"java --module" - Launching Program from Module JAR

Java Tools Tutorials - Herong's Tutorial Examples

∟"java --module" - Launching Program from Module JAR

This section provides a tutorial example on how to use 'java --module' command to launch a program that is packaged in a module JAR file.

You can also launch a program that is packaged in a module JAR file using the "java --module" command. You need to specify the JAR file in the module path.

For example, I have a program class called HelloModularized.java packaged in a Java module called com.herongyang. Here is the module class file directory structure generated by the above "javac" command:

herong> tree /F .\cls
.\CLS
|---com.herongyang
    |   module-info.class
    |
    |---com
        |---herongyang
            |---util
                    HelloModularized.class

Here is how I created a module JAR file by archiving the entire class file directory tree:

herong> jar --create --verbose --file com.herongyang.jar \
   -C .\cls\com.herongyang .

added manifest
added module-info: module-info.class
adding: com/(in = 0) (out= 0)(stored 0%)
adding: com/herongyang/(in = 0) (out= 0)(stored 0%)
adding: com/herongyang/util/(in = 0) (out= 0)(stored 0%)
adding: com/herongyang/util/HelloModularized.class(in = 472) (out= 315)

Here is how I used the "java --module" command to launch my program from the module JAR file:

herong> java --module-path com.herongyang.jar \
   --module com.herongyang/com.herongyang.util.HelloModularized

Hello world! - Modularized

I can also use the "java --describe-module" command to print information from my module:

herong> java --module-path com.herongyang.jar \
   --describe-module com.herongyang

com.herongyang file:///C:/herong/com.herongyang.jar
exports com.herongyang.util
requires java.base