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Swing Worker应用举例

Gavin Li — Sun, 26 Jun 2011 03:10:00 GMT

    在开发Java Swing应用�E�序的过�E�中�Q�有两个原则是必��要牢记的：
    1.耗时的操作（例如从数据库查询大量数据�Q�读取URI资源�{�）一定不能运行在EDT(事�g�z�֏��U�程)上，否则会导致Swing用户界面失去响应�?br />    2.只能在EDT�U�程上对Swing Components�q�行讉K��?br />    ��Z��上面两点原因�Q�在一个Java Swing�E�序中，要想使用��L��面响应灵敏，臛_��应该有两个线�E�；一个线�E�用来执行耗时操作�Q�EDT�U�程用来执行所有与Swing Components的交互，例如更新文本�Q�重�l�图形等�{�。这��p��求两个线�E�之间要�怺�通讯�Q�给�E�序的开发带来了不少的难度，Swing Worker的出��C��Ҏ��上解决了�q�个问题�Q��ɽE�序员快速开发反应灵敏的的Swing�E�序成�ؓ可能。SwingWoker被设计应用在此种场景下，你有一个耗时操作需要运行在后台�Q�在该操作完成或部分完成�Ӟ��你要利用操作�q�回的结果去更新用户界面�?br />    让我们假��x��q�样一个应用场景，我有一个保存联�p�M�h的文�Ӟ��我需要从中读取�ƈ解析出所有联�p�M�h的信息，�q�及时更新在一个JTable中；假设�q�个文�g非常的大�Q�解析出所有联�p�M�h的信息需要花费几分钟的时��_��如果不能很好的协调这个�Q务和EDT�U�程�Q�则很有可能会造成用户在几分钟旉��里得不到�l�果�Q�而Swing界面处于无响应状态。在�q�种情况下，SwingWorker��是一个绝佳的选择。我们首先看一下SwingWorker的定义：
    public abstract class SwingWorker extends Object implements RunnableFuture
昄��Q�这时一个抽象的模板�c�，在应用的时候，我们需要��承SwingWorker�q�实例化模板参数。那么，�q�两个模板类型究竟是什么意思呢�Q�T参数代表的是你的耗时��d��执行完成时返回的�l�果�c�d��Q�V代表的是你的耗时��d��部分完成时返回的�l�果�c�d��。在我们的场景中�Q�假设�Q务完成时我们需要一个List(BeanContact是一个保存联�p�M�h信息的JavaBean),每当从文件中解析��Z��个联�p�M�h信息�Ӟ��我们会新��Z��个BeanContact�q��要更新到JTable中。那么我们的T��是List,而V��是BeanContact,则应该定义如下的�c�：
     public class LoadContactsTask extends SwingWorker, BeanContact> {

     @Override
    protected List doInBackground() throws Exception {
        //To do the task and return the result
    }

     }
    从上面可以看刎ͼ�我们�q�必��覆盖SwingWorker的doInBackground�Ҏ��Q�该�Ҏ��执行我们的耗时操作�Q��ƈ且返回模板实例化时的T�c�d��l�果。下面是具体的代码实玎ͼ�

    @Override
    protected List doInBackground() throws Exception {
        BufferedReader reader = new BufferedReader(new FileReader("c:/contacts.cff"));
        String line = null;
        while ((line = reader.readLine()) != null) {
            String[] strContacts = line.split(",");
            BeanContact contact = new BeanContact();
            contact.setName(strContacts[0]);
            contact.setSex(strContacts[1]);
            contact.setPhone(strContacts[2]);
            contact.setEmail(strContacts[3]);

            lineCnt++;
            publish(contact);/*********/
           contacts.add(contact);

            Thread.sleep(100);
        }
        return contacts;
    }

     该方法很��单，��是从文件中��d��一个联�p�M�h的记录�ƈ且新��Z��个BeanContact实例��d��到结果集中。我们需要注意的是其中的publish�Ҏ��Q�该�Ҏ��用来发布部分执行�l�果�Q�每��d��一个联�p�M�h信息�Q�我们就用该�Ҏ��把新建的BeanContact发布出去。我们需要知道的是，在publish若干个结果后�Q�可能是一个或多个�Q�由SwingWorker�c�d��玎ͼ�SwingWorker�cȝ��process�Ҏ��会被自动回调�Q�而我们可以在其中��L��新用��L��面，SwingWorker保证process�Ҏ��中所有操作都�q�行在EDT�U�程中。下面是我们的具体实玎ͼ�
    @Override
    protected void process(List chunks) {
        if (progressHandle != null) {
            progressHandle.processInProgress(chunks, lineCnt * 100 / 10000);
        }
    }
    我们的实��C��Q�process中会调用IProgressHandle�Q�自定义的一个接口，用来更新用户界面�Q�详见后面代码）的processInProgress�Ҏ��来更新用��L��面，大家会注意到process�Ҏ��的参数是一个List,��Z��么不是一个BeanContact呢，�{�案��是我们在上面讲�q�的�Q�有可能publish若干�ơ后才调用process�Ҏ��?br />    与此�c�M��Q�在doInBackground完成后，SwingWorker会自动调用done�Ҏ��Q�下面是我们的实玎ͼ�
    @Override
    protected void done() {
        if (progressHandle != null) {
            progressHandle.processComplete(contacts);
        }
    }
    客户端如何来使用用SwingWork呢，很简单，只需要新��Z��个实例�ƈ且调用它的execute�Ҏ��卛_��Q�他会自动调用doInBackground�Ҏ��来完成操作；以下是完整的代码实现�Q?br />

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package swingworkertest;

/**
*
* @author Administrator
*/
public class BeanContact {
    private String name=null;
    private String sex=null;
    private String phone=null;
    private String email=null;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @return the sex
     */
    public String getSex() {
        return sex;
    }

    /**
     * @param sex the sex to set
     */
    public void setSex(String sex) {
        this.sex = sex;
    }

    /**
     * @return the phone
     */
    public String getPhone() {
        return phone;
    }

    /**
     * @param phone the phone to set
     */
    public void setPhone(String phone) {
        this.phone = phone;
    }

    /**
     * @return the email
     */
    public String getEmail() {
        return email;
    }

    /**
     * @param email the email to set
     */
    public void setEmail(String email) {
        this.email = email;
    }

}

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/

/*
* Contacts.java
*
* Created on 2011-6-25, 10:40:13
*/
package swingworkertest;

import javax.swing.JFileChooser;

/**
*
* @author Administrator
*/
public class Contacts extends javax.swing.JFrame {

    /** Creates new form Contacts */
    public Contacts() {
        initComponents();
        handle = new DefaultProgressHandle();
        handle.setTable(jTable1);
        handle.setProgressBar(jProgressBar1);
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    //
    private void initComponents() {

        jButton1 = new javax.swing.JButton();
        jTextField1 = new javax.swing.JTextField();
        jScrollPane1 = new javax.swing.JScrollPane();
        jTable1 = new javax.swing.JTable();
        jButton2 = new javax.swing.JButton();
        jProgressBar1 = new javax.swing.JProgressBar();

setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jButton1.setText("��览");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

jTextField1.setEditable(false);

jTable1.setModel(new javax.swing.table.DefaultTableModel(
new Object [][] {

            },
            new String [] {
                "姓名", "性别", "电话", "电子邮�g"
            }
        ) {
            Class[] types = new Class [] {
                java.lang.String.class, java.lang.String.class, java.lang.String.class, java.lang.String.class
            };

            public Class getColumnClass(int columnIndex) {
                return types [columnIndex];
            }
        });
        jScrollPane1.setViewportView(jTable1);

        jButton2.setText("加蝲联系�?);
        jButton2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton2ActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                    .addComponent(jScrollPane1, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 557, Short.MAX_VALUE)
                    .addComponent(jProgressBar1, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 557, Short.MAX_VALUE)
                    .addComponent(jButton2, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 557, Short.MAX_VALUE)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(jButton1, javax.swing.GroupLayout.DEFAULT_SIZE, 97, Short.MAX_VALUE)
                        .addGap(18, 18, 18)
                        .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 442, javax.swing.GroupLayout.PREFERRED_SIZE)))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jButton2)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 120, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(jProgressBar1, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

layout.linkSize(javax.swing.SwingConstants.VERTICAL, new java.awt.Component[] {jButton1, jButton2, jTextField1});

pack();
}//

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

        ContactsFileFilter filter = new ContactsFileFilter();

        JFileChooser chooser = new JFileChooser();
        chooser.setFileFilter(filter);
        int returnVal = chooser.showOpenDialog(null);
        if(returnVal == JFileChooser.APPROVE_OPTION){
            jTextField1.setText(chooser.getSelectedFile().getAbsolutePath());
        }
    }

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
        LoadContactsTask task = new LoadContactsTask(jTextField1.getText());
        task.setProgressHandle(handle);
        task.execute();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                Contacts contacts = new Contacts();
                contacts.setTitle("Contacts");;
                contacts.setVisible(true);
            }
        });
    }
    DefaultProgressHandle handle = null;
    // Variables declaration - do not modify
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JProgressBar jProgressBar1;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTable jTable1;
    private javax.swing.JTextField jTextField1;
    // End of variables declaration
}

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package swingworkertest;

import java.io.File;
import javax.swing.filechooser.FileFilter;

/**
*
* @author Administrator
*/
public class ContactsFileFilter extends FileFilter{

    public boolean accept(File pathname) {
        if(pathname.isDirectory()){
            return true;
        }else{
            return pathname.getName().endsWith(".cff");
        }
    }

    @Override
    public String getDescription() {
        return "Text Files";
    }

}

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package swingworkertest;

import java.util.List;
import javax.swing.JProgressBar;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;

/**
*
* @author Administrator
*/
public class DefaultProgressHandle implements IProgressHandle {

private JTable table = null;
private JProgressBar progressBar = null;

    public void processInProgress(List contacts, int progress) {
        DefaultTableModel model = (DefaultTableModel) table.getModel();
        for (BeanContact contact : contacts) {
            String[] strArray = {contact.getName(), contact.getSex(), contact.getPhone(), contact.getEmail()};
            model.addRow(strArray);
        }
        progressBar.setValue(progress);
    }

    public void processComplete(List contacts) {
        progressBar.setValue(progressBar.getMaximum());
    }

    /**
     * @param table the table to set
     */
    public void setTable(JTable table) {
        this.table = table;
    }

    /**
     * @param progressBar the progressBar to set
     */
    public void setProgressBar(JProgressBar progressBar) {
        this.progressBar = progressBar;
    }
}

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package swingworkertest;

import java.util.List;

/**
*
* @author Administrator
*/
public interface IProgressHandle {
public abstract void processInProgress(List contacts,int progress);
public abstract void processComplete(List contacts);
}

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package swingworkertest;

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.List;
import javax.swing.SwingWorker;

/**
*
* @author Administrator
*/
public class LoadContactsTask extends SwingWorker, BeanContact> {

    private String fileName = null;
    private IProgressHandle progressHandle = null;
    private List contacts = null;
    private int lineCnt = 0;

    public LoadContactsTask(String fileName) {
        this.fileName = fileName;
        contacts = new ArrayList();
    }

            lineCnt++;
            publish(contact);
            contacts.add(contact);

            Thread.sleep(100);
        }
        return contacts;
    }

    /**
     * @param progressHandle the progressHandle to set
     */
    public void setProgressHandle(IProgressHandle progressHandle) {
        this.progressHandle = progressHandle;
    }

    @Override
    protected void process(List chunks) {
        if (progressHandle != null) {
            progressHandle.processInProgress(chunks, lineCnt * 100 / 10000);
        }
    }

    @Override
    protected void done() {
        if (progressHandle != null) {
            progressHandle.processComplete(contacts);
        }
    }
}

Gavin Li 2011-06-26 11:10 发表评论

Gavin Li — Tue, 14 Jun 2011 14:53:00 GMT

    我们知道�Q�在Java中设�|�变量值的操作�Q�除了long和double�c�d��的变量外都是原子操作�Q�也��是��_��对于变量值的��单读写操作没有必要进行同步。这在JVM 1.2之前�Q�Java的内存模型实现��L��从主存读取变量，是不需要进行特别的注意的。而随着JVM的成熟和优化�Q�现在在多线�E�环境下volatile关键字的使用变得非常重要。在当前的Java内存模型下，�U�程可以把变量保存在本地内存�Q�比如机器的寄存器）中，而不是直接在��d��中进行读写。这��可能造成一个线�E�在��d��中修改了一个变量的��|��而另外一个线�E�还�l�箋使用它在寄存器中的变量值的拯��Q�造成数据的不一致。把变量声明为volatile�Q�不�E�_��的）�Q�这��指�C�JVM�Q�这个变量是不稳定的�Q�每�ơ��用它都到��d��中进行读取。一般说来，多�Q务环境下各�Q务间�׃�n的标志都应该加volatile修饰�?/span>
    在一些情况下�Q��用volatile可以辑ֈ�同步的目的，在某�U�程度上相当于synchronized关键字；��Z��么说是一定程度上呢，�q�就要从synchronized同步关键字说起了�Q�synchronized在Java语言中可以实��C��个功能，互斥性和可见性。互斥性是指�Q意时��d��能有一个线�E�持有特定的锁，从而可以实现对�׃�n数据的协调访问；而可见性说的是�Q��Q意线�E�修改的�׃�n数据对于其他�U�程必须是可见的�Q�也��是说不允许其他�U�程拿到旧的数据。而volatile关键字只能实现可见性，也就是说用volatile修饰的变量的修改对于其他�U�程是可见的�Q�如果该��D��修改�Q�其他线�E�可以立卛_��到新倹{��下面的代码��单展�C�Z��volatile的一个简单应用，�U�程的退出：

1public class Monitor implements Runnable {
2
3    private volatile Thread blinker;
4    boolean isRunning = false;
5
6
7    @Override
8    public void run() {
9
10        Thread thisThread = Thread.currentThread();
11        while (blinker == thisThread) {
12            try {
13                thisThread.sleep(50);
14            } catch (InterruptedException e) {
15            }
16            //To do you task
17        }
18
19    }
20
21
22    public void startMonitor() {
23        blinker = new Thread(this);
24        blinker.start();
25    }
26
27    public void stopMonitor() {
28        blinker = null;
29    }
30
31}

Gavin Li 2011-06-14 22:53 发表评论

Gavin Li — Wed, 08 Jun 2011 15:28:00 GMT

对于Java集合中的List来讲�Q�删除是一个常见的操作�Q�但是也是最�Ҏ��犯错误的地方,��其对于新手更是如此。笔者在工作中也�l�常看到一些工作了很长旉��的老程序员在这个问题上犯错误；在这里，我将通过一个例子，�l�大家展�C�如何从List中安全的删除元素。先看下面的例子�Q?br /> 假如我有一个List,其中包含�?个元素，我想删除其中的前�?个，应该如何做；好多�E�序员不加思烦�Q�写下了下面的代码：

1private void unSafeDeleteTopByCount(List list) {
2        try {
3            for (int i = 0; i < 4; i++) {
4                list.remove(i);
5            }
6        } catch (Exception e) {
7            e.printStackTrace();
8        }

    大家可以新徏一个List,然后新徏一个类在main中调用一下这个方法，看看�l�果会如何：看到了吧�Q�程序抛��Z��异常�Q�如下：
    java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
at java.util.ArrayList.RangeCheck(Unknown Source)
at java.util.ArrayList.remove(Unknown Source)
at com.lpx.collection.TestArrayDeletion.unSafeDeleteTopByCount(TestArrayDeletion.java:59)
at com.lpx.collection.TestArrayDeletion.main(TestArrayDeletion.java:26)
    看到�q�里�Q�可能大家已�l�明白了�Q�对了，在删除的�q�程中，List的size发生了变化，但是index没有变化�Q�就会造成index>=size的情况发生，抛出IndexOutOfBoundsException是一定的。这�q�算好的�Q�至��你知道有异常，但是�q�有一�U�更隐蔽的情况，如果你删除的个数�?个，IndexOutOfBoundsException是不会发生的�Q�但是删除后的List不是你想要的�l�果。具体是

private void unSafeDeleteTopByCount(int count) {
        try {
            for (int i = 0; i < count; i++) {
                list.remove(i);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            print();
        }
    }

private void print() {
        for (String str : list) {
            System.out.println(str);
        }
    }

List<String> list = new ArrayList<String>();
for(int i=0;i<6;i++){
       list.add("str"+i);
}
unSafeDeleteTopByCount(3);

   什么意思呢�Q�大家可以看一下上面的代码�Q�如果运行的话，打印出的�l�果是：
    str1
    str3
    str5
   ��Z��么呢�Q�当我们删除了index�?的元素【str0】后�Q�由于List的size变化�Q�index�?的元素会变�ؓstr1,而index�?的元素会变�ؓstr2,�q�时�?

private void safeDeletionTopByCountMethod1(int count) {
        System.out.println("*********safeDeletionTopByCountMethod1*********");
        for (int i = count - 1; i >= 0; i--) {
            list.remove(i);
        }
        print();
    }

    private void safeDeletionTopByCountMethod2(int count) {
        System.out.println("*********safeDeletionTopByCountMethod2*********");
        for (int i = 0; i < count; i++) {
            list.remove(0);
        }
        print();
    }

    private void safeDeletionTopByCountMethod3(int count) {
        System.out.println("*********safeDeletionTopByCountMethod3*********");
        List<String> localList = new ArrayList<String>();
        for (int i = 0; i < count; i++) {
            localList.add(list.get(i));
        }
        list.removeAll(localList);
        print();
    }

    private void safeDeletionTopByCountMethod4(int count) {
        System.out.println("*********safeDeletionTopByCountMethod4*********");
        List<String> localList = new ArrayList<String>();
        localList.addAll(list);
        for (int i = 0; i < count; i++) {
            String str = localList.get(i);
            list.remove(str);
        }
        print();
    }

于index�?�Q�所以str2会被删除�Q�你可以自己��L��一下结果�?br />如何解决�q�个问题呢，�W�者在上面�l�出�?�U�方法供大家参考，最后给��Z��完整的代码�?br />*****************************************************************************

package com.lpx.collection;

import java.util.ArrayList;
import java.util.List;

public class TestArrayDeletion {

private List list = null;
public static String[] array = { "str0", "str1", "str2", "str3", "str4",
"str5" };

public TestArrayDeletion() {
super();
list = new ArrayList();
}

/**
* @param args
*/
public static void main(String[] args) {
  TestArrayDeletion arrayDeletion = new TestArrayDeletion();
  arrayDeletion.initList();
  arrayDeletion.unSafeDeleteTopByCount(3);

arrayDeletion.initList();
arrayDeletion.unSafeDeleteTopByCount(4);

arrayDeletion.initList();
arrayDeletion.safeDeletionTopByCountMethod1(4);

arrayDeletion.initList();
arrayDeletion.safeDeletionTopByCountMethod2(4);

arrayDeletion.initList();
arrayDeletion.safeDeletionTopByCountMethod3(4);

arrayDeletion.initList();
arrayDeletion.safeDeletionTopByCountMethod4(4);

}

private void initList() {
  list.clear();
  for (String str : array) {
   list.add(str);
  }
}

private void print() {
  for (String str : list) {
   System.out.println(str);
  }
}

private void unSafeDeleteTopByCount(int count) {
  System.out.println("*********unSafeDeleteTopByCount*********");
  try {
   for (int i = 0; i < count; i++) {
    list.remove(i);
   }
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   print();
  }
}

private void safeDeletionTopByCountMethod2(int count) {
  System.out.println("*********safeDeletionTopByCountMethod2*********");
  for (int i = 0; i < count; i++) {
   list.remove(0);
  }
  print();
}

private void safeDeletionTopByCountMethod3(int count) {
  System.out.println("*********safeDeletionTopByCountMethod3*********");
  List localList = new ArrayList();
  for (int i = 0; i < count; i++) {
   localList.add(list.get(i));
  }
  list.removeAll(localList);
  print();
}

private void safeDeletionTopByCountMethod4(int count) {
  System.out.println("*********safeDeletionTopByCountMethod4*********");
  List localList = new ArrayList();
  localList.addAll(list);
  for (int i = 0; i < count; i++) {
   String str = localList.get(i);
   list.remove(str);
  }
  print();
}
}

Gavin Li 2011-06-08 23:28 发表评论