全国统一招生热线
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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] view plaincopy
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] view plaincopy
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
StringBuffer buffer = new StringBuffer();
URL url;
try {
if (parameters != null && !parameters.isEmpty()) {
for (Map.Entry
// 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 = new byte[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 = new byte[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] view plaincopy
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
.synchronizedMap(new HashMap
public Bitmap get(String id) {
if (!cache.containsKey(id))
return null;
SoftReference
return ref.get();
}
public void put(String id, Bitmap bitmap) {
cache.put(id, new SoftReference
}
public void clear() {
cache.clear();
}
}
ImageLoader.java
[java] view plaincopy
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
.synchronizedMap(new WeakHashMap
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~
