<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.example.thread.MainActivity" >    <EditText        android:id="@+id/et_path"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:hint="请输入下载路径"        android:text="下载文件" />    <Button        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:onClick="downLoad"        android:text="下载" />    <ProgressBar        android:id="@+id/pd"        style="?android:attr/progressBarStyleHorizontal"        android:layout_width="fill_parent"        android:layout_height="wrap_content" />    <TextView        android:id="@+id/tv"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="下载进度" /></LinearLayout>

package com.example.thread;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.text.TextUtils;import android.view.View;import android.widget.EditText;import android.widget.ProgressBar;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends Activity {    private static EditText et_path;    private static ProgressBar pb;    private static TextView tv;    public static int runningThread = 3;    protected static final int DOWN_LOAD_ERROR = 1;    protected static final int SERVER_ERROR = 2;    protected static final int DOWN_LOAD_FINSIH = 3;    protected static final int SHOW_TEXT = 4;    public static int currentProcess = 0;// 当前进度    private Handler handler = new Handler() {        public void handleMessage(android.os.Message msg) {            switch (msg.what) {            case DOWN_LOAD_ERROR:                Toast.makeText(getApplicationContext(), "下载失败", 0).show();                break;            case SERVER_ERROR:                Toast.makeText(getApplicationContext(), "服务器异常", 0).show();                break;            case DOWN_LOAD_FINSIH:                Toast.makeText(getApplicationContext(), "文件下载完毕", 0).show();                break;            case SHOW_TEXT:                Toast.makeText(getApplicationContext(),                        "下载进度" + pb.getProgress() * 100 / pb.getMax() + "%", 0)                        .show();                break;            default:                break;            }        };    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        et_path = (EditText) findViewById(R.id.et_path);        pb = (ProgressBar) findViewById(R.id.pd);        tv = (TextView) findViewById(R.id.tv);    }    public void downLoad(View view) {        String path = et_path.getText().toString().trim();        final int thread = 3;        if (TextUtils.isEmpty(path)) {            Toast.makeText(this, "路径读取失败", 0).show();            return;        }        new Thread() {            public void run() {                try {                    // 1:连接服务器，获取一个文件，获取文件的长度，在本地创建一个大小跟服务器文件大小                    String path = "http://dldx.csdn.net/fd.php?i=545080895071440&s=28f87f3d754b743fc81fb8b82848dcd1";                    URL url = new URL(path);                    HttpURLConnection conn = (HttpURLConnection) url                            .openConnection();                    conn.setConnectTimeout(5000);                    conn.setRequestMethod("GET");                    int code = conn.getResponseCode();                    if (code == 200) {                        // 服务器返回的数据的长度                        int length = conn.getContentLength();                        pb.setMax(length);// 设置进度条的最大值                        System.out.println("文件总长度" + length);                        // 在客户端本地创建出来一个大小跟服务器端文件大小的临时文件                        RandomAccessFile raFile = new RandomAccessFile(                                "/sdcard/spider_demo.rar", "rwd");                        // 指定创建的这个文件的长度                        raFile.setLength(length);                        raFile.close();                        // 平均每一个线程下载的文件的大小                        int blockSize = length / thread;                        for (int i = 1; i <= thread - 1; i++) {                            // 第一个线程下载的开始位置                            int startIndex = (i - 1) * blockSize;                            int endIndex = i * blockSize - 1;                            if (i == thread) {// 最后一个线程的长度要稍微长一点                                endIndex = length;                            }                            System.out.println("线程:" + i + "下载:----"                                    + startIndex + "----->" + endIndex);                            new DownLoadthread(i, startIndex, endIndex, path)                                    .start();                        }                    } else {                        Message msg = new Message();                        msg.what = SERVER_ERROR;                        handler.sendMessage(msg);                    }                } catch (Exception e) {                    e.printStackTrace();                    Message msg = new Message();                    msg.what = DOWN_LOAD_ERROR;                    handler.sendMessage(msg);                }            };        }.start();    }    /**     * 下载文件的子线程，每一个线程下载对应位置的文件     *      * */    public class DownLoadthread extends Thread {        private int threadId;        private int startIndex;        private int endIndex;        private String path;        /**         * @param threadId线程id         * @param startIndex         *            线程下载的开始位置         * @param endIndex         *            线程下载的结束位置         * @param path下载文件在服务器上的路径         *          * */        public DownLoadthread(int threadId, int startIndex, int endIndex,                String path) {            this.threadId = threadId;            this.startIndex = startIndex;            this.endIndex = endIndex;            this.path = path;        }        @Override        public void run() {            try {                // 检查是否存在记录下载的文件,如果存在读取这个文件的数据                // ----------------------替换成数据库----------------------------                File tempFile = new File("/sdcard/" + threadId + ".txt");                if (tempFile.exists() && tempFile.length() > 0) {                    FileInputStream fis = new FileInputStream(tempFile);                    byte[] temp = new byte[1024];                    int leng = fis.read(temp);                    String downloadLen = new String(temp, 0, leng);                    int downloadInt = Integer.parseInt(downloadLen);                    startIndex += downloadInt;// 修改下载的真正的开始位置                    fis.close();                }                // ----------------------替换成数据库----------------------------                URL url = new URL(path);                HttpURLConnection conn = (HttpURLConnection) url                        .openConnection();                conn.setConnectTimeout(5000);                conn.setRequestMethod("GET");                // 重要:请求服务器下载部分的文件，需要置顶文件的位置                conn.setRequestProperty("Range", "bytes=" + startIndex + "-"                        + endIndex);                // 从服务器请求全部资源,如果从服务器请求部分资源为206                int code = conn.getResponseCode();                System.out.println("code=" + code);                /*                 * if (code == 200) { InputStream is =                 * conn.getInputStream();//返回全部的资源 }                 */                InputStream is = conn.getInputStream();// 返回部分的资源                RandomAccessFile raFile = new RandomAccessFile(                        "/sdcard/spider_demo.rar", "rwd");                // 随机写文件的时候，从哪个文件开始写                raFile.seek(startIndex);                int len = 0;                byte[] buffer = new byte[1024];                int total = 0;// 已经下载的数据的长度                File file = new File("/sdcard/" + threadId + ".txt");// 作用:记录当前线程下载的数据长度                while ((len = is.read(buffer)) != -1) {                    // 如果你是固态硬盘,那么必须这样写数据                    // RandomAccessFile info = new RandomAccessFile(                    // threadId + ".txt", "rwd");                    FileOutputStream fos = new FileOutputStream(file);                    raFile.write(buffer, 0, len);                    total += len;                    fos.write(String.valueOf(total).getBytes());                    fos.close();                    // 更新进度条                    synchronized (MainActivity.this) {                        currentProcess += len;// 获取所以进程下载的总进度总进度                        pb.setProgress(currentProcess);// 更该界面上progressbar进度条的进度                        Message message = Message.obtain();// 返回一个消息实例，防止创建太多对象                        message.what = SHOW_TEXT;                        // message.obj                        handler.sendMessage(message);                        // 特殊情况，progressbar                        // progressdialog进度条对话框可以直接在子线程里面更新界面，它内部处理过了                    }                }                is.close();                raFile.close();                System.out.println("线程:" + threadId + "下载完毕了...");                File deleteFile = new File("/sdcard/" + threadId + ".txt");                deleteFile.delete();            } catch (Exception e) {                // TODO Auto-generated catch block                e.printStackTrace();            } finally {                threadFinish();            }        }        private synchronized void threadFinish() {            runningThread--;            if (runningThread == 0) {                for (int i = 1; i <= 3; i++) {                    File file = new File("/sdcard/" + i + ".txt");                    file.delete();                }                System.out.println("文件下载完毕,删除所以的下载记录");                Message msg = new Message();                msg.what = DOWN_LOAD_FINSIH;                handler.sendMessage(msg);            }        }    }}

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.thread"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk        android:minSdkVersion="8"        android:targetSdkVersion="21" />    <uses-permission android:name="android.permission.INTERNET"/>    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>    <application        android:allowBackup="true"        android:icon="@drawable/ic_launcher"        android:label="@string/app_name"        android:theme="@style/AppTheme" >        <activity            android:name=".MainActivity"            android:label="@string/app_name" >            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>