Android Okhttp缓存：精细化每一个Request的CacheControl缓存控制策略（二）

Android Okhttp缓存：精细化每一个Request的CacheControl缓存控制策略（二）

之前我写的附录文章1，只是简单的使用缺省的方法实现Okhttp的缓存。现在使用CacheControl，精细化到每一个Request的缓存控制策略。
改造附录1代码：

package zhangphil.app;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Bundle;import android.support.annotation.Nullable;import android.support.v7.app.AppCompatActivity;import android.widget.ImageView;import java.io.File;import java.io.IOException;import java.util.concurrent.TimeUnit;import okhttp3.Cache;import okhttp3.CacheControl;import okhttp3.Call;import okhttp3.Callback;import okhttp3.OkHttpClient;import okhttp3.Request;import okhttp3.Response;public class MainActivity extends AppCompatActivity {    private OkHttpClient mOkHttpClient;    @Override    public void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        final ImageView image = (ImageView) findViewById(R.id.image);        File cacheDir = new File(this.getCacheDir(), "zhangphilcache");        Cache mCache = new Cache(cacheDir, 8 * 1024 * 1024); //8M缓存空间        OkHttpClient.Builder mBuilder = new OkHttpClient.Builder();        mOkHttpClient = mBuilder                .connectTimeout(10, TimeUnit.SECONDS) //连接超时阈值                .writeTimeout(10, TimeUnit.SECONDS) //写超时阈值                .readTimeout(10, TimeUnit.SECONDS)  //读超时阈值                .retryOnConnectionFailure(true) //当失败后重试                .cache(mCache)                .build();        String url = "https://www.baidu.com/img/bd_logo1.png";        CacheControl mCacheControl = new CacheControl.Builder()                .noTransform()                .maxAge(60 * 60, TimeUnit.SECONDS) //缓存有效期时长                .build();        Request mRequest = new Request.Builder()                .url(url)                .cacheControl(mCacheControl)                .build();        mOkHttpClient.newCall(mRequest).enqueue(new Callback() {            @Override            public void onFailure(Call call, IOException e) {            }            @Override            public void onResponse(Call call, Response response) throws IOException {                if (response.isSuccessful()) {                    byte[] bytes = response.body().bytes();                    final Bitmap bmp = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);                    runOnUiThread(new Runnable() {                        @Override                        public void run() {                            image.setImageBitmap(bmp);                        }                    });                }            }        });    }    @Override    protected void onDestroy() {        super.onDestroy();        //取消所有Okhttp的网络请求        mOkHttpClient.dispatcher().cancelAll();    }}

maxAge 缓存有效期，Okhttp源代码中maxAge的实现：

 /**     * Sets the maximum age of a cached response. If the cache response's age exceeds {@code     * maxAge}, it will not be used and a network request will be made.     *     * @param maxAge a non-negative integer. This is stored and transmitted with {@link     * TimeUnit#SECONDS} precision; finer precision will be lost.     */    public Builder maxAge(int maxAge, TimeUnit timeUnit) {      if (maxAge < 0) throw new IllegalArgumentException("maxAge < 0: " + maxAge);      long maxAgeSecondsLong = timeUnit.toSeconds(maxAge);      this.maxAgeSeconds = maxAgeSecondsLong > Integer.MAX_VALUE          ? Integer.MAX_VALUE          : (int) maxAgeSecondsLong;      return this;    }

CacheControl.Builder在build时候的常用方法：
noCache 不使用缓存。
noStore 不要把网络数据缓存。
noTransform 不要转码。

Okhttp定义了若干常量缓存模型：
CacheControl.FORCE_NETWORK  强制使用网络数据。
CacheControl.FORCE_CACHE  强制使用缓存。


注意看Okhttp源码实现，在Okhttp源代码文件CacheControl.java中，CacheControl.FORCE_NETWORK的代码实现：

public static final CacheControl FORCE_NETWORK = new Builder().noCache().build();

CacheControl.FORCE_CACHE的代码实现：

/**   * Cache control request directives that uses the cache only, even if the cached response is   * stale. If the response isn't available in the cache or requires server validation, the call   * will fail with a {@code 504 Unsatisfiable Request}.   */  public static final CacheControl FORCE_CACHE = new Builder()      .onlyIfCached()      .maxStale(Integer.MAX_VALUE, TimeUnit.SECONDS)      .build();

附录：
1，《Android Okhttp缓存：Cache，创建OkHttpClient实现（一）》链接：http://blog.csdn.net/zhangphil/article/details/78326497