Creating Custom Runtime Images

Custom runtime images are a useful tool for optimized and efficient deployment of Java applications. A custom runtime image includes only the necessary components required to run the application and none of the extra components that are present in a full JDK installation. This reduces the application's size and increases its performance.

To create a custom runtime image, you will need to follow these steps:

1. Create a module description file

A module description file specifies which modules are required to run the application. This file should be named module-info.java and should be located in the root directory of the application.

Here is an example of a module-info.java file:

module MyApplication {
    requires java.base;
    requires java.sql;
    requires mymodule;
}

2. Compile the module

Compile the module using the javac command.

Here is an example of how to compile the module:

javac --module-source-path src -d out $(find src -name "*.java")

3. Create a modular JAR file

Create a modular JAR file that contains the compiled module and its dependencies. This JAR file should be located in the out directory.

Here is an example of how to create a modular JAR file:

jar --create --file out/myapplication.jar --main-class=com.example.Main --module-version=1.0 -C out/MyApplication .

4. Create a custom runtime image

Create a custom runtime image using the jlink command. A custom runtime image includes only the specified modules and their dependencies.

Here is an example of how to create a custom runtime image:

jlink --module-path $JAVA_HOME/jmods:out --add-modules MyApplication --output myruntime

5. Run the application

Run the application using the java command from the custom runtime image.

Here is an example of how to run the application:

./myruntime/bin/java -jar myapplication.jar

Creating custom runtime images allows for more efficient and optimized deployment of Java applications. By including only the necessary components, custom runtime images reduce the application's size and increase its performance.