如何在Web应用程序中调用Java并发线程

Question

Am working on some web application and i got struck in some where and i need your help. I developed one java web application using struts framworks. This application takes source folder from user and copied in unique directory inside server and it will execute batch process on each source folder and batch will write logs on inside respective folder. Uploading and copying source folder is working fine but real issue am facing is executing batch concurrently. When one user upload source folder and start batch execution and same time another user also upload source folder and start batch and i need to know when first user batch completes and second user completes.How to track concurrent threads completed or not.Am using Executor executor= Executors.newCachedThreadPool(); Please find below code

 private class BackgroundTask extends SwingWorker<Integer, String> {
        String srcpath;
 String log;
         BackgroundTask(String path)
         {
             this.srcpath=path;
         }
            private int status;

            public BackgroundTask() {

            }
            @Override
            protected Integer doInBackground() {
                try {
                    final File batchFile = new File("D://chetan//bin//runner.bat");
                 ProcessBuilder builder = new ProcessBuilder();
                  builder.directory(new File(srcpath));
                  String[] cmd = { "cmd", "/c",batchFile.getAbsolutePath(),"-X"};

                  for (int x = 0; x < cmd.length; x++) {
                        System.out.println("Command :" + cmd[x]);   

                    }
                     builder.command(cmd);

                     Process process;
                     process = builder.start();
                     InputStream is1 = process.getInputStream();
                        InputStreamReader isr = new InputStreamReader(is1);
                        BufferedReader br = new BufferedReader(isr);
                        String line;
                     File logfile;
                     File logpath=new File(srcpath+File.separator+"LOG");
                     if(logpath.isDirectory())
                     {
                          logfile=new File(logpath+File.separator+"runner.log");

                     }
                     else
                     {
                         logpath.mkdir();
                         logfile=new File(logpath+File.separator+"runner.log");
                     }
                     logfile.createNewFile();
                     while ((line = br.readLine()) != null) {                           
                            //appendText(line);                     
                         log+=line+"\n";                    
                     }
                     FileUtils.writeStringToFile(logfile,log);           

                    process.getInputStream().close();
                    process.getOutputStream().close();
                    process.getErrorStream().close();
                    process.destroy();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                return status;
            }
            @Override
            protected void process(java.util.List<String> messages) {
               // statusLabel.setText((this.getState()).toString());               
            }

            @Override
            protected void done() {

            }

        }

Second Class

public class RunnerAnalysisAction extends ActionSupport implements SessionAware {
 private BackgroundTask backgroundTask;

 public String execute() {
  String projectRoot="D:\\Sample_DemoProjects\\DEMO_375530\\";
 backgroundTask = new BackgroundTask(projectRoot+ProjectName);
 Executor executor= Executors.newCachedThreadPool();
 executor.execute(backgroundTask);
return SUCCESS;  
 }
}

The above code working fine and creates log file in corresponding source folder but i need to know when the batch will completes the task because once batch completes its task this application will trigger email to user with log.How to know the particular task completed or not.Please provide some sample code.Thanks.

Answer 1

You didn't specify the nature of your web application. If it is not clustered (running single instance) then keep a static variable (or an instance variable inside ActionServlet , which is singleton ). Set this variable to "true" when a thread (worker task) from previous user is already running and reset to false when thread completes. Use this flag to check whether another thread (from another user) can run- true means can't run, false means can run. Alternatively define the ExecutorService as a shared (static) instance and then make it a SingleThreaded pool and submit workers to it. Hope you got the idea.

Answer 2

To track concurrent threads I have used java.util.concurrent.Future . A Future represents the result of an asynchronous computation. Methods are provided to check if the computation is complete, to wait for its completion, and to retrieve the result of the computation. The result can only be retrieved using method get when the computation has completed, blocking if necessary until it is ready.

You can try this complete example