📄 06-套接字编程（下3）.htm
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<TD>Listing 6: MCClient.java<BR>// MCClient.java<BR><BR>import java.io.*;<BR>import java.net.*;<BR><BR>class MCClient<BR>{<BR> public static void main (String [] args) throws IOException<BR> {<BR> // Create a MulticastSocket bound to local port 10000. All<BR> // multicast packets from the server program are received<BR> // on that port.<BR><BR> MulticastSocket s = new MulticastSocket (10000);<BR><BR> // Obtain an InetAddress object that contains the multicast<BR> // group address 231.0.0.1. The InetAddress object is used by<BR> // DatagramPacket.<BR><BR> InetAddress group = InetAddress.getByName ("231.0.0.1");<BR><BR> // Join the multicast group so that datagram packets can be<BR> // received.<BR><BR> s.joinGroup (group);<BR><BR> // Read several datagram packets from the server program.<BR><BR> for (int i = 0; i < 10; i++)<BR> {<BR> // No line will exceed 256 bytes.<BR><BR> byte [] buffer = new byte [256];<BR><BR> // The DatagramPacket object needs no addressing<BR> // information because the socket contains the address.<BR><BR> DatagramPacket dgp = new DatagramPacket (buffer,<BR> buffer.length);<BR><BR> // Receive a datagram packet.<BR><BR> s.receive (dgp);<BR><BR> // Create a second byte array with a length that matches<BR> // the length of the sent data.<BR><BR> byte [] buffer2 = new byte [dgp.getLength ()];<BR><BR> // Copy the sent data to the second byte array.<BR><BR> System.arraycopy (dgp.getData (),<BR> 0,<BR> buffer2,<BR> 0,<BR> dgp.getLength ());<BR><BR> // Print the contents of the second byte array. (Try<BR> // printing the contents of buffer. You will soon see why<BR> // buffer2 is used.)<BR><BR> System.out.println (new String (buffer2));<BR> }<BR><BR> // Leave the multicast group.<BR><BR> s.leaveGroup (group);<BR><BR> // Close the socket.<BR><BR> s.close ();<BR> }<BR>}</TD></TR></TBODY></TABLE><BR> MCClient创建了一个绑定端口号10000的MulticastSocket对象，接下来他获得了一个InetAddress子类对象，该子类对象包含多点传送组的IP地址231.0.0.0，然后通过joinGroup(InetAddress addr)方法加入多点传送组中，接下来MCClient接收10个自寻址包，同时输出他们的内容，然后使用leaveGroup(InetAddress addr)方法离开传送组，最后关闭套接字。<BR><BR> 也许你对使用两个字节数组buffer 和 buffer2感到奇怪，当接收到一个自寻址包后，getData()方法返回一个引用，自寻址包的长度是256个字节，如果要输出所有数据，在输出完实际数据后会有很多空格，这显然是不合理的，所以我们必须去掉这些空格，因此我们创建一个小的字节数组buffer2，buffer2的实际长度就是数据的实际长度，通过调用DatagramPacket's getLength()方法来得到这个长度。从buffer 到 buffer2快速复制getLength()的长度的方法是调用System.arraycopy()方法。<BR><BR> List7 MCServer的源代码显示了服务程序是怎样工作的。<BR><BR>
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<TD>Listing 7: MCServer.java<BR>// MCServer.java<BR><BR>import java.io.*;<BR>import java.net.*;<BR><BR>class MCServer<BR>{<BR> public static void main (String[] args) throws IOException<BR> {<BR> System.out.println ("Server starting...\n"); <BR><BR> // Create a MulticastSocket not bound to any port.<BR><BR> MulticastSocket s = new MulticastSocket ();<BR><BR> // Because MulticastSocket subclasses DatagramSocket, it is<BR> // legal to replace MulticastSocket s = new MulticastSocket ();<BR> // with the following line.<BR><BR>
<SCRIPT language=Javascript>document.write("<img src='http://counter.yesky.com/servlet/counter.counter?CID=72348977504190464&AID=1601474&refer="+escape(document.referrer)+"&cur="+escape(document.URL)+"' border='0' alt='' width='0' height='0'>");</SCRIPT>
<IMG height=0 alt="" src="http://counter.yesky.com/servlet/counter.counter?CID=72348977504190464&AID=1601474&refer=http%3A//www.yesky.com/SoftChannel/72342371961929728/20030110/1647918_1.shtml&cur=http%3A//www.yesky.com/SoftChannel/72342371961929728/20030110/1647918_2.shtml" width=0 border=0> // DatagramSocket s = new DatagramSocket ();<BR><BR> // Obtain an InetAddress object that contains the multicast<BR> // group address 231.0.0.1. The InetAddress object is used by<BR> // DatagramPacket.<BR><BR> InetAddress group = InetAddress.getByName ("231.0.0.1");<BR><BR> // Create a DatagramPacket object that encapsulates a reference<BR> // to a byte array (later) and destination address<BR> // information. The destination address consists of the<BR> // multicast group address (as stored in the InetAddress object)<BR> // and port number 10000 -- the port to which multicast datagram<BR> // packets are sent. (Note: The dummy array is used to prevent a<BR> // NullPointerException object being thrown from the<BR> // DatagramPacket constructor.)<BR><BR> byte [] dummy = new byte [0];<BR><BR> DatagramPacket dgp = new DatagramPacket (dummy,<BR> 0,<BR> group,<BR> 10000);<BR><BR> // Send 30000 Strings to the port.<BR><BR> for (int i = 0; i < 30000; i++)<BR> {<BR> // Create an array of bytes from a String. The platform's<BR> // default character set is used to convert from Unicode<BR> // characters to bytes.<BR><BR> byte [] buffer = ("Video line " + i).getBytes ();<BR><BR> // Establish the byte array as the datagram packet's<BR> // buffer.<BR><BR> dgp.setData (buffer);<BR><BR> // Establish the byte array's length as the length of the<BR> // datagram packet's buffer.<BR><BR> dgp.setLength (buffer.length);<BR><BR> // Send the datagram to all members of the multicast group<BR> // that listen on port 10000.<BR><BR> s.send (dgp);<BR> }<BR><BR> // Close the socket.<BR><BR> s.close ();<BR> }<BR>} </TD></TR></TBODY></TABLE><BR> MCServer创建了一个MulticastSocket对象，由于他是DatagramPacket对象的一部分，所以他没有绑定端口号，DatagramPacket有多点传送组的IP地址（231.0.0.0），一旦创建DatagramPacket对象，MCServer就进入一个发送30000条的文本的循环中，对文本的每一行均要创建一个字节数组，他们的引用均存储在前面创建的DatagramPacket对象中，通过send()方法，自寻址包发送给所有的组成员。<BR><BR> 在编译了MCServer 和 MCClient后，通过输入java MCServer开始运行MCServer，最后再运行一个或多个MCClient。<BR><BR> <B><FONT color=#ac000>结论</FONT></B><BR><BR> 本文通过研究套接字揭示了Java的网络API的应用方法，我们介绍了套接自的慨念和套接字的组成，以及流套接字和自寻址套接字，以及如何使用InetAddress, Socket, ServerSocket, DatagramPacket, DatagramSocket和MulticastSocket类。在完成本文后就可以编写基本的底层通讯程序。<br><br> </DIV> </TD> </TR> <TR> <TD class=center01> <div align="center">来源：天极网 作者：<div> </TD> <TD width="280" class=center01> <div align="center"> <font color=#0000FF><a href='chapter.php?id=387&volume=3&chapter=5'>上一页</a></font> <font color=#0000FF><a href="serialize.php?id=387">回书目</a></font> <font color=#0000FF><a href='chapter.php?id=387&volume=3&chapter=7'>下一页</a></font> </div> </TD> </TR> </TBODY></TABLE><table><tr><td width="760"> <table width="760" height="10" border="0" cellpadding="0" cellspacing="0"> <tr> <td></td> </tr> </table> <!------------ 评论 ----------------> <table width="760" border="0" cellpadding="0" cellspacing="0"> <tr> <td><iframe width="100%" id=vs frameborder=0 scrolling=no src="comment_list1.php?id=387"></iframe> </td> </tr> </table><br><script language=javascript>function CheckNetwordForm(theForm){ if("" == theForm.content.value) { alert("写两句吧~~"); theForm.content.focus(); return false; } var index; for(index=0;index<theForm.content.value.length;index++) { if(" " != theForm.content.value.charAt(index)) break; } if(index == theForm.content.value.length) { alert("写两句吧~~"); theForm.content.focus(); return false; } if (theForm.content.value.length>100){ alert("评论字数不能超过100哦"); theForm.content.focus(); return false; } return true;}</script> <!------------------ 评论 ---------------> <form name=netword method=post action="insertnetword.php" onsubmit="javascript: return CheckNetwordForm(this);"> <table width="760" border="0" cellpadding="0" cellspacing="0"> <tr> <td height="25" class="text6"> 给此书打分：<a name="1"></a> <select name="score"> <option value=5 selected>非常好</option> <option value=4>还凑合</option> <option value=3>一般吧</option> <option value=2>不太行</option> <option value=1>太差了</option> </select> 用户名： <input name="id" value=387 type="hidden" id="id"> <input name="backurl" value=/book/chapter.php?id=387&volume=3&chapter=6 type="hidden"> <input name="username" type="text" id="username" size="20" maxlength="20"> <font color="#666666">*评论字数请控制在一百字以内</font> </td> </tr> </table> <br> <textarea name="content" cols="80" rows="4" wrap="OFF" id="description"></textarea> <input type="submit" name="Submit" value="提交"> </form> </td> </tr></table></td></tr></table> <TABLE cellSpacing=0 cellPadding=0 width=760 border=0> <TBODY> <TR> <TD width="1003" height=9 background=images/t_bj01.gif><IMG height=1 src="images/ccc.gif" width=1></TD> </TR> </TBODY></TABLE><TABLE cellSpacing=0 cellPadding=0 width=760 bgColor=#ffffff border=0> <TBODY> <TR> <TD><HR width=760 noShade SIZE=1> </TD> </TR> <TR> <TD align=middle><A class=black href="http://www.chinaren.com/" target=_blank>ChinaRen</A> - <A class=black href="http://big5.www.sohu.com/" target=_blank>繁体版</A> - <A class=black href="http://hr.sohu.com/hrm.html" target=_blank>搜狐招聘</A> - <A class=black href="http://add.sohu.com/" target=_blank>网站登录</A> - <A class=black href="http://help.sohu.com/" target=_blank>帮助中心</A> - <A class=black href="http://book.news.sohu.com/onClick=this.style.behavior='url(#default#homepage)';this.setHomePage('http://www.sohu.com');return" target=_blank false;>设置首页</A> - <A class=black href="http://adinfo.sohu.com/" target=_blank>广告服务</A> - <A class=black href="http://www.sohu.com/about/lianxi.htm" target=_blank>联系方式</A> - <A class=black href="http://www.sohu.com/about/privacy.html" target=_blank>保护隐私权</A> - <A class=black href="http://www.sohu.com/about/" target=_blank>About SOHU</A> - <A class=black href="http://www.sohu.com/about/" target=_blank>公司介绍</A><BR> <SPAN class=eng>Copyright © 2004 Sohu.com Inc. 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