Friday, March 30, 2012

Running Java Program Without Console


How to run a java executable or jar without popping up the command prompt window?

This can be done by running the following command instead of "java", assuming the jar file is named "Main.jar"

javaw -jar -Xms1024m -Xmx1024m Main.jar

For example, lets start with the following simple snippet, it just creates a frame and we will the run the program without the black console window. Lets name the file as FacelessVoid.java

import javax.swing.*;

public class FacelessVoid {
    public static void main(String[] args) throws Exception {
        JFrame frame = new JFrame("FrameDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
}

Running the program from IDE's will straight show you the window, which contains nothing at all. This is just for demonstration purpose, so fill free to try something else if you need. Now, we will create a jar file containing this class (we are in windows os).

javac FacelessVoid.java
echo Main-Class: FacelessVoid > manifest.txt
jar cfm Main.jar manifest.txt FacelessVoid.class

Note, if you have more than one source file, i.e. .java files, you can write *.java instead of where we put FacelessVoid.java in line 1. In line 2, the main class name should be the class which contains the main() method. In line 3, if there are more than one class file to be put into jar file, you can use *.class instead of just FacelessVoid.class in our example.

If everything goes fine, the jar file named Main.jar should be created without any problem. Now we can create a batch file in the same directory where the Main.jar is located, lets call it Main.bat, we just put the following line into it:

start javaw -jar -Xms1024m -Xmx1024m Main.jar

Now double clicking on Main.bat will open the window without any command prompt window.

How can I vanish the window totally but still keep the program running?

There are a few ways to do this, I am presenting here a simple way using the previous files, the only thing needed to change is frame.setVisible(true); to frame.setVisible(false); This will hide the window now completely but the program is still running. Note, you will need to create the jar file again, i.e. re-compile and the make jar again. Now if you click on the bat file, it will start executing, but you wont be able to see it any more.

This can be helpful for servers which remains idle and waits for clients. We can just put them beyond visibility and they still keeps executing. For example, this code is just a modification of the previous one, and it will wait for a client to connect on the specified port. However, whenever a client gets a connection, we just change the visibility just to show that the program was actually running even though we were not able to see it. So you may wish to remove the line frame.setVisible(true); from the while loop and write your own program logic and make it permanently invisible.

import javax.swing.*;
import java.net.*;

public class FacelessVoid {
    public static void main(String[] args) throws Exception {
        JFrame frame = new JFrame("FrameDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 300);
        frame.setVisible(false);
        ServerSocket ss = new ServerSocket(8080);
        Socket client = null;
        while((client = ss.accept()) != null) {
            frame.setVisible(true);
        }
    }
}

Now, we can keep the server running without being able to see it. Here is a sample client program at your disposal

import java.net.*;

public class Client {
    public static void main(String[] args) throws Exception {
        Socket sock = new Socket("localhost", 8080);
    }
}

You just run and compile it and the server window will pop in from nowhere :D

Let me know if this works for you too...


3 comments:

  1. Good post, you could have added the manual method to jar creation with multiple external jars added.
    And good to have a post again.

    ReplyDelete
    Replies
    1. Oh, I missed that. Anyways, it's great to see you back in blogging world :)

      Delete
  2. Hello, sir i would like to ask that what is the scope of java training, what all topics should be covered and it is kinda bothering me … and has anyone studies from this course http://www.wiziq.com/course/1779-core-and-advance-java-concepts of core and advance java online ?? or tell me any other guidance...
    would really appreciate help… and Also i would like to thank for all the information you are providing on java concepts.

    ReplyDelete