Android 异步加载网络图片并缓存到本地 软引用 学习分享

http://software.intel.com/zh-cn/blogs/2014/02/20/android/?utm_campaign=CSDN&utm_source=intel.csdn.net&utm_medium=Link&utm_content=others-ruanyinyong

迪 王. 于 星期四, 20/02/2014 - 21:36 提交

在android应用开发的时候，加载网络图片是一个非常重要的部分，很多图片不可能放在本地，所以就必须要从服务器或者网络读取图片。

软引用是一个现在非常流行的方法，用户体验比较好，不用每次都需要从网络下载图片，如果下载后就存到本地，下次读取时首先查看本地有没有，如果没有再从网络读取。

记得2月份在和爱奇艺公司的项目总监一起搞联通的OTT盒子的时候他就提了一下软引用，奇艺做的手机客户端就是采用这种方法，所以你会发现奇艺客户端占用很大的空间，下面就分享一下异步加载网络图片的方法吧。

FileCache.java

[java]
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import java.io.File; 
import android.content.Context; 
 
public class FileCache { 

 
    private File cacheDir; 
 
    public FileCache(Context context) { 
        // 找一个用来缓存图片的路径 
        if (android.os.Environment.getExternalStorageState().equals( 
                android.os.Environment.MEDIA_MOUNTED)) 
            cacheDir = new File(android.os.Environment.getExternalStorageDirectory(), 
                    "文件夹名称"); 
        else 
            cacheDir = context.getCacheDir(); 
        if (!cacheDir.exists()) 
            cacheDir.mkdirs(); 
    } 
 
    public File getFile(String url) { 
        String filename = String.valueOf(url.hashCode()); 
        File f = new File(cacheDir, filename); 

        return f; 
    } 
 
    public void clear() { 
        File[] files = cacheDir.listFiles(); 
        if (files == null) 
            return; 
        for (File f : files) 
            f.delete(); 
    } 
 
} 

HttpUtil.java

[java]
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import java.io.ByteArrayOutputStream; 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import java.io.UnsupportedEncodingException; 

import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.ProtocolException; 
import java.net.URL; 
import java.net.URLEncoder; 
import java.util.Map; 
 
/**
* Http 请求工具类
*
* @author Scorpio.Liu
*
*/ 
public class HttpUtil { 

 
    /**
     * 获取响应字符串
     *
     * @param path
     *            路径
     * @param parameters
     *            参数
     * @return 响应字符串
     */ 
    public static String getResponseStr(String path, Map<String, String> parameters) { 
        StringBuffer buffer = new StringBuffer(); 

        URL url; 
        try { 
            if (parameters != null && !parameters.isEmpty()) { 
                for (Map.Entry<String, String> entry : parameters.entrySet()) { 
                    // 完成转码操作 
                    buffer.append(entry.getKey()).append("=") 
                            .append(URLEncoder.encode(entry.getValue(),"UTF-8")).append("&"); 

                } 
                buffer.deleteCharAt(buffer.length() - 1); 
            } 
            url = new URL(path); 
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); 
            urlConnection.setConnectTimeout(3000); 

            urlConnection.setRequestMethod("POST"); 
            urlConnection.setDoInput(true);// 表示从服务器获取数据 
            urlConnection.setDoOutput(true);// 表示向服务器写数据 
            // 获得上传信息的字节大小以及长度 
            byte[] mydata = buffer.toString().getBytes(); 
            // 表示设置请求体的类型是文本类型 
            urlConnection.setRequestProperty("Content-Type", 
                    "application/x-www-form-urlencoded"); 
            urlConnection.setRequestProperty("Content-Length", String.valueOf(mydata.length)); 
            // 获得输出流,向服务器输出数据 
            OutputStream outputStream = urlConnection.getOutputStream(); 
            outputStream.write(mydata, 0, mydata.length); 
            outputStream.close(); 
            int responseCode = urlConnection.getResponseCode(); 
            if (responseCode == 200) { 
                return changeInputStream(urlConnection.getInputStream()); 
            } 
        } catch (UnsupportedEncodingException e) { 

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

            e.printStackTrace(); 
        } catch (ProtocolException e) { 
            e.printStackTrace(); 
        } catch (IOException e) { 
            e.printStackTrace(); 
        } 
        return null; 

    } 
 
    private static String changeInputStream(InputStream inputStream) { 
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); 
        byte[] data = new
byte[1024]; 
        int len = 0; 

        String result = ""; 
        if (inputStream != null) { 
            try { 
                while ((len = inputStream.read(data)) != -1) { 
                    outputStream.write(data, 0, len); 
                } 
                result = new String(outputStream.toByteArray(),"UTF-8"); 

            } catch (IOException e) { 
                e.printStackTrace(); 
            } 
        } 
        return result; 
    } 
 
    public static InputStream getInputStream(String path) { 
        URL url; 
        try { 
            url = new URL(path); 
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); 
            urlConnection.setConnectTimeout(3000); 

            urlConnection.setRequestMethod("GET"); 

            urlConnection.setDoInput(true);// 表示从服务器获取数据 
            urlConnection.connect(); 
            if (urlConnection.getResponseCode() ==
200) 
                return urlConnection.getInputStream(); 
        } catch (MalformedURLException e) { 

            // TODO Auto-generated catch block 

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

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

            e.printStackTrace(); 
        } 
        return null; 

    } 
 
    public static byte[] readStream(InputStream inStream)throws Exception { 

        ByteArrayOutputStream outSteam = new ByteArrayOutputStream(); 
        byte[] buffer = newbyte[1024]; 

        int len = -1; 

        while ((len = inStream.read(buffer)) != -1) { 
            outSteam.write(buffer, 0, len); 

 
        } 
        outSteam.close(); 
        inStream.close(); 
        return outSteam.toByteArray(); 
    } 
 
    public static void CopyStream(String url, File f) { 
        FileOutputStream fileOutputStream = null; 

        InputStream inputStream = null; 
        try { 
            inputStream = getInputStream(url); 
            byte[] data = newbyte[1024]; 

            int len = 0; 

            fileOutputStream = new FileOutputStream(f); 
            while ((len = inputStream.read(data)) != -1) { 
                fileOutputStream.write(data, 0, len); 
            } 
        } catch (FileNotFoundException e) { 

            e.printStackTrace(); 
        } catch (IOException e) { 
            e.printStackTrace(); 
        } finally { 
            if (inputStream != null) { 
                try { 
                    inputStream.close(); 
                } catch (IOException e) { 
                    e.printStackTrace(); 
                } 
            } 
            if (fileOutputStream != null) { 
                try { 
                    fileOutputStream.close(); 
                } catch (IOException e) { 
                    e.printStackTrace(); 
                } 
            } 
        } 
    } 
 
} 

MemoryCache.java

[java]
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import java.lang.ref.SoftReference; 
import java.util.Collections; 
import java.util.HashMap; 
import java.util.Map; 
import android.graphics.Bitmap; 
 
public class MemoryCache { 
    private Map<String, SoftReference<Bitmap>> cache = Collections 
            .synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());// 软引用 
 
    public Bitmap get(String id) { 
        if (!cache.containsKey(id)) 
            return null; 

        SoftReference<Bitmap> ref = cache.get(id); 
        return ref.get(); 
    } 
 
    public void put(String id, Bitmap bitmap) { 
        cache.put(id, new SoftReference<Bitmap>(bitmap)); 
    } 
 
    public void clear() { 
        cache.clear(); 
    } 
} 

ImageLoader.java

[java]
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import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.UnsupportedEncodingException; 

import java.net.URLEncoder; 
import java.util.Collections; 
import java.util.Map; 
import java.util.WeakHashMap; 
import java.util.concurrent.ExecutorService; 

import java.util.concurrent.Executors; 
import android.app.Activity; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.drawable.BitmapDrawable; 

import android.widget.ImageView; 
 
public class ImageLoader { 
 
    private MemoryCache memoryCache = new MemoryCache(); 
    private FileCache fileCache; 
    private Map<ImageView, String> imageViews = Collections 
            .synchronizedMap(new WeakHashMap<ImageView, String>()); 
    private ExecutorService executorService; 

    private boolean isSrc; 
 
    /**
     * @param context
     *            上下文对象
     * @param flag
     *            true为source资源，false为background资源

     */ 
    public ImageLoader(Context context, boolean flag) { 
        fileCache = new FileCache(context); 

        executorService = Executors.newFixedThreadPool(5); 
        isSrc = flag; 
    } 
 
    final int stub_id = R.drawable.ic_launcher; 
 
    public void DisplayImage(String url, ImageView imageView) { 
        String u1 = url.substring(0, url.lastIndexOf("/") +1); 

        String u2 = url.substring(url.lastIndexOf("/") +1); 

        try { 
            u2 = URLEncoder.encode(u2, "UTF-8"); 

        } catch (UnsupportedEncodingException e) { 

            e.printStackTrace(); 
        } 
        url = u1 + u2; 
        imageViews.put(imageView, url); 
        Bitmap bitmap = memoryCache.get(url); 
        if (bitmap != null) { 
            if (isSrc) 
                imageView.setImageBitmap(bitmap); 
            else 
                imageView.setBackgroundDrawable(new BitmapDrawable(bitmap)); 
        } else { 
            queuePhoto(url, imageView); 
            if (isSrc) 
                imageView.setImageResource(stub_id); 
            else 
                imageView.setBackgroundResource(stub_id); 
        } 
    } 
 
    private void queuePhoto(String url, ImageView imageView) { 
        PhotoToLoad p = new PhotoToLoad(url, imageView); 
        executorService.submit(new PhotosLoader(p)); 
    } 
 
    private Bitmap getBitmap(String url) { 
        try { 
            File f = fileCache.getFile(url); 
            // 从sd卡 
            Bitmap b = onDecodeFile(f); 
            if (b != null) 
                return b; 
            // 从网络 
            Bitmap bitmap = null; 
            System.out.println("ImageLoader-->download"); 
            HttpUtil.CopyStream(url, f); 
            bitmap = onDecodeFile(f); 
 
            return bitmap; 
        } catch (Exception ex) { 
            ex.printStackTrace(); 
            return null; 

        } 
    } 
 
    public Bitmap onDecodeFile(File f) { 
        try { 
            return BitmapFactory.decodeStream(new FileInputStream(f)); 
        } catch (FileNotFoundException e) { 

            // TODO Auto-generated catch block 

            e.printStackTrace(); 
        } 
        return null; 

    } 
 
    /**
     * 解码图像用来减少内存消耗
     *
     * @param f
     * @return
     */ 
    public Bitmap decodeFile(File f) { 
        try { 
            // 解码图像大小 
            BitmapFactory.Options o = new BitmapFactory.Options(); 
            o.inJustDecodeBounds = true; 
            BitmapFactory.decodeStream(new FileInputStream(f),null, o); 

            // 找到正确的刻度值，它应该是2的幂。 
            final int REQUIRED_SIZE =70; 

            int width_tmp = o.outWidth, height_tmp = o.outHeight; 
            int scale = 1; 
            while (true) { 
                if (width_tmp / 2 < REQUIRED_SIZE || height_tmp /2 < REQUIRED_SIZE) 

                    break; 
                width_tmp /= 2; 
                height_tmp /= 2; 
                scale *= 2; 
            } 
            BitmapFactory.Options o2 = new BitmapFactory.Options(); 
            o2.inSampleSize = scale; 
            return BitmapFactory.decodeStream(new FileInputStream(f),null, o2); 

        } catch (FileNotFoundException e) { 

        } 
        return null; 

    } 
 
    /**
     * 任务队列
     *
     * @author Scorpio.Liu
     *
     */ 
    private class PhotoToLoad { 
        public String url; 
        public ImageView imageView; 
 
        public PhotoToLoad(String u, ImageView i) { 
            url = u; 
            imageView = i; 
        } 
    } 
 
    class PhotosLoader implements Runnable { 
        PhotoToLoad photoToLoad; 
 
        PhotosLoader(PhotoToLoad photoToLoad) { 
            this.photoToLoad = photoToLoad; 

        } 
 
        @Override 
        public void run() { 
            if (imageViewReused(photoToLoad)) 

                return; 
            Bitmap bmp = getBitmap(photoToLoad.url); 
            memoryCache.put(photoToLoad.url, bmp); 
            if (imageViewReused(photoToLoad)) 

                return; 
            BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad); 
            Activity a = (Activity) photoToLoad.imageView.getContext(); 
            a.runOnUiThread(bd); 
        } 
    } 
 
    boolean imageViewReused(PhotoToLoad photoToLoad) { 
        String tag = imageViews.get(photoToLoad.imageView); 
        if (tag == null || !tag.equals(photoToLoad.url)) 
            return true; 

        return false; 

    } 
 
    /**
     * 显示位图在UI线程
     *
     * @author Scorpio.Liu
     *
     */ 
    class BitmapDisplayer implements Runnable { 
        Bitmap bitmap; 
        PhotoToLoad photoToLoad; 
 
        public BitmapDisplayer(Bitmap b, PhotoToLoad p) { 
            bitmap = b; 
            photoToLoad = p; 
        } 
 
        public void run() { 
            if (imageViewReused(photoToLoad)) 

                return; 
            if (bitmap != null) { 
                if (isSrc) 
                    photoToLoad.imageView.setImageBitmap(bitmap); 

                else 
                    photoToLoad.imageView.setBackgroundDrawable(new BitmapDrawable(bitmap)); 
            } else { 
                if (isSrc) 
                    photoToLoad.imageView.setImageResource(stub_id); 

                else 
                    photoToLoad.imageView.setBackgroundResource(stub_id); 
            } 
        } 
    } 
 
    public void clearCache() { 
        memoryCache.clear(); 
        fileCache.clear(); 
    } 
 
} 

使用的时候用ImageLoader这个类就ok了，很方便~

如需更全面地了解编译器优化，请参阅优化注意事项。