文件下载（实现断点续传） Android
文件下载（实现断点续传） Android 希望给代码，【有用的多给分。。。。】

[解决办法]
下载时，记录一下下载了的数据，然后下次从哪里再开始下载就行了。

以下代码就可以从文件的第4096字节的位置开始下载。

URL url = new URL("http://target.com/test.zip");
HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection();

//设置User-Agent
httpConnection.setRequestProperty("User-Agent","NetFox");
//设置断点续传的开始位置
httpConnection.setRequestProperty("RANGE","bytes=4096");
//获得输入流
InputStream input = httpConnection.getInputStream();





[解决办法]
应该就是楼上的原理，好像在哪个论坛有人发过源码的，可以搜搜看
[解决办法]
http://www.goprogram.org/blog/?p=66
[解决办法]
我原封不动的复制的。。。

Java code

import java.io.File;import java.net.URL;import java.net.URLConnection;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.os.Handler;import android.os.Message;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.ProgressBar;import android.widget.TextView;/** *  Copyright (C) 2010 ideasandroid *  演示android多线程下载 *  欢迎访问http://www.ideasandroid.com *  让程序开发不再那么神秘 */public class FileDownloadDemo extends Activity {     private EditText downloadUrl;    private EditText downloadFileName;    private EditText downloadThreadNum;    private Button downloadBt;    private ProgressBar downloadProgressBar;    private TextView progressMessage;    private int downloadedSize = 0;    private int fileSize = 0;     @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);         downloadUrl = (EditText) findViewById(R.id.downloadUrl);        downloadFileName = (EditText) findViewById(R.id.downloadFileName);        downloadThreadNum = (EditText) findViewById(R.id.downloadThreadNum);        progressMessage = (TextView) findViewById(R.id.progressMessage);        downloadBt = (Button) findViewById(R.id.downloadBt);        downloadProgressBar = (ProgressBar) findViewById(R.id.downloadProgressBar);        downloadProgressBar.setVisibility(View.VISIBLE);        downloadProgressBar.setMax(100);        downloadProgressBar.setProgress(0);        downloadBt.setOnClickListener(new OnClickListener() {            public void onClick(View v) {                download();            }        });    }     private void download() {        // 获取SD卡目录        String dowloadDir = Environment.getExternalStorageDirectory()                + "/ideasdownload/";        File file = new File(dowloadDir);        //创建下载目录        if (!file.exists()) {            file.mkdirs();        }         //读取下载线程数，如果为空，则单线程下载        int downloadTN = Integer.valueOf("".equals(downloadThreadNum.getText()                .toString()) ? "1" : downloadThreadNum.getText().toString());        //如果下载文件名为空则获取Url尾为文件名        int fileNameStart = downloadUrl.getText().toString().lastIndexOf("/");        String fileName = "".equals(downloadFileName.getText().toString()) ? downloadUrl                .getText().toString().substring(fileNameStart)                : downloadFileName.getText().toString();        //开始下载前把下载按钮设置为不可用        downloadBt.setClickable(false);        //进度条设为0        downloadProgressBar.setProgress(0);        //启动文件下载线程        new downloadTask(downloadUrl.getText().toString(), Integer                .valueOf(downloadTN), dowloadDir + fileName).start();    }     Handler handler = new Handler() {        @Override        public void handleMessage(Message msg) {            //当收到更新视图消息时，计算已完成下载百分比，同时更新进度条信息            int progress = (Double.valueOf((downloadedSize * 1.0 / fileSize * 100))).intValue();            if (progress == 100) {                downloadBt.setClickable(true);                progressMessage.setText("下载完成！");            } else {                progressMessage.setText("当前进度:" + progress + "%");            }            downloadProgressBar.setProgress(progress);        }     };     /**     * @author ideasandroid     * 主下载线程     */    public class downloadTask extends Thread {        private int blockSize, downloadSizeMore;        private int threadNum = 5;        String urlStr, threadNo, fileName;         public downloadTask(String urlStr, int threadNum, String fileName) {            this.urlStr = urlStr;            this.threadNum = threadNum;            this.fileName = fileName;        }         @Override        public void run() {            FileDownloadThread[] fds = new FileDownloadThread[threadNum];            try {                URL url = new URL(urlStr);                URLConnection conn = url.openConnection();                //获取下载文件的总大小                fileSize = conn.getContentLength();                //计算每个线程要下载的数据量                blockSize = fileSize / threadNum;                // 解决整除后百分比计算误差                downloadSizeMore = (fileSize % threadNum);                File file = new File(fileName);                for (int i = 0; i < threadNum; i++) {                    //启动线程，分别下载自己需要下载的部分                    FileDownloadThread fdt = new FileDownloadThread(url, file,                            i * blockSize, (i + 1) * blockSize - 1);                    fdt.setName("Thread" + i);                    fdt.start();                    fds[i] = fdt;                }                boolean finished = false;                while (!finished) {                    // 先把整除的余数搞定                    downloadedSize = downloadSizeMore;                    finished = true;                    for (int i = 0; i < fds.length; i++) {                        downloadedSize += fds[i].getDownloadSize();                        if (!fds[i].isFinished()) {                            finished = false;                        }                    }                    //通知handler去更新视图组件                    handler.sendEmptyMessage(0);                    //休息1秒后再读取下载进度                    sleep(1000);                }            } catch (Exception e) {             }         }    }}