Java Swingworker Publish Process Example

Java Swing Tutorials - Herong's Tutorial Examples

∟SwingWorker - The Background Task Worker

∟SwingWorker Example using publish() Method

This section provides a tutorial example on how to use java.swing.SwingWorker class with the publish() method to send out intermediate values from the doInBackground() method. The process() method must be implemented to catch those intermediate values in the dispatch thread.

Example 2: Publish intermediate values and catch them - This example shows the another way of using the SwingWorker class to just publish intermediate values while performing the background task and catch them result in the Dispatch thread. Only 2 methods need to be implemented:

• T doInBackground() - Instance method to be implemented to perform the task. Inside doInBackground(), the publish(V...) method is called multiple times to publish intermediate values.
• void process(List<V>) - Instance method to be implemented, if you want to catch intermediate values published by the publish() method calls inside doInBackground().

Here is the source code of the example program, SwingWorkerUsingDone.java:

/* SwingWorkerUsingPublish.java  * Copyright (c) 2014, HerongYang.com, All Rights Reserved.  */ import javax.swing.SwingWorker; import java.util.List; import java.util.Random; import java.time.LocalTime; public class SwingWorkerUsingPublish     extends SwingWorker<Object, Integer> {    int total = 100;    int wait = 10;  // Extending the SwingWorker class    protected Object doInBackground() {       logMessage("doInBackground() started");       int i = 0;       Random r = new Random();       try {          while (i<total) {             Thread.sleep(wait);             Integer n = new Integer(r.nextInt());             publish(n);             i++;          }       } catch (Exception e) {       	 e.printStackTrace();       }       logMessage("doInBackground() ended");       return null;    }        protected void process(List<Integer> v) {       logMessage("process() receiving values: "+v.size());    }     // Launching my extended SwingWorker class    public static void main(String[] a) {       try {          SwingWorker worker = new SwingWorkerUsingPublish();          dumpThreads();          worker.execute();          while (true) {             dumpThreads();             Thread.sleep(200);          }       } catch (Exception e) {       	 e.printStackTrace();       }    }    public static void dumpThreads() {       System.out.println(LocalTime.now()+" Thread dump:");       Thread.currentThread().getThreadGroup().list();    }    public static void logMessage(String s) {       System.out.println(LocalTime.now()+" "          +Thread.currentThread().getName()+": "+s);    } }        

Notes on the sample program:

• When extending SwingWorker<T,V>, I am setting T to be Object because I am not returning any result; and setting V to be Integer to publish intermediate values.
• Object doInBackground() is implemented to generate some random numbers. Whenever a random number is generated, I call the publish() method to publish it the Dispatch thread.
• void process(List<V>) is implemented to catch intermediate values published by the Worker thread. Note that this publish-catch process is an asynchronous process. One invocation of process() could catch multiple intermediate values from multiple publish() calls. This is why received intermediate values are passed in as a List<V> object.

If you compile and run this example with JDK 1.8, you should get output messages similar to these:

C:\>java SwingWorkerUsingPublish  22:50:44.146 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]  22:50:44.186 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     Thread[SwingWorker-pool-1-thread-1,5,main] 22:50:44.196 SwingWorker-pool-1-thread-1: doInBackground() started 22:50:44.236 AWT-EventQueue-0: process() receiving values: 4 22:50:44.286 AWT-EventQueue-0: process() receiving values: 5 22:50:44.336 AWT-EventQueue-0: process() receiving values: 5  22:50:44.386 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     22:50:44.386 AWT-EventQueue-0: process() receiving values: 5 Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main] 22:50:44.436 AWT-EventQueue-0: process() receiving values: 5 22:50:44.486 AWT-EventQueue-0: process() receiving values: 5 22:50:44.536 AWT-EventQueue-0: process() receiving values: 5 22:50:44.586 AWT-EventQueue-0: process() receiving values: 5  22:50:44.596 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main] 22:50:44.636 AWT-EventQueue-0: process() receiving values: 5 22:50:44.686 AWT-EventQueue-0: process() receiving values: 5 22:50:44.736 AWT-EventQueue-0: process() receiving values: 5 22:50:44.786 AWT-EventQueue-0: process() receiving values: 5  22:50:44.796 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main] 22:50:44.836 AWT-EventQueue-0: process() receiving values: 5 22:50:44.886 AWT-EventQueue-0: process() receiving values: 5 22:50:44.936 AWT-EventQueue-0: process() receiving values: 5 22:50:44.986 AWT-EventQueue-0: process() receiving values: 5  22:50:44.996 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main] 22:50:45.036 AWT-EventQueue-0: process() receiving values: 5 22:50:45.086 AWT-EventQueue-0: process() receiving values: 5 22:50:45.136 AWT-EventQueue-0: process() receiving values: 5 22:50:45.186 AWT-EventQueue-0: process() receiving values: 5  22:50:45.196 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     22:50:45.196 SwingWorker-pool-1-thread-1: doInBackground() ended Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main] 22:50:45.236 AWT-EventQueue-0: process() receiving values: 1  22:50:45.406 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main]  22:50:45.606 Thread dump: java.lang.ThreadGroup[name=main,maxpri=10]     Thread[main,5,main]     Thread[SwingWorker-pool-1-thread-1,5,main]     Thread[AWT-Shutdown,5,main]     Thread[AWT-Windows,6,main]     Thread[AWT-EventQueue-0,6,main]        

Some interesting notes on the output:

• The log message in the output: "22:50:44.236 AWT-EventQueue-0: process() receiving values: 4" shows that the process() method was called in the "AWT-EventQueue-0" thread. So "AWT-EventQueue-0" is a Dispatch thread in our example.
• The log message in the output: "22:50:44.236 AWT-EventQueue-0: process() receiving values: 4" also shows that the process() method is called only once after 4 calls of publish(), because 4 intermediate values were passed in as the argument.
• The log message in the output: "22:50:45.236 AWT-EventQueue-0: process() receiving values: 1" shows that the last call of process() occurred after doInBackground() is ended.

The picture below gives you an idea on how the Launching thread, the Worker thread, and the Dispatch thread worked together in this example where I am repeatedly publishing intermediate values inside the doInBackground() method, and using the process() method to catch them:

Last update: 2014.

Table of Contents

About This Book

Introduction of Java Swing Package

Graphics Environment of the Local System

JFrame - Main Frame Class

JLabel - Swing Label Class

JButton - Swing Button Class

JRadioButton - Swing Radio Button Class

JTextField - Swing Text Field Class

Menu Bar, Menus, Menu Items and Listeners

Creating Internal Frames inside the Main Frame

Layout of Components in a Container

LookAndFeel and UIManager

Option Dialog Boxes

JEditorPane - The Editor Pane Class

►SwingWorker - The Background Task Worker

What Is SwingWorker Class?

SwingWorker Example using done() Method

►SwingWorker Example using publish() Method

SwingWorker Example using "progress" Property

SwingWorker Example using JProgressBar

References

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