Java捕获进程的所有输出并将其记录到文件中

Question

I'm trying log all output from an Application in java and for some reason it only capturing the first 2 lines i know the application outputs a lot more than this this is my code

logOut = new BufferedWriter(new FileWriter("WebAdmin.log"));

        ProcessBuilder procBuild = new ProcessBuilder(
            "java", "-Xmx1G", "-Xms512M", "-jar", "TekkitServer\\Tekkit.jar", "nogui", "-nojline"
        );
        server = procBuild.start();

        inputStream = new BufferedReader(new InputStreamReader(server.getInputStream()));
        errorStream = new BufferedReader(new InputStreamReader(server.getErrorStream()));
        outputStream = new BufferedWriter(new OutputStreamWriter(server.getOutputStream()));

        String line = "";

        while(!shutdown){
            while((line = inputStream.readLine()) != null){
                logOut.write(line+"\r\n");
                logOut.flush();
                System.out.println(line);
            }
            System.out.println("checking error stream");
            while((line = errorStream.readLine()) != null){
                logOut.write(line+"\r\n");
                logOut.flush();
                System.out.println(line);
            }
        }

        System.out.println("Stoped Reading");
        logOut.close();
        server.destroy();

I'm not even seeing "checking error stream" in my console.

Answer 1

I don't think there is a need for outer while, reading from the output stream blocks until there is some data available, and if the sub process ends you'll get a null and the inner while will break. Also you could use ProcessBuilder 's redirectErrorStream(true) to redirect stderr to stdout so you will catch them both in only one loop.

Answer 2

You must read the stdout and stderr streams in its own thread. Otherwise you will get all kinds of blocking situations (depending on operating system and output patterns).

If you merge the error stream with the output stream ( redirectErrorStream(true) ), you can get along with a single (additional) background thread. You can avoid this, when you use redirectOutput(File) (or inheritIO).

Answer 3

The first two lines in a minecraft server go to STDOUT (tested on bukkit, tekkit, and vanilla), but the rest go to STDERR for what ever reason. Your application isn't doing anything with errorStream . You can try using redirection functionality by doing this:.

ProcessBuilder procBuild = new ProcessBuilder(
        "java", "-Xmx1G", "-Xms512M", "-jar", "TekkitServer\\Tekkit.jar",
        "nogui", "-nojline", "2>&1");

Let me know if this works, as this may be a bash-only trick.