Java Command Line - Sending Command Input To Java via command line pipe

Java Command Line 

This example shows how to redirect a command output to a Java Program as input. For example:

externalCommand | myJavaProgram

The Java Program needs to get the input via System.in.

Following example just echoes back whatever input it receives:

package com.logicbig.example;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ExampleMain {
  public static void main(String[] args) {
      System.out.println("----- ExampleMain started -------");
      try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
          String line = null;
          while (true) {
              if ((line = reader.readLine()) != null) {
                  System.out.println("echo>> " + line);
              } else {
                  //input finishes
                  break;
              }
          }
      } catch (Exception e) {
          System.err.println(e);
      }
  }
}

Compile above class:

D:\java-pipe-input>mvn -q compile

Create a batch file to run the main class:

myJavaProgram.bat

@echo off
java -classpath target\classes com.logicbig.example.ExampleMain

Output

D:\java-pipe-input>dir d:\test | myJavaProgram
----- ExampleMain started -------
echo>>  Volume in drive D is Data
echo>>  Volume Serial Number is 68F9-EDFA
echo>> 
echo>>  Directory of d:\test
echo>> 
echo>> 05/12/2017  01:32 AM    <DIR>          .
echo>> 05/12/2017  01:32 AM    <DIR>          ..
echo>> 05/12/2017  01:35 AM             2,508 logging.properties
echo>> 05/09/2017  09:25 AM                19 one.txt
echo>> 05/03/2017  10:20 PM    <DIR>          testDir1
echo>> 05/03/2017  10:21 PM    <DIR>          testDir2
echo>> 04/28/2017  09:00 AM                 0 two.txt
echo>>                3 File(s)          2,527 bytes
echo>>                4 Dir(s)  20,635,299,840 bytes free

D:\java-pipe-input>ps -s | myJavaProgram
----- ExampleMain started -------
echo>>    PID  TTY        STIME COMMAND
echo>>   22316 pty0     12:00:59 /d/Program Files/JetBrains/IntelliJ IDEA Community Edition 2018.2.5/bin/idea64
echo>>   36784 cons2    16:16:05 /usr/bin/ps
echo>>   22608 pty0     12:00:46 /usr/bin/bash
echo>>   10356 ?        12:00:45 /usr/bin/mintty

D:\java-pipe-input>dir c:\ | findstr "Program*" | myJavaProgram
----- ExampleMain started -------
echo>> 12/18/2018  07:18 PM    <DIR>          Program Files
echo>> 12/19/2018  10:20 AM    <DIR>          Program Files (x86)

Example Project

Dependencies and Technologies Used:

• JDK 11
• Maven 3.5.4