Java NIO系列教程（十） Java NIO DatagramChannel

Love The Way You Lie 2023-10-17 12:33 6阅读 0赞

本文转载至：[http://ifeve.com/datagram-channel/][http_ifeve.com_datagram-channel]

Java NIO中的DatagramChannel是一个能收发UDP包的通道。因为UDP是无连接的网络协议，所以不能像其它通道那样读取和写入。它发送和接收的是数据包。

#### 打开 DatagramChannel ####

下面是 DatagramChannel 的打开方式：

<table style="margin:0px!important; padding:0px!important; border-collapse:collapse!important; width:auto!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; font-size:1em!important; direction:ltr!important"> 
 <tbody style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:1em!important; direction:ltr!important"> 
  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:1em!important; direction:ltr!important"> 
   <td style="border:0px!important; padding:0px!important; margin:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; color:rgb(120,120,120)!important"> <code style="margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; background:none!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:block!important">2</code></td> 
   <td style="border-width:0px 0px 0px 1px!important; border-top-style:initial!important; border-right-style:initial!important; border-bottom-style:initial!important; border-left-style:solid!important; border-top-color:initial!important; border-right-color:initial!important; border-bottom-color:initial!important; border-left-color:rgb(212,208,200)!important; padding:0px 0px 0px 0.5em!important; margin:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important"> <code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">channel.socket().bind(</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-weight:bold!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(127,0,85)!important">new</code>&nbsp;<code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">InetSocketAddress(</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(0,153,0)!important">9999</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">));</code></td> 
  </tr> 
 </tbody> 
</table>

这个例子打开的 DatagramChannel可以在UDP端口9999上接收数据包。

#### 接收数据 ####

通过receive()方法从DatagramChannel接收数据，如：

receive()方法会将接收到的数据包内容复制到指定的Buffer. 如果Buffer容不下收到的数据，多出的数据将被丢弃。

#### 发送数据 ####

通过send()方法从DatagramChannel发送数据，如:

<table style="margin:0px!important; padding:0px!important; border-collapse:collapse!important; width:auto!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; font-size:1em!important; direction:ltr!important"> 
 <tbody style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-size:1em!important; direction:ltr!important"> 
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   <td style="border:0px!important; padding:0px!important; margin:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; color:rgb(120,120,120)!important"> <code style="margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; background:none!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:block!important">8</code></td> 
   <td style="border-width:0px 0px 0px 1px!important; border-top-style:initial!important; border-right-style:initial!important; border-bottom-style:initial!important; border-left-style:solid!important; border-top-color:initial!important; border-right-color:initial!important; border-bottom-color:initial!important; border-left-color:rgb(212,208,200)!important; padding:0px 0px 0px 0.5em!important; margin:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important"> <code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-weight:bold!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(127,0,85)!important">int</code>&nbsp;<code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">bytesSent = channel.send(buf,&nbsp;</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-weight:bold!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(127,0,85)!important">new</code>&nbsp;<code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">InetSocketAddress(</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(42,0,255)!important">"jenkov.com"</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">,&nbsp;</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(0,153,0)!important">80</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">));</code></td> 
  </tr> 
 </tbody> 
</table>

这个例子发送一串字符到”jenkov.com”服务器的UDP端口80。 因为服务端并没有监控这个端口，所以什么也不会发生。也不会通知你发出的数据包是否已收到，因为UDP在数据传送方面没有任何保证。

#### 连接到特定的地址 ####

可以将DatagramChannel“连接”到网络中的特定地址的。由于UDP是无连接的，连接到特定地址并不会像TCP通道那样创建一个真正的连接。而是锁住DatagramChannel ，让其只能从特定地址收发数据。

这里有个例子:

<table style="margin:0px!important; padding:0px!important; border-collapse:collapse!important; width:auto!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; font-size:1em!important; direction:ltr!important"> 
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   <td style="border:0px!important; padding:0px!important; margin:0px!important; outline:0px!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; color:rgb(120,120,120)!important"> <code style="margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; background:none!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:block!important">1</code></td> 
   <td style="border-width:0px 0px 0px 1px!important; border-top-style:initial!important; border-right-style:initial!important; border-bottom-style:initial!important; border-left-style:solid!important; border-top-color:initial!important; border-right-color:initial!important; border-bottom-color:initial!important; border-left-color:rgb(212,208,200)!important; padding:0px 0px 0px 0.5em!important; margin:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important"> <code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">channel.connect(</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-weight:bold!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(127,0,85)!important">new</code>&nbsp;<code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">InetSocketAddress(</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(42,0,255)!important">"jenkov.com"</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">,&nbsp;</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important; color:rgb(0,153,0)!important">80</code><code style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; background:none!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,Courier,monospace!important; font-size:1em!important; direction:ltr!important; display:inline!important">));</code></td> 
  </tr> 
 </tbody> 
</table>

当连接后，也可以使用read()和write()方法，就像在用传统的通道一样。只是在数据传送方面没有任何保证。这里有几个例子：

[查看源代码][Link 1]

[打印][Link 2] [帮助][Link 3]

java 示例代码

[http_ifeve.com_datagram-channel]: http://ifeve.com/datagram-channel/
[Link 1]: http://ifeve.com/datagram-channel/#viewSource
[Link 2]: http://ifeve.com/datagram-channel/#printSource
[Link 3]: http://ifeve.com/datagram-channel/#about