Java lang processbuilder directory

Java ProcessBuilder

Java ProcessBuilder tutorial shows how to create operating system processes with ProcessBuilder .

Java ProcessBuilder

• command
• environment
• working directory
• source of input
• destination for standard output and standard error output
• redirectErrorStream

Java ProcessBuilder running program

A program is executed with command . With waitFor we can wait for the process to finish.

package com.zetcode; import java.io.IOException; public class ExecuteProgram < public static void main(String[] args) throws IOException, InterruptedException < var processBuilder = new ProcessBuilder(); processBuilder.command("notepad.exe"); var process = processBuilder.start(); var ret = process.waitFor(); System.out.printf("Program exited with code: %d", ret); >>

The program executes the Windows Notepad application. It returns its exit code.

Java ProcessBuilder command output

The following example executes a command and shows its output.

package com.zetcode; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class ProcessBuilderEx < public static void main(String[] args) throws IOException < var processBuilder = new ProcessBuilder(); processBuilder.command("cal", "2022", "-m 2"); var process = processBuilder.start(); try (var reader = new BufferedReader( new InputStreamReader(process.getInputStream()))) < String line; while ((line = reader.readLine()) != null) < System.out.println(line); >> > >

The example runs Linux cal command.

processBuilder.command("cal", "2022", "-m 2");

The command executes the cal program. The other parameters are the options of the program. In order to run a command on Windows machine, we could use the following: processBuilder.command(«cmd.exe», «/c», «ping -n 3 google.com») .

var process = processBuilder.start();

The process is lauched with start .

try (var reader = new BufferedReader( new InputStreamReader(process.getInputStream()))) 
With the getInputStream method we get the input stream from the standard output of the process.
$ java ProcessBuilderEx.java Február 2022 Ne Po Ut St Št Pi So 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
 
Java ProcessBuilder redirect output
 
With redirectOutput , we can redirect the process builder's standard output destination.
 
package com.zetcode; import java.io.BufferedReader; import java.io.File; import java.io.IOException; import java.io.InputStreamReader; public class RedirectOutputEx < public static void main(String[] args) throws IOException < var homeDir = System.getProperty("user.home"); var processBuilder = new ProcessBuilder(); processBuilder.command("date"); var fileName = new File(String.format("%s/Documents/output.txt", homeDir)); processBuilder.redirectOutput(fileName); var process = processBuilder.start(); try (var reader = new BufferedReader( new InputStreamReader(process.getInputStream()))) < String line; while ((line = reader.readLine()) != null) < System.out.println(line); >> > >
 
The program redirects the builder's output to a file. It runs the Windows date command.
 
processBuilder.redirectOutput(fileName);
 
We redirect the process builders standard output to a file.
 
try (var reader = new BufferedReader( new InputStreamReader(process.getInputStream()))) < String line; while ((line = reader.readLine()) != null) < System.out.println(line); >>
 
Now the output goes to the file.
 
$ java RedirectOutputEx.java $ cat ~/Documents/output.txt Ne 17. júl 2022, 10:23:45 CEST
 
The current date was written to the output.txt file.
 
Java ProcessBuilder redirect input and output
 
The next example redirects both input and output.
 
sky blue steel morning coffee earth forest
 
This are the contents of the input.txt file.
 
package com.zetcode; import java.io.File; import java.io.IOException; public class ProcessBuilderRedirectIOEx < public static void main(String[] args) throws IOException < var processBuilder = new ProcessBuilder(); processBuilder.command("cat") .redirectInput(new File("src/resources", "input.txt")) .redirectOutput(new File("src/resources/", "output.txt")) .start(); >>
 
In the program, we redirect input from an input.txt file to the cat command and redirect the command's output to the output.txt file.
 
Java ProcessBuilder inherit IO
 
The inheritIO sets the source and destination for subprocess standard I/O to be the same as those of the current Java process.
 
package com.zetcode; import java.io.IOException; public class ProcessBuilderInheritIOEx < public static void main(String[] args) throws IOException, InterruptedException < var processBuilder = new ProcessBuilder(); processBuilder.command("cmd.exe", "/c", "dir"); var process = processBuilder.inheritIO().start(); int exitCode = process.waitFor(); System.out.printf("Program ended with exitCode %d", exitCode); >>
 
By inheriting the IO of the executed command, we can skip the reading step. The program outputs the contents of the project directory and the message showing the exit code.
 
02/14/2019 04:55 PM . 02/14/2019 04:55 PM .. 02/19/2019 01:11 PM .idea 02/14/2019 04:55 PM out 02/14/2019 04:52 PM 433 ProcessBuilderInheritIOEx.iml 02/14/2019 04:53 PM src 1 File(s) 433 bytes 5 Dir(s) 157,350,264,832 bytes free Program ended with exitCode 0
 
We get both the output of the executed command and of our own Java program.
 
Java ProcessBuilder environment
 
The environment method returns a string map view of the process builder's environment.
 
package com.zetcode; public class ProcessBuilderEnvEx < public static void main(String[] args) < var pb = new ProcessBuilder(); var env = pb.environment(); env.forEach((s, s2) ->< System.out.printf("%s %s %n", s, s2); >); System.out.printf("%s %n", env.get("PATH")); > >
 
The program shows all environment variables.
 
configsetroot C:\WINDOWS\ConfigSetRoot USERDOMAIN_ROAMINGPROFILE LAPTOP-OBKOFV9J LOCALAPPDATA C:\Users\Jano\AppData\Local PROCESSOR_LEVEL 6 USERDOMAIN LAPTOP-OBKOFV9J LOGONSERVER \\LAPTOP-OBKOFV9J JAVA_HOME C:\Users\Jano\AppData\Local\Programs\Java\openjdk-11\ SESSIONNAME Console .
 
This is a sample output on Windows.
 
In the next program, we define a custom environment variable.
 
package com.zetcode; import java.io.IOException; public class ProcessBuilderEnvEx2 < public static void main(String[] args) throws IOException < var pb = new ProcessBuilder(); var env = pb.environment(); env.put("mode", "development"); pb.command("cmd.exe", "/c", "echo", "%mode%"); pb.inheritIO().start(); >>
 
The program defines a mode variable and outputs it on Windows.
 
pb.command("cmd.exe", "/c", "echo", "%mode%");
 
The %mode% is a Windows syntax for environment variables; on Linux we use $mode .
 
Java ProcessBuilder directory
 
The directory method sets the process builder's working directory.
 
package com.zetcode; import java.io.BufferedReader; import java.io.File; import java.io.IOException; import java.io.InputStreamReader; public class ProcessBuilderDirectoryEx < public static void main(String[] args) throws IOException < var homeDir = System.getProperty("user.home"); var pb = new ProcessBuilder(); pb.command("cmd.exe", "/c", "dir"); pb.directory(new File(homeDir)); var process = pb.start(); try (var reader = new BufferedReader( new InputStreamReader(process.getInputStream()))) < String line; while ((line = reader.readLine()) != null) < System.out.println(line); >> > >
 
The example sets the home directory to be the process builder's current directory. We show the contents of the home directory.
 
var homeDir = System.getProperty("user.home");
 
We get the user's home directory.
 
We define a command which executes the dir program on Windows.
 
pb.directory(new File(homeDir));
 
We set the process builder's directory.
 
Volume in drive C is Windows Volume Serial Number is 4415-13BB Directory of C:\Users\Jano 02/14/2019 11:48 AM . 02/14/2019 11:48 AM .. 10/13/2018 08:38 AM .android 01/31/2019 10:58 PM 281 .bash_history 12/17/2018 03:02 PM .config .
 
Java ProcessBuilder non-blocking operation
 
In the following example, we create a process which is asynchronous.
 
package com.zetcode; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.TimeUnit; import java.util.concurrent.TimeoutException; import java.util.stream.Collectors; public class ProcessBuilderNonBlockingEx < public static void main(String[] args) throws InterruptedException, ExecutionException, TimeoutException, IOException < var executor = Executors.newSingleThreadExecutor(); var processBuilder = new ProcessBuilder(); processBuilder.command("cmd.exe", "/c", "ping -n 3 google.com"); try < var process = processBuilder.start(); System.out.println("processing ping command . "); var task = new ProcessTask(process.getInputStream()); Future> future = executor.submit(task); // non-blocking, doing other tasks System.out.println("doing task1 . "); System.out.println("doing task2 . "); var results = future.get(5, TimeUnit.SECONDS); for (String res : results) < System.out.println(res); >> finally < executor.shutdown(); >> private static class ProcessTask implements Callable> < private InputStream inputStream; public ProcessTask(InputStream inputStream) < this.inputStream = inputStream; >@Override public List call() < return new BufferedReader(new InputStreamReader(inputStream)) .lines() .collect(Collectors.toList()); >> >
 
The program creates a process that runs the ping command on the console. It is executed in a separate thread with the help of the Executors.newSingleThreadExecutor method.
 
processing ping command . doing task1 . doing task2 . Pinging google.com [2a00:1450:4001:825::200e] with 32 bytes of data: Reply from 2a00:1450:4001:825::200e: time=108ms Reply from 2a00:1450:4001:825::200e: time=111ms Reply from 2a00:1450:4001:825::200e: time=112ms Ping statistics for 2a00:1450:4001:825::200e: Packets: Sent = 3, Received = 3, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 108ms, Maximum = 112ms, Average = 110ms
 
Java ProcessBuilder pipe operation
 
A pipe is a technique for passing information from one program process to another.
 
package com.zetcode; import java.io.File; import java.io.IOException; public class ProcessBuilderPipeEx < public static void main(String[] args) throws IOException < var homeDir = System.getProperty("user.home"); var processBuilder = new ProcessBuilder(); processBuilder.command("cmd.exe", "/c", "dir | grep [dD]o"); processBuilder.directory(new File(homeDir)); processBuilder.inheritIO().start(); >>
 
The example sends information from a dir commmand to the grep command through the pipe (|).
 
Volume in drive C is Windows 11/14/2018 06:57 PM .dotnet 02/18/2019 10:54 PM Documents 02/17/2019 01:11 AM Downloads
 
In this article we have used Java's ProcessBuilder to execute OS processes.
 
Author
 
My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.
 
Источник
 
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