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Android 异步加载网络图片并缓存到本地

长沙北大青鸟作者：科泰校区

摘要：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

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<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 = 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();
}
}
}
}
}