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效果图
白话分析:
多线程:肯定是多个线程咯
断点:线程停止下载的位置
续传:线程从停止下载的位置上继续下载，直到完成任务为止。
核心分析:
断点:
当前线程已经下载的数据长度
续传:
向服务器请求上次线程停止下载位置的数据
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con.setrequestproperty("range", "bytes=" + start + "-" + end);
分配线程:
int currentpartsize = filesize / mthreadnum;
定义位置
定义线程开始下载的位置和结束的位置
for (int i = 0; i < mthreadnum; i++) {
int start = i * currentpartsize;//计算每条线程下载的开始位置
int end = start + currentpartsize-1;//线程结束的位置
if(i==mthreadnum-1){
end=filesize;
}}
创建数据库:
由于每一个文件要分成多个部分，要被不同的线程同时进行下载。当然要创建线程表，保存当前线程下载开始的位置和结束的位置，还有完成进度等。创建file表，保存当前下载的文件信息，比如：文件名，url，下载进度等信息
线程表:
public static final string create_table_sql="create table "+table_name+"(_id integer primary "
+"key autoincrement, threadid, start , end, completed, url)";
file表：
public static final string create_table_sql="create table "+table_name+"(_id integer primary" +
" key autoincrement ,filename, url, length, finished)";
创建线程类
无非就2个类，一个是线程管理类downloadmanager.java，核心方法：start(),stop(),restart(),addtask().clear()。另一个是线程任务类
downloadtask.java，就是一个线程类，用于下载线程分配好的任务。后面会贴出具体代码。
创建数据库方法类
无非就是单例模式，封装一些增删改查等基础数据库方法，后面会贴出具体代码。
创建实体类
也就是创建threadinfo和fileinfo这2个实体类，把下载文件信息和线程信息暂时存储起来。
引入的第三方开源库
numberprogressbar是一个关于进度条的开源库，挺不错的。直达链接
代码具体分析
1.首先是创建实体类，文件的实体类fileinfo，肯定有filename,url,length,finised,isstop,isdownloading这些属性。线程的实体类threadinfo肯定有threadid,start,end,completed,url这些属性。这些都很简单
//thredinfo.java
public class fileinfo {
private string filename; //文件名
private string url; //下载地址
private int length; //文件大小
private int finished; //下载已完成进度
private boolean isstop=false; //是否暂停下载
private boolean isdownloading=false; //是否正在下载
public fileinfo(){
}
public fileinfo(string filename,string url){
this.filename=filename;
this.url=url;
}
public string getfilename() {
return filename;
}
public void setfilename(string filename) {
this.filename = filename;
}
public string geturl() {
return url;
}
public void seturl(string url) {
this.url = url;
}
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;
}
public boolean isstop() {
return isstop;
}
public void setstop(boolean stop) {
isstop = stop;
}
public boolean isdownloading() {
return isdownloading;
}
public void setdownloading(boolean downloading) {
isdownloading = downloading;
}
@override
public string tostring() {
return "fileinfo{" +
"filename='" + filename + '\'' +
", url='" + url + '\'' +
", length=" + length +
", finished=" + finished +
", isstop=" + isstop +
", isdownloading=" + isdownloading +
'}';
}}
//fileinfo.java
public class fileinfo {
private string filename; //文件名
private string url; //下载地址
private int length; //文件大小
private int finished; //下载已完成进度
private boolean isstop=false; //是否暂停下载
private boolean isdownloading=false; //是否正在下载
public fileinfo(){
}
public fileinfo(string filename,string url){
this.filename=filename;
this.url=url;
}
public string getfilename() {
return filename;
}
public void setfilename(string filename) {
this.filename = filename;
}
public string geturl() {
return url;
}
public void seturl(string url) {
this.url = url;
}
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;
}
public boolean isstop() {
return isstop;
}
public void setstop(boolean stop) {
isstop = stop;
}
public boolean isdownloading() {
return isdownloading;
}
public void setdownloading(boolean downloading) {
isdownloading = downloading;
}
@override
public string tostring() {
return "fileinfo{" +
"filename='" + filename + '\'' +
", url='" + url + '\'' +
", length=" + length +
", finished=" + finished +
", isstop=" + isstop +
", isdownloading=" + isdownloading +
'}';
}}
2.实体类写完了，那么接下来写创建一个类，继承sqliteopenhelper类，来管理数据库连接，主要作用：管理数据库的初始化，并允许应用程序通过该类获取sqlitedatabase对象。
public class threadhelper extends sqliteopenhelper{
public static final string table_name="downthread";
public static final string create_table_sql="create table "+table_name+"(_id integer primary "
+"key autoincrement, threadid, start , end, completed, url)";
public threadhelper(context context, string name, int version) {
super(context, name, null, version);
}
@override
public void oncreate(sqlitedatabase db) {
db.execsql(create_table_sql);
}
@override
public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {
}}
3.接下来封装一些数据库的增删改查操作，用的单例模式，用双重检验锁实现单例。好处:既能很大程度上确保线程安全，又能实现延迟加载。 缺点:使用volatile关键字会使jvm对该代码的优化丧失，影响性能。并且在一些高并发的情况，仍然可能会创建多个实例，这称为双重检验锁定失效。单例模式
public class thread {
private sqlitedatabase db;
public static final string db_name="downthread.db3";
public static final int version=1;
private context mcontext;
private volatile static thread t=null;
private thread(){
mcontext= baseapplication.getcontext();
db=new threadhelper(mcontext,db_name,version).getreadabledatabase();
}
public static thread getinstance(){
if(t==null){
synchronized (thread.class){
if(t==null){
t=new thread();
}
}
}
return t;
}
public sqlitedatabase getdb(){
return db;
}
//保存当前线程下载进度
public synchronized void insert(threadinfo threadinfo){
contentvalues values=new contentvalues();
values.put("threadid",threadinfo.getthreadid());
values.put("start",threadinfo.getstart());
values.put("end",threadinfo.getend());
values.put("completed",threadinfo.getcompeleted());
values.put("url",threadinfo.geturl());
long rowid=db.insert(threadhelper.table_name,null,values);
if(rowid!=-1){
utilslog.i("插入线程记录成功");
}else{
utilslog.i("插入线程记录失败");
}
}
//查询当前线程 下载的进度
public synchronized threadinfo query(string threadid,string queryurl){
cursor cursor=db.query(threadhelper.table_name,null,"threadid= ? and url= ?",new string[]{threadid,queryurl},null,null,null);
threadinfo info=new threadinfo();
if(cursor!=null){
while (cursor.movetonext()){
int start=cursor.getint(2);
int end=cursor.getint(3);
int completed=cursor.getint(4);
string url=cursor.getstring(5);
info.setthreadid(threadid);
info.setstart(start);
info.setend(end);
info.setcompeleted(completed);
info.seturl(url);
}
cursor.close();
}
return info;
}
//更新当前线程下载进度
public synchronized void update(threadinfo info){
contentvalues values=new contentvalues();
values.put("start",info.getstart());
values.put("completed",info.getcompeleted());
db.update(threadhelper.table_name,values,"threadid= ? and url= ?",new string[]{info.getthreadid(),info.geturl()});
}
//关闭db
public void close(){
db.close();
}
//判断多线程任务下载 是否第一次创建线程
public boolean isexist(string url){
cursor cursor=db.query(threadhelper.table_name,null,"url= ?",new string[]{url},null,null,null);
boolean isexist=cursor.movetonext();
cursor.close();
return isexist;
}
public synchronized void delete(threadinfo info){
long rowid=db.delete(threadhelper.table_name,"url =? and threadid= ?",new string[]{info.geturl(),info.getthreadid()});
if(rowid!=-1){
utilslog.i("删除下载线程记录成功");
}else{
utilslog.i("删除下载线程记录失败");
}
}
public synchronized void delete(string url){
long rowid=db.delete(threadhelper.table_name,"url =? ",new string[]{url});
if(rowid!=-1){
utilslog.i("删除下载线程记录成功");
}else{
utilslog.i("删除下载线程记录失败");
}
}}
4.基本的准备操作我们已经完成了，那么开始写关于下载的类吧。首先写的肯定是downloadmanager类，就是管理任务下载的类。不多说，直接看代码。
public class downloadmanager {
private map<string, fileinfo> map = new hashmap<>();
private static int mthreadnum;
private int filesize;
private boolean flag = false; //true第一次下载 false不是第一次下载
private list<downloadtask> threads;
private static fileinfo minfo;
private static resultlistener mlistener;
public static executorservice executorservice = executors.newcachedthreadpool();
public static file file;
private int totalcomleted;
private downloadmanager() {
threads = new arraylist<>();
}
public static downloadmanager getinstance(fileinfo info, int threadnum,resultlistener listener) {
mlistener = listener;
mthreadnum = threadnum;
minfo = info;
return downloadmanagerholder.dlm;
}
private static class downloadmanagerholder {
private static final downloadmanager dlm = new downloadmanager();
}
public void start() {
totalcomleted=0;
clear();
final fileinfo newinfo = download.getinstance().querydata(minfo.geturl());
newinfo.setdownloading(true);
map.put(minfo.geturl(),newinfo);
prepare(newinfo);
}
//停止下载任务
public void stop() {
map.get(minfo.geturl()).setdownloading(false);
map.get(minfo.geturl()).setstop(true);
}
public void clear(){
if(threads.size()>0){
threads.clear();
}
}
//重新下载任务
public void restart() {
stop();
try {
file file = new file(com.cmazxiaoma.downloader.download.downloadmanager.file_path, map.get(minfo.geturl()).getfilename());
if (file.exists()) {
file.delete();
}
java.lang.thread.sleep(100);
} catch (interruptedexception e) {
e.printstacktrace();
}
download.getinstance().resetdata(minfo.geturl());
start();
}
//获取当前任务状态, 是否在下载
public boolean getcurrentstate() {
return map.get(minfo.geturl()).isdownloading();
}
//添加下载任务
public void addtask(fileinfo info) {
//判断数据库是否已经存在此下载信息
if (!download.getinstance().isexist(info)) {
download.getinstance().insertdata(info);
map.put(info.geturl(), info);
} else {
download.getinstance().delete(info);
download.getinstance().insertdata(info);
utilslog.i("map已经更新");
map.remove(info.geturl());
map.put(info.geturl(), info);
}
}
private void prepare(final fileinfo newinfo) {
new java.lang.thread(){
@override
public void run() {
httpurlconnection con = null;
randomaccessfile raf=null;
try {
//连接资源
url url = new url(newinfo.geturl());
utilslog.i("url=" + url);
con = (httpurlconnection) url.openconnection();
con.setconnecttimeout(2 * 1000);
con.setrequestmethod("get");
int length = -1;
utilslog.i("responsecode=" + con.getresponsecode());
if (con.getresponsecode() == 200) {
length = con.getcontentlength();
utilslog.i("文件大小=" + length);
}
if (length <= 0) {
return;
}
//创建文件保存路径
file dir = new file(com.cmazxiaoma.downloader.download.downloadmanager.file_path);
if (!dir.exists()) {
dir.mkdirs();//建立多级文件夹
}
newinfo.setlength(length);
filesize = length;
utilslog.i("当前线程id=" + java.lang.thread.currentthread().getid() + ",name=" + java.lang.thread.currentthread().getname());
int currentpartsize = filesize / mthreadnum;
file = new file(com.cmazxiaoma.downloader.download.downloadmanager.file_path, newinfo.getfilename());
raf = new randomaccessfile(file, "rwd");
raf.setlength(filesize);
if (thread.getinstance().isexist(newinfo.geturl())) {
flag = false;
} else {
flag = true;
}
for (int i = 0; i < mthreadnum; i++) {
if (flag) {
utilslog.i("第一次多线程下载");
int start = i * currentpartsize;//计算每条线程下载的开始位置
int end = start + currentpartsize-1;//线程结束的位置
if(i==mthreadnum-1){
end=filesize;
}
string threadid = "xiaoma" + i;
threadinfo threadinfo = new threadinfo(threadid, start, end, 0,newinfo.geturl());
thread.getinstance().insert(threadinfo);
downloadtask thread = new downloadtask(threadinfo,newinfo, threadid, start, end, 0);
downloadmanager.executorservice.execute(thread);
threads.add(thread);
} else {
utilslog.i("不是第一次多线程下载");
threadinfo threadinfo = thread.getinstance().query("xiaoma" + i, newinfo.geturl());
downloadtask thread = new downloadtask(threadinfo,newinfo,threadinfo.getthreadid(),threadinfo.getstart(),threadinfo.getend(),threadinfo.getcompeleted());//这里出现过问题
downloadmanager.executorservice.execute(thread);
threads.add(thread);
}
}
boolean iscompleted=false;
while(!iscompleted){
iscompleted=true;
for(downloadtask thread:threads){
totalcomleted+=thread.completed;
if(!thread.iscompleted){
iscompleted=false;
}
}
if(newinfo.isstop()){
totalcomleted=0;
return;
}
message message=new message();
message.what=0x555;
message.arg1=filesize;
message.arg2=totalcomleted;
handler.sendmessage(message);
if(iscompleted){
totalcomleted=0;
//任务线程全部完成，清空集合
clear();
handler.sendemptymessage(0x666);
return;
}
totalcomleted=0;
java.lang.thread.sleep(1000);
}
}catch (exception e) {
e.printstacktrace();
}finally {
try {
if (con != null) {
con.disconnect();
}
if(raf!=null){
raf.close();
}
} catch (ioexception e) {
e.printstacktrace();
}
}
}
}.start();
}
private handler handler=new handler(){
@override
public void handlemessage(message msg) {
super.handlemessage(msg);
switch (msg.what){
case 0x555:
if(mlistener!=null){
mlistener.progress(msg.arg1,msg.arg2);
}
break;
case 0x666:
if(mlistener!=null){
mlistener.comleted();
}
break;
}
}
};}
5.接下来呢，就是downloadtask类了，就是一个线程下载类。
public class downloadtask extends java.lang.thread{
private int start;//当前线程的开始下载位置
private int end;//当前线程结束下载的位置
private randomaccessfile raf;//当前线程负责下载的文件大小
public int completed=0;//当前线程已下载的字节数
private string threadid;//自己定义的线程id
private fileinfo info;
private threadinfo threadinfo;
public boolean iscompleted=false; //true为当前线程完成任务,false为当前线程未完成任务
//保存新的start
public int finshed=0;
public int newstart=0;
public downloadtask(threadinfo threadinfo,fileinfo info,string threadid, int start, int end,int completed){
this.threadinfo=threadinfo;
this.info=info;
this.threadid=threadid;
this.start=start;
this.end=end;
this.completed=completed;
}
@override
public void run() {
httpurlconnection con = null;
try {
utilslog.i("start="+start+",end="+end+",completed="+completed+",threadid="+getthreadid());
url url = new url(info.geturl());
con = (httpurlconnection) url.openconnection();
con.setconnecttimeout(2 * 1000);
con.setrequestmethod("get");
con.setrequestproperty("range", "bytes=" + start + "-"+end);//重点
raf=new randomaccessfile(downloadmanager.file,"rwd");
//从文件的某一位置写入
raf.seek(start);
if (con.getresponsecode() == 206) { //文件部分下载 返回码是206
inputstream is = con.getinputstream();
byte[] buffer = new byte[4096];
int hasread = 0;
while ((hasread = is.read(buffer)) != -1) {
//写入文件
raf.write(buffer, 0, hasread);
//单个文件的完成程度
completed += hasread;
threadinfo.setcompeleted(completed);
//保存新的start
finshed=finshed+hasread;//这里出现过问题，嘻嘻
newstart=start+finshed;
threadinfo.setstart(newstart);
//utilslog.i("thread:"+getthreadid()+",completed=" + completed);
//停止下载
if (info.isstop()) {
utilslog.i("isstop="+info.isstop());
//保存下载进度
utilslog.i("现在thread:"+getthreadid()+",completed=" + completed);
thread.getinstance().update(threadinfo);
return;
}
}
//删除该线程下载记录
thread.getinstance().delete(threadinfo);
iscompleted=true;
thread.getinstance().update(threadinfo);
utilslog.i("thread:"+getthreadid()+"已经完成任务!--"+"completed="+completed);
}
} catch (exception e) {
if (con != null) {
con.disconnect();
}
try {
if (raf != null) {
raf.close();
}
} catch (ioexception e1) {
e1.printstacktrace();
}
}
}
public string getthreadid() {
return threadid;
}}
6.接口，就是一个监听下载进度的接口，也是很简单。
public interface resultlistener{
void progress(int max, int progress);
void comleted();}
结束
大致操作就是这样，其实多线程也挺简单的。
以上所述是小编给大家介绍的android多线程+单线程+断点续传+进度条显示下载功能，希望对大家有所帮助
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