图片压缩与缓存

package com.wangzhen.util;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import android.annotation.SuppressLint;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Bitmap.CompressFormat;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;
import android.util.Log;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;

/**
 * 图片工具类
 * 
 * @author Administrator
 * 
 */
public class ImageLoader {

    private static String mURL = "";
    private static ImageView mImageView;
    private LruCache<String, Bitmap> mCaches;// LruCache缓存算法

    public ImageLoader() {
        // 获取最大可用内存
        int MaxMemory = (int) Runtime.getRuntime().maxMemory();
        // 设置缓存可用空间
        int CacheSize = MaxMemory / 4;
        mCaches = new LruCache<String, Bitmap>(CacheSize) {
            @SuppressLint("NewApi")
            @Override
            protected int sizeOf(String key, Bitmap value) {
                // 每次存入缓存的时候调用
                return value.getByteCount();
            }
        };
    }

    /**
     * 将图片存入缓存
     * 
     * @param url
     * @param bitmap
     */
    private void AddBitmapToCache(String url, Bitmap bitmap) {
        if (GetBitmapFromCache(url) == null) {
            mCaches.put(url, bitmap);
        }
    }

    /**
     * 从缓存中取出图片
     * 
     * @param url
     * @return
     */
    private Bitmap GetBitmapFromCache(String url) {
        return mCaches.get(url);
    }

    /**
     * 以线程方式下载图片
     * 
     * @param imageView
     * @param path
     */
    public void GetImageByThread(ImageView imageView, String path) {
        mURL = path;
        mImageView = imageView;
        new Thread() {
            public void run() {
                // 首先判断缓存中是否已存在当前图片
                Bitmap bitmap = GetBitmapFromCache(mURL);
                if (bitmap == null) {
                    bitmap = CompressBitmap(GetBitmapFromURL(mURL));
                    Message message = Message.obtain();
                    message.obj = bitmap;
                    mHandler.sendMessage(message);
                } else {
                    mImageView.setImageBitmap(bitmap);
                }
            };
        }.start();
    }

    /**
     * 通过URL获取图片
     * 
     * @return
     */
    private Bitmap GetBitmapFromURL(String path) {
        Bitmap bitmap = null;
        try {
            URL url = new URL(path);
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();
            bitmap = BitmapFactory.decodeStream(connection.getInputStream());
            connection.disconnect();
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return bitmap;
    }

    /**
     * 图片压缩：质量压缩
     * 
     * @param bitmap
     * @return
     */
    private Bitmap CompressBitmap(Bitmap bitmap) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        // 质量压缩方法，这里100表示不压缩，将压缩后的数据放入到baos中
        bitmap.compress(CompressFormat.JPEG, 100, baos);
        Log.i("Compress", "压缩前：" + baos.toByteArray().length / 1024 + "KB");
        int options = 100;
        while (baos.toByteArray().length / 1024 > 50) {
            // 重置BAOS，即清空
            baos.reset();
            bitmap.compress(CompressFormat.JPEG, options, baos);
            options -= 10;
        }
        Log.i("Compress", "压缩后：" + baos.toByteArray().length / 1024 + "KB");
        // 将压缩后数据存放到ByteArrayInputStream中
        ByteArrayInputStream is = new ByteArrayInputStream(baos.toByteArray());
        // 把ByteArrayInputStream解码为图片
        Bitmap image = BitmapFactory.decodeStream(is);
        return image;
    }

    Handler mHandler = new Handler() {
        @SuppressLint("NewApi")
        public void handleMessage(Message msg) {
            Bitmap bitmap =(Bitmap) msg.obj;
            AddBitmapToCache(mURL, bitmap);
            mImageView.setImageBitmap(bitmap);
            //按比例扩大图片的size居中显示，使得图片长(宽)等于或大于View的长(宽) 
            mImageView.setScaleType(ScaleType.CENTER_CROP);
        };
    };

}