Merge pull request #5256 from square/jwilson.0701.java8

Add a note on Java 8 to the upgrade guide

CHANGELOG.md

@@ -1812,7 +1812,7 @@ Initial release.
  [conscrypt]: https://github.com/google/conscrypt/
  [conscrypt_dependency]: https://github.com/google/conscrypt/#download
  [https_server_sample]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/HttpsServer.java
- [require_android_5]: https://medium.com/square-corner-blog/okhttp-3-13-requires-android-5-818bb78d07ce
+ [require_android_5]: https://cashapp.github.io/2019-02-05/okhttp-3-13-requires-android-5
  [obsolete_apache_client]: https://gist.github.com/swankjesse/09721f72039e3a46cf50f94323deb82d
  [obsolete_url_factory]: https://gist.github.com/swankjesse/dd91c0a8854e1559b00f5fc9c7bfae70
  [tls_configuration_history]: https://square.github.io/okhttp/tls_configuration_history/

docs/upgrading_to_okhttp_4.md

@@ -233,6 +233,41 @@ between ProGuard, OkHttp 4.x, and Kotlin-originated `.class` files. Make sure yo
 release if you’re using ProGuard,
 
 
+Gradle
+------
+
+OkHttp 4’s minimum requirements are Java 8+ and Android 5+. These requirements were
+[first introduced][require_android_5] with OkHttp 3.13.
+
+Here’s what you need in `build.gradle` to target Java 8 byte code for Kotlin, Java, and Android
+plugins respectively.
+
+```
+compileKotlin {
+  kotlinOptions {
+    jvmTarget = "1.8"
+  }
+}
+compileTestKotlin {
+  kotlinOptions {
+    jvmTarget = "1.8"
+  }
+}
+
+compileJava {
+  sourceCompatibility = JavaVersion.VERSION_1_8
+  targetCompatibility = JavaVersion.VERSION_1_8
+}
+
+android {
+  compileOptions {
+    sourceCompatibility JavaVersion.VERSION_1_8
+    targetCompatibility JavaVersion.VERSION_1_8
+  }
+}
+```
+
+
  [advanced_profiling_bug]: https://issuetracker.google.com/issues/135141615
  [japicmp]: https://github.com/siom79/japicmp
  [japicmp_gradle]: https://github.com/melix/japicmp-gradle-plugin
@@ -240,4 +275,5 @@ release if you’re using ProGuard,
  [kotlin_sams]: https://youtrack.jetbrains.com/issue/KT-11129
  [mockito]: https://site.mockito.org/
  [proguard_problems]: https://github.com/square/okhttp/issues/5167
+ [require_android_5]: https://cashapp.github.io/2019-02-05/okhttp-3-13-requires-android-5
  [r8]: https://developer.android.com/studio/releases#r8-default