远程服务器中的processbuilder监视器日志文件

Question

I am trying to:

1. Execute Bash script
2. Read log file

I have following code using processBuilder which has readLog function that reads log file and executeBash which executes the command and then destroys processbuilder's readlog process. But as readLog file is reading a live log file executeBash never gets called.

How do I read the log file in real time and display it simultaneously with executeBash?

---

public void performAction(OssSystem system) {
        readLog(system);
        executeBash(system);
    }

---

public void executeBash(OssSystem system) {
    try {
        Process process = new ProcessBuilder().command("/bin/sh", system.getCommand_path(), system.getParam()).start();

        BufferedReader reader
                = new BufferedReader(new InputStreamReader(process.getInputStream()));
        StringBuilder builder = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            builder.append(line);
            builder.append(System.getProperty("line.separator"));
        }
        int status = process.waitFor();
        cmdResult = builder.toString() + " command status " + status;
        int exitValue = process.exitValue();            
        readProcess.destroy();
    } catch (IOException ex) {
        LOG.log(Level.SEVERE, null, ex);
    } catch (InterruptedException ex) {
        LOG.log(Level.SEVERE, null, ex);
    }

}

---

String logOutput;

Process readProcess;

public void readLog(OssSystem system) {

    String user = system.getUsername() + "@" + system.getIp();
    String cmd = "tail -f " + system.getLog_dir() + " | less";      
    try {
        readProcess = new ProcessBuilder().command("/usr/bin/ssh", user, cmd).start();
        int status = readProcess.waitFor();
        BufferedReader reader
                = new BufferedReader(new InputStreamReader(readProcess.getInputStream()));
        StringBuilder builder = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            builder.append(line);
            builder.append(System.getProperty("line.separator"));
        }
        logOutput = builder.toString() + " command status " + status;
    } catch (IOException ex) {
        Logger.getLogger(Shell.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InterruptedException ex) {
        Logger.getLogger(Shell.class.getName()).log(Level.SEVERE, null, ex);
    }
}

Answer 1

According to javadoc,

Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated. This method returns immediately if the subprocess has already terminated. If the subprocess has not yet terminated, the calling thread will be blocked until the subprocess exits.

So the readProcess.waitFor(); will block the main thread and you can never expect executeBash(system); to be called before readProcess has terminated.

You can start a thread to launch readProcess .

public void performAction(OssSystem system) {
    readLog(system);
    ExecuteBashThread thread = new ExecuteBashThread(system);
    thread.start();
}

class ExecuteBashThread extends Thread{
    private OssSystem system;
    public ExecuteBashThread(OssSystem system){
        this.system = system;
    }
    @Override
    public void run(){
        executeBash(system);
    }
}