我使用gradle在一个没有网络的环境中构建了这个项目，我把所有的项目依赖项都放到了项目根目录下的libs目录中，一切正常。因为它是一个spring-boot项目，所以我需要使用gradle插件org.springframework.boot来打包它。所以我把插件spring-boot-gradle-plugin-2. 2. 0. RELEASE. jar的jar文件放到了项目的但是我已经使用了很多方法来指定插件目录中的插件，但都不管用。
项目目录如下：

projectRoot
├── build.gradle
├── gradle
│   └── wrapper
├── gradlew
├── gradlew.bat
├── libs
│   └── xxx.jar
├── plugins
│   ├── dependency-management-plugin-1.0.11.RELEASE.jar
│   └── spring-boot-gradle-plugin-2.2.0.RELEASE.jar
├── resource
├── settings.gradle
└── src
    ├── main
    └── test

设置.gradle文件如下所示：

pluginManagement {
    repositories {
        mavenLocal()
        flatDir { dirs 'plugins' }
    }

}
rootProject.name = 'example'

build.gradle文件如下所示：

plugins {
    id 'org.springframework.boot' version '2.2.0.RELEASE'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
}

apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.example'
version = '1.0.0-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
    mavenLocal()
}

dependencies {
    implementation files('libs/xxx.jar','libs/others_of_libs.jar')
}

但当我通过离线模式执行时：./gradlew build --offline，我得到以下错误：

Plugin [id: 'org.springframework.boot', version: '2.2.0.RELEASE'] 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:2.2.0.RELEASE')
  Searched in the following repositories:
    maven(file:/User/myName/example/plugins/)

这种情况具体是如何指定的？我需要将插件目录中的两个jar安装到本地maven存储库中吗？
我发现了很多在网络上离线编译特定插件的方法，包括：

buildscript {

    repositories {
        mavenLocal()
        maven { url('plugins') }
    }

    dependencies {
        classpath fileTree(include: ['*.jar'], dir: 'plugins')
        classpath files('plugins/dependency-management-plugin-1.0.11.RELEASE.jar')
        classpath files('plugins/spring-boot-gradle-plugin-2.2.0.RELEASE.jar')
        classpath "io.spring.dependency-management:io.spring.dependency-management.gradle.plugin:1.0.11.RELEASE"
        classpath "org.springframework.boot:spring-boot-gradle-plugin:2.2.0.RELEASE"
    }

}

我仍然得到相同的错误。