Android的HTTP多线程下载示例代码

本示例介绍在android平台下通过http协议实现断点续传下载。

多线程断点需要的功能

1.多线程下载，

2.支持断点。

使用多线程的好处：使用多线程下载会提升文件下载的速度。

多线程下载文件的过程是： 

(1)首先获得下载文件的长度，然后设置本地文件的长度。

   httpurlconnection.getcontentlength();//获取下载文件的长度
  randomaccessfile file = new randomaccessfile("qqwubisetup.exe","rwd");
    file.setlength(filesize);//设置本地文件的长度

(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

如：文件的长度为6m，线程数为3，那么，每条线程下载的数据长度为2m，每条线程开始下载的位置如下图所示。

例如10m大小，使用3个线程来下载，

线程下载的数据长度   (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4m，第三个线程下载长度为2m

下载开始位置：线程id*每条线程下载的数据长度 = ?

下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

(3)使用http的range头字段指定每条线程从文件的什么位置开始下载，下载到什么位置为止，

如：指定从文件的2m位置开始下载，下载到位置(4m-1byte)为止

httpurlconnection.setrequestproperty("range", "bytes=2097152-4194303");

(4)保存文件，使用randomaccessfile类指定每条线程从本地文件的什么位置开始写入数据。

randomaccessfile threadfile = new randomaccessfile("qqwubisetup.exe ","rwd");
threadfile.seek(2097152);//从文件的什么位置开始写入数据

mainactivity中代码:

package com.android.downloader;
import java.io.file;

import com.android.network.downloadprogresslistener;
import com.android.network.filedownloader;

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.widget.button;
import android.widget.edittext;
import android.widget.progressbar;
import android.widget.textview;
import android.widget.toast;

public class mainactivity extends activity {
  private edittext downloadpathtext;
  private textview resultview;
  private progressbar progressbar;
  
  /**
   * 当handler被创建会关联到创建它的当前线程的消息队列，该类用于往消息队列发送消息
   * 消息队列中的消息由当前线程内部进行处理
   */
  private handler handler = new handler(){

    @override
    public void handlemessage(message msg) {      
      switch (msg.what) {
      case 1:        
        progressbar.setprogress(msg.getdata().getint("size"));
        float num = (float)progressbar.getprogress()/(float)progressbar.getmax();
        int result = (int)(num*100);
        resultview.settext(result+ "%");
        
        if(progressbar.getprogress()==progressbar.getmax()){
          toast.maketext(mainactivity.this, r.string.success, 1).show();
        }
        break;
      case -1:
        toast.maketext(mainactivity.this, r.string.error, 1).show();
        break;
      }
    }
  };
  
  /** called when the activity is first created. */
  @override
  public void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.main);
    
    downloadpathtext = (edittext) this.findviewbyid(r.id.path);
    progressbar = (progressbar) this.findviewbyid(r.id.downloadbar);
    resultview = (textview) this.findviewbyid(r.id.resultview);
    button button = (button) this.findviewbyid(r.id.button);
    
    button.setonclicklistener(new view.onclicklistener() {
      
      @override
      public void onclick(view v) {
        // todo auto-generated method stub
        string path = downloadpathtext.gettext().tostring();
        system.out.println(environment.getexternalstoragestate()+"------"+environment.media_mounted);
        
        if(environment.getexternalstoragestate().equals(environment.media_mounted)){
          download(path, environment.getexternalstoragedirectory());
        }else{
          toast.maketext(mainactivity.this, r.string.sdcarderror, 1).show();
        }
      }
    });
  }
  
   /**
    * 主线程(ui线程)
    * 对于显示控件的界面更新只是由ui线程负责，如果是在非ui线程更新控件的属性值，更新后的显示界面不会反映到屏幕上
    * @param path
    * @param savedir
    */
  private void download(final string path, final file savedir) {
    new thread(new runnable() {      
      @override
      public void run() {
        filedownloader loader = new filedownloader(mainactivity.this, path, savedir, 3);
        progressbar.setmax(loader.getfilesize());//设置进度条的最大刻度为文件的长度
        
        try {
          loader.download(new downloadprogresslistener() {
            @override
            public void ondownloadsize(int size) {//实时获知文件已经下载的数据长度
              message msg = new message();
              msg.what = 1;
              msg.getdata().putint("size", size);
              handler.sendmessage(msg);//发送消息
            }
          });
        } catch (exception e) {
          handler.obtainmessage(-1).sendtotarget();
        }
      }
    }).start();
  }
} 

dbopenhelper中代码： 

package com.android.service;
import android.content.context;
import android.database.sqlite.sqlitedatabase;
import android.database.sqlite.sqliteopenhelper;

public class dbopenhelper extends sqliteopenhelper {
  private static final string dbname = "down.db";
  private static final int version = 1;
  
  public dbopenhelper(context context) {
    super(context, dbname, null, version);
  }
  
  @override
  public void oncreate(sqlitedatabase db) {
    db.execsql("create table if not exists filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid integer, downlength integer)");
  }

  @override
  public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {
    db.execsql("drop table if exists filedownlog");
    oncreate(db);
  }
}

fileservice中代码：

package com.android.service;
import java.util.hashmap;
import java.util.map;

import android.content.context;
import android.database.cursor;
import android.database.sqlite.sqlitedatabase;

public class fileservice {
  private dbopenhelper openhelper;

  public fileservice(context context) {
    openhelper = new dbopenhelper(context);
  }
  
  /**
   * 获取每条线程已经下载的文件长度
   * @param path
   * @return
   */
  public map<integer, integer> getdata(string path){
    sqlitedatabase db = openhelper.getreadabledatabase();
    cursor cursor = db.rawquery("select threadid, downlength from filedownlog where downpath=?", new string[]{path});
    map<integer, integer> data = new hashmap<integer, integer>();
    
    while(cursor.movetonext()){
      data.put(cursor.getint(0), cursor.getint(1));
    }
    
    cursor.close();
    db.close();
    return data;
  }
  
  /**
   * 保存每条线程已经下载的文件长度
   * @param path
   * @param map
   */
  public void save(string path, map<integer, integer> map){//int threadid, int position
    sqlitedatabase db = openhelper.getwritabledatabase();
    db.begintransaction();
    
    try{
      for(map.entry<integer, integer> entry : map.entryset()){
        db.execsql("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)",
            new object[]{path, entry.getkey(), entry.getvalue()});
      }
      db.settransactionsuccessful();
    }finally{
      db.endtransaction();
    }
    
    db.close();
  }
  
  /**
   * 实时更新每条线程已经下载的文件长度
   * @param path
   * @param map
   */
  public void update(string path, map<integer, integer> map){
    sqlitedatabase db = openhelper.getwritabledatabase();
    db.begintransaction();
    
    try{
      for(map.entry<integer, integer> entry : map.entryset()){
        db.execsql("update filedownlog set downlength=? where downpath=? and threadid=?",
            new object[]{entry.getvalue(), path, entry.getkey()});
      }
      
      db.settransactionsuccessful();
    }finally{
      db.endtransaction();
    }
    
    db.close();
  }
  
  /**
   * 当文件下载完成后，删除对应的下载记录
   * @param path
   */
  public void delete(string path){
    sqlitedatabase db = openhelper.getwritabledatabase();
    db.execsql("delete from filedownlog where downpath=?", new object[]{path});
    db.close();
  }
} 

downloadprogresslistener中代码：

package com.android.network;
public interface downloadprogresslistener {
  public void ondownloadsize(int size);
} 

filedownloader中代码：

package com.android.network;
import java.io.file;
import java.io.randomaccessfile;
import java.net.httpurlconnection;
import java.net.url;
import java.util.linkedhashmap;
import java.util.map;
import java.util.uuid;
import java.util.concurrent.concurrenthashmap;
import java.util.regex.matcher;
import java.util.regex.pattern;

import com.android.service.fileservice;

import android.content.context;
import android.util.log;

public class filedownloader {
  private static final string tag = "filedownloader";
  private context context;
  private fileservice fileservice;  
  
  /* 已下载文件长度 */
  private int downloadsize = 0;
  
  /* 原始文件长度 */
  private int filesize = 0;
  
  /* 线程数 */
  private downloadthread[] threads;
  
  /* 本地保存文件 */
  private file savefile;
  
  /* 缓存各线程下载的长度*/
  private map<integer, integer> data = new concurrenthashmap<integer, integer>();
  
  /* 每条线程下载的长度 */
  private int block;
  
  /* 下载路径 */
  private string downloadurl;
  
  /**
   * 获取线程数
   */
  public int getthreadsize() {
    return threads.length;
  }
  
  /**
   * 获取文件大小
   * @return
   */
  public int getfilesize() {
    return filesize;
  }
  
  /**
   * 累计已下载大小
   * @param size
   */
  protected synchronized void append(int size) {
    downloadsize += size;
  }
  
  /**
   * 更新指定线程最后下载的位置
   * @param threadid 线程id
   * @param pos 最后下载的位置
   */
  protected synchronized void update(int threadid, int pos) {
    this.data.put(threadid, pos);
    this.fileservice.update(this.downloadurl, this.data);
  }
  
  /**
   * 构建文件下载器
   * @param downloadurl 下载路径
   * @param filesavedir 文件保存目录
   * @param threadnum 下载线程数
   */
  public filedownloader(context context, string downloadurl, file filesavedir, int threadnum) {
    try {
      this.context = context;
      this.downloadurl = downloadurl;
      fileservice = new fileservice(this.context);
      url url = new url(this.downloadurl);
      if(!filesavedir.exists()) filesavedir.mkdirs();
      this.threads = new downloadthread[threadnum];          
      
      httpurlconnection conn = (httpurlconnection) url.openconnection();
      conn.setconnecttimeout(5*1000);
      conn.setrequestmethod("get");
      conn.setrequestproperty("accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
      conn.setrequestproperty("accept-language", "zh-cn");
      conn.setrequestproperty("referer", downloadurl); 
      conn.setrequestproperty("charset", "utf-8");
      conn.setrequestproperty("user-agent", "mozilla/4.0 (compatible; msie 8.0; windows nt 5.2; trident/4.0; .net clr 1.1.4322; .net clr 2.0.50727; .net clr 3.0.04506.30; .net clr 3.0.4506.2152; .net clr 3.5.30729)");
      conn.setrequestproperty("connection", "keep-alive");
      conn.connect();
      printresponseheader(conn);
      
      if (conn.getresponsecode()==200) {
        this.filesize = conn.getcontentlength();//根据响应获取文件大小
        if (this.filesize <= 0) throw new runtimeexception("unkown file size ");
            
        string filename = getfilename(conn);//获取文件名称
        this.savefile = new file(filesavedir, filename);//构建保存文件
        map<integer, integer> logdata = fileservice.getdata(downloadurl);//获取下载记录
        
        if(logdata.size()>0){//如果存在下载记录
          for(map.entry<integer, integer> entry : logdata.entryset())
            data.put(entry.getkey(), entry.getvalue());//把各条线程已经下载的数据长度放入data中
        }
        
        if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据长度
          for (int i = 0; i < this.threads.length; i++) {
            this.downloadsize += this.data.get(i+1);
          }
          
          print("已经下载的长度"+ this.downloadsize);
        }
        
        //计算每条线程下载的数据长度
        this.block = (this.filesize % this.threads.length)==0? this.filesize / this.threads.length : this.filesize / this.threads.length + 1;
      }else{
        throw new runtimeexception("server no response ");
      }
    } catch (exception e) {
      print(e.tostring());
      throw new runtimeexception("don't connection this url");
    }
  }
  
  /**
   * 获取文件名
   * @param conn
   * @return
   */
  private string getfilename(httpurlconnection conn) {
    string filename = this.downloadurl.substring(this.downloadurl.lastindexof('/') + 1);
    
    if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称
      for (int i = 0;; i++) {
        string mine = conn.getheaderfield(i);
        
        if (mine == null) break;
        
        if("content-disposition".equals(conn.getheaderfieldkey(i).tolowercase())){
          matcher m = pattern.compile(".*filename=(.*)").matcher(mine.tolowercase());
          if(m.find()) return m.group(1);
        }
      }
      
      filename = uuid.randomuuid()+ ".tmp";//默认取一个文件名
    }
    
    return filename;
  }
  
  /**
   * 开始下载文件
   * @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null
   * @return 已下载文件大小
   * @throws exception
   */
  public int download(downloadprogresslistener listener) throws exception{
    try {
      randomaccessfile randout = new randomaccessfile(this.savefile, "rw");
      if(this.filesize>0) randout.setlength(this.filesize);
      randout.close();
      url url = new url(this.downloadurl);
      
      if(this.data.size() != this.threads.length){
        this.data.clear();
        
        for (int i = 0; i < this.threads.length; i++) {
          this.data.put(i+1, 0);//初始化每条线程已经下载的数据长度为0
        }
      }
      
      for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载
        int downlength = this.data.get(i+1);
        
        if(downlength < this.block && this.downloadsize<this.filesize){//判断线程是否已经完成下载,否则继续下载  
          this.threads[i] = new downloadthread(this, url, this.savefile, this.block, this.data.get(i+1), i+1);
          this.threads[i].setpriority(7);
          this.threads[i].start();
        }else{
          this.threads[i] = null;
        }
      }
      
      this.fileservice.save(this.downloadurl, this.data);
      boolean notfinish = true;//下载未完成
      
      while (notfinish) {// 循环判断所有线程是否完成下载
        thread.sleep(900);
        notfinish = false;//假定全部线程下载完成
        
        for (int i = 0; i < this.threads.length; i++){
          if (this.threads[i] != null && !this.threads[i].isfinish()) {//如果发现线程未完成下载
            notfinish = true;//设置标志为下载没有完成
            
            if(this.threads[i].getdownlength() == -1){//如果下载失败,再重新下载
              this.threads[i] = new downloadthread(this, url, this.savefile, this.block, this.data.get(i+1), i+1);
              this.threads[i].setpriority(7);
              this.threads[i].start();
            }
          }
        }  
        
        if(listener!=null) listener.ondownloadsize(this.downloadsize);//通知目前已经下载完成的数据长度
      }
      
      fileservice.delete(this.downloadurl);
    } catch (exception e) {
      print(e.tostring());
      throw new exception("file download fail");
    }
    return this.downloadsize;
  }
  
  /**
   * 获取http响应头字段
   * @param http
   * @return
   */
  public static map<string, string> gethttpresponseheader(httpurlconnection http) {
    map<string, string> header = new linkedhashmap<string, string>();
    
    for (int i = 0;; i++) {
      string mine = http.getheaderfield(i);
      if (mine == null) break;
      header.put(http.getheaderfieldkey(i), mine);
    }
    
    return header;
  }
  
  /**
   * 打印http头字段
   * @param http
   */
  public static void printresponseheader(httpurlconnection http){
    map<string, string> header = gethttpresponseheader(http);
    
    for(map.entry<string, string> entry : header.entryset()){
      string key = entry.getkey()!=null ? entry.getkey()+ ":" : "";
      print(key+ entry.getvalue());
    }
  }

  private static void print(string msg){
    log.i(tag, msg);
  }
} 

downloadthread 中代码:

package com.android.network;
import java.io.file;
import java.io.inputstream;
import java.io.randomaccessfile;
import java.net.httpurlconnection;
import java.net.url;

import android.util.log;

public class downloadthread extends thread {
  private static final string tag = "downloadthread";
  private file savefile;
  private url downurl;
  private int block;
  
  /* 下载开始位置 */
  private int threadid = -1;  
  private int downlength;
  private boolean finish = false;
  private filedownloader downloader;
  
  public downloadthread(filedownloader downloader, url downurl, file savefile, int block, int downlength, int threadid) {
    this.downurl = downurl;
    this.savefile = savefile;
    this.block = block;
    this.downloader = downloader;
    this.threadid = threadid;
    this.downlength = downlength;
  }
  
  @override
  public void run() {
    if(downlength < block){//未下载完成
      try {
        httpurlconnection http = (httpurlconnection) downurl.openconnection();
        http.setconnecttimeout(5 * 1000);
        http.setrequestmethod("get");
        http.setrequestproperty("accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
        http.setrequestproperty("accept-language", "zh-cn");
        http.setrequestproperty("referer", downurl.tostring()); 
        http.setrequestproperty("charset", "utf-8");
        int startpos = block * (threadid - 1) + downlength;//开始位置
        int endpos = block * threadid -1;//结束位置
        http.setrequestproperty("range", "bytes=" + startpos + "-"+ endpos);//设置获取实体数据的范围
        http.setrequestproperty("user-agent", "mozilla/4.0 (compatible; msie 8.0; windows nt 5.2; trident/4.0; .net clr 1.1.4322; .net clr 2.0.50727; .net clr 3.0.04506.30; .net clr 3.0.4506.2152; .net clr 3.5.30729)");
        http.setrequestproperty("connection", "keep-alive");
        
        inputstream instream = http.getinputstream();
        byte[] buffer = new byte[1024];
        int offset = 0;
        print("thread " + this.threadid + " start download from position "+ startpos);
        randomaccessfile threadfile = new randomaccessfile(this.savefile, "rwd");
        threadfile.seek(startpos);
        
        while ((offset = instream.read(buffer, 0, 1024)) != -1) {
          threadfile.write(buffer, 0, offset);
          downlength += offset;
          downloader.update(this.threadid, downlength);
          downloader.append(offset);
        }
        
        threadfile.close();
        instream.close();
        print("thread " + this.threadid + " download finish");
        this.finish = true;
      } catch (exception e) {
        this.downlength = -1;
        print("thread "+ this.threadid+ ":"+ e);
      }
    }
  }
  
  private static void print(string msg){
    log.i(tag, msg);
  }
  
  /**
   * 下载是否完成
   * @return
   */
  public boolean isfinish() {
    return finish;
  }
  
  /**
   * 已经下载的内容大小
   * @return 如果返回值为-1,代表下载失败
   */
  public long getdownlength() {
    return downlength;
  }
} 

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。