Java™ Application Development on Linux - Dator

112Chapter 4Where Am I? Execution Contexton the opposite side of the I/O fence. The external program’s output becomesour input.)Example 4.4 shows a Java program that can invoke an arbitrary Linuxprogram. The output of the program is displayed.Example 4.4 Java program to execute any Linux programimport java.io.*;public classExec{public static voidmain(String [] args)throws IOException{String ln;Process p = Runtime.getRuntime().exec(args);BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));while((ln = br.readLine()) != null) {System.out.println(ln);}System.out.println("returns:" + p.exitValue());} // main} // class ExecThe command-line arguments are taken to be the command to be executedand its arguments. For example:$ java Exec ls -lBe aware that in this example, only the standard output is captured anddisplayed from the invoked process. Error messages written to standard errwill be lost, unless you modify the program to handle this. We leave that as anexercise for the reader.Check your Linux knowledge—see if you understand the distinction. Ifyou invoke the sample Exec program as: