效果图
download.gif
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
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
//ThreadInfo.java
public class ThreadInfo {
private String threadId;
private int start;
private int end;
private int compeleted;
private String url;
public ThreadInfo(){
}
public ThreadInfo(String threadId, int start, int end, int compeleted, String url) {
this.threadId = threadId;
this.start = start;
this.end = end;
this.compeleted = compeleted;
this.url = url;
}
public String getThreadId() {
return threadId;
}
public void setThreadId(String threadId) {
this.threadId = threadId;
}
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 getCompeleted() {
return compeleted;
}
public void setCompeleted(int compeleted) {
this.compeleted = compeleted;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
}
//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。
