无法创建JAR文件

Question

I've been trying for hours to turn the program I wrote into a JAR file, none of the examples I've found seem to be working. I use JCreator to write my code, and I'm not particularly familiar with using the command prompt. If anyone can try to walk me through making a JAR file, I'm sure I could ask questions and create one.

Answer 1

In Java, it is common to combine several classes in one .jar ("java archive") file. Library classes are stored that way. Larger projects (such as the Case Study in the AP program) use jar files. You can create your own jar file combining several classes, too.

jar files are created using the jar.exe utility program from JDK. You can make your jar file runnable by telling jar.exe which class has main. To do that, you need to create a manifest file. A manifest is a one-line text file with a "Main-Class" directive. For example:

Main-Class: Craps

This line must end with a newline.

A jar file created with a main class manifest can be used both as a library and a runnable jar. If you use it as a library, you can edit and compile any of the classes included in the jar, and add it to your project. Then it will override the one in the jar file.

You can create a manifest file in any text editor, or even by using the MS-DOS echo command. You can give your manifest file any name, but it's better to use something standard, such as manifest.txt.

Once you have a manifest and all your classes have been compiled, you need to run JDK's jar.exe utility. It is located in the JDK's bin folder, the same place where javac.exe and java.exe are. jar.exe takes command-line arguments; if you run it without any arguments, it will display the usage information and examples. You need

C\\mywork> jar cvfm MyJarName.jar manifest.txt *.class

cvfm means "create a jar; show verbose output; specify the output jar file name; specify the manifest file name." This is followed by the name you wish to give to your jar file, the name of your manifest file, and the list of .class files that you want included in the jar. *.class means all class files in the current directory.

Actually, if your manifest contains only the Main-Class directive, you can specify the main class directly on the jar.exe's command line, using the e switch, instead of m. Then you do not need a separate manifest file; jar will add the required manifest to your jar file for you. For example:

C\\mywork> jar cvfe MyJarName.jar MyMainClass *.class

Below is a reference for creating a jar file in the detailed steps for doing this in Command Prompt and in JCreator.

Creating a jar File in JCreator

You can configure a "tool" that will automate the jar creation process. You only need to do it once.

1. Click on Configure/Options.
2. Click on Tools in the left column.
3. Click New, and choose Create Jar file.
4. Click on the newly created entry Create Jar File in the left column under Tools.

5. Edit the middle line labeled Arguments: it should have

   cvfm $[PrjName].jar manifest.txt *.class

6. Click OK.

Creating a jar File in Command Prompt

1. Start Command Prompt.

2. Navigate to the folder that holds your class files:

   C:\\>cd \\mywork

3. Set path to include JDK's bin. For example:

   C:\\mywork> path c:\\Program Files\\Java\\jdk1.7.0_25\\bin;%path%

4. Compile your class(es):

   C:\\mywork> javac *.java

5. Create a manifest file and your jar file:

   C:\\mywork> echo Main-Class: Craps >manifest.txt
C:\\mywork> jar cvfm Craps.jar manifest.txt *.class
   or
   C:\\mywork> jar cvfe Craps.jar Craps *.class

6. Test your jar:

   C:\\mywork> Craps.jar or C:\\mywork> java -jar Craps.jar