Question

I’ve inherited a Java web-services code-base (BEA/Oracle Weblogic) and need to start/launch an external background application from a web-service.

I’ve already tried:

ProcessBuilder pb = new ProcessBuilder(arg); pb.start(); 

as well as:

Runtime.exec(cmdString); 

But am experiencing strange behaviors when launching applications in this manner (i.e. the launched application stops working even though the process is still active. — The application works fine when manually run from a normal command line).

Is there a better way to launch an external processes?

EDIT: ———————-

I have some additional information that may help shed some light on the problem.

• The process we are trying to start will require hours to complete so waiting for completion (using waitfor()) in the webservice will not be an ideal scenario.
• Yes, the process we are trying to start from the webservice was created by a fellow team member [cue: your eyes roll… now]

I have had success when I use process builder to start a bash script, where the external application is launched as a background process (using ‘&’).

#!/bin/bash java -jar myApp.jar & 

This obviously creates an orphaned process but at least the application does continue to execute.

Answer 1

Simply put: if the launched application writes to SDTOUT/STDIN and you don’t flush them frequently (see Process.getErrorStream/Process.getInputStream) then the process will block when the buffer is full (that is really small, 4KB or less).

I recommend you to invoke ProcessBuilder.redirectErrorStream() before starting the process. Then, after that, create a thread with the run() method along the lines of:

public void run() {     BufferedReader reader =          new BufferedReader(new InputStreamReader(process.getInputStream()));     String line;     while ((line = reader.readLine()) != null) {         System.out.println(line);     } }