How To Create A JAR File Using Command Line Eclipse Netbeans

What is JAVA?
Originally known as oak, Java is a programming language developed by James Gosling and others at Sun Microsystems. It was first introduced to the public in 1995 and is widely used to create Internet applications and other software programs. Today, Java is maintained and owned by Oracle.
When used on the Internet, Java allows applets to be downloaded and used through a browser, which enables the browser to perform a function or feature not normally available. Unlike JavaScript, the users must download or install the applet or program before being able to utilize the Java program.
Below is an example of a Java applet from Sun and a method of testing if Java is installed on your computer. If Java is installed on your computer, you should see additional information about the installed Java version and your operating system.
            Java is also used as the programming language for many different software programs, games, and add-ons. Some examples of the more widely used programs written in Java or that use Java include the Adobe Creative suite, Eclipse, Lotus Notes, Minecraft, OpenOffice, Runescape, and Vuze.

What is JAR?
A JAR (Java ARchive) file is a file that contains the class, image, and sound files for a Java application or applet gathered into a single file and possibly compressed. When a programmer gets a Java program development kit, a small program or utility called "jar" is included. The jar utility lets the programmer create, list, or extract the individual files from a JAR file. In an enterprise, a Java application can be started with a set of JAR files for use during execution. An off-the-shelf open source package can be delivered as a JAR file and run with XML data.
On the Web, a JAR file containing an applet may accompany a Web page. By putting the applet components in a single file and compressing that file, download time is saved. Ordinarily, a browser user will not need to "open" or view a JAR file directly. It is opened when the Web page is received and the applet is in some manner initiated.
The JAR format is based on the popular zip file format and is somewhat comparable to the Unix tar file.

Creating JAR file in java from command prompt
It is always been little tricky for many of us even if IDE like Netbeans and Eclipse provide support to export java program as JAR file simply because we don’t create jar often and not familiar with manifest file or jar command as whole. JAR file in Java is a kind of zip file which holds all contents of a Java application including Class files, resources such as images, sound files and optional Manifest file. JAR stands for Java Archive and provides a platform independent deliverable for java programs, libraries and framework. you can execute same jar file in any operating system.
 E.g. Windows 7, windows 8, Macintosh or Linux. Apart from platform independence and standard delivery method jar file also provides compression of contents which results in faster download if you are downloading java program from internet specially in case of mobile devices where you install Java program by OTA. In this article we will some JAR command examples and learn how to create and execute jar file, how to view contents of jar file from command prompt and Eclipse and Netbeans.
Example to create and execute JAR file in Java from Command line Eclipse and Netbeansjar command in Java allows you to create jar file from command prompt, what is required is that you must have jar command included in System PATH variable. you can check this by typing "jar" in command prompt if it doesn't throw error as "jar is not recognized as an internal or external command" they you are ready to go. When you create jar file in Java, command also creates Manifest file which is optional and you can control whether to create it or not by jar command line options, but if you want to create executable jar file they you must need Manifest file which we will discuss in further sections. Now here is jar command example to create jar file from command prompt, this will work both in windows and Linux operating system.

AR command Examples in Java

javin@localhost:~/Java jar -cvf HelloWorld.jar HelloWorld.class
added manifest
adding: HelloWorld.class(in = 450) (out= 311)(deflated 30%)

This command will create Helloworld. jar which contains Helloworld.class file. this will also create manifest file but without Main-Class entry as shown below:

javin@localhost:~/Java cat MANIFEST.MF
Manifest-Version: 1.0
Created-By: 1.6.0-beta2 (Sun Microsystems Inc.)

This jar cannot be executed and you will get error when you try to run this jar file:

javin@localhost:~/Java java -jar HelloWorld.jar

Failed to load Main-Class manifest attribute from HelloWorld.jar
You just need to provide Main-Class entry to get rid of this error which we will see in coming Section.

AR command Examples in Java
To create an executable JAR in Java, you need to provide a manifest file and include your Main Class in Manifest. When you create jar file , jar command also creates manifest file inside META-INF as MANIFEST.MF but doesn't create Main-Class entry which is required for executable jar file. You can create executable jar file in Java by two ways either provide a self created Manifest file or specify entry point using "-e" jar option. If you provide external Manifest file than you need to use jar -m option to include that manifest file inside jar. Let's see example of both ways to create executable jar file in Java.

Executable JAR File Example with External Manifest
Create MANIFEST.MF file by using any text editor e.g. notepad in windows or Vim in Unix and add following entry in file, remember last line must end with either new line or carriage return:

Manifest-version: 1.0
Main-Class: HelloWorld

Important thing to remember is that we need to specified full classified class name here. suppose if our main class was inside com/example/HelloWorld than we should have to specify com.example.HelloWorld here, don't put .class extension here it’s not required. Apart from specifying Main-Class you can also specify Java Classpath in Manifest file which is important if your application is depended on external library jars. "Classpath" entry supersede both -cp and CLASSPATH environment variable. to learn more see How ClassPath works in Java.
Execute following jar command to create executable jar

javin@localhost:~/Java jar -cvfm HelloWorld.jar MANIFEST.MF HelloWorld.class
added manifest
adding: HelloWorld.class(in = 450) (out= 311)(deflated 30%)

here -m is used for including manifest file and remember specify name of manifest file after jar name. now you have an executable jar file in java which you run by command specified earlier.

Executable JAR File Example with External Manifest
This seems to me an easy way to create executable jars in Java, as you need not have to create manifest file explicitly and it will be create by jar command itself along with Main-Class entry. What you need to provide is a new jar option "-e" and you main class name while running jar command. here is example of jar command with entry option:

javin@localhost:~/Java jar -cvfe HelloWorld.jar HelloWorld HelloWorld.class
added manifest
adding: HelloWorld.class(in = 450) (out= 311)(deflated 30%)

jar -e for entry point and entry point or main class name should come after jar file name and before directory or file needs to be included in JAR. You can now run your executable jar file by issuing "java -jar" command as shown in following example:

javin@localhost:~/Java java -jar HelloWorld.jar

Executing Java Program from JAR file

How to execute Java Program from Jar file
Executing jar program from jar archive is very easy one thing required is jar must be executable and must have Main-Class entry in MANIFEST.MF file. here is a Java command example for running java program from jar file:

javin@localhost:~/Java java -jar HelloWorld.jar

Executing Java Program from JAR file
Here we have specified jar file name with -jar option and it will run main class declared as “Main-Class” attribute in manifest file.

How to view contents of a JAR file in Java
Jar command in Java allows you to view files and directories inside of a jar file without extracting or unzipping original jar. "-t" jar option is used to list files from jar archive as shown in jar command example below:

javin@localhost:~/Java jar -tvf HelloWorld.jar
0 Wed Dec 07 22:36:12 VET 2011 META-INF/
95 Wed Dec 07 22:36:12 VET 2011 META-INF/MANIFEST.MF
450 Wed Dec 07 21:36:04 VET 2011 HelloWorld.class

here "-t" for listing and "-v" and "-f" for verbose and jar file name.

How to extract contents of JAR File
use jar option "-v" for extracting files form JAR files as shown in jar command example below:

javin@localhost:~/Java jar -xvf HelloWorld.jar
created: META-INF/
inflated: HelloWorld.class

here -x for extracting , -v is for verbose and -f specify jar file name.

How to create jar file in Eclipse
Creating JAR file in  Eclipse IDE is a cakewalk once you know the process. here is step by step guide of creating JAR file from Eclipse IDE: In Jar file main class is specified as “Main-Class” attribute inside manifest file and used as program entry point if you double click on JAR or run jar from java command.
1) Select Project for which you want to create jar file.
2) Go to File Menu and select Export
3) Expand Java folder and select JAR file
Now you just need to click next and follow instruction as displayed. you can select what contents you want to export to jar file and specify Main Class entry as well. If you like Eclipse IDE then you may like my earlier post on eclipse as well e.g. Java debugging tips in Eclipse and  How to setup java remote debugging in Eclipse.

How to create jar file in Netbeans
In Netbeans to create jar file you need to build the project which execute project ant file and creates JAR file inside dist folder. You can go on properties of project and specify main class there which will be run when you run the project and same will be used to create “Main-Class” attribute in JAR file.

jar is not recognized as an internal or external command
If you get this error while executing jar command from command prompt in Windows or Unix it means your Java Path is not set properly. JAR command is a binary which resides in JDK_HOME/bin folder where JDK_HOME is JDK installation directory. In order to use jar command from command prompt this bin folder must be in your System's PATH variable. Don't worry if its not there in PATH you can check this link toSet PATH for Java in Windows and Unix.It shows how you can do it in both Windows and Unix. Once your PATH is property set, you will see following output when you execute jar command from command  line:

javin@localhost:~ jar
Usage: jar {ctxui}[vfm0Me] [jar-file] [manifest-file] [entry-point] [-C dir] files ...
-c  create new archive
-t  list table of contents for archive

And now you are ready to use jar from command prompt.

WAR and EAR -  related JAR like fies in Java
WAR file
WAR file in Java stands for Web application archive and it is used to package a Java application together you can package all your Servlet, JSP, CSS, images, html in one WAR file and then deploy it to any Java web or application server like Tomcat, Weblogic or webshere. WAR files provide a clean and faster way to package and deploy Java web application just like JAR file provides for core java apps. Since WAR file also compacts resources inside it is comparatively download faster than downloading individual components.

EAR file
EAR file stands for Enterprise Java Archive and used to package an Enterprise Java application, like earlier WAR and JAR file. What separates EAR archive to WAR file is inclusion of Enterprise Java Beans(EJB). EAR file contains all web resources including Servlet, JSP, html, javascript, css, images along-with EJB. You can not deploy EAR files into web servers like Tomcat because it doesn't support EJB and can only be deploy-able in Application servers like WebSphere or Weblogic.

JAR File format in Java
Few words about java jar file format, its similar to zip format and use .jar extension. you can open JAR file in windows by using either winzip or winrar zip utilities.
That’s all on how to create jar file from command line, Eclipse, Netbeans. How to extract contents, how to run Java program from jar file etc. Let me know if you face any issue while creating JAR file in java.

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