JAR (First Steps) - Web Tutorial

by Michael Thomas

JAR Home Page

On the JAR Home page, you can download the whole JAR site (all content, tutorials & examples) !!!

Objectives

• Create your first simple JAR file.
• Run a Java Application from the JAR file.

Fast Track

• You may want to download the whole JAR site (on the JAR Home Page) and just look at the examples.
• List of files and brief description.
   

  Topic	Info
  Directory Structure	Directories tutorial_firststeps_jar\src - 2 simple Java Classes that output to the Java console. tutorial_firststeps_jar\build - all files that are created during a build. tutorial_firststeps_jar\build\classes - complied classes. tutorial_firststeps_jar\build\jar - JAR file
  Main Example Files	tutorial_firststeps_jar - list of files _setpathjdk.bat - batch file to check the JAVA_HOME environment variables HelloWorld_build_1_compile.bat - compile the ".java" files. HelloWorld_build_2_jar.bat - create the ".jar" file. HelloWorld_build_2_jar_manifest.txt - the manifest.mf config file for the JAR. HelloWorld_build_3_run.bat - runs the classes HelloWorld_build_4_run_jar.bat - automatically runs the main class in the JAR.

Warnings - I Got You Type

• Make sure you have at least 1 blank line at the end The JAR's Manifest file or the last attribute will not be read by the JAR java application.
  • Example Error:
    Failed to load Main-Class manifest attribute from
    build\jar\HelloWorld.jar
    • Solution: Edit the manifest file and make sure there is a blank line at the end of the file.  The last attribute in the file is not being read!

Hello World JAR Tutorial

• Remember, you can download (see top) all of the content of this Tutorial including all of the example files to save you time if you want to setup this example on your local computer.
• Create the following directory structure:
   

  tutorial_firststeps_jar tutorial_firststeps_jar\src tutorial_firststeps_jar\src\firststeps

• Optional:  DOS Batch file to verify the JAVA_HOME environment variable with option to hard code.
   

  Filename: tutorial_firststeps_jar\_setpathjdk.bat

  rem Override the enrionment system variable here if needed. rem set JAVA_HOME="C:\Program Files\Java\jdk1.5.0\bin" if "%JAVA_HOME%" == "" goto error_no_java_home if exist "%JAVA_HOME%\bin\javac.exe" goto setPath goto error_invalid_java_home :error_no_java_home echo off echo ############################## echo Warning... echo ############################## echo The system environment variable JAVA_HOME has not been created. echo Alternate Option - Create the system variable at the top of this file ( _setpathjdk.bat ). pause exit :error_invalid_java_home echo off echo ############################## echo Warning... echo ############################## echo The JAVA_HOME environment system variable points to a missing directory. echo JAVA_HOME = %JAVA_HOME% pause exit goto end :SetPath set path="%JAVA_HOME%\bin";%path% :end

• Create the following 2 .java files and place them in the directory: tutorial_firststeps_jar\src\firststeps
   

  Filename: tutorial_firststeps_jar\src\firststeps\HelloWorld1.java

  package firststeps; public class HelloWorld1 { public static void main(String[] args) { System.out.println("Hello World #1"); } }

  Filename: tutorial_firststeps_jar\src\firststeps\HelloWorld1.java

  package firststeps; public class HelloWorld2 { public static void main(String[] args) { System.out.println("Hello World #2"); } }

• Compile batch file - create the following batch file to compile all the .java files.
   

  Filename: tutorial_firststeps_jar\HelloWorld_build_1_compile.bat

  rd build /s /q md build md build\classes md build\classes\firststeps call _setpathjdk.bat rem javac -help javac -sourcepath src -d build\classes src\firststeps\*.java pause

  • This batch file removes any old build files, creates the new build directories, verifies the JDK compile environment then compiles, them compiles the .java files.
  • Run this batch file and make sure it compiles your files.
• Generate the JAR file - create the following 2 files to create the JAR file.
   

  Filename: tutorial_firststeps_jar\HelloWorld_build_2_jar.bat

  rd build\jar /s /q md build\jar call _setpathjdk.bat jar cfmv build\jar\HelloWorld.jar HelloWorld_build_2_jar_manifest.txt -C build\classes . jar -ft build\jar\HelloWorld.jar pause

  • Command:
    jar cfmv build\jar\HelloWorld.jar HelloWorld_build_2_jar_manifest.txt -C build\classes .
    Description:
    • Calls the jar.exe file in your %JAVA_HOME% directory.
    • Jar command line options:
      jar {ctxui}[vfm0Me] [jar-file] [manifest-file] [entry-point] [-C dir] fil
      (note: Jar.exe Command Help - if your interested in all the options.)
    • Jar Options used:
      -c create new archive
      -f specify archive file name
      -m include manifest information from specified manifest file
      -v generate verbose output on standard output
      -C  change to the specified directory and include the following file
    • Manifest File - HelloWorld_build_2_jar_manifest.txt - here we define which class will be run by default (if any).
  • Command:
    jar -ft build\jar\HelloWorld.jar
    Description:
    • Lists the Table of Contents for the JAR.
      Options:
      -f  specify archive file name
      -t  list table of contents for archive
    • returns:
      

      META-INF/
      META-INF/MANIFEST.MF
      firststeps/
      firststeps/HelloWorld1.class
      firststeps/HelloWorld2.class

  Filename: tutorial_firststeps_jar\HelloWorld_build_2_jar_manifest.txt

  Main-Class: firststeps.HelloWorld1

  • WARNING: Make sure you have at least 1 blank line at the end The JAR's Manifest file or the last attribute will not be read by the JAR java application.
    Example error: Failed to load Main-Class manifest attribute from ...
  • Description - the "Main-Class:" attribute, if it exists, specifies which file will be run by default.
• Run the Classes (not using the JAR) - create the following batch file to test your compile
   

  HelloWorld_build_3_run.bat

  call _setpathjdk.bat java -cp build\classes firststeps.HelloWorld1 java -cp build\classes firststeps.HelloWorld2 pause

  • Description - runs each java class.
• Run the default class in the JAR - create the following file to test your JAR file.
   

  HelloWorld_build_4_run_jar.bat

  call _setpathjdk.bat rem Run the class defined in the manifest file created during the Jar build. java -jar build\jar\HelloWorld.jar pause

  • Description - because of the manifest files attribute "Main-Class" this will run the java class "firststeps.HelloWorld1" within the JAR file.
• Finished - go have another cup of Java!