三级缓存处理图片

权限

<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

创建一个MD5工具类

package com.wzq.bitmapcache;

import java.security.MessageDigest;

/**
* 工具类，把url进行MD5加密,加密后以字符串的形式返回
*/

public class EncoderUtils {

public static String encode(String string) throws Exception {
    byte[] hash = MessageDigest.getInstance("MD5").digest(
            string.getBytes("UTF-8"));
    StringBuilder hex = new StringBuilder(hash.length * 2);
    for (byte b : hash) {
        if ((b & 0xFF) < 0x10) {
            hex.append("0");
        }
        hex.append(Integer.toHexString(b & 0xFF));
    }
    return hex.toString();
    }
}

图片缓存工具类

package com.wzq.bitmapcache;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
* 处理三级缓存
* 内存缓存(LruCache——>最近最少使用算法，当缓存慢的时候，自动把最近使用最少的删除，腾出来的空间添加新的缓存内容)
*/

public class ImagesUtils {
Handler handler;
private File cacheDir;
private ExecutorService newFixedThreadPool;
private LruCache<String, Bitmap> lruCache;

public ImagesUtils(Context context, Handler handler) {
    //获得你手机上的最大内存
    long maxMemory = Runtime.getRuntime().maxMemory();
    int maxSize = (int) (maxMemory / 10);
    this.handler = handler;

    lruCache = new LruCache<String, Bitmap>(maxSize) {

        @Override
        protected int sizeOf(String key, Bitmap value) {
            return value.getRowBytes() * value.getHeight();
        }

    };
    //得到本地qpp在SD卡上缓存的文件夹
    cacheDir = context.getCacheDir();
    //初始化5个线程池，供程序使用
    newFixedThreadPool = Executors.newFixedThreadPool(5);

}


public Bitmap getBitMap(String path) {

    Bitmap bitmap = lruCache.get(path);
    if (bitmap != null) {
        System.out.println("我走了内存");
        return bitmap;
    }
    //从本直去取，sd卡去取bitmap
    bitmap = getBitMapFromLocal(path);
    if (bitmap != null) {
        System.out.println("我走了本地缓存");
        return bitmap;
    }

    // 从网络去取
    getBitmapFromNet(path);

    return null;
}


/**
 * 从网络
 *
 * @param path
 */
private void getBitmapFromNet(final String path) {
    newFixedThreadPool.execute(new Runnable() {

        @Override
        public void run() {

            try {
                URL url = new URL(path);
                HttpURLConnection connection = (HttpURLConnection) url
                        .openConnection();
                connection.setConnectTimeout(5000);
                connection.setReadTimeout(5000);
                int responseCode = connection.getResponseCode();
                if (responseCode == 200) {
                    InputStream inputStream = connection.getInputStream();
                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                    Message msg = new Message();
                    msg.what = 111;
                    msg.obj = bitmap;
                    Bundle data = new Bundle();
                    data.putString("tag", path);
                    msg.setData(data);
                    handler.sendMessage(msg);
                    //缓存到本地
                    saveBitmapToLocal(bitmap, path);
                    //缓存到内存
                    lruCache.put(path, bitmap);
                }

            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    });

}


protected void saveBitmapToLocal(Bitmap bitmap, String path) {
    try {
        String encode = EncoderUtils.encode(path);

        FileOutputStream fileOutputStream = new FileOutputStream(cacheDir
                + "/" + encode);

        //图片二次裁剪
        bitmap.compress(CompressFormat.JPEG, 80, fileOutputStream);

    } catch (Exception e) {
        e.printStackTrace();
    }

}

/**
 * 从本地取   Md5   a.jpg  b.jpg
 * aafdgsgsgsggg.jpg
 *
 * @param path
 */
private Bitmap getBitMapFromLocal(String path) {

    try {
        String encode = EncoderUtils.encode(path);
        FileInputStream fileInputStream = new FileInputStream(cacheDir
                + "/" + encode);
        Bitmap bitmap = BitmapFactory.decodeStream(fileInputStream);
        //存到内存
        lruCache.put(path, bitmap);
        return bitmap;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
    }

}

主界面

package com.wzq.bitmapcache;

import android.graphics.Bitmap;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

private GridView gv;
ImagesUtils imags;
String[] imageUrls = new String[]{
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383299_1976.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383291_6518.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383291_8239.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383290_9329.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383290_1042.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383275_3977.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383265_8550.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383264_3954.jpg",
        "https://img-my.youkuaiyun.com/uploads/201407/26/1406383264_4787.jpg",
};

private Handler handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);

        if (msg.what == 0) {
            Bitmap bitmap = (Bitmap) msg.obj;
            // 设置给imageView
            String tag = msg.getData().getString("tag");
            // 根据标记取出imageView
            ImageView imageView = (ImageView) gv.findViewWithTag(tag);
            if (imageView != null && bitmap != null) {
                // 从网络获取图片
                imageView.setImageBitmap(bitmap);
                Log.i("tag", "从网络中获取图片");
            }
        }
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    imags = new ImagesUtils(this, handler);
    gv = (GridView) findViewById(R.id.gv);
    gv.setAdapter(new MyAdapter());
}

class MyAdapter extends BaseAdapter {

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return imageUrls.length;
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ImageView iv = new ImageView(MainActivity.this);
        iv.setTag(imageUrls[position]);

        Bitmap bitmap = imags.getBitMap(imageUrls[position]);

        // 从内存中或者缓存中
        if (bitmap != null) {
            iv.setImageBitmap(bitmap);
        }
        // 获取图片
        return iv;
        }
    }
}

布局

<GridView
    android:id="@+id/gv"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:numColumns="3" />