不同的ProcessBuilder.redirectInput()有什么区别？

Question

I went through the documentation of ProcessBuilder but I am having trouble understanding the difference between

1. processBuiler.inheritIO()
2. processBuilder.redirectInput(ProcessBuilder.Redirect.PIPE)
3. processBuilder.redirectInput(ProcessBuilder.Redirect.INHERIT)

FROM DOC: ProcessBuilder.Redirect PIPE: Indicates that subprocess I/O will be connected to the current Java process over a pipe. This is the default handling of subprocess standard I/O.

1. what is a pipe here?

2. when and where would you use each one of them?

3. based on the docs what is the diff between 1 and 3 then?

If this question is not fit for stackoverflow, please point me in the right direction as to where to ask this.

Answer 1

PIPE means that the I/O streams of the process will be obtainable via Process#getInputStream , Process#getErrorStream and Process#getOutputStream . This is different from INHERIT , which merges a stream with the stream of the current Java process, that is, System.out , System.in , or System.err .

When you call ProcessBuilder#inheritIO , you are redirecting all I/O streams to the System .

When you call redirectInput(ProcessBuilder.Redirect.PIPE) , you are redirecting only the input to the PIPE .

When you call redirectInput(ProcessBuilder.Redirect.INHERIT) , you are redirecting only the input to the System .

So, the difference between 1st and 3d is that 3d call redirects only the input of the process, while the 1st one redirects all I/O streams.

You should use INHERIT when you want to use a stream of the Process via the stream of the System .

And you should use PIPE when you want to handle a stream of the Process separately. Consider following example:

public class ProcessTest {
    @Test
    public void testProcess() throws IOException {

        //all streams go to System streams
        new ProcessBuilder("java","--version").inheritIO().start();

        //all streams are kept separate, and are obtained via .get...Stream() calls 
        Process process2=new ProcessBuilder("java","--version").start();
        BufferedReader bufferedReader=new BufferedReader(new InputStreamReader(process2.getInputStream()));
        String s;
        while ((s=bufferedReader.readLine())!=null)
        {
            System.out.println(s);
        }
        bufferedReader.close();

        //only the output of the Process is going to the System.out
        new ProcessBuilder("java","--version").redirectOutput(ProcessBuilder.Redirect.INHERIT).start();

    }
}