编译配置已弃用，应由实现或api取代。

你可以在API和实现分离部分阅读文档。

简短的部分是

The key difference between the standard Java plugin and the Java Library plugin is that the latter introduces the concept of an API exposed to consumers. A library is a Java component meant to be consumed by other components. It's a very common use case in multi-project builds, but also as soon as you have external dependencies. The plugin exposes two configurations that can be used to declare dependencies: api and implementation. The api configuration should be used to declare dependencies which are exported by the library API, whereas the implementation configuration should be used to declare dependencies which are internal to the component.

进一步的解释请参考这张图片。

门外汉术语的简单区别是:

如果你正在处理一个接口或模块，它通过公开所声明的依赖关系的成员来为其他模块提供支持，你应该使用'api'。 如果你正在创建一个应用程序或模块，要在内部实现或使用声明的依赖项，请使用'implementation'。 'compile'与'api'工作方式相同，但是，如果你只是实现或使用任何库，'implementation'将更好地工作并节省资源。

阅读@aldok的回答以获得一个全面的示例。

implementation: mostly we use implementation configuration. It hides the internal dependency of the module to its consumer to avoid accidental use of any transitive dependency, hence faster compilation and less recompilation. api: must be used very carefully, since it leaks the to consumer’s compile classpath, hence misusing of api could lead to dependency pollution. compileOnly: when we don’t need any dependency at runtime, since compileOnly dependency won’t become the part of the final build. we will get a smaller build size. runtimeOnly: when we want to change or swap the behaviour of the library at runtime (in final build).

我已经创建了一个深入了解每个工作示例的帖子:源代码

https://medium.com/@gauraw.negi/how-gradle-dependency-configurations-work-underhood-e934906752e5

在继续之前先做一些笔记;compile已弃用，并且文档声明您应该使用implementation，因为compile将在Gradle 7.0版本中被删除。 如果你使用——warning-mode运行Gradle构建，你会看到以下消息:

对于依赖项声明，compile配置已弃用。这将失败，并在Gradle 7.0中出现错误。请改用实现配置。

只要看看帮助页上的图片，就很有意义了。

你有蓝色框compileClasspath和runtimeClassPath。 当运行gradle build时，compileClasspath是成功构建所必需的。编译时将出现在类路径上的库将是在gradle构建中使用compileOnly或implementation配置的所有库。

然后我们有runtimeClasspath，这些都是使用实现或runtimeOnly添加的包。所有这些库都将添加到您部署到服务器上的最终构建文件中。

如图所示，如果您希望一个库既用于编译，又希望将它添加到构建文件中，那么应该使用实现。

runtimeOnly的示例可以是数据库驱动程序。 compileOnly的一个例子可以是servlet-api。 实现的一个例子是spring-core。

+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| Name               | Role                 | Consumable? | Resolveable? | Description                             |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| api                | Declaring            |      no     |      no      | This is where you should declare        |
|                    | API                  |             |              | dependencies which are transitively     |
|                    | dependencies         |             |              | exported to consumers, for compile.     |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| implementation     | Declaring            |      no     |      no      | This is where you should                |
|                    | implementation       |             |              | declare dependencies which are          |
|                    | dependencies         |             |              | purely internal and not                 |
|                    |                      |             |              | meant to be exposed to consumers.       |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| compileOnly        | Declaring compile    |     yes     |      yes     | This is where you should                |
|                    | only                 |             |              | declare dependencies                    |
|                    | dependencies         |             |              | which are only required                 |
|                    |                      |             |              | at compile time, but should             |
|                    |                      |             |              | not leak into the runtime.              |
|                    |                      |             |              | This typically includes dependencies    |
|                    |                      |             |              | which are shaded when found at runtime. |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| runtimeOnly        | Declaring            |      no     |      no      | This is where you should                |
|                    | runtime              |             |              | declare dependencies which              |
|                    | dependencies         |             |              | are only required at runtime,           |
|                    |                      |             |              | and not at compile time.                |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| testImplementation | Test dependencies    |      no     |      no      | This is where you                       |
|                    |                      |             |              | should declare dependencies             |
|                    |                      |             |              | which are used to compile tests.        |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| testCompileOnly    | Declaring test       |     yes     |      yes     | This is where you should                |
|                    | compile only         |             |              | declare dependencies                    |
|                    | dependencies         |             |              | which are only required                 |
|                    |                      |             |              | at test compile time,                   |
|                    |                      |             |              | but should not leak into the runtime.   |
|                    |                      |             |              | This typically includes dependencies    |
|                    |                      |             |              | which are shaded when found at runtime. |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+
| testRuntimeOnly    | Declaring test       |      no     |      no      | This is where you should                |
|                    | runtime dependencies |             |              | declare dependencies which              |
|                    |                      |             |              | are only required at test               |
|                    |                      |             |              | runtime, and not at test compile time.  |
+--------------------+----------------------+-------------+--------------+-----------------------------------------+

当你在gradle项目中声明一个依赖项时 代码库+它的依赖关系(声明为api)可以被gradle项目的消费者使用。

让我们举个例子

我们有一级，二级，三级gradle项目。

Level 1使用Level 2。Level 2使用Level 3。

一级<-二级<-三级

使用API和实现，我们可以控制是否应该将级别3的类公开到级别1。

这如何使构建更快:

关卡3的任何变化。不需要重新编译级别1。 特别是在开发过程中，节省时间。