[JAVA] Spring Boot 2 multi-project in Gradle

How to create a Spring Boot 2 multi-project using Gradle.

environment

Java

openjdk 10.0.2 2018-07-17

Gradle

4.10

Spring Boot

2.0.4

Target multi-project

|-settings.gradle
|-build.gradle
|
|-foo/
| |-build.gradle
| :
|
`-bar/
  |-build.gradle
  :

--The foo project references the bar project --The implementation content is not relevant this time, so it is omitted.

Bad pattern setting

/build.gradle

buildscript {
    ext {
		springBootVersion = '2.0.4.RELEASE'
    }
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}

subprojects {
    apply plugin: "java"
    apply plugin: 'org.springframework.boot'
    apply plugin: 'io.spring.dependency-management'

    repositories {
        mavenCentral()
    }

    sourceCompatibility = 10
    targetCompatibility = 10
}

--Plug-ins etc. are set in common for the entire subproject (foo, bar). --ʻIo.spring.dependency-managementis a guy who made it possible to use the mechanism to control the version of the dependent library using Maven's BOM in Gradle. --Reference: [If you want to use BOM with Gradle, it seems better to use the Dependency management plugin provided by the Spring team --Create something](http://create-something.hatenadiary.jp/entry/2015/05/08) / 063000) --You can omit the version specification ofdependencies related to Spring Boot. --At the time of 1.x, ʻorg.springframework.boot was used internally, but in 2.x it seems to have been taken out.

/foo/build.gradle

dependencies {
    compile project(":bar")
    compile "org.springframework.boot:spring-boot-starter-web"
}

--Declare dependency on : bar and dependency on spring-boot-starter-web

Compile result

> gradle :foo:compileJava

> Task :foo:compileJava FAILED
...\Foo.java:12:error:Can't find symbol
        return new Bar().bar();
                        ^
symbol:Method bar()
place:Class Bar
1 error

FAILURE: Build failed with an exception.

bar The project class cannot be resolved and an error occurs.

Description

--Check the build result of the bar project

> dir /b bar\build\
classes
tmp

--bar Project jar has not been generated --In 1.x, the jar file bar.jar was output under bar \ build \ libs, and I feel that the foo project was supposed to refer to that jar. --Somehow, it seems that from 2.x, the jar plugin ʻenabled is set to falseby default. - https://docs.spring.io/spring-boot/docs/current/gradle-plugin/reference/html/#packaging-executable-and-normal --It seems that thejar task does not generate the jar file, but the bootJar` task now generates it.

Workaround

java - Spring Boot multi module project with Gradle doesn't build - Stack Overflow

--Here, the method of setting true to jar.enabled is introduced. -Sure, if you set this, you will be able to build

Gradle multi-project build dependencies of subprojects cannot be resolved · Issue #11594 · spring-projects/spring-boot

――However, looking at the official GitHub Issue, the subproject (bar project) on the dependent side is not a Spring Boot project in the first place, so even the subproject ʻorg.springframework.boot` It is explained that applying the plugin is wrong ――I think that's true, so I'll fix it this way.

OK pattern

/build.gradle

buildscript {
    ext {
        springBootVersion = '2.0.4.RELEASE'
    }
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}

subprojects {
    apply plugin: "java"
    apply plugin: "io.spring.dependency-management"

    repositories {
        mavenCentral()
    }

    dependencyManagement {
        imports {
            mavenBom "org.springframework.boot:spring-boot-dependencies:$springBootVersion"
        }
    }

    sourceCompatibility = 10
    targetCompatibility = 10
}

/foo/build.gradle

apply plugin: "org.springframework.boot"

dependencies {
    compile project(":bar")
    compile "org.springframework.boot:spring-boot-starter-web"
}

Compile result

> gradle :foo:compileJava
BUILD SUCCESSFUL in 17s

Description

/build.gradle

buildscript {
    ext {
        springBootVersion = '2.0.4.RELEASE'
    }
    ...
}

subprojects {
    apply plugin: "java"
    apply plugin: "io.spring.dependency-management"

    ...

    dependencyManagement {
        imports {
            mavenBom "org.springframework.boot:spring-boot-dependencies:$springBootVersion"
        }
    }

    ...
}

--Stop setting ʻorg.springframework.bootfor all subprojects --And adddependencyManagement` to load the Spring Boot BOM

/foo/build.gradle

apply plugin: "org.springframework.boot"

...

--Apply ʻorg.springframework.bootonly to thefoo` project