android异步加载图片

 

import java.io.BufferedOutputStream;  

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.WeakHashMap;

import org.apache.http.HttpStatus;

import com.android.lalala.util.lalalaApplication;

import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.widget.ImageView;

/**
 * 图片下载与缓存 思路是，先查看内存，后检查SDcard，没有的话联网进行下载。
 */
public class ImageLoader {
    private ImageView imageView = null;
    private String urlPath = "";
    private WeakHashMap<String, Bitmap> picsHashMap = null;
    private String urlHashCode = "";
    private String filePath = "";
    private Handler handler = null;
    private Bitmap handlerBitmap = null;

    /**
     * 构造器
     *
     * @param imageView
     *            imageview对象
     * @param urlPath
     *            下载的url地址
     * @param filePath
     *            缓存文件夹名称
     */

    public ImageLoader(ImageView imageView, String urlPath, String filePath) {
        super();
        this.imageView = imageView;
        this.urlPath = urlPath;
        this.filePath = filePath;
        urlHashCode = String.valueOf(urlPath.hashCode());
        // 从application中获取picHashMap对象
        picsHashMap = lalalaApplication.getInstance().getPicHashMap();
        handler = new Handler();
        new imageLoaderThread().start();
    }

    /**
     * 图片下载线程
     */
    private class imageLoaderThread extends Thread {
        @Override
        public void run() {
            super.run();
            if (readFromRAM()) {
                return;
            }
            if (readFromSDcard()) {
                return;
            }
            httpDownload();
        }
    }

    /**
     * 开始下载
     */
    private void httpDownload() {
        try {
            URL url = new URL(urlPath);
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();
            connection.setConnectTimeout(10 * 1000);
            if (connection.getResponseCode() == HttpStatus.SC_OK) {
                InputStream is = connection.getInputStream();
                Bitmap bitmap = BitmapFactory.decodeStream(is);
                setBitmap(bitmap);
                lalalaApplication.getInstance().getPicHashMap()
                        .put(urlHashCode, bitmap);
                saveToSDcard(bitmap);
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 将bitmap保存至SD卡上
     *
     * @param bitmap
     *            bitmap
     */
    private void saveToSDcard(Bitmap bitmap) {
        try {
            String fileName = filePath + "/" + urlHashCode + ".JPG";
        File file = new File(filePath);
        if (!file.exists()) {
            file.mkdir();
        }
            BufferedOutputStream outputStream = new BufferedOutputStream(
                    new FileOutputStream(new File(fileName)));
            bitmap.compress(CompressFormat.JPEG, 100, outputStream);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

    }

    /**
     * 从内存中读取bitmap图片数据
     *
     * @return true内存中有数据 false 内存中无数据
     */
    private boolean readFromRAM() {
        if (picsHashMap.containsKey(urlHashCode)) {
            Bitmap bitmap = picsHashMap.get(urlHashCode);
            setBitmap(bitmap);
            return true;
        }
        return false;
    }

    /**
     * 从SD卡读取图片
     *
     * @return trueSDcard中有数据 false SDcard中无数据
     */
    private boolean readFromSDcard() {
        String fileName = filePath + "/" + urlHashCode + ".JPG";
        File file = new File(fileName);
        if (!file.exists()) {
            return false;
        } else {
            Bitmap bitmap = BitmapFactory.decodeFile(fileName);
            picsHashMap.put(urlHashCode, bitmap);
            setBitmap(bitmap);
            return true;
        }

    }

    /**
     * 设置图片
     *
     * @param bitmap
     *            图片
     */
    private void setBitmap(Bitmap bitmap) {
        this.handlerBitmap = bitmap;
        handler.post(new Runnable() {
            @Override
            public void run() {
                imageView.setImageBitmap(handlerBitmap);
            }
        });
    }



}