如何在Spring Boot Gradle项目中成功切换至Java 11？

问题 #

使用IntelliJ创建Spring Boot Gradle项目时选择了Java 17，build.gradle中配置sourceCompatibility = '17'。但系统JAVA_HOME为Java 11，不想切换系统Java版本或重建项目。尝试将sourceCompatibility改为'11'，并在IntelliJ的File -> Project Structure -> Project Settings -> Project中切换SDK为11后，无论通过IDE运行还是执行./gradlew clean build，均出现兼容报错，部分错误信息如下：

> Could not resolve org.springframework.boot:spring-boot-gradle-plugin:3.0.1-SNAPSHOT.
  Required by:
      project : > org.springframework.boot:org.springframework.boot.gradle.plugin:3.0.1-SNAPSHOT:20221222.181044-39
   > No matching variant of org.springframework.boot:spring-boot-gradle-plugin:3.0.1-SNAPSHOT:20221222.181044-39 was found. The consumer was configured to find a runtime of a library compatible with Java 11, packaged as a jar, and its dependencies declared externally, as well as attribute 'org.gradle.plugin.api-version' with value '7.6' but:
       - Variant 'apiElements' capability org.springframework.boot:spring-boot-gradle-plugin:3.0.1-SNAPSHOT declares a library, packaged as a jar, and its dependencies declared externally:
           - Incompatible because this component declares an API of a component compatible with Java 17 and the consumer needed a runtime of a component compatible with Java 11
           - Other compatible attribute:
               - Doesn't say anything about org.gradle.plugin.api-version (required '7.6')
       - Variant 'javadocElements' capability org.springframework.boot:spring-boot-gradle-plugin:3.0.1-SNAPSHOT declares a runtime of a component, and its dependencies declared externally:

解决方法 #

1. 降级Spring Boot版本到Java 11兼容分支 #

Spring Boot 3.x及以上最低要求Java 17，需切换到2.x系列（推荐2.7.x稳定分支）。

修改项目根目录的构建文件：

Groovy DSL (build.gradle)

plugins {
    id 'org.springframework.boot' version '2.7.14'
    id 'io.spring.dependency-management' version '1.0.15.RELEASE'
    id 'java'
}

sourceCompatibility = '11'
targetCompatibility = '11'

Kotlin DSL (build.gradle.kts)

plugins {
    id("org.springframework.boot") version "2.7.14"
    id("io.spring.dependency-management") version "1.0.15.RELEASE"
    java
}

java {
    sourceCompatibility = JavaVersion.VERSION_11
    targetCompatibility = JavaVersion.VERSION_11
}

2. 配置Gradle使用Java 11（不依赖系统JAVA_HOME） #

方式一：通过gradle.properties指定JDK路径

在项目根目录的gradle.properties中添加：

org.gradle.java.home=/path/to/your/java11/jdk

替换路径为本地Java 11的实际安装目录（如Mac下/Library/Java/JavaVirtualMachines/jdk-11.jdk/Contents/Home，Windows下C:\Program Files\Java\jdk-11.0.20）。

方式二：IntelliJ中指定Gradle JVM

打开File -> Settings -> Build, Execution, Deployment -> Build Tools -> Gradle，在Gradle JVM下拉菜单选择本地已安装的Java 11 SDK，点击Apply保存后同步项目（点击右上角Sync Project with Gradle Files）。

3. 确认模块级SDK配置 #

打开File -> Project Structure -> Project Settings -> Modules：

• 切换到Sources标签，设置Language level为11 - Local variable syntax for lambda parameters；
• 切换到Dependencies标签，设置Module SDK为Java 11。

4. 清理并重新构建项目 #

执行命令行：

./gradlew clean build

或在IntelliJ中选择Build -> Rebuild Project。

内容的提问来源于stack exchange，提问作者aCarella