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

客官°小女子只卖身不卖艺 2024-02-18 16:01 50阅读 0赞

**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