Android Okhttp缓存Cache，创建OkHttpClient实现

Android Okhttp使用缓存通过Cache实现。在创建OkHttpClient实现。构造Cache需要传递一个缓存文件目录已经缓存的大小尺寸。

下面演示一个简单功能，加载一张图片到一个ImageView，如果该连接下图片已经存在，那么即便在断网时候，也能使用缓存加载出来。

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.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);
        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";
        Request mRequest = new Request.Builder().url(url).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();
    }
}