在安卓中，可以直接用java的java.net.URL包访问网络下载数据。不同的是，安卓程序需要权限，需要在AndroidManifest.xml文件中声明权限

<!-- 网络权限 -->
   <uses-permission android:name="android.permission.INTERNET"/>
   <!-- 操作sd卡权限 -->
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

不过有个需要注意的是，我使用的是最新的adt安卓开发集成eclipse的安装包，在使用网络服务的时候，处理网络请求的代码，不能在主线程中进行，不然安卓会提示错误。

 

但是，有些组件设置值，他必须是在主线程的循环中，才可以。

Looper loop = Looper.getMainLooper();
handler = new Handler(loop){
    @Override
    public void handleMessage(Message msg) {
        // TODO Auto-generated method stub
        super.handleMessage(msg);
        switch (msg.what) {
            case SETTEXT:
                //主线程ui更新text值
                text.setText(msg.obj.toString());
                break;
        }
    }
};

download.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View arg0) {
        //新线程下载
        new Thread(new Runnable() {
            @Override
            public void run() {
                //新建一个下载
                Download load = new Download(url);
                String value = load.downloadAsString();
                Message msg = handler.obtainMessage();
                msg.obj = value;
                msg.what = SETTEXT;
                msg.sendToTarget();
            }
        }).start();
    }
});

Looper loop = Looper.getMainLooper();handler = new Handler(loop){	@Override	public void handleMessage(Message msg) {		// TODO Auto-generated method stub		super.handleMessage(msg);		switch (msg.what) {			case SETTEXT:				//主线程ui更新text值				text.setText(msg.obj.toString());				break;		}	}};		download.setOnClickListener(new View.OnClickListener() {	@Override	public void onClick(View arg0) {		//新线程下载		new Thread(new Runnable() {			@Override			public void run() {				//新建一个下载				Download load = new Download(url);				String value = load.downloadAsString();				Message msg = handler.obtainMessage();				msg.obj = value;				msg.what = SETTEXT;				msg.sendToTarget();			}		}).start();	}});

Download类：

 

package com.example.org.suju.download;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

import android.os.Environment;
import android.util.Log;


public class Download {
    /** 连接url */
    private String urlstr;
    /** sd卡目录路径 */
    private String sdcard;
    /** http连接管理类 */
    private HttpURLConnection urlcon;

    public Download(String url)
    {
        this.urlstr = url;
        //获取设备sd卡目录
        this.sdcard = Environment.getExternalStorageDirectory() + "/";
        urlcon = getConnection();
    }

    /*
     * 读取网络文本
     */
    public String downloadAsString()
    {
        StringBuilder sb = new StringBuilder();
        String temp = null;
        try {
            InputStream is = urlcon.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            while ((temp = br.readLine()) != null) {
                sb.append(temp);
            }
            br.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sb.toString();
    }

    /*
     * 获取http连接处理类HttpURLConnection
     */
    private HttpURLConnection getConnection()
    {
        URL url;
        HttpURLConnection urlcon = null;
        try {
            url = new URL(urlstr);
            urlcon = (HttpURLConnection) url.openConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return urlcon;
    }

    /*
     * 获取连接文件长度。
     */
    public int getLength()
    {
        return urlcon.getContentLength();
    }

    /*
     * 写文件到sd卡 demo
     * 前提需要设置模拟器sd卡容量，否则会引发EACCES异常
     * 先创建文件夹，在创建文件
     */
    public int down2sd(String dir, String filename, downhandler handler)
    {
        StringBuilder sb = new StringBuilder(sdcard)
                            .append(dir);
        File file = new File(sb.toString());
        if (!file.exists()) {
            file.mkdirs();
            //创建文件夹
            Log.d("log", sb.toString());
        }
        //获取文件全名
        sb.append(filename);
        file = new File(sb.toString());

        FileOutputStream fos = null;
        try {
            InputStream is = urlcon.getInputStream();
            //创建文件
            file.createNewFile();
            fos = new FileOutputStream(file);
            byte[] buf = new byte[1024];
            while ((is.read(buf)) != -1) {
                fos.write(buf);
                //同步更新数据
                handler.setSize(buf.length);
            }
            is.close();
        } catch (Exception e) {
            return 0;
        } finally {
            try {
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return 1;
    }

    /*
     * 内部回调接口类
     */
    public abstract class downhandler
    {
        public abstract void setSize(int size);
    }
}

package com.example.org.suju.download;import java.io.BufferedReader;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.net.HttpURLConnection;import java.net.URL;import android.os.Environment;import android.util.Log;public class Download {	/** 连接url */	private String urlstr;	/** sd卡目录路径 */	private String sdcard;	/** http连接管理类 */	private HttpURLConnection urlcon;		public Download(String url)	{		this.urlstr = url;		//获取设备sd卡目录		this.sdcard = Environment.getExternalStorageDirectory() + "/";		urlcon = getConnection();	}		/*	 * 读取网络文本	 */	public String downloadAsString()	{		StringBuilder sb = new StringBuilder();		String temp = null;		try {			InputStream is = urlcon.getInputStream();			BufferedReader br = new BufferedReader(new InputStreamReader(is));			while ((temp = br.readLine()) != null) {				sb.append(temp);			}			br.close();		} catch (Exception e) {			e.printStackTrace();		}		return sb.toString();	}		/*	 * 获取http连接处理类HttpURLConnection	 */	private HttpURLConnection getConnection()	{		URL url;		HttpURLConnection urlcon = null;		try {			url = new URL(urlstr);			urlcon = (HttpURLConnection) url.openConnection();		} catch (Exception e) {			e.printStackTrace();		}		return urlcon;	}		/*	 * 获取连接文件长度。	 */	public int getLength()	{		return urlcon.getContentLength();	}		/*	 * 写文件到sd卡 demo	 * 前提需要设置模拟器sd卡容量，否则会引发EACCES异常	 * 先创建文件夹，在创建文件	 */	public int down2sd(String dir, String filename, downhandler handler)	{		StringBuilder sb = new StringBuilder(sdcard)							.append(dir);		File file = new File(sb.toString());		if (!file.exists()) {			file.mkdirs();			//创建文件夹			Log.d("log", sb.toString());		}		//获取文件全名		sb.append(filename);		file = new File(sb.toString());				FileOutputStream fos = null;		try {			InputStream is = urlcon.getInputStream();			//创建文件			file.createNewFile();			fos = new FileOutputStream(file);			byte[] buf = new byte[1024];			while ((is.read(buf)) != -1) {				fos.write(buf);				//同步更新数据				handler.setSize(buf.length);			}			is.close();		} catch (Exception e) {			return 0;		} finally {			try {				fos.close();			} catch (IOException e) {				e.printStackTrace();			}		}		return 1;	}		/*	 * 内部回调接口类	 */	public abstract class downhandler	{		public abstract void setSize(int size);	}}

线程下载提示Activity：

 

用一个线程循环处理网络下载，并使用下载类回调函数，发送处理消息给主线程消息处理方法，同步更新滚动条值。

      @Override
rotected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.download);

text = (TextView) findViewById(R.id.label);
load = (ProgressBar) findViewById(R.id.load);

//获取传递的Intent的Bundle的url键值
final String url = getIntent().getExtras().getString("url");

final Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        //这里就一条消息
        int pro = load.getProgress() + msg.arg1;
        load.setProgress(pro);
        text.setText(Integer.toString(pro));
        if (pro >= load.getMax()) {
            finish();   //结束下载进度框
        }
    }
};

@Override	protected void onCreate(Bundle savedInstanceState) {		// TODO Auto-generated method stub		super.onCreate(savedInstanceState);		setContentView(R.layout.download);				text = (TextView) findViewById(R.id.label);		load = (ProgressBar) findViewById(R.id.load);		//获取传递的Intent的Bundle的url键值		final String url = getIntent().getExtras().getString("url");				final Handler handler = new Handler(){			@Override			public void handleMessage(Message msg) {				super.handleMessage(msg);				//这里就一条消息				int pro = load.getProgress() + msg.arg1;				load.setProgress(pro);				text.setText(Integer.toString(pro));				if (pro >= load.getMax()) {					finish();	//结束下载进度框				}			}		};

new Thread(new Runnable() {
    @Override
    public void run() {
        //另起线程执行下载，安卓最新sdk规范，网络操作不能再主线程。
        Download l = new Download(url);
        load.setMax(l.getLength());

        /**
         * 下载文件到sd卡，虚拟设备必须要开始设置sd卡容量
         * downhandler是Download的内部类，作为回调接口实时显示下载数据
         */
        int status = l.down2sd("downtemp/", "1.ddd", l.new downhandler() {
            @Override
            public void setSize(int size) {
                Message msg = handler.obtainMessage();
                msg.arg1 = size;
                msg.sendToTarget();
                Log.d("log", Integer.toString(size));
            }
        });
        //log输出
        Log.d("log", Integer.toString(status));

    }
}).start();

new Thread(new Runnable() {			@Override			public void run() {				//另起线程执行下载，安卓最新sdk规范，网络操作不能再主线程。				Download l = new Download(url);				load.setMax(l.getLength());								/**				 * 下载文件到sd卡，虚拟设备必须要开始设置sd卡容量				 * downhandler是Download的内部类，作为回调接口实时显示下载数据				 */				int status = l.down2sd("downtemp/", "1.ddd", l.new downhandler() {					@Override					public void setSize(int size) {						Message msg = handler.obtainMessage();						msg.arg1 = size;						msg.sendToTarget();						Log.d("log", Integer.toString(size));					}				});				//log输出				Log.d("log", Integer.toString(status));							}		}).start();	}

 

 

对话框模式的Activity需要设置一个属性android:theme。

<activity
android:name="com.example.org.suju.download.DownloadActivity"
android:theme="@android:style/Theme.Dialog"
            ></activity>

使用一个按钮启动下载对话框Activity，并传递数据

 

down2sd.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View arg0) {
        Intent intent = new Intent();
        intent.setClass(MainActivity.this, DownloadActivity.class);
        Bundle bundle = new Bundle();
        bundle.putString("url", urlstr.getText().toString());
        intent.putExtras(bundle);
        startActivity(intent);
    }
});

down2sd.setOnClickListener(new View.OnClickListener() {	@Override	public void onClick(View arg0) {		Intent intent = new Intent();		intent.setClass(MainActivity.this, DownloadActivity.class);		Bundle bundle = new Bundle();		bundle.putString("url", urlstr.getText().toString());		intent.putExtras(bundle);		startActivity(intent);	}});

 

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