??? 最近用到了MulticastSocket，發(fā)現(xiàn)在有些情況下它不能工作，當(dāng)然這是編碼的問(wèn)題，是一個(gè)BUG，不過(guò)這個(gè)BUG較少出現(xiàn)，一旦出現(xiàn)了也讓人摸不著頭緒。
??? 由于以前沒(méi)有用過(guò)這個(gè)東東，首先在網(wǎng)上找了個(gè)簡(jiǎn)單的例子：
??? Server端：
?1?import?java.net.DatagramPacket;
?2?import?java.net.InetAddress;
?3?import?java.net.MulticastSocket;
?4?
?5?public?class?Server?{
?6???public?static?void?main(String?[]?arstring)?{
?7?????try?{
?8???????//?Create?a?multicast?datagram?socket?for?receiving?IP
?9???????//??multicast?packets.??Join?the?multicast?group?at
10???????//??230.0.0.1,?port?7777.
11???????MulticastSocket?multicastSocket?=?new?MulticastSocket(7777);
12???????InetAddress?inetAddress?=?InetAddress.getByName("230.0.0.1");
13???????multicastSocket.joinGroup(inetAddress);
14???????//?Loop?forever?and?receive?messages?from?clients.??Print
15???????//??the?received?messages.
16???????while?(true)?{
17?????????byte?[]?arb?=?new?byte?[100];
18?????????DatagramPacket?datagramPacket?=?new?DatagramPacket(arb,?arb.length);
19?????????multicastSocket.receive(datagramPacket);
20?????????System.out.println(new?String(arb));
21???????}
22?????}
23?????catch?(Exception?exception)?{
24???????exception.printStackTrace();
25?????}
26???}
27?}
??? Client端：
?1?public?class?Client?{
?2???public?static?void?main(String?[]?arstring)?{
?3?????try?{
?4???????//?Create?a?datagram?package?and?send?it?to?the?multicast
?5???????//??group?at?230.0.0.1,?port?7777.
?6???????for?(;?;)?{
?7?????????byte?[]?arb?=?new?byte?[]{'h',?'e',?'l',?'l',?'o'};
?8?????????InetAddress?inetAddress?=?InetAddress.getByName("230.0.0.1");
?9?????????DatagramPacket?datagramPacket?=
10?????????????????new?DatagramPacket(arb,?arb.length,?inetAddress,?7777);
11?????????MulticastSocket?multicastSocket?=?new?MulticastSocket();
12?//??????multicastSocket.joinGroup(inetAddress);
13?????????multicastSocket.send(datagramPacket);
14???????}
15?????}
16?????catch?(Exception?exception)?{
17???????exception.printStackTrace();
18?????}
19???}
20?}
???
在公司編譯、運(yùn)行都正常，回到家里發(fā)現(xiàn)Server不能收到broadcast消息了。跟蹤程序也沒(méi)有發(fā)現(xiàn)問(wèn)題，網(wǎng)上也沒(méi)有找到答案。后來(lái)考慮到公司和家
里的網(wǎng)絡(luò)情況不同：公司里是通過(guò)內(nèi)網(wǎng)連接到INTERNET；在家則是在局域網(wǎng)上撥號(hào)連接到INTERNET，相當(dāng)于有兩個(gè)邏輯的網(wǎng)絡(luò)接口卡。于是在上述
例子中增加如下代碼：
multicastSocket.setNetworkInterface(NetworkInterface.getByInetAddress(InetAddress.getLocalHost()));
??? 再次測(cè)試，成功！
??? 總結(jié)：使用MulticastSocket時(shí)，如果發(fā)現(xiàn)broadcast不成功，要注意是否使用了多個(gè)網(wǎng)絡(luò)接口卡（物理的或邏輯的）。