Added retrofit2 module. (AsyncHttpClient#1419)

Author: bfg

extras/pom.xml

@@ -19,6 +19,7 @@
         <module>rxjava</module>
         <module>rxjava2</module>
         <module>simple</module>
+        <module>retrofit2</module>
     </modules>
 
     <dependencies>

extras/retrofit2/README.md

@@ -0,0 +1,57 @@
+# Async-http-client Retrofit2 Call Adapter
+
+An `okhttp3.Call.Factory` for implementing async-http-client powered [Retrofit][1] type-safe HTTP clients.
+
+## Download
+
+Download [the latest JAR][2] or grab via [Maven][3]:
+
+```xml
+<dependency>
+  <groupId>org.asynchttpclient</groupId>
+  <artifactId>async-http-client-extras-retrofit2</artifactId>
+  <version>latest.version</version>
+</dependency>
+```
+
+or [Gradle][3]:
+
+```groovy
+compile "org.asynchttpclient:async-http-client-extras-retrofit2:latest.version"
+```
+
+ [1]: http://square.github.io/retrofit/
+ [2]: https://search.maven.org/remote_content?g=org.asynchttpclient&a=async-http-client-extras-retrofit2&v=LATEST
+ [3]: http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22org.asynchttpclient%22%20a%3A%22async-http-client-extras-retrofit2%22
+ [snap]: https://oss.sonatype.org/content/repositories/snapshots/
+
+## Example usage
+
+```java
+// instantiate async-http-client
+AsyncHttpClient httpClient = ...
+
+// instantiate async-http-client call factory
+Call.Factory callFactory = AsyncHttpClientCallFactory.builder()
+    .httpClient(httpClient)                 // required
+    .onRequestStart(onRequestStart)         // optional
+    .onRequestFailure(onRequestFailure)     // optional
+    .onRequestSuccess(onRequestSuccess)     // optional
+    .requestCustomizer(requestCustomizer)   // optional
+    .build();
+
+// instantiate retrofit
+Retrofit retrofit = new Retrofit.Builder()
+    .callFactory(callFactory) // use our own call factory
+    .addConverterFactory(ScalarsConverterFactory.create())
+    .addConverterFactory(JacksonConverterFactory.create())
+    // ... add other converter factories
+    // .addCallAdapterFactory(RxJavaCallAdapterFactory.createAsync())
+    .validateEagerly(true) // highly recommended!!!
+    .baseUrl("https://api.github.com/");
+
+// time to instantiate service
+GitHub github = retrofit.create(Github.class);
+
+// enjoy your type-safe github service api! :-)
+```

extras/retrofit2/pom.xml

@@ -0,0 +1,63 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <artifactId>async-http-client-extras-parent</artifactId>
+        <groupId>org.asynchttpclient</groupId>
+        <version>2.1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>async-http-client-extras-retrofit2</artifactId>
+    <name>Asynchronous Http Client Retrofit2 Extras</name>
+    <description>The Async Http Client Retrofit2 Extras.</description>
+
+    <properties>
+      <retrofit2.version>2.3.0</retrofit2.version>
+      <lombok.version>1.16.16</lombok.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>retrofit</artifactId>
+            <version>${retrofit2.version}</version>
+        </dependency>
+
+        <!-- for tests -->
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>converter-scalars</artifactId>
+            <version>${retrofit2.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>converter-jackson</artifactId>
+            <version>${retrofit2.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>adapter-rxjava</artifactId>
+            <version>${retrofit2.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>adapter-rxjava2</artifactId>
+            <version>${retrofit2.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>