Android读取网络图片并缓存

先看一下代码：

package com.example.testjsonpic;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import android.os.Bundle;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.widget.ImageView;

public class MainActivity extends Activity
{

	public static final String DATA="http://www.baidu.com/img/baidu_sylogo1.gif";
	public static final String DATA_="http://x.limgs.cn/f2/c1/up201301/342a0432638526a1c79471d86f3d7192.jpg";
	ImageView image = null,image02 = null;
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		initsView();
	}
	public void initsView()
	{
		//通过第一种方法获取
		this.image = (ImageView) findViewById(R.id.image);
		image.setImageBitmap(getHttpBitmap(DATA));
		
		//通过第二种方法获取
		this.image02 = (ImageView) findViewById(R.id.image02);
		image02.setImageBitmap(getBitmap(DATA_));
		
	}
	
	//第一种方法
	public Bitmap getHttpBitmap(String data)
	{
		Bitmap bitmap = null;
		try
		{
			//初始化一个URL对象
			URL url = new URL(data);
			//获得HTTPConnection网络连接对象
			HttpURLConnection connection = (HttpURLConnection) url.openConnection();
			connection.setConnectTimeout(5*1000);
			connection.setDoInput(true);
			connection.connect();
			//得到输入流
			InputStream is = connection.getInputStream();
			Log.i("TAG", "*********inputstream**"+is);
			bitmap = BitmapFactory.decodeStream(is);
			Log.i("TAG", "*********bitmap****"+bitmap);
			//关闭输入流
			is.close();
			//关闭连接
			connection.disconnect();
		} catch (Exception e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		return bitmap;
	}
	
	//第二种方法
	public Bitmap getBitmap(String s)
	{
		Bitmap bitmap = null;
		try
		{
			URL url = new URL(s);
			bitmap = BitmapFactory.decodeStream(url.openStream());
		} catch (Exception e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		return bitmap;
	}

}

需要运行，还要在AndroidManifest.xml中加入网络权限。

<uses-permission android:name="android.permission.INTERNET"/>

发现在4.0以上版本的模拟器中，用HttpUrlConnection.getInputStream()，也就是第一种方法，不能运行解析出图片，会报错，而通过URL.openStream()方法则没有问题。原因在于，4.0以后的版本要求必须开一个线程来执行网络数据请求，不能直接写入主线程了，所以改代码如下：

package com.itehema.NetText;

import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.graphics.Bitmap;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;

public class MainActivity extends Activity implements OnClickListener{

	private EditText pathText;
	private ImageView Image;
	private NetService service;
	private Button goButton;
	private Handler handler = new Handler();

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		String path="http://www.baidu.com/img/baidu_sylogo1.gif"; 
		pathText = (EditText) this.findViewById(R.id.pathEdit);
		pathText.setText(path);
		Image = (ImageView) this.findViewById(R.id.imageView1);
		service = new NetService();
		goButton = (Button) this.findViewById(R.id.pathGo);
		goButton.setOnClickListener(this);
	}
	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		new Thread(){
				public void run() {
					try {
						String path = pathText.getText().toString().trim();
						final Bitmap image = service.getImage(path);
						handler.post(new Runnable() {	
							@Override
							public void run() {
								// TODO Auto-generated method stub
								Image.setImageBitmap(image);
							}
						});
					} catch (Exception e) {
						// TODO: handle exception
					}
				}
		}.start();
	}
}

package com.itehema.NetText;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class NetService {

	public Bitmap getImage(String path) throws Exception {
		URL url = new URL(path);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		File file = new File("/mnt/sdcard/" + URLEncoder.encode(path, "UTF-8"));
		if (file.exists())									// 判断是否有缓存文件
			conn.setIfModifiedSince(file.lastModified());	// 如果文件存在, 发送最后修改时间
		
		int code = conn.getResponseCode();
		System.out.println(code);
		if (code == 200) {
			InputStream in = conn.getInputStream();							// 获取输入流
			ByteArrayOutputStream out = new ByteArrayOutputStream();		
			byte[] buffer = new byte[8192];
			int length;
			while ((length = in.read(buffer)) != -1)						// 读取数据
				out.write(buffer, 0, length);								// 写到内存
			in.close();
			out.close();
			byte[] data = out.toByteArray();
			Bitmap image = BitmapFactory.decodeByteArray(data, 0, data.length);		// 把数据解码为图片
			FileOutputStream fos = new FileOutputStream(file);	
			fos.write(data);	// 把图片缓存到本地
			fos.close();
			return image;
		}
		else if (code == 304) {
			return BitmapFactory.decodeFile(file.getAbsolutePath());	// 读取本地文件
		}
		throw new RuntimeException("网络异常: " + code);
	}
}