Service Locator (Java ServiceLoader) – Maven Multi-Module Project

This project demonstrates the Service Locator pattern in Java using the ServiceLoader API and the Java Module System (module-info.java). It consists of three modules:

• api: defines the Service API (an interface)
• impl: provides an implementation of Service and declares it with provides ... with ... in module-info.java
• app: consumes the service via ServiceLoader and declares uses ... in module-info.java

Requirements

• Java 21 (or Java 17+ should work as well)
• Maven 3.8+

Structure

service-locator-maven/
    ├─ pom.xml                 # parent/aggregator
    api/
    └─ src/main/java/
        ├─ com/example/api/User.java
        ├─ com/example/api/UserService.java
        └─ module-info.java
    
    impl/
    └─ src/main/java/
        ├─ com/example/impl/UserServiceImpl.java
        └─ module-info.java
    
    app/
    └─ src/main/java/
        ├─ com/example/app/UserController.java
        ├─ com/example/app/UserServiceLocator.java
        └─ module-info.java

Compile & Run with javac/java

Compile (Git Bash)

javac \
  -d out/api \
  api/src/main/java/module-info.java \
  $(find api/src/main/java -name "*.java" -not -name "module-info.java")

javac \
  --module-path out/api \
  -d out/impl \
  impl/src/main/java/module-info.java \
  $(find impl/src/main/java -name "*.java" -not -name "module-info.java")

javac \
  --module-path out/api \
  -d out/app \
  app/src/main/java/module-info.java \
  $(find app/src/main/java -name "*.java" -not -name "module-info.java")
  

Run

java --module-path "out/api;out/impl;out/app" --module com.example.app/com.example.app.Main

C) One-shot compile using --module-source-path (if you flatten sources)

If you prefer a single javac command, put sources under a common root like:

api/
└─ src/main/java/
    ├─ com/example/api/User.java
    ├─ com/example/api/UserService.java
    └─ module-info.java

impl/
└─ src/main/java/
    ├─ com/example/impl/UserServiceImpl.java
    └─ module-info.java

app/
└─ src/main/java/
    ├─ com/example/app/UserController.java
    ├─ com/example/app/UserServiceLocator.java
    └─ module-info.java

Then compile and run:

javac --module-source-path src -d out -m com.example.api,com.example.impl,com.example.app
java --module-path out --module com.example.app/com.example.app.Main "Hello"