step-3-adding-non-jdk-modules

Adding Non-JDK Modules to a Runtime

In this excerise we will walk through steps of adding a Non-JDK module to a runtime image built with JLink.

The Program

This is a simple program that's using the StringUtils.reverse() located in the apache commons lang3 library to reverse a user-provided value.

💡 Note: You will need to download the library from maven central and place it in the /libs directory to complete this exercise.

package foo;

import org.apache.commons.lang3.StringUtils;

public class ReverseString{
        public static void main(String... args){
                String reversedString = StringUtils.reverse(args[0]);
                System.out.println(reversedString);
        }
}

Using JDeps to Resolve external JDK Modules

While we already know that we need to bring in the org.apache.commons.lang3 module, understanding how to look up this information is important.

Using jdeps we will need to use the --module-path option, and pass it the location of where the apache-commons-lang3.jar is located, which sould be the libs directory.

$ jdeps --module-path libs --multi-release 21  foo/ReverseString.class

This will return a table, like in the previous excerise.

ReverseString.class -> java.base
ReverseString.class -> org.apache.commons.lang3
   foo                                                -> java.io                                            java.base
   foo                                                -> java.lang                                          java.base
   foo                                                -> org.apache.commons.lang3                           org.apache.commons.lang3

Building a Runtime with a Non-JDK Module

Building a runtime with a Non-JDK module is similar to building a runtime like we have done in the previous exercise, we just need to include the path to where the additional modules are located, in this case libs like we did in the previous step using jdeps:

$ jlink --module-path libs --add-modules java.base,org.apache.commons.lang3 --output reverse-string-image

We can use this runtime, like in the previous exercises to run the ReserveString program:

$ ./reverse-string-image/bin/java foo.ReverseString Java
avaJ

In the next exercise we will walk through the steps of creating our own module and adding it to a runtime image.