一个简单的界面：

<LinearLayout xmlns:android="//schemas.android.com/apk/res/android"

    xmlns:tools="//schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    tools:context=".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（网址）：" />

    <EditText

        android:id="@+id/et_threadCount"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="请输入开启线程数量（建议不超过5）：" />

    <Button

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:onClick="click"

        android:text="开始下载" />

    <LinearLayout

        android:id="@+id/ll_pb"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:orientation="vertical"

        ></LinearLayout></LinearLayout>

item.xml:

<?xml version="1.0" encoding="utf-8"?><ProgressBar xmlns:android="//schemas.android.com/apk/res/android"

    android:id="@+id/progressBar1"

    style="?android:attr/progressBarStyleHorizontal"

    android:layout_width="match_parent"

    android:layout_height="wrap_content" />

代码：

package org.dreamtech.download;

import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.InputStream;import java.io.InputStreamReader;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;import java.util.ArrayList;import java.util.List;

import android.os.Bundle;import android.os.Environment;import android.app.Activity;import android.view.View;import android.widget.EditText;import android.widget.LinearLayout;import android.widget.ProgressBar;

public class MainActivity extends Activity {

    private EditText et_path;

    private EditText et_threadCount;

    private LinearLayout ll_pb_layout;

    private static int runningThread;

    private String path;

    private int threadCount;

    private List<ProgressBar> pbLists;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        et_path = (EditText) findViewById(R.id.et_path);

        et_threadCount = (EditText) findViewById(R.id.et_threadCount);

        ll_pb_layout = (LinearLayout) findViewById(R.id.ll_pb);

        pbLists = new ArrayList<ProgressBar>();

    }

    public void click(View v) {

        path = et_path.getText().toString().trim();

        threadCount = Integer.parseInt(et_threadCount.getText().toString()

                .trim());

        ll_pb_layout.removeAllViews();

        pbLists.clear();

        for (int i = 0; i < threadCount; i++) {

            ProgressBar pbView = (ProgressBar) View.inflate(

                    getApplicationContext(), R.layout.item, null);

            pbLists.add(pbView);

            ll_pb_layout.addView(pbView);

        }

        new Thread() {

            public void run() {

                try {

                    URL url = new URL(path);

                    HttpURLConnection conn = (HttpURLConnection) url

                            .openConnection();

                    conn.setRequestMethod("GET");

                    conn.setConnectTimeout(5000);

                    int code = conn.getResponseCode();

                    if (code == 200) {

                        int length = conn.getContentLength();

                        runningThread = threadCount;

                        System.out.println("length:" + length);

                        RandomAccessFile rafAccessFile = new RandomAccessFile(

                                getFilename(path), "rw");

                        rafAccessFile.setLength(length);

                        int blockSize = length / threadCount;

                        for (int i = 0; i < threadCount; i++) {

                            int startIndex = i * blockSize;

                            int endIndex = (i + 1) * blockSize - 1;

                            if (i == threadCount - 1) {

                                endIndex = length - 1;

                            }

                            DownLoadThread downLoadThread = new DownLoadThread(

                                    startIndex, endIndex, i);

                            downLoadThread.start();

                        }

                    }

                } catch (Exception e) {

                    e.printStackTrace();

                }

            }

        }.start();

    }

    private class DownLoadThread extends Thread {

        private int startIndex;

        private int endIndex;

        private int threadId;

        private int PbMaxSize;

        private int pblastPosition;

        public DownLoadThread(int startIndex, int endIndex, int threadId) {

            this.startIndex = startIndex;

            this.endIndex = endIndex;

            this.threadId = threadId;

        }

        @Override

        public void run() {

            try {

                PbMaxSize = endIndex - startIndex;

                URL url = new URL(path);

                HttpURLConnection conn = (HttpURLConnection) url

                        .openConnection();

                conn.setRequestMethod("GET");

                conn.setConnectTimeout(5000);

                File file = new File(Environment.getExternalStorageDirectory()

                        .getPath()

                        + "/"

                        + getFilename(path)

                        + threadId

                        + ".txt");

                if (file.exists() && file.length() > 0) {

                    FileInputStream fis = new FileInputStream(file);

                    BufferedReader bufr = new BufferedReader(

                            new InputStreamReader(fis));

                    String lastPositionn = bufr.readLine();

                    int lastPosition = Integer.parseInt(lastPositionn);

                    pblastPosition = lastPosition - startIndex;

                    startIndex = lastPosition + 1;

                    fis.close();

                }

                conn.setRequestProperty("Range", "bytes=" + startIndex + "-"

                        + endIndex);

                int code = conn.getResponseCode();

                if (code == 206) {

                    RandomAccessFile raf = new RandomAccessFile(

                            getFilename(path), "rw");

                    raf.seek(startIndex);

                    InputStream in = conn.getInputStream();

                    int len = -1;

                    byte[] buffer = new byte[1024 * 1024];

                    int total = 0;

                    while ((len = in.read(buffer)) != -1) {

                        raf.write(buffer, 0, len);

                        total += len;

                        int currentThreadPosition = startIndex + total;

                        RandomAccessFile raff = new RandomAccessFile(

                                getFilename(path) + threadId + ".txt", "rwd");

                        raff.write(String.valueOf(currentThreadPosition)

                                .getBytes());

                        raff.close();

                        pbLists.get(threadId).setMax(PbMaxSize);

                        pbLists.get(threadId).setProgress(

                                pblastPosition + total);

                    }

                    raf.close();

                    synchronized (DownLoadThread.class) {

                        runningThread--;

                        if (runningThread == 0) {

                            for (int i = 0; i < threadCount; i++) {

                                File delteFile = new File(getFilename(path) + i

                                        + ".txt");

                                delteFile.delete();

                            }

                        }

                    }

                }

            } catch (Exception e) {

            }

        }

    }

    public String getFilename(String path) {

        int start = path.lastIndexOf("/") + 1;

        String subString = path.substring(start);

        String filename = Environment.getExternalStorageDirectory().getPath()+"/"+subString;

        return filename;

    }

}

开权限：

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

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

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