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Creating your own JAR files

From: Java Essential Training

Video: Creating your own JAR files

The process of packaging a Java application for deployment is radically different from one platform to the next. You don't package a console application and a web application the same or a mobile application or a desktop application, they each have their own rules, but the one thing that all Java platforms have in common is the use of JAR files. A JAR file is a Java archive file, a compressed file in zip format that contains compiled Java classes, but has a file extension of .jar. I'm going to show you how to create a jar file from within Eclipse.

Creating your own JAR files

The process of packaging a Java application for deployment is radically different from one platform to the next. You don't package a console application and a web application the same or a mobile application or a desktop application, they each have their own rules, but the one thing that all Java platforms have in common is the use of JAR files. A JAR file is a Java archive file, a compressed file in zip format that contains compiled Java classes, but has a file extension of .jar. I'm going to show you how to create a jar file from within Eclipse.

You can also do the same thing from the command line using the JAR command from the JDK. I'm working in a version of my application called CreateJAR, and the first thing I'll do is Run the application and make sure that it runs correctly. This version of the application outputs the names of the olives that I'm crushing and how many units of oil I have and where the first all of this from. I do this before I try to package the application to make sure I'm running valid code. Now, to create the JAR File, go to the menu and choose File, Export.

In the Export dialog choose Java, JAR File and click Next. Make sure you've selected your entire application including all of the applications packages, but deselect the options for the class path and project files on the right. These are Eclipse configuration files that you don't need to include in your deployed JAR File. The first option here in this list should be selected, Export generated class files and resources. For a console application that doesn't include any graphical assets or other files, you can deselect everything else.

Next, indicate the location and name of your JAR file. I have already filled in the value with my project name and the name of the JAR file I want to create, separated with a slash character, use a backslash on Windows and a forward slash on Mac, alternatively you can click Browse and select a location anywhere on your disk to create the file. I am creating my JAR File in my project folder, Create JAR and I'm giving it a name of olivepressapp.jar. You can name the file anything you want, just make sure you don't include any spaces or special characters, but you must use a .jar extension.

I've selected the option to compress the contents of the JAR File and deselected the other options. I'll click Next and show you these two options. For debugging I recommend selecting these options, Export class files with compile errors and warnings. For final production, you might want to deselect these options. And on this final screen, there are options for the manifest file. A manifest file is a text file that's automatically included in your JAR. It includes metadata about your application, but again, for a simple console application, you can accept all of these default values, click Finish and your new JAR File will be created.

If you created it in your project folder as I did, it should show up right away in the package Explorer. Now let's take a look at the contents of the JAR File. I'll go to my desktop to my Exercise Files folder, from there I'll go down to 12 Deployment to the Create JAR Folder and here's the .jar file that I just created. I'm going to copy it and paste it so that I create a new version, and then I'm going to rename this version of the file and give it a file extension of .zip. This will allow me to easily extract its contents, so I can see what's inside.

Next, I'll extract its contents. On Windows, I'll right-click and choose Extract All and Extract. On Mac, just double-click on the file. If you have any special archive utilities installed on your system, such as WinZip on Windows, you can extract the file with that tool. Here is the contents of the JAR File, there is a folder called MetaINF in and within that the manifest file. I'll open that up with a text editor and show you that for a simple console application like this, it's pretty much empty.

Now I'll go back to the main folder and show you that your packages have been translated to folders within the JAR file. Here is com, Lynda, olivepress, my main package. Here is my main compiled class and then within the press package, there is olivepress.class and within the olives package my three olive classes. So that's all a JAR File is. It's a zip file; it has a file extension of .jar, and its purpose is to package up your application for deployment.

If you're using Java in another development environment such as say Android, take a look at the documentation for that development environment to learn about deployment options for that platform, regardless of how you're deploying your Java application, JAR Files are almost certainly going to be involved.

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This video is part of

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Java Essential Training

71 video lessons · 69711 viewers

David Gassner
Author

 
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  1. 10m 8s
    1. Welcome
      1m 3s
    2. Is this course for you?
      5m 35s
    3. Using the exercise files
      3m 30s
  2. 31m 24s
    1. The history of Java
      5m 19s
    2. Java compilation and syntax
      8m 54s
    3. Understanding the principles of Java
      8m 28s
    4. Choosing a development environment
      8m 43s
  3. 19m 5s
    1. Installing Java on Windows
      6m 42s
    2. Installing Eclipse on Windows
      3m 19s
    3. Exploring Java on Mac OS X Leopard and Snow Leopard
      2m 27s
    4. Installing Java on Mac OS X Lion
      3m 27s
    5. Installing Eclipse on Mac OS X
      3m 10s
  4. 46m 10s
    1. Creating a Hello World application
      11m 7s
    2. Exploring the Eclipse IDE
      8m 55s
    3. Compiling and running from the command line
      8m 2s
    4. Passing arguments to the application
      8m 17s
    5. Using the Java API documentation
      4m 5s
    6. Memory management and garbage collection
      5m 44s
  5. 58m 57s
    1. Everything is an object
      5m 59s
    2. Declaring and initializing variables
      9m 15s
    3. Working with numbers
      8m 32s
    4. Converting numeric values
      6m 40s
    5. Understanding operators
      7m 58s
    6. Working with character values
      5m 14s
    7. Working with boolean values
      5m 13s
    8. Outputting primitive values as strings
      5m 33s
    9. Creating a simple calculator application
      4m 33s
  6. 53m 40s
    1. Writing conditional code
      5m 35s
    2. Using the switch statement
      8m 50s
    3. Repeating code blocks with loops
      7m 35s
    4. Creating reusable code with methods
      6m 31s
    5. Declaring methods with arguments
      5m 41s
    6. Overloading method names with different signatures
      5m 53s
    7. Passing arguments by reference or by value
      5m 35s
    8. Creating a more complex calculator application
      8m 0s
  7. 20m 30s
    1. Using the String class
      5m 44s
    2. Building strings with StringBuilder
      3m 34s
    3. Parsing string values
      3m 19s
    4. Working with date values
      7m 53s
  8. 20m 44s
    1. Understanding compile-time vs. runtime errors
      4m 5s
    2. Handling exceptions with try/catch
      4m 55s
    3. Throwing exceptions in methods
      2m 50s
    4. Using the debugger
      8m 54s
  9. 32m 22s
    1. Using simple arrays
      4m 47s
    2. Using two-dimensional arrays
      6m 17s
    3. Managing resizable arrays with ArrayList
      7m 14s
    4. Managing unordered data with HashMap
      6m 5s
    5. Looping through collections with iterators
      7m 59s
  10. 52m 2s
    1. Understanding encapsulation
      5m 59s
    2. Creating and instantiating custom classes
      8m 8s
    3. Organizing classes with packages
      6m 47s
    4. Creating and using instance methods
      6m 52s
    5. Storing data in instance variables
      6m 56s
    6. Using constructor methods
      5m 40s
    7. Managing instance data with getter and setter methods
      8m 26s
    8. Using class variables and Enum classes
      3m 14s
  11. 41m 15s
    1. Understanding inheritance and polymorphism
      9m 12s
    2. Extending custom classes
      9m 1s
    3. Overriding superclass methods
      3m 8s
    4. Casting subclass objects
      5m 3s
    5. Understanding interfaces and implementing classes
      4m 2s
    6. Creating your own interfaces
      4m 14s
    7. Using abstract classes and methods
      6m 35s
  12. 32m 17s
    1. Managing files with the core class library
      7m 46s
    2. Managing files with Apache Commons FileUtils
      7m 32s
    3. Reading a text file from a networked resource
      7m 52s
    4. Parsing an XML file with DOM
      9m 7s
  13. 17m 39s
    1. Creating your own JAR files
      4m 54s
    2. Understanding the classpath
      5m 2s
    3. Documenting code with Javadoc
      7m 43s
  14. 47s
    1. Goodbye
      47s

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