Lesson 3: Create a layered multi-project application

Step-by-step instructions

These instructions follow on from what was achieved in the previous lesson.

Add model subproject

in settings.gradle.kts add model to list of subprojects to include
```
include("app", "model")
```
see new subproject by running ./gradlew projects
add model directory
add build.gradle.kts in model directory
in build script apply java-library plugin
```
plugins {
    `java-library`
}
```
in model add directories src/main/java
add com.tomgregory.maxirail.model package

add TrainTime.java class

package com.tomgregory.maxirail.model;

import java.time.LocalTime;

public record TrainTime(String departureStation, String destinationStation,
                        LocalTime departureTime, LocalTime arrivalTime) {
}

Run ./gradlew build and see build directory is created in model

Add service subproject

in settings.gradle.kts add service to list of subprojects to include
```
include("app", "model", "service")
```
add service directory
add build.gradle.kts in service directory
in build script apply java-library plugin
```
plugins {
    `java-library`
}
```

in build script add spring-boot-starter dependency

dependencies {
    implementation("org.springframework.boot:spring-boot-starter:2.6.4")
}

in build script add Maven Central repository
```
repositories {
    mavenCentral()
}
```
create a src/main/java directory
add com.tomgregory.maxirail.service package

add a TrainTimeService.java class

package com.tomgregory.maxirail.service;

import com.tomgregory.maxirail.model.TrainTime;
import org.springframework.stereotype.Service;

import java.time.LocalTime;
import java.util.Arrays;
import java.util.List;

@Service
public class TrainTimeService {
    public List<TrainTime> getTrainTimes() {
        return Arrays.asList(
                new TrainTime("London", "Brighton", LocalTime.of(9, 35), LocalTime.of(10, 30)),
                new TrainTime("London", "Brighton", LocalTime.of(15, 5), LocalTime.of(16, 0)),
                new TrainTime("Brighton", "London", LocalTime.of(11, 0), LocalTime.of(12, 0)),
                new TrainTime("Brighton", "London", LocalTime.of(16, 30), LocalTime.of(17, 30))
        );
    }
}

Notice how TrainTime isn’t available though? Add this project dependency to service’s build script.
```
api(project(":model"))
```

Update MaxiRailController

in app subproject’s build script add a dependency on service subproject
```
implementation(project(":service"))
```

modify MaxiRailController class to inject TrainTimeService and call its getTrainTimes method

package com.tomgregory.maxirail.controller;

import com.tomgregory.maxirail.model.TrainTime;
import com.tomgregory.maxirail.service.TrainTimeService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
public class MaxiRailController {
    private final TrainTimeService trainTimeService;

    public MaxiRailController(TrainTimeService trainTimeService) {
        this.trainTimeService = trainTimeService;
    }

    @GetMapping(path = "/")
    public List<TrainTime> getTimes() {
        return trainTimeService.getTrainTimes();
    }
}

run ./gradlew bootRun
see updated API response at localhost:8080

Well done! You just created a layered multi-project Java application.

GitHub repository

The gradle-multi-project-masterclass repository contains the final code solution for lessons 2-5.