从BufferedReader读取

Question

I am trying to execute commands on the terminal. using

        ProcessBuilder builder = new ProcessBuilder("/bin/bash");
        builder.redirectErrorStream(true);
        Process process = builder.start();
        OutputStream stdin = process.getOutputStream();
        InputStream stdout = process.getInputStream();

        reader = new BufferedReader(new InputStreamReader(stdout));
        writer = new BufferedWriter(new OutputStreamWriter(stdin));

I am going to use this reader and and writer to continuously communicate with the process.

I'm using the following loop to read

        while ((line = reader.readLine()) != null) {
        System.out.println("line);
        }

ISSUE: The problem here is that, when the reader starts reading from the buffer its forever in the while loop. It never exits.

I tried to put the reading in a thread

public void run() {
        try {
            String line;
            outputText = "";
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException ex) {
            Logger.getLogger(ThreadReader.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

But now i have no control on when the reader starts and finishes reading.

GOAL: I need to execute a command and read the output and then the next command.

Answer 1

Your Java program is communicating with an external interactive process. It has only the process's output and error streams to work with to determine how to proceed from any given point. If you want it to recognize subdivisions of the output, such as responses to individual commands, then you need to teach it what the boundaries of those subdivisions look like.

There are any number of ways you might approach the problem. For example, if the external program emits a prompt when it is ready to accept a new command, then it seems natural to watch for that prompt. Alternatively, perhaps you can tweak the input to the program so as to cause it to produce a recognizable marker at the end of each command's output.

Do also consider that this is a solved problem (many times over). The canonical utility for general-purpose scripting of interactive programs is a Tcl program called "Expect". It has inspired work-alikes in many languages, including many in Java. Google gives me three distinct examples among the first five hits, but I have no specific experience with any of them so I make no recommendation.