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Programming language: Java
Tags: Projects     Processes    
Latest version: v3.1.1

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README

ch.vorburger.exec

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This project is a small library allowing to launch external processes from Java code in the background, and conveniently correctly pipe their output e.g. into slf4j, await either their termination or specific output, etc.

[Release Notes are in CHANGES.md](CHANGES.md).

Usage

Launching external processes from Java using the raw java.lang.ProcessBuilder API directly can be a little cumbersome. Apache Commons Exec makes it a bit easier, but lacks some convenience. This library makes it truly convenient:

ManagedProcessBuilder pb = new ManagedProcessBuilder("someExec")
    .addArgument("arg1")
    .setWorkingDirectory(new File("/tmp"))
    .getEnvironment().put("ENV_VAR", "...")
    .setDestroyOnShutdown(true)
    .addStdOut(new BufferedOutputStream(new FileOutputStream(outputFile)))
    .setConsoleBufferMaxLines(7000);  // used by startAndWaitForConsoleMessageMaxMs

ManagedProcess p = pb.build();
p.start();
p.isAlive();
p.waitForExit();
// OR: p.waitForExitMaxMsOrDestroy(5000);
// OR: p.startAndWaitForConsoleMessageMaxMs("Successfully started", 3000);
p.exitValue();
// OR: p.destroy();

// This works even while it's running, not just when it exited
String output = p.getConsole();

If you need to, you can also attach a listener to get notified when the external process ends, by using setProcessListener() on the ManagedProcessBuilder with a ManagedProcessListener that implements onProcessComplete() and onProcessFailed().

We currently internally use Apache Commons Exec by building on top, extending and wrapping it, but without exposing this in its API, so that theoretically in the future this implementation detail could be changed.

Advantages

  • automatically logs external process's STDOUT and STDERR using SLF4j out of the box (can be customized)
  • automatically logs and throws for common errors (e.g. executable not found), instead of silently ignoring like j.l.Process
  • automatically destroys external process with JVM shutdown hook (can be disabled)
  • lets you await appearance of certain messages on the console
  • lets you write tests against the expected output

History

Historically, this code was part of MariaDB4j (and this is why it's initial version was 3.0.0), but was it later split into a separate project. This was done to make it usable in separate projects (originally to launch Ansible Networking CLI commands from OpenDaylight, later to manage etcd servers in tests, both from OpenDaylight).

ToDo

This library is currently used to control daemon style external executables. To launch a process which returns binary (or massive textual) output to its STDOUT (and, presumably, have that piped into a java.io.OutputStream), it would need some tweaks. This would include making the enabled-by-default logging into slf4j, and the built-in startAndWaitForConsoleMessageMaxMs which collects output, a more configurable option.

Contributions & patches more than welcome!