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