Process API Improvement

Java has improved its process API in Java 9 version by adding new methods in Process class and new interfaces ProcessHandle and ProcessHandle.Info.

It is helpful in controlling and managing processes whether OS-based or application processes. We can create processes, get information about processes like process id, owner name, waiting time, process status, etc.

Two new interfaces in Process API:

• java.lang.ProcessHandle
• java.lang.ProcessHandle.Info

The Process class in Java provides several methods to handle the process and perform operations like check waiting for the process to complete, checking the exit status of the process, and destroying (killing) the process, etc.

The following are some methods that added in Java 9 version to the Process class.

Java Process class Methods (Only Java 9 methods)

Example: Find Process Id

Let's understand the process handling by a simple example. Here, we are getting process id using the pid() method of Process class.

public class Main { 
	public static void main(String[] args){
		ProcessHandle currentProcess = ProcessHandle.current();
        System.out.println("Process Id: "+currentProcess.pid());    
	}
}

Process Id: 16458

Java ProcessHandle Interface

Java added this interface that identifies and provides control of native processes. It can be helpful to get list of its children, information of a process or destroy a process etc. The syntax of the method is given below.

public interface ProcessHandle extends Comparable<ProcessHandle>

Interface Methods

Following are the methods of ProcessHandle Interface. It contains one nested interface called Info.

In our previous example, we fetched the process id of the currently running process. However, we can start a new process by own and handle it.

Example: Start Vi Editor in Linux

Now, let's create a new process by using the start() method of ProcessBuilder class. Here, we are starting a process of vim editor in Linux and getting process id using the pid() method.

public class Main { 
	public static void main(String[] args) throws IOException{
		 Process p = new ProcessBuilder("vim").start();
	      System.out.println(p.pid()); 
	}
}

13834

Example: Process Information

This example explains how can we get information of a process. We used pid(), isAlive(), info(), hashCode(), etc methods of Process class.

import java.io.IOException;

public class Main { 
	public static void main(String[] args) throws IOException{
		 Process p = new ProcessBuilder("vim").start();
		 // Get process ID
	     System.out.println(p.pid());
	     // Check is Alive?
	     System.out.println(p.isAlive());
	     // Get process Info
	     System.out.println(p.info());
	     // Get Hahscode
	     System.out.println(p.hashCode());
	     // Get child process
	     System.out.println(p.children());
	     // Get className
	     System.out.println(p.getClass());
	}
}

14413
true
[user: Optional[root], cmd: /usr/bin/vim.basic, startTime: Optional[2020-07-23T19:02:42.310Z], totalTime: Optional[PT0S]]
1418481495
java.util.stream.ReferencePipeline$2@65ab7765
class java.lang.ProcessImpl

Java ProcessHandle.Info Interface

This interface provides information snapshots about the process. It is a nested interface of ProcessHandle interface. Each operating system's process attributes are not similar and are not available in all implementations. Information about processes is limited by the operating system privileges of the process making the request. The signature of this interface is given below.

public static interface ProcessHandle.Info

ProcessHandle.Info Methods

The following are the methods of ProcessHandle.info interface which is a static and nested interface

Example:

Here, we are using ProcessHandle.Info interface methods to get information about the process.

import java.io.IOException;
import java.time.Duration;

public class Main { 
	public static void main(String[] args) throws IOException{
		ProcessHandle.Info info = ProcessHandle.current().info();
		System.out.println(info.arguments());
		System.out.println(info.command().orElse("Not Found"));
		String[] argz = info.arguments().orElse(new String[] {});
		for (String arg: argz)
	         System.out.printf("   %s%n", arg);
		System.out.println("Owner: "+info.user());
		System.out.println("RunTime: "+info.totalCpuDuration().orElse(Duration.ofMillis(0)).toMillis());
		
	}
}

Optional[[Ljava.lang.String;@1f32e575]
/usr/lib/jvm/java-11-openjdk-amd64/bin/java
-Dfile.encoding=UTF-8
-classpath
/home/root/eclipse/myjavaproject/bin:/home/root/Downloads/mongo-java-driver-3.12.4.jar:/home/root/Downloads/opencsv-3.8.jar:/home/root/Downloads/commons-logging-1.2/commons-logging-1.2.jar:/home/root/Downloads/pdfbox-2.0.12.jar:/home/root/Downloads/fontbox-2.0.12.jar
myjavaproject.Main
Owner: Optional[root]
RunTime: 100