Gradle Implementation vs API configuration

分手后的思念是犯贱 2021-09-20 02:48 304阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

注:

可以把 Implementation理解为java类的private, 使用Implementation则外部依赖本库的代码引用不到本库Implementation的代码, 也就是降低依赖树的层级, 这样就可以避免外部代码编译时候, 导致本库依赖的库的代码发生编译. 从而降低编译时间

I think this topic needs a bit more coverage because maybe is not so immediate for every developer.

Gradle `compile` keyword has been deprecated in favor of the new `api` and `implementation`keywords.

I will not explain `api`, because it's the same thing as using the old `compile`, so if you replace all your `compile` with `api` everything will works as always.

To understand the `implementation` keyword we need an example.

**EXAMPLE**

We have this library called `MyLibrary` where internally we are using another library called `InternalLibrary`. Something like this:

//internal library module
    public class InternalLibrary {
        public static String giveMeAString(){
            return "hello";
        }
    }
    
    //my library module
    public class MyLibrary {
        public String myString(){
            return InternalLibrary.giveMeAString();
        }
    }

The `build.gradle` dependencies of `MyLibrary` its like this:

dependencies {
        api project(':InternalLibrary')
    }

Now in your code you want to use `MyLibrary` so you should have a `build.gradle` with this dependency

dependencies {
        api project(':MyLibrary')
    }

In your application code, with the `api` keyword (or using the old `compile`) you can access both `MyLibrary` and `InternalLibrary`.

//so you can access the library (as it should)
    MyLibrary myLib = new MyLibrary();
    System.out.println(myLib.myString());
    
    //but you can access the internal library too (and you shouldn't)
    System.out.println(InternalLibrary.giveMeAString());

In this way you are potentially "leaking" the internal implementation of something that you shouldn't use because it's not directly imported by you.

To prevent this, Gradle has created the new `implementation` keyword, so now if you switch `api` to `implementation` in your `MyLibrary`

dependencies {
        implementation project(':InternalLibrary')
    }

And in your app `build.gradle`

dependencies {
        implementation project(':MyLibrary')
    }

you won't be able to call `InternalLibrary.giveMeAString()` in your app code anymore. While if `MyLibrary` uses the `api` keyword to import `InternalLibrary`, in your app you will be able to call `InternalLibrary.giveMeAString()` without problems, independently if you use `api` or `implementation` to add `MyLibrary` to your app.

Using this sort of boxing strategy the Android Gradle plugin knows that if you edit something in `InternalLibrary` it will trigger the recompilation of `MyLibrary` only. It will not trigger the recompilation of your entire app because you don't have access to `InternalLibrary`. This mechanism when you have a lot of nested dependencies can speed-up the build a lot.*(Watch the video linked at the end for a full understanding of this)*

**CONCLUSIONS**

*  When you switch to the new Android Gradle plugin 3.X.X, you should replace all your `compile`with the `implementation` keyword **(1\*)**. Then try to compile and test your app. If everything it's ok leave the code as is, if you have problems you probably have something wrong with your dependencies or you used something that now is private and not more accessible. *Suggestion by Android Gradle plugin engineer Jerome Dochez **(1*****)\***)
 *  If you are a library mantainer you should use `api` for every dependency which is needed for the public API of your library, while use `implementation` for test dependencies or dependencies which must not be used by the final users.

[Useful article][] Showcasing the difference between **implementation** and **api**

**REFERENCES** (This is the same video splitted up for time saving)

[Google I/O 2017 - How speed up Gradle builds (FULL VIDEO)][Google I_O 2017 - How speed up Gradle builds _FULL VIDEO]

[Google I/O 2017 - How speed up Gradle builds (NEW GRADLE PLUGIN 3.0.0 PART ONLY)][Google I_O 2017 - How speed up Gradle builds _NEW GRADLE PLUGIN 3.0.0 PART ONLY]

[Google I/O 2017 - How speed up Gradle builds (reference to **1\***)][Google I_O 2017 - How speed up Gradle builds _reference to_1]

[Android documentation][]

转载于:https://my.oschina.net/sfshine/blog/3005548

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20210726/5c85c3d8b753481f92bab3ac1d810131.png
[Useful article]: https://medium.com/mindorks/implementation-vs-api-in-gradle-3-0-494c817a6fa
[Google I_O 2017 - How speed up Gradle builds _FULL VIDEO]: https://www.youtube.com/watch?v=7ll-rkLCtyk
[Google I_O 2017 - How speed up Gradle builds _NEW GRADLE PLUGIN 3.0.0 PART ONLY]: https://youtu.be/7ll-rkLCtyk?t=22m21s
[Google I_O 2017 - How speed up Gradle builds _reference to_1]: https://youtu.be/7ll-rkLCtyk?t=30m37s
[Android documentation]: https://developer.android.com/studio/preview/features/new-android-plugin-migration.html#new_configurations