图片缓存

mport java.io.File;

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;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.Bitmap.CompressFormat;

import android.graphics.BitmapFactory;

import android.os.Handler;

import android.os.Message;

import android.support.v4.util.LruCache;

/**

* @author andong

* 图片工具类, 用来抓取图片, 缓存图片.

*/

public class ImageCacheUtils {

public static final int SUCCESS = 0; // 请求成功

public static final int FAILED = 1; // 请求失败

private Handler handler;

private LruCache<String, Bitmap> mMemoryCache;

private File cacheDir; // 本地缓存的目录

private ExecutorService mExecutorService;

public ImageCacheUtils(Context context, Handler handler) {

this.handler = handler;

cacheDir = context.getCacheDir();

// 获取模拟器运行时可以使用的内存大小 / 8

long maxMemory = Runtime.getRuntime().maxMemory() / 8;

mMemoryCache = new LruCache<String, Bitmap>((int) maxMemory) {

@Override

protected int sizeOf(String key, Bitmap value) {

// 返回当前图片的大小, 给Lrucache去计算当前缓存的内存大小

return value.getRowBytes() * value.getHeight();

}

};

// 获得一个固定线程为5个的线程池对象.

mExecutorService = Executors.newFixedThreadPool(5);

}

/**

* 根据url请求图片

* 取图片的顺序:

* 1. 从内存取.

* 2. 从本地取.

* 3. 从网络取.

* @param url

* @param tag 当前请求的标识

* @return

*/

public Bitmap getBitmapFromUrl(String url, int tag) {

// 1. 从内存取.

Bitmap bm = mMemoryCache.get(url);

if(bm != null) {

System.out.println("从内存中取");

return bm;

}

// 2. 从本地取.

bm = getBitmapFromLocal(url);

if(bm != null) {

System.out.println("从本地取");

return bm;

}

// 3. 从网络取.

System.out.println("从网络中取");

getBitmapFromNet(url, tag);

return null;

}

/**

* 根据url, 从本地取图片

* @param url

* @return

*/

private Bitmap getBitmapFromLocal(String url) {

try {

String fileName = MD5Encoder.encode(url).substring(0, 10);

File file = new File(cacheDir, fileName);

if(file.exists()) {

return BitmapFactory.decodeFile(file.getPath());

}

} catch (Exception e) {

e.printStackTrace();

}

return null;

}

/**

* 根据url请求网络得到图片, 使用子线程执行.

* @param url

*/

private void getBitmapFromNet(String url, int tag) {

// new Thread(new RequestNetRunnable(url, tag)).start();

mExecutorService.execute(new RequestNetRunnable(url, tag));

}

/**

* @author andong

* 请求网络的任务类

*/

class RequestNetRunnable implements Runnable {

private String url;

private int tag; // 当前这次请求, 得到的图片需要设置给某个ImageView(身上有个tag和当前tag一样的ImageView)

public RequestNetRunnable(String url, int tag) {

this.url = url;

this.tag = tag;

}

@Override

public void run() {

HttpURLConnection conn = null;

try {

URL mURL = new URL(url);

conn = (HttpURLConnection) mURL.openConnection();

conn.setRequestMethod("GET");

conn.setConnectTimeout(5000); // 设置连接超时时间为: 5秒钟

conn.setReadTimeout(5000); // 设置读取超时时间为: 5秒钟

// conn.connect();

int responseCode = conn.getResponseCode();

if(responseCode == 200) {

InputStream is = conn.getInputStream();

// 把流转换成Bitmap对象

Bitmap bm = BitmapFactory.decodeStream(is);

// 把图片发送到主线程.

Message msg = handler.obtainMessage();

msg.obj = bm;

msg.arg1 = tag;

msg.what = SUCCESS;

msg.sendToTarget(); // 把消息发送给PhotosMenuPager中消息处理器

// 向内存中存储一个.

mMemoryCache.put(url, bm);

// 向本地中存储一个.

writeToLocal(bm, url);

return;

}

} catch (Exception e) {

e.printStackTrace();

} finally {

if(conn != null) {

conn.disconnect(); // 断开连接.

}

}

handler.obtainMessage(FAILED).sendToTarget();

}

}

/**

* 把图片缓存在本地

* @param bm

* @param url

*/

public void writeToLocal(Bitmap bm, String url) {

try {

String fileName = MD5Encoder.encode(url).substring(0, 10);

FileOutputStream fos = new FileOutputStream(new File(cacheDir, fileName));

bm.compress(CompressFormat.JPEG, 100, fos);

} catch (Exception e) {

e.printStackTrace();

}

}

}