发布于 2016-07-03 21:46:37 | 154 次阅读 | 评论: 0 | 来源: 网友投递

这里有新鲜出炉的Java并发编程示例,程序狗速度看过来!

Java程序设计语言

java 是一种可以撰写跨平台应用软件的面向对象的程序设计语言,是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java平台(即JavaEE(j2ee), JavaME(j2me), JavaSE(j2se))的总称。


其实断点续传的原理很简单,就是在Http的请求上和一般的下载有所不同而已,本文将详细介绍Java如何实现HTTP断点续传功能,需要的朋友可以参考下
(一)断点续传的原理
其实断点续传的原理很简单,就是在Http的请求上和一般的下载有所不同而已。
打个比方,浏览器请求服务器上的一个文时,所发出的请求如下:
假设服务器域名为wwww.sjtu.edu.cn,文件名为down.zip。
GET /down.zip HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-
excel, application/msword, application/vnd.ms-powerpoint, */*
Accept-Language: zh-cn
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
Connection: Keep-Alive
服务器收到请求后,按要求寻找请求的文件,提取文件的信息,然后返回给浏览器,返回信息如下
200
Content-Length=106786028
Accept-Ranges=bytes
Date=Mon, 30 Apr 2001 12:56:11 GMT
ETag=W/"02ca57e173c11:95b"
Content-Type=application/octet-stream
Server=Microsoft-IIS/5.0
Last-Modified=Mon, 30 Apr 2001 12:56:11 GMT
所谓断点续传,也就是要从文件已经下载的地方开始继续下载。所以在客户端浏览器传给
Web服务器的时候要多加一条信息--从哪里开始。
下面是用自己编的一个"浏览器"来传递请求信息给Web服务器,要求从2000070字节开始。
GET /down.zip HTTP/1.0
User-Agent: NetFox
RANGE: bytes=2000070-
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
仔细看一下就会发现多了一行RANGE: bytes=2000070-
这一行的意思就是告诉服务器down.zip这个文件从2000070字节开始传,前面的字节不用传了。
服务器收到这个请求以后,返回的信息如下:
206
Content-Length=106786028
Content-Range=bytes 2000070-106786027/106786028
Date=Mon, 30 Apr 2001 12:55:20 GMT
ETag=W/"02ca57e173c11:95b"
Content-Type=application/octet-stream
Server=Microsoft-IIS/5.0
Last-Modified=Mon, 30 Apr 2001 12:55:20 GMT
和前面服务器返回的信息比较一下,就会发现增加了一行:
Content-Range=bytes 2000070-106786027/106786028
返回的代码也改为206了,而不再是200了。
知道了以上原理,就可以进行断点续传的编程了。
(二)Java实现断点续传的关键几点
(1)用什么方法实现提交RANGE: bytes=2000070-。
当然用最原始的Socket是肯定能完成的,不过那样太费事了,其实Java的net包中提供了这种功能。代码如下:
URL url = new URL("http://www.sjtu.edu.cn/down.zip");
HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection();
//设置User-Agent
httpConnection.setRequestProperty("User-Agent","NetFox");
//设置断点续传的开始位置
httpConnection.setRequestProperty("RANGE","bytes=2000070");
//获得输入流
InputStream input = httpConnection.getInputStream();
从输入流中取出的字节流就是down.zip文件从2000070开始的字节流。
大家看,其实断点续传用Java实现起来还是很简单的吧。
接下来要做的事就是怎么保存获得的流到文件中去了。
保存文件采用的方法。
我采用的是IO包中的RandAccessFile类。
操作相当简单,假设从2000070处开始保存文件,代码如下:
 
RandomAccess oSavedFile = new RandomAccessFile("down.zip","rw"); 
long nPos = 2000070; 
//定位文件指针到nPos位置 
oSavedFile.seek(nPos); 
byte[] b = new byte[1024]; 
int nRead; 
//从输入流中读入字节流,然后写到文件中 
while((nRead=input.read(b,0,1024)) > 0) 
{ 
oSavedFile.write(b,0,nRead); 
} 

怎么样,也很简单吧。
接下来要做的就是整合成一个完整的程序了。包括一系列的线程控制等等。
(三)断点续传内核的实现
主要用了6个类,包括一个测试类。
SiteFileFetch.java负责整个文件的抓取,控制内部线程(FileSplitterFetch类)。
FileSplitterFetch.java负责部分文件的抓取。
FileAccess.java负责文件的存储。
SiteInfoBean.java要抓取的文件的信息,如文件保存的目录,名字,抓取文件的URL等。
Utility.java工具类,放一些简单的方法。
TestMethod.java测试类。
下面是源程序:
 
/* 
**SiteFileFetch.java 
*/ 
package NetFox; 
import java.io.*; 
import java.net.*; 
public class SiteFileFetch extends Thread { 
SiteInfoBean siteInfoBean = null; //文件信息Bean 
long[] nStartPos; //开始位置 
long[] nEndPos; //结束位置 
FileSplitterFetch[] fileSplitterFetch; //子线程对象 
long nFileLength; //文件长度 
boolean bFirst = true; //是否第一次取文件 
boolean bStop = false; //停止标志 
File tmpFile; //文件下载的临时信息 
DataOutputStream output; //输出到文件的输出流 
public SiteFileFetch(SiteInfoBean bean) throws IOException 
{ 
siteInfoBean = bean; 
//tmpFile = File.createTempFile ("zhong","1111",new File(bean.getSFilePath())); 
tmpFile = new File(bean.getSFilePath()+File.separator + bean.getSFileName()+".info"); 
if(tmpFile.exists ()) 
{ 
bFirst = false; 
read_nPos(); 
} 
else 
{ 
nStartPos = new long[bean.getNSplitter()]; 
nEndPos = new long[bean.getNSplitter()]; 
} 
} 
public void run() 
{ 
//获得文件长度 
//分割文件 
//实例FileSplitterFetch 
//启动FileSplitterFetch线程 
//等待子线程返回 
try{ 
if(bFirst) 
{ 
nFileLength = getFileSize(); 
if(nFileLength == -1) 
{ 
System.err.println("File Length is not known!"); 
} 
else if(nFileLength == -2) 
{ 
System.err.println("File is not access!"); 
} 
else 
{ 
for(int i=0;i<nStartPos.length;i++) 
{ 
nStartPos[i] = (long)(i*(nFileLength/nStartPos.length)); 
} 
for(int i=0;i<nEndPos.length-1;i++) 
{ 
nEndPos[i] = nStartPos[i+1]; 
} 
nEndPos[nEndPos.length-1] = nFileLength; 
} 
} 
//启动子线程 
fileSplitterFetch = new FileSplitterFetch[nStartPos.length]; 
for(int i=0;i<nStartPos.length;i++) 
{ 
fileSplitterFetch[i] = new FileSplitterFetch(siteInfoBean.getSSiteURL(), 
siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(), 
nStartPos[i],nEndPos[i],i); 
Utility.log("Thread " + i + " , nStartPos = " + nStartPos[i] + ", nEndPos = " + nEndPos[i]); 
fileSplitterFetch[i].start(); 
} 
// fileSplitterFetch[nPos.length-1] = new FileSplitterFetch(siteInfoBean.getSSiteURL(), 
siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(),nPos[nPos.length-1],nFileLength,nPos.length-1); 
// Utility.log("Thread " + (nPos.length-1) + " , nStartPos = " + nPos[nPos.length-1] + ", 
nEndPos = " + nFileLength); 
// fileSplitterFetch[nPos.length-1].start(); 
//等待子线程结束 
//int count = 0; 
//是否结束while循环 
boolean breakWhile = false; 
while(!bStop) 
{ 
write_nPos(); 
Utility.sleep(500); 
breakWhile = true; 
for(int i=0;i<nStartPos.length;i++) 
{ 
if(!fileSplitterFetch[i].bDownOver) 
{ 
breakWhile = false; 
break; 
} 
} 
if(breakWhile) 
break; 
//count++; 
//if(count>4) 
// siteStop(); 
} 
System.err.println("文件下载结束!"); 
} 
catch(Exception e){e.printStackTrace ();} 
} 
//获得文件长度 
public long getFileSize() 
{ 
int nFileLength = -1; 
try{ 
URL url = new URL(siteInfoBean.getSSiteURL()); 
HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection (); 
httpConnection.setRequestProperty("User-Agent","NetFox"); 
int responseCode=httpConnection.getResponseCode(); 
if(responseCode>=400) 
{ 
processErrorCode(responseCode); 
return -2; //-2 represent access is error 
} 
String sHeader; 
for(int i=1;;i++) 
{ 
//DataInputStream in = new DataInputStream(httpConnection.getInputStream ()); 
//Utility.log(in.readLine()); 
sHeader=httpConnection.getHeaderFieldKey(i); 
if(sHeader!=null) 
{ 
if(sHeader.equals("Content-Length")) 
{ 
nFileLength = Integer.parseInt(httpConnection.getHeaderField(sHeader)); 
break; 
} 
} 
else 
break; 
} 
} 
catch(IOException e){e.printStackTrace ();} 
catch(Exception e){e.printStackTrace ();} 
Utility.log(nFileLength); 
return nFileLength; 
} 
//保存下载信息(文件指针位置) 
private void write_nPos() 
{ 
try{ 
output = new DataOutputStream(new FileOutputStream(tmpFile)); 
output.writeInt(nStartPos.length); 
for(int i=0;i<nStartPos.length;i++) 
{ 
// output.writeLong(nPos[i]); 
output.writeLong(fileSplitterFetch[i].nStartPos); 
output.writeLong(fileSplitterFetch[i].nEndPos); 
} 
output.close(); 
} 
catch(IOException e){e.printStackTrace ();} 
catch(Exception e){e.printStackTrace ();} 
} 
//读取保存的下载信息(文件指针位置) 
private void read_nPos() 
{ 
try{ 
DataInputStream input = new DataInputStream(new FileInputStream(tmpFile)); 
int nCount = input.readInt(); 
nStartPos = new long[nCount]; 
nEndPos = new long[nCount]; 
for(int i=0;i<nStartPos.length;i++) 
{ 
nStartPos[i] = input.readLong(); 
nEndPos[i] = input.readLong(); 
} 
input.close(); 
} 
catch(IOException e){e.printStackTrace ();} 
catch(Exception e){e.printStackTrace ();} 
} 
private void processErrorCode(int nErrorCode) 
{ 
System.err.println("Error Code : " + nErrorCode); 
} 
//停止文件下载 
public void siteStop() 
{ 
bStop = true; 
for(int i=0;i<nStartPos.length;i++) 
fileSplitterFetch[i].splitterStop(); 
} 
} 
/* 
**FileSplitterFetch.java 
*/ 
package NetFox; 
import java.io.*; 
import java.net.*; 
public class FileSplitterFetch extends Thread { 
String sURL; //File URL 
long nStartPos; //File Snippet Start Position 
long nEndPos; //File Snippet End Position 
int nThreadID; //Thread's ID 
boolean bDownOver = false; //Downing is over 
boolean bStop = false; //Stop identical 
FileAccessI fileAccessI = null; //File Access interface 
public FileSplitterFetch(String sURL,String sName,long nStart,long nEnd,int id) throws IOException 
{ 
this.sURL = sURL; 
this.nStartPos = nStart; 
this.nEndPos = nEnd; 
nThreadID = id; 
fileAccessI = new FileAccessI(sName,nStartPos); 
} 
public void run() 
{ 
while(nStartPos < nEndPos && !bStop) 
{ 
try{ 
URL url = new URL(sURL); 
HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection (); 
httpConnection.setRequestProperty("User-Agent","NetFox"); 
String sProperty = "bytes="+nStartPos+"-"; 
httpConnection.setRequestProperty("RANGE",sProperty); 
Utility.log(sProperty); 
InputStream input = httpConnection.getInputStream(); 
//logResponseHead(httpConnection); 
byte[] b = new byte[1024]; 
int nRead; 
while((nRead=input.read(b,0,1024)) > 0 && nStartPos < nEndPos && !bStop) 
{ 
nStartPos += fileAccessI.write(b,0,nRead); 
//if(nThreadID == 1) 
// Utility.log("nStartPos = " + nStartPos + ", nEndPos = " + nEndPos); 
} 
Utility.log("Thread " + nThreadID + " is over!"); 
bDownOver = true; 
//nPos = fileAccessI.write (b,0,nRead); 
} 
catch(Exception e){e.printStackTrace ();} 
} 
} 
//打印回应的头信息 
public void logResponseHead(HttpURLConnection con) 
{ 
for(int i=1;;i++) 
{ 
String header=con.getHeaderFieldKey(i); 
if(header!=null) 
//responseHeaders.put(header,httpConnection.getHeaderField(header)); 
Utility.log(header+" : "+con.getHeaderField(header)); 
else 
break; 
} 
} 
public void splitterStop() 
{ 
bStop = true; 
} 
} 
/* 
**FileAccess.java 
*/ 
package NetFox; 
import java.io.*; 
public class FileAccessI implements Serializable{ 
RandomAccessFile oSavedFile; 
long nPos; 
public FileAccessI() throws IOException 
{ 
this("",0); 
} 
public FileAccessI(String sName,long nPos) throws IOException 
{ 
oSavedFile = new RandomAccessFile(sName,"rw"); 
this.nPos = nPos; 
oSavedFile.seek(nPos); 
} 
public synchronized int write(byte[] b,int nStart,int nLen) 
{ 
int n = -1; 
try{ 
oSavedFile.write(b,nStart,nLen); 
n = nLen; 
} 
catch(IOException e) 
{ 
e.printStackTrace (); 
} 
return n; 
} 
} 
/* 
**SiteInfoBean.java 
*/ 
package NetFox; 
public class SiteInfoBean { 
private String sSiteURL; //Site's URL 
private String sFilePath; //Saved File's Path 
private String sFileName; //Saved File's Name 
private int nSplitter; //Count of Splited Downloading File 
public SiteInfoBean() 
{ 
//default value of nSplitter is 5 
this("","","",5); 
} 
public SiteInfoBean(String sURL,String sPath,String sName,int nSpiltter) 
{ 
sSiteURL= sURL; 
sFilePath = sPath; 
sFileName = sName; 
this.nSplitter = nSpiltter; 
} 
public String getSSiteURL() 
{ 
return sSiteURL; 
} 
public void setSSiteURL(String value) 
{ 
sSiteURL = value; 
} 
public String getSFilePath() 
{ 
return sFilePath; 
} 
public void setSFilePath(String value) 
{ 
sFilePath = value; 
} 
public String getSFileName() 
{ 
return sFileName; 
} 
public void setSFileName(String value) 
{ 
sFileName = value; 
} 
public int getNSplitter() 
{ 
return nSplitter; 
} 
public void setNSplitter(int nCount) 
{ 
nSplitter = nCount; 
} 
} 
/* 
**Utility.java 
*/ 
package NetFox; 
public class Utility { 
public Utility() 
{ 
} 
public static void sleep(int nSecond) 
{ 
try{ 
Thread.sleep(nSecond); 
} 
catch(Exception e) 
{ 
e.printStackTrace (); 
} 
} 
public static void log(String sMsg) 
{ 
System.err.println(sMsg); 
} 
public static void log(int sMsg) 
{ 
System.err.println(sMsg); 
} 
} 
/* 
**TestMethod.java 
*/ 
package NetFox; 
public class TestMethod { 
public TestMethod() 
{ ///xx/weblogic60b2_win.exe 
try{ 
SiteInfoBean bean = new SiteInfoBean("http://localhost/xx/weblogic60b2_win.exe","L:\\temp","weblogic60b2_win.exe",5); 
//SiteInfoBean bean = new SiteInfoBean("http://localhost:8080/down.zip","L:\\temp","weblogic60b2_win.exe",5); 
SiteFileFetch fileFetch = new SiteFileFetch(bean); 
fileFetch.start(); 
} 
catch(Exception e){e.printStackTrace (); 
} } public static void main(String[] args) { new TestMethod(); } }


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