从网络下载的图片加缓存功能

package com.example.getimg;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

import android.os.Bundle;
import android.os.Message;
import android.view.View;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;

import java.net.URL;

public class MyActivity extends Activity {
/**
* Called when the activity is first created.
*/
private ImageView img;
android.os.Handler handler = new android.os.Handler(){
//用handlemessage来更新ui线程
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 0:

img.setImageBitmap((Bitmap) msg.obj);
break;
case 1:
Toast.makeText(MyActivity.this,"没有响应",Toast.LENGTH_SHORT).show();
break;
}

}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
img = (ImageView) findViewById(R.id.img);

findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
final String path = "http://192.168.21.1:8080/ok/point_one.png";
final File file = new File(getCacheDir(),getFeilName(path));
@Override
public void onClick(View view) {
//判断缓存是否存在，因为这个是在主线程里，可以直接设置
if(file.exists()){
Toast.makeText(MyActivity.this,"从缓存读取",Toast.LENGTH_SHORT).show();
Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
img.setImageBitmap(bitmap);
}
else{
System.out.print("从网络中读取");
//创建子线程来链接网络，并且使用get方法下载图片
Thread thread = new Thread(){
@Override
public void run() {
{

//uri
try {
URL url = new URL(path);
//获得链接
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
//设置参数
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setReadTimeout(5000);
//正式链接
conn.connect();
if(conn.getResponseCode()==200){
InputStream is = conn.getInputStream();
//把InputStream通过bitmap转化成图片
//   Bitmap bitmap = BitmapFactory.decodeStream(is);

//把从网络中读取的图片放到缓存中
FileOutputStream fos = new FileOutputStream(file);
byte[] b = new byte[1024];
int len = 0;
while((len=is.read(b))!=-1){
fos.write(b,0,len);
}
//从本地读取bitmap
Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
//创建消息对象
Message msg = new Message();
msg.what = 0;
//传递bitmap所需要的数据,如果是多个数据可以传递数组啊！
msg.obj = bitmap;
//给消息队列发送消息
handler.sendMessage(msg);

}else{
//一般不会new，这样会节省内存
Message msg = handler.obtainMessage();
//传递参数为了判断是谁发送的message
msg.what = 1;
handler.sendMessage(msg);

}

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

};
thread.start();

}

}
});
}

private String getFeilName(String path){
int index = path.lastIndexOf("/");
return path.substring(index + 1);
}
}