read the output from java exec

Question

Hello i have some question about java. here is my code:

public static void main(String[] args) throws Exception {     Process pr = Runtime.getRuntime().exec("java -version");      BufferedReader in = new BufferedReader(new InputStreamReader(pr.getInputStream()));     String line;     while ((line = in.readLine()) != null) {         System.out.println(line);     }     pr.waitFor();     System.out.println("ok!");      in.close();     System.exit(0); } 

in that code i'am trying to get a java version command execute is ok, but i can't read the output it just return null. Why?

Answer 1

Use getErrorStream().

BufferedReader in = new BufferedReader(new InputStreamReader(pr.getErrorStream())); 

EDIT:

You can use ProcessBuilder (and also read the documentation)

ProcessBuilder   ps=new ProcessBuilder("java.exe","-version");  //From the DOC:  Initially, this property is false, meaning that the  //standard output and error output of a subprocess are sent to two  //separate streams ps.redirectErrorStream(true);  Process pr = ps.start();    BufferedReader in = new BufferedReader(new InputStreamReader(pr.getInputStream())); String line; while ((line = in.readLine()) != null) {     System.out.println(line); } pr.waitFor(); System.out.println("ok!");  in.close(); System.exit(0);