Process. When run, programs occupy their own processes. These are at the level of the operating system. And one process, in a Java program, cannot contain another one.
Starting processes. But with ProcessBuilder, in java.lang.ProcessBuilder, we construct and invoke operating system commands. We launch external processes—like EXEs.
An example program. This program creates an instance of ProcessBuilder. It then calls command() to set the command. We use two arguments: two strings.
Detail We pass a variable number of arguments to command—it combines these strings into a command string.
Start With start we invoke the command. On a Windows operating system, Notepad opens the specified file.
import java.io.IOException;
import java.lang.ProcessBuilder;
public class Program {
public static void main(String[] args) throws IOException {
// Create ProcessBuilder.
ProcessBuilder p = new ProcessBuilder();
// Use command "notepad.exe" and open the file.
p.command("notepad.exe", "C:\\file.txt");
p.start();
}
}
Folder, EXE. In this example we invoke a specific executable at a known location on the computer. We concat a folder path and an executable name. Here I invoke photoshop.exe.
Tip To pass an argument to the exe, specify a second argument to command. This can be a target file location to open.
import java.io.IOException;
import java.lang.ProcessBuilder;
public class Program {
public static void main(String[] args) throws IOException {
String folder = "C:\\Program Files\\Adobe\\Adobe Photoshop CC\\";
String exe = "photoshop.exe";
// Create and start Process with ProcessBuilder.
ProcessBuilder p = new ProcessBuilder();
p.command(folder + exe);
p.start();
}
}
RedirectOutput. This program uses the redirectOutput method to have an executable program write to a file. It uses the 7-Zip EXE, a compression utility, and writes to "test.txt."
Detail The file must exist on the disk for this example to correctly work. We can separately create the file.
Detail The program runs 7za.exe with no arguments, so the EXE does nothing of importance. We can pass further arguments to the EXE.
import java.io.File;
import java.io.IOException;
public class Program {
public static void main(String[] args) throws IOException {
// Create ProcessBuilder and target 7-Zip executable.
ProcessBuilder b = new ProcessBuilder();
b.command("C:\\7za.exe");
// Redirect output to this file.
b.redirectOutput(new File("C:\\folder\\test.txt"));
b.start();
}
}7-Zip (A) 9.07 beta Copyright (c) 1999-2009 Igor Pavlov 2009-08-29
Usage: 7za <command> [<switches>...] <archive_name> [<file_names>...]
[<@listfiles...>]
ArrayList, command. The ProcessBuilder class supports an ArrayList (or any List) as an argument. We can separate parts of a command into an ArrayList and then execute them.
Note This program starts Internet Explorer and opens Wikipedia in it. This is not ideal for systems that use other browsers.
Note 2 Sometimes a specific browser is standardized upon in an organization. This command would work there.
import java.io.IOException;
import java.util.ArrayList;
public class Program {
public static void main(String[] args) throws IOException {
ProcessBuilder b = new ProcessBuilder();
// Create an ArrayList with two values.// ... This starts a specific browser, which is not ideal.
ArrayList<String> values = new ArrayList<>();
values.add("C:\\Program Files\\Internet Explorer\\iexplore.exe");
values.add("http://en.wikipedia.org/");
// Pass List to command method.
b.command(values);
b.start();
}
}
DestroyForcibly. Things in life do not always go our way. With destroyForcibly we kill a process. This is sometimes needed if a process has finished or has frozen.
import java.io.IOException;
import java.lang.ProcessBuilder;
public class Program {
public static void main(String[] args)
throws IOException, InterruptedException {
ProcessBuilder p = new ProcessBuilder();
p.command("notepad.exe");
// Start notepad.
Process notepad = p.start();
System.out.println("Start");
// Sleep for 5 seconds.
Thread.sleep(5000);
// Kill notepad.
notepad.destroyForcibly();
System.out.println("End");
}
}Start
End
Throws IOException. As with file handling, launching processes is prone to failure. This is not our fault. But we must protect against it.
Handling exceptions. We can specify the method throws exceptions in its declaration. Alternatively we can handle the exceptions with try and catch statements.
With external processes, we often can make our programs simpler. We can replace threads (which are complex) with external processes (which are isolated). This is maintainable.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Sep 16, 2024 (edit).