints.fill = GridBagConstraints.BOTH;    add(wordTextField, constraints);    constraints = new GridBagConstraints();    constraints.gridx = 0;    constraints.gridy = 1;    constraints.insets = new Insets(2, 2, 2, 2);    add(new JLabel("Path: "), constraints);    directoryPathTextField = new JTextField();    directoryPathTextField.setText("C:\\Users\\Albert\\Work\\JavaCreed\\examples");    constraints = new GridBagConstraints();    constraints.gridx = 1;    constraints.gridy = 1;    constraints.gridwidth = 1;    constraints.insets = new Insets(2, 2, 2, 2);    constraints.weightx = 1;    constraints.fill = GridBagConstraints.BOTH;    add(directoryPathTextField, constraints);    constraints = new GridBagConstraints();    constraints.gridx = 2;    constraints.gridy = 1;    constraints.insets = new Insets(2, 2, 2, 2);    add(new JButton(browseAction), constraints);    messagesTextArea = new JTextArea();    messagesTextArea.setEditable(false);    constraints = new GridBagConstraints();    constraints.gridx = 0;    constraints.gridy = 2;    constraints.gridwidth = 3;    constraints.insets = new Insets(2, 2, 2, 2);    constraints.weightx = 1;    constraints.weighty = 1;    constraints.fill = GridBagConstraints.BOTH;    add(new JScrollPane(messagesTextArea), constraints);    searchProgressBar = new JProgressBar();    searchProgressBar.setStringPainted(true);    searchProgressBar.setVisible(false);    constraints = new GridBagConstraints();    constraints.gridx = 0;    constraints.gridy = 3;    constraints.gridwidth = 2;    constraints.insets = new Insets(2, 2, 2, 2);    constraints.weightx = 1;    constraints.fill = GridBagConstraints.BOTH;    add(searchProgressBar, constraints);    constraints = new GridBagConstraints();    constraints.gridx = 2;    constraints.gridy = 3;    constraints.insets = new Insets(2, 2, 2, 2);    constraints.weightx = 0;    add(new JButton(searchCancelAction), constraints);  }  private void search() {    final String word = wordTextField.getText();    final File directory = new File(directoryPathTextField.getText());    messagesTextArea.setText("Searching for word '" + word + "' in text files under: " + directory.getAbsolutePath()        + "\n");    searchWorker = new SearchForWordWorker(word, directory, messagesTextArea);    searchWorker.addPropertyChangeListener(new PropertyChangeListener() {      @Override      public void propertyChange(final PropertyChangeEvent event) {        switch (event.getPropertyName()) {        case "progress":          searchProgressBar.setIndeterminate(false);          searchProgressBar.setValue((Integer) event.getNewValue());          break;        case "state":          switch ((StateValue) event.getNewValue()) {          case DONE:            searchProgressBar.setVisible(false);            searchCancelAction.putValue(Action.NAME, "Search");            searchWorker = null;            break;          case STARTED:          case PENDING:            searchCancelAction.putValue(Action.NAME, "Cancel");            searchProgressBar.setVisible(true);            searchProgressBar.setIndeterminate(true);            break;          }          break;        }      }    });    searchWorker.execute();  }}

入口：

 

import javax.swing.JFrame;import javax.swing.SwingUtilities;public class Main {  public static void main(final String[] args) {    SwingUtilities.invokeLater(new Runnable() {      @Override      public void run() {        final Application frame = new Application();        frame.setTitle("Swing Worker Demo");        frame.setSize(600, 400);        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        frame.setVisible(true);      }    });  }}

 

引用：http://www.javacreed.com/swing-worker-example/