Docker离线运行SpringBoot项目Gradle插件找不到问题修复

原有配置仅缓存了项目业务代码依赖的jar包，未缓存Gradle第三方插件的依赖包。plugins块中声明的org.springframework.boot属于第三方Gradle插件，默认从Gradle中央插件仓库拉取，断网运行时本地无对应插件缓存，抛出如下错误：

Plugin [id: 'org.springframework.boot', version '2.6.3'] was not found in any of the following sources:

• Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
• Plugin Repositories (could not resolve plugin artifact 'org.springframework.boot:org.springframework.boot.gradle.plugin:2.6.3') Searched in the following repositories: Gradle Central Plugin Repository

实现完全离线运行需要把插件依赖也纳入预下载、本地读取的逻辑，具体修改步骤如下：

1. 新增settings.gradle配置 #

在项目根目录新建settings.gradle文件，配置插件仓库的离线读取逻辑：

pluginManagement {
    buildscript {
        repositories {
            mavenLocal()
            def skipDownload = gradle.startParameter.projectProperties.getOrDefault("skipDownload", "false").toBoolean()
            if (skipDownload) {
                flatDir {
                    dirs 'pluginlibs'
                }
            } else {
                mavenCentral()
                gradlePluginPortal()
            }
        }
        dependencies {
            def skipDownload = gradle.startParameter.projectProperties.getOrDefault("skipDownload", "false").toBoolean()
            if (skipDownload) {
                classpath fileTree(dir: 'pluginlibs', include: ['*.jar'])
            }
        }
    }
}
// 替换为实际项目名称
rootProject.name = 'spring-boot-k8s-service'

2. 修改build.gradle配置 #

保留原有业务依赖、测试依赖的离线逻辑，新增插件依赖导出任务：

plugins {
  id 'org.springframework.boot' version '2.6.3'
  id 'java'
}

ext {
    skipDownload = project.hasProperty('skipDownload') ? project.getProperty('skipDownload') as boolean : false
}

repositories {
    mavenLocal()
    if (skipDownload) {
        flatDir {
            dirs 'libs'
        }
    } else {
        mavenCentral()
    }
}

dependencies {
  if (skipDownload) {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    testImplementation fileTree(dir: 'testlibs', include: ['*.jar'])
  } else {
    implementation group: 'org.springframework.boot', name: 'spring-boot-starter-web', version: '2.6.3'
  }
}

task getDeps(type: Copy) {
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
    from configurations.compileClasspath into "libs/"
    from configurations.runtimeClasspath into "libs/"
}

task getTestDeps(type: Copy) {
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
    from configurations.testCompileClasspath into "testlibs/"
    from configurations.testRuntimeClasspath into "testlibs/"
}

// 新增：导出Gradle插件及传递依赖到本地pluginlibs目录
task getPluginDeps(type: Copy) {
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
    from buildscript.configurations.classpath into "pluginlibs/"
}

3. 修改Dockerfile配置 #

在镜像构建阶段新增插件依赖下载步骤，确保所有依赖都在build阶段固化到镜像内：

FROM gradle:7.3-jdk11
WORKDIR /app
COPY . .
# 联网构建阶段下载所有依赖：业务依赖、测试依赖、Gradle插件依赖
RUN gradle --no-daemon test getDeps getTestDeps getPluginDeps
# 默认启动命令：离线执行构建，无需联网
CMD ["sh", "-c", "gradle build -PskipDownload=true"]

• 重新构建镜像：执行docker build -t service-test .
• 断开网络后运行容器：执行docker run --rm -it service-test，即可正常完成离线构建，不会再抛出插件找不到的错误
• 如需离线启动服务调试，执行命令：docker run --rm -it -p 8080:8080 service-test gradle bootRun -PskipDownload=true

• 后续新增第三方Gradle插件时，不需要调整依赖导出逻辑，重新执行docker build即可自动缓存新插件的所有依赖
• 不要修改skipDownload参数的判断逻辑，确保镜像构建阶段（联网）走远程仓库拉取依赖，容器运行阶段（断网）走本地flatDir读取依赖

内容的提问来源于stack exchange，提问作者Ramanujan R