Postcode Checker Demo Application

The Postcode application is a project used to demonstrate the use of the coolest add-on to the JDK 9: The Jigsaw Project.

Requirements

• JDK 9

One-liner Builder

It's important to go over the commands below and try to understand them. However, if you want to quickly build and run the application, do the following:

• GSON from Source
  • ./build.sh
• GSON from JAR
  • ./fat_build.sh

Using GSON from Source

In this part, and also in the one-liner, I use the latest GSON source code and convert it to a Java 9 Module. If you are wondering how I found out which packages the GSON library depends on, so I could create a module out of it, please check the command below:

• jdeps --generate-module-info . jars/gson-2.8.1.jar

The command above will generate the module-info.java descriptor that we need.

Remark: jdeps only works with JAR files that are not modularized.

Build the Modules

• javac -p . -d nl.ekholabs.postcode.validator $(find src/nl.ekholabs.postcode.validator -name "*.java")
• javac -p com.google.gson -d com.google.gson $(find src/com.google.gson -name "*.java")
• javac -p . -d nl.ekholabs.address.checker $(find src/nl.ekholabs.address.checker -name "*.java")

Create a Modular JAR (make sure 'bin' exists)

• jar --create --file bin/postcodevalidator.jar --module-version=1.0 -C nl.ekholabs.postcode.validator .

Create the GSON library JAR Module

• jar --create --file bin/gson.jar --module-version=1.0 -C com.google.gson .

Specify the Main-Class

• jar --create --file bin/addresschecker.jar --module-version=1.0 --main-class=nl.ekholabs.address.checker.api.Application -C nl.ekholabs.address.checker .

Run the Application Module

• java -p bin -m nl.ekholabs.address.checker 3452RG nl

Create a Java Runtime Image

• jlink -p $JAVA_HOME/jmods:bin --add-modules nl.ekholabs.address.checker --output linkedmod

List Modules from the Image

• linkedmod/bin/java --list-modules

Run the Application from the Image

• linkedmod/bin/java -m nl.ekholabs.address.checker 3452RG nl

Reduce the Image Size

• rm -rf linkedmod
• jlink -p $JAVA_HOME/jmods:jars:bin --add-modules nl.ekholabs.address.checker --output linkedmod --compress=2

Using GSON from JAR file

If you want to build it quicly, please execute the fat_build.sh script. If you want to try it out, please make sure you modify the module-info.java file descriptors in both modules.

Although you can use the JAR file with Java 9 modularized code, you cannot create Java Images with JLink. Unfortunately, the jlink tool need a module-info.class packed with the JAR. Since it's not there, it will fail during execution.

If you are a persistent person, as I'm, there is a way out. However, it involves work arounds and I'm not documenting it here.

You do not have to change anything in the com.google.gson module. Remember: we are not using the source, Luke!

Update the Module Descriptor

The change is expected to be made on both nl.ekholabs.address.checker and nl.ekholabs.postcode.validator modules.

• Replace com.google.gson with only gson.

Build the Modules

• javac -p .:jars -d nl.ekholabs.postcode.validator $(find src/nl.ekholabs.postcode.validator -name "*.java")
• javac -p .:jars -d nl.ekholabs.address.checker $(find src/nl.ekholabs.address.checker -name "*.java")

Create a Modular JAR (make sure 'bin' exists)

• jar --create --file bin/postcodevalidator.jar --module-version=1.0 -C nl.ekholabs.postcode.validator .

Specify the Main-Class

• jar --create --file bin/addresschecker.jar --module-version=1.0 --main-class=nl.ekholabs.address.checker.api.Application -C nl.ekholabs.address.checker .

Run the Application Module

• java -p bin:jars -m nl.ekholabs.address.checker 3452RG nl