Demonstrate HTTP caching with OkHttp 2.5.0 and Retrofit 1.9.0.

CacheTest.java

/*
 * Copyright (C) 2013 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.transloc.android;

import com.squareup.okhttp.Cache;
import com.squareup.okhttp.OkHttpClient;
import com.squareup.okhttp.mockwebserver.MockResponse;
import com.squareup.okhttp.mockwebserver.MockWebServer;
import java.io.File;
import java.util.UUID;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.RobolectricTestRunner;
import org.robolectric.annotation.Config;
import org.robolectric.shadows.ShadowLog;
import retrofit.RestAdapter;
import retrofit.android.AndroidLog;
import retrofit.client.OkClient;
import retrofit.http.GET;
import retrofit.http.Path;

import static junit.framework.Assert.assertEquals;

@RunWith(RobolectricTestRunner.class)
@Config(manifest=Config.NONE)
public class CacheTest {
  interface SodaService {
    @GET("/{brand}") Object cola(@Path("brand") String brand);
  }

  @Before public void setUp() throws Exception {
    ShadowLog.stream = System.out;
  }

  @Test public void testWhenCacheThenSuccess() throws Exception {
    MockWebServer mockWebServer = new MockWebServer();
    mockWebServer.start();

    // Create an HTTP client that uses a cache on the file system. Android applications should use
    // their Context to get a cache directory.
    OkHttpClient okHttpClient = new OkHttpClient();
    File cacheDir = new File(System.getProperty("java.io.tmpdir"), UUID.randomUUID().toString());
    Cache cache = new Cache(cacheDir, 1024);
    okHttpClient.setCache(cache);

    // Create a Retrofit RestAdapter for our SodaService interface.
    Executor executor = Executors.newCachedThreadPool();
    RestAdapter restAdapter = new RestAdapter.Builder()
        .setExecutors(executor, executor)
        .setClient(new OkClient(okHttpClient))
        .setEndpoint(mockWebServer.url("/").toString())
        .setLog(new AndroidLog("SodaService"))
        .setLogLevel(RestAdapter.LogLevel.FULL)
        .build();
    SodaService sodaService = restAdapter.create(SodaService.class);

    // /pepsi hits the web server and returns a response that will be fully cached for 60 seconds.
    mockWebServer.enqueue(new MockResponse().addHeader("Cache-Control: max-age=60")
        .setBody("\"You got the right one, baby\""));
    assertEquals(sodaService.cola("pepsi"), "You got the right one, baby");
    assertEquals(cache.getRequestCount(), 1);
    assertEquals(cache.getNetworkCount(), 1);
    assertEquals(cache.getHitCount(), 0);

    // /coke hits the web server and returns a response that will be conditionally cached.
    mockWebServer.enqueue(new MockResponse().addHeader("ETag: v1").setBody("\"Always Coca-Cola\""));
    assertEquals(sodaService.cola("coke"), "Always Coca-Cola");
    assertEquals(cache.getRequestCount(), 2);
    assertEquals(cache.getNetworkCount(), 2);
    assertEquals(cache.getHitCount(), 0);

    // /pepsi returns a response from the cache.
    assertEquals(sodaService.cola("pepsi"), "You got the right one, baby");
    assertEquals(cache.getRequestCount(), 3);
    assertEquals(cache.getNetworkCount(), 2);
    assertEquals(cache.getHitCount(), 1);

    // /coke validates the cached response. The server says the cached version is still good.
    mockWebServer.enqueue(new MockResponse().setResponseCode(304));
    assertEquals(sodaService.cola("coke"), "Always Coca-Cola");
    assertEquals(cache.getRequestCount(), 4);
    assertEquals(cache.getNetworkCount(), 3);
    assertEquals(cache.getHitCount(), 2);

    mockWebServer.shutdown();
  }
}

See this tweet for explanation: https://twitter.com/JakeWharton/status/651220291763331073

Logging in Retrofit v1 is an approximation.