了解Java ExecutorService
作者：互联网
我正在尝试学习如何使用Java的executorservice,
我正在阅读以下讨论Java thread simple queue
在这里有一个示例
ExecutorService service = Executors.newFixedThreadPool(10);
// now submit our jobs
service.submit(new Runnable() {
public void run() {
do_some_work();
}
});
// you can submit any number of jobs and the 10 threads will work on them
// in order
...
// when no more to submit, call shutdown
service.shutdown();
// now wait for the jobs to finish
service.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
我尝试实现这个解决方案,为此我创建了一个表单并放置了启动和停止按钮,但我面临的问题是,如果我在启动按钮上调用此过程,它将挂起完整的表单,我们需要等到所有进程完成了.
我也尝试阅读以下https://www3.ntu.edu.sg/home/ehchua/programming/java/J5e_multithreading.html
但到目前为止,我无法理解如何使其工作,因为点击开始按钮后,我应该获得访问权限,假设我想要停止该过程.
有人可以指导我正确的方向.
谢谢
为了使我的情况更清楚,我正在添加我正在测试的代码.
问题
1)程序执行时,完整表格保持冻结状态.
2)进度条不起作用,只有在所有过程完成后才会显示状态.
private void btnStartActionPerformed(java.awt.event.ActionEvent evt) {
TestConneciton();
}
private void btnStopActionPerformed(java.awt.event.ActionEvent evt) {
flgStop = true;
}
private static final int MYTHREADS = 30;
private boolean flgStop = false;
public void TestConneciton() {
ExecutorService executor = Executors.newFixedThreadPool(MYTHREADS);
String[] hostList = { "http://crunchify.com", "http://yahoo.com",
"http://www.ebay.com", "http://google.com",
"http://www.example.co", "https://paypal.com",
"http://bing.com/", "http://techcrunch.com/",
"http://mashable.com/", "http://thenextweb.com/",
"http://wordpress.com/", "http://wordpress.org/",
"http://example.com/", "http://sjsu.edu/",
"http://ebay.co.uk/", "http://google.co.uk/",
"http://www.wikipedia.org/",
"http://en.wikipedia.org/wiki/Main_Page" };
pbarStatus.setMaximum(hostList.length-1);
pbarStatus.setValue(0);
for (int i = 0; i < hostList.length; i++) {
String url = hostList[i];
Runnable worker = new MyRunnable(url);
executor.execute(worker);
}
executor.shutdown();
// Wait until all threads are finish
// while (!executor.isTerminated()) {
//
// }
System.out.println("\nFinished all threads");
}
public class MyRunnable implements Runnable {
private final String url;
MyRunnable(String url) {
this.url = url;
}
@Override
public void run() {
String result = "";
int code = 200;
try {
if(flgStop == true)
{
//Stop thread execution
}
URL siteURL = new URL(url);
HttpURLConnection connection = (HttpURLConnection) siteURL
.openConnection();
connection.setRequestMethod("GET");
connection.connect();
code = connection.getResponseCode();
pbarStatus.setValue(pbarStatus.getValue()+1);
if (code == 200) {
result = "Green\t";
}
} catch (Exception e) {
result = "->Red<-\t";
}
System.out.println(url + "\t\tStatus:" + result);
}
}
解决方法:
根据ExecutorService API,这阻止：
service.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
API报价：
Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
如果您不希望这阻止当前线程,那么您可能应该在另一个线程中调用它.另外,你的是Swing应用程序,然后考虑使用SwingWorker,我认为它使用了“引擎盖下的ExecutorServices”.
根据您最新的代码,我会使用
>一个SwingWorker来管理所有后台线程.
>我给SwingWorker一个ExecutorService
>以及使用ExecutorService初始化的ExecutorCompletionService,这样我就可以在完成任务时获取任务结果
>我用Callables填充它,而不是Runnables,因为这将允许任务返回一些东西,也许是一个字符串来表示进度.
>我将SwingWorker的progress属性设置为(100 * taskCount)/ totalTaskCount,让我的JProgressBar从0到100.
>然后我使用SwingWorker的发布/处理方法对提取可调用返回的字符串.
>我将使用PropertyChangeListener在GUI中监听SwingWorker的进度
>然后从此侦听器中更改GUI.
>我会改变if(code == 200){to if(code == HttpURLConnection.HTTP_OK){以避免幻数.
> JButton的Action会自行禁用,然后创建一个新的SwingWorker对象,将worker的ProperChangeListener添加到worker,然后执行worker.
例如
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;
@SuppressWarnings("serial")
public class SwingExecutorCompletionService extends JPanel {
public static final int MYTHREADS = 10;
private static final int LIST_PROTOTYPE_SIZE = 120;
private static final String LIST_PROTOTYPE_STRING = "%" + LIST_PROTOTYPE_SIZE + "s";
public static final String[] HOST_LIST = {
"http://crunchify.com",
"http://yahoo.com",
"http://www.ebay.com",
"http://google.com",
"http://www.example.co",
"https://paypal.com",
"http://bing.com/",
"http://techcrunch.com/",
"http://mashable.com/",
"http://thenextweb.com/",
"http://wordpress.com/",
"http://wordpress.org/",
"http://example.com/",
"http://sjsu.edu/",
"http://ebay.co.uk/",
"http://google.co.uk/",
"http://www.wikipedia.org/",
"http://en.wikipedia.org/wiki/Main_Page" };
private JProgressBar pbarStatus = new JProgressBar(0, 100);
private JButton doItButton = new JButton(new DoItAction("Do It", KeyEvent.VK_D));
private DefaultListModel<String> listModel = new DefaultListModel<>();
private JList<String> resultList = new JList<>(listModel);
public SwingExecutorCompletionService() {
resultList.setVisibleRowCount(10);
resultList.setPrototypeCellValue(String.format(LIST_PROTOTYPE_STRING, ""));
resultList.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 12));
add(pbarStatus);
add(doItButton);
add(new JScrollPane(resultList, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED));
}
public void addToCompletionList(String element) {
listModel.addElement(element);
}
public void setStatusValue(int progress) {
pbarStatus.setValue(progress);
}
class DoItAction extends AbstractAction {
public DoItAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
setEnabled(false);
DoItWorker worker = new DoItWorker(HOST_LIST, MYTHREADS);
SwingExecutorCompletionService gui = SwingExecutorCompletionService.this;
PropertyChangeListener workerListener = new WorkerChangeListener(gui, this);
worker.addPropertyChangeListener(workerListener);
worker.execute();
}
}
private static void createAndShowGui() {
SwingExecutorCompletionService mainPanel = new SwingExecutorCompletionService();
JFrame frame = new JFrame("Swing ExecutorCompletionService");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class MyCallable implements Callable<String> {
private static final String RED = "->Red<-";
private static final String GREEN = "Green";
private final String url;
private volatile boolean flgStop;
MyCallable(String url) {
this.url = url;
}
@Override
public String call() throws Exception {
String result = "";
int code = HttpURLConnection.HTTP_OK;
try {
// if(flgStop == true)
if (flgStop) {
// Stop thread execution
}
URL siteURL = new URL(url);
HttpURLConnection connection = (HttpURLConnection) siteURL
.openConnection();
connection.setRequestMethod("GET");
connection.connect();
code = connection.getResponseCode();
// No don't set the prog bar in a background thread!
// !! pbarStatus.setValue(pbarStatus.getValue()+1);
// avoid magic numbers
if (code == HttpURLConnection.HTTP_OK) {
result = GREEN;
}
} catch (Exception e) {
result = RED;
}
return String.format("%-40s %s", url + ":", result);
}
}
class WorkerChangeListener implements PropertyChangeListener {
private Action action;
private SwingExecutorCompletionService gui;
public WorkerChangeListener(SwingExecutorCompletionService gui, Action button) {
this.gui = gui;
this.action = button;
}
@Override
public void propertyChange(PropertyChangeEvent evt) {
DoItWorker worker = (DoItWorker)evt.getSource();
if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
action.setEnabled(true);
try {
worker.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
} else if (DoItWorker.INTERMEDIATE_RESULT.equals(evt.getPropertyName())) {
gui.addToCompletionList(evt.getNewValue().toString());
} else if ("progress".equals(evt.getPropertyName())) {
gui.setStatusValue(worker.getProgress());
}
}
}
class DoItWorker extends SwingWorker<Void, String> {
public static final String INTERMEDIATE_RESULT = "intermediate result";
private static final long TIME_OUT = 5;
private static final TimeUnit UNIT = TimeUnit.MINUTES;
private String intermediateResult;
private ExecutorService executor;
private CompletionService<String> completionService;
private String[] hostList;
public DoItWorker(String[] hostList, int myThreads) {
this.hostList = hostList;
executor = Executors.newFixedThreadPool(myThreads);
completionService = new ExecutorCompletionService<>(executor);
}
@Override
protected Void doInBackground() throws Exception {
for (int i = 0; i < hostList.length; i++) {
String url = hostList[i];
Callable<String> callable = new MyCallable(url);
completionService.submit(callable);
}
executor.shutdown();
for (int i = 0; i < hostList.length; i++) {
String result = completionService.take().get();
publish(result);
int progress = (100 * i) / hostList.length;
setProgress(progress);
}
executor.awaitTermination(TIME_OUT, UNIT);
setProgress(100);
return null;
}
@Override
protected void process(List<String> chunks) {
for (String chunk : chunks) {
setIntermediateResult(chunk);
}
}
private void setIntermediateResult(String intermediateResult) {
String oldValue = this.intermediateResult;
String newValue = intermediateResult;
this.intermediateResult = intermediateResult;
firePropertyChange(INTERMEDIATE_RESULT, oldValue, newValue);
}
}
哪个看起来和运行如下：
标签：java,multithreading,swing,executorservice,swingworker 来源： https://codeday.me/bug/20190716/1476932.html