一.建立实体类

1.文件实体类

package com.example.zjw.myapplication.dao;

import java.io.Serializable;

/**
 * 预下载文件实体类
 * Created by Administrator on 2016/6/20.
 */
public class FileInfo implements Serializable {
    //文件id
    private int id;
    //文件下载地址
    private String url;
    //文件名
    private String name;
    //文件长度
    private int length;
    //文件下载完成进度
    private int finished;

    public FileInfo(){}
    public FileInfo(int id, String url, String name, int length, int finished) {
        this.id = id;
        this.url = url;
        this.name = name;
        this.length = length;
        this.finished = finished;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getLength() {
        return length;
    }

    public void setLength(int length) {
        this.length = length;
    }

    public int getFinished() {
        return finished;
    }

    public void setFinished(int finished) {
        this.finished = finished;
    }

    @Override
    public String toString() {
        return "FileInfo{" +
                "id=" + id +
                ", url='" + url + '\'' +
                ", name='" + name + '\'' +
                ", length=" + length +
                ", finished=" + finished +
                '}';
    }
}

2.线程实体类

package com.example.zjw.myapplication.dao;

import java.io.Serializable;

/**下载线程实体类
 * Created by Administrator on 2016/6/20.
 */
public class ThreadInfo implements Serializable{

    //线程id
    private int id;
    //下载地址
    private String url;
    //下载的开始位置
    private int start;
    //下载的结束位置
    private int end;
    //下载完成进度
    private int finished;

    public ThreadInfo(){}
    public ThreadInfo(int id, String url, int start, int end, int finished) {
        this.id = id;
        this.url = url;
        this.start = start;
        this.end = end;
        this.finished = finished;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public int getStart() {
        return start;
    }

    public void setStart(int start) {
        this.start = start;
    }

    public int getEnd() {
        return end;
    }

    public void setEnd(int end) {
        this.end = end;
    }

    public int getFinished() {
        return finished;
    }

    public void setFinished(int finished) {
        this.finished = finished;
    }

    @Override
    public String toString() {
        return "ThreadInfo{" +
                "id=" + id +
                ", url='" + url + '\'' +
                ", start=" + start +
                ", end=" + end +
                ", finished=" + finished +
                '}';
    }
}

二、建立数据库

1.建立数据库帮助类

package com.example.zjw.myapplication.db;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**数据库帮助类
 * Created by Administrator on 2016/6/20.
 */
public class DBHelper extends SQLiteOpenHelper {

    //数据库名称
    private static final String DB_NAME="download.db";
    //数据库版本
    private static final int VERSION=1;
    //创建数据库表sql语句
    private static final String SQL_CREATE="create table thread_info(id integer primary key autoincrement,thread_id integer,url text,start integer,end integer,finished integer)";
    //删除数据库表语句
    private static final String SQL_DROP="drop table if exists thread_info";

    public DBHelper(Context context) {
        super(context,DB_NAME,null,VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
            db.execSQL(SQL_CREATE);
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL(SQL_DROP);
    }
}

2.建立数据库访问接口

package com.example.zjw.myapplication.db;

import com.example.zjw.myapplication.dao.ThreadInfo;

import java.util.List;

/**
 * 数据访问接口
 * Created by Administrator on 2016/6/20.
 */
public interface ThreadDao {

    void addThreadInfo(ThreadInfo threadInfo);
    void deleteThreadInfo(String url,int thread_id);
    void updateThreadInfo(String url,int thread_id,int finished);
    List<ThreadInfo>getThreadInfo(String url);
    boolean findThreadInfo(String url,int thread_id);
}

3.实现数据库访问接口

package com.example.zjw.myapplication.db;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

import com.example.zjw.myapplication.dao.ThreadInfo;

import java.util.ArrayList;
import java.util.List;

/**数据库接口访问实现
 * Created by Administrator on 2016/6/20.
 */
public class ThreadDaoImpl implements ThreadDao {

    private DBHelper dbHelper =null;

    public ThreadDaoImpl(Context context) {
        this.dbHelper = new DBHelper(context);
    }

    @Override
    public void addThreadInfo(ThreadInfo threadInfo) {

        SQLiteDatabase writableDatabase = dbHelper.getWritableDatabase();
        writableDatabase.execSQL("insert into thread_info(thread_id,url,start,end,finished) values(?,?,?,?,?)",new Object[]{
        threadInfo.getId(),threadInfo.getUrl(),threadInfo.getStart(),threadInfo.getEnd(),threadInfo.getFinished()});
        writableDatabase.close();
    }
    @Override
    public void deleteThreadInfo(String url, int thread_id) {
        SQLiteDatabase writableDatabase = dbHelper.getWritableDatabase();
        writableDatabase.execSQL("delete from thread_info where url=?and thread_id=?", new Object[]{url,thread_id});
        writableDatabase.close();
    }
    @Override
    public void updateThreadInfo(String url, int thread_id,int finished) {

        SQLiteDatabase writableDatabase = dbHelper.getWritableDatabase();
        writableDatabase.execSQL("update thread_info set finished=? where url=?and thread_id=?", new Object[]{finished,url,thread_id});
        writableDatabase.close();
    }

    @Override
    public List<ThreadInfo> getThreadInfo(String url) {

        SQLiteDatabase readableDatabase = dbHelper.getReadableDatabase();
        List<ThreadInfo>list = new ArrayList<>();

        Cursor cursor = readableDatabase.rawQuery("select * from thread_info where url=?",new String[]{url});
        while (cursor.moveToNext()){
       ThreadInfo thread  =new ThreadInfo();
            thread.setId(cursor.getInt(cursor.getColumnIndex("thread_id")));
            thread.setUrl(cursor.getString(cursor.getColumnIndex("url")));
            thread.setStart(cursor.getInt(cursor.getColumnIndex("start")));
            thread.setEnd(cursor.getInt(cursor.getColumnIndex("end")));
            thread.setFinished(cursor.getInt(cursor.getColumnIndex("finished")));
            list.add(thread);

        }

         readableDatabase.close();
        cursor.close();
        return list;
    }
    @Override
    public boolean findThreadInfo(String url, int thread_id) {
        SQLiteDatabase readableDatabase = dbHelper.getReadableDatabase();
        List<ThreadInfo>list = new ArrayList<>();
        Cursor cursor = readableDatabase.rawQuery("select * from thread_info where url=? and thread_id=?",new String[]{url,thread_id+""});
        boolean b = cursor.moveToNext();
        readableDatabase.close();
        cursor.close();
        return b;
    }
}

三、建立下载服务Service

package com.example.zjw.myapplication.service;

import android.app.Service;
import android.content.Intent;
import android.os.Environment;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.util.Log;

import com.example.zjw.myapplication.dao.FileInfo;
import com.example.zjw.myapplication.dao.ThreadInfo;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * 下载文件服务
 */
public class DownloadService extends Service {

    public static final String ACTION_START="ACTION_START";
    public static final String ACTION_STOP="ACTION_STOP";
    public static final int MSG_INIT=10;
    public static final String UPDATE="UPDATE";
    private DownloadTask task;
    public static  String path = Environment.getExternalStorageDirectory().getAbsolutePath()+"/MyDownload";

    public DownloadService() {
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        //获取activity传来的参数
            if(ACTION_START.equals(intent.getAction())){
                FileInfo fileInfo = (FileInfo)intent.getSerializableExtra("fileInfo");
                Log.d("TAG-----", "onStartCommand: 开始下载"+fileInfo.toString());
                new Thread(new InitThread(fileInfo)).start();
            }
        if(ACTION_STOP.equals(intent.getAction())){
            Serializable fileInfo = (FileInfo)intent.getSerializableExtra("fileInfo");
            Log.d("TAG-----", "onStartCommand: 暂停下载"+fileInfo);
            if(task!=null){
                task.isDownload=true;
            }
            }
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    private Handler handler  =new Handler(){

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            switch (msg.what){

                case MSG_INIT:
                    FileInfo fileInfo = (FileInfo) msg.obj;
                    Log.d("TAG", "handleMessage:-------------> "+fileInfo);

                    //启动下载任务
                     task = new DownloadTask(fileInfo,DownloadService.this);
                      task.download();
                    break;
            }
        }
    };
    /**
     * 初始化子线程
     */

    private class InitThread implements Runnable{

        private FileInfo fileInfo;
        private RandomAccessFile ws;

        public InitThread(FileInfo threadInfo){

             this.fileInfo=threadInfo;
        }

        @Override
        public void run() {
            HttpURLConnection conn=null;
            try {
                URL url  =new URL(fileInfo.getUrl());
                conn= (HttpURLConnection) url.openConnection();
                conn.setConnectTimeout(5*1000);
                conn.setRequestMethod("GET");
                conn.connect();
                int length=-1;
                if(conn.getResponseCode()==HttpURLConnection.HTTP_OK){
                  length=conn.getContentLength();//获取下载文件长度
                }

                if(length<=0){
                    return;
                }
                //创建文件夹
                File dir = new File(path);
                if(!dir.exists()){
                    dir.mkdir();
                }
                File file = new File(dir,fileInfo.getName());
                this.ws = new RandomAccessFile(file,"rwd");
                ws.setLength(length);
                fileInfo.setLength(length);
                Message msg =new Message();
                msg.obj=fileInfo;
                msg.what=MSG_INIT;
                handler.sendMessage(msg);
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                conn.disconnect();
                try {
                    if(ws!=null)
                    ws.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

四、建立下载任务类

package com.example.zjw.myapplication.service;

import android.content.Context;
import android.content.Intent;
import android.util.Log;

import com.example.zjw.myapplication.dao.FileInfo;
import com.example.zjw.myapplication.dao.ThreadInfo;
import com.example.zjw.myapplication.db.ThreadDao;
import com.example.zjw.myapplication.db.ThreadDaoImpl;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;

/**下载任务类
 * Created by Administrator on 2016/6/20.
 */
public class DownloadTask {

    private FileInfo fileInfo=null;
    private Context context;
    private ThreadDao threadDao;
    public boolean isDownload;
    private int finished;

    public DownloadTask(FileInfo fileInfo, Context context) {
        this.fileInfo = fileInfo;
        this.context = context;
        this.threadDao=new ThreadDaoImpl(context);
    }

    //下载文件
    public void download(){

        //读取数据库线程信息
       List<ThreadInfo> threadInfos = threadDao.getThreadInfo(fileInfo.getUrl());
        ThreadInfo threadInfo =null;
        if(threadInfos.size()==0){

           threadInfo =new ThreadInfo(0,fileInfo.getUrl(),0,fileInfo.getLength(),0);
        }else {
            threadInfo=threadInfos.get(0);
            Log.d("TAG----------", threadInfo.getEnd()+"---download: ---"+threadInfo.getFinished());
        }
        //创建子线程下载文件
        new Thread(new DownloadThread(threadInfo)).start();
    }

    //实现下载
    private class DownloadThread implements Runnable{
        private ThreadInfo threadInfo;
        public DownloadThread(ThreadInfo threadInfo) {
            this.threadInfo = threadInfo;
        }

        @Override
        public void run() {
             //向数据库插入线程信息
                  if(!threadDao.findThreadInfo(threadInfo.getUrl(),threadInfo.getId())){
                      threadDao.addThreadInfo(threadInfo);
                  }
            try {
                URL url  =new URL(threadInfo.getUrl());
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5*1000);
                //设置下载位置
                int start=threadInfo.getStart()+threadInfo.getFinished();
                conn.setRequestProperty("Range","bytes="+start+"-"+threadInfo.getEnd());
                //设置文件写入位置
                File file  =new File(DownloadService.path,fileInfo.getName());
                RandomAccessFile ws = new RandomAccessFile(file,"rwd");
                ws.seek(start);
                //开始下载
                //注意别写成200了不然就无法完成断点下载，206 Partial Content 客户发送了一个带有Range头的GET请求，服务器完成了它（HTTP 1.1新）。
                if(conn.getResponseCode()==206){

                    InputStream inputStream = conn.getInputStream();
                    byte[] data = new byte[1024];
                    int len=-1;
                    Intent intent=new Intent(DownloadService.UPDATE);
                    finished=threadInfo.getFinished();

                    //读取文件
                    while ((len=inputStream.read(data))!=-1){
                        //写入文件
                        ws.write(data,0,len);
                        //发送广播更新进度条
                        finished+=len;

                            intent.putExtra("finished", finished * 100 / fileInfo.getLength());
                            context.sendBroadcast(intent);
                        Log.d("TAG----******-----", threadInfo.getEnd()+"---download: ---"+finished);
                        //下载暂停，保存下载进度
                        if(isDownload){

                            threadDao.updateThreadInfo(threadInfo.getUrl(),threadInfo.getId(),finished);

                            return;
                        }

                    }

                    //删除线程信息
                    threadDao.deleteThreadInfo(threadInfo.getUrl(),threadInfo.getId());
                     ws.close();
                    inputStream.close();
                    conn.disconnect();
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

}

 五、在acticity中调用

package com.example.zjw.myapplication;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

import com.example.zjw.myapplication.dao.FileInfo;
import com.example.zjw.myapplication.dao.ThreadInfo;
import com.example.zjw.myapplication.db.ThreadDaoImpl;
import com.example.zjw.myapplication.service.DownloadService;

import java.util.List;

public class DownloadActivity extends AppCompatActivity {

    private ProgressBar progressBar;
    private TextView tv;

    private boolean isDownload;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_download);
        this.progressBar= (ProgressBar) this.findViewById(R.id.progressBar);
        progressBar.setMax(100);
        this.tv = (TextView) this.findViewById(R.id.progressTv);

        //开始下载
        findViewById(R.id.start).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(!isDownload){
                FileInfo fileInfo  =new FileInfo(0,"http://b.hiphotos.baidu.com/image/pic/item/0823dd54564e925838c205c89982d158ccbf4e26.jpg","110.jpg",0,0);
                Intent intent = new Intent(DownloadActivity.this,DownloadService.class);
                intent.setAction(DownloadService.ACTION_START);
                intent.putExtra("fileInfo",fileInfo);
                startService(intent);
                    isDownload=true;
            }
            }
        });
        //停止下载
        findViewById(R.id.stop).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
               //  downloadFileUtil.setIsDownload(false);
                isDownload=false;
                FileInfo fileInfo  =new FileInfo(0,"http://b.hiphotos.baidu.com/image/pic/item/0823dd54564e925838c205c89982d158ccbf4e26.jpg","112.jpg",0,0);
                Intent intent = new Intent(DownloadActivity.this,DownloadService.class);
                intent.setAction(DownloadService.ACTION_STOP);
                intent.putExtra("fileInfo",fileInfo);
                startService(intent);
            }
        });

        init();

    }
    //初始化
    private void init() {

        //当打开下载界面显示历史下载进度
        ThreadDaoImpl dao  =new ThreadDaoImpl(this);
        List<ThreadInfo> threadInfos = dao.getThreadInfo("http://b.hiphotos.baidu.com/image/pic/item/0823dd54564e925838c205c89982d158ccbf4e26.jpg");
        if(threadInfos.size()>0){
            ThreadInfo threadInfo = threadInfos.get(0);
            int value=threadInfo.getFinished()*100/threadInfo.getEnd();
            progressBar.setProgress(value);
            tv.setText(value+"%");
        }
        //注册广播
        IntentFilter intent = new IntentFilter();
        intent.addAction(DownloadService.UPDATE);
        registerReceiver(reciver,intent);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(reciver);
    }

    BroadcastReceiver reciver  =new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
             int finished = intent.getIntExtra("finished",-1);
             if(finished!=-1){
                 if ( finished<=100) {
                     progressBar.setProgress( finished);
                     tv.setText( finished+"%");
                     if( finished==100){
                         isDownload=false;
                         Toast.makeText(DownloadActivity.this, "下载完成", Toast.LENGTH_SHORT).show();
                     }
                 }
             }
         }
     };
}

六、运行效果