关于SCTP:
本人理解为:
1.构建于IP协议之上,与TCP,UDP平级. 但提供了与TCP一样的可靠性传输
2.基于消息的发送(而不是像TCP按可能的非完整字节发送,有过做过断包,粘包处理经验的应该能理解). 即上层应用程序发送的消息在接收端能完整接收到,SCTP已经自动帮我们进行了消息字节流的完整组装
3.接收端多IP+端口号支持. 提供一组IP和相同端口给SCTP发送端,当接收端的某个IP无法接收消息时,SCTP自动选择另外的有效IP发送,达到容错目的.以前这种需要应用层处理的复杂业务现由传输层提供了
对于SCTP的更多分析参见;
http://www.cnblogs.com/qlee/archive/2011/07/13/2105717.html
本例子使用官方提供的例子:
参见: http://www.oracle.com/technetwork/articles/javase/index-139946.html
注意: 文中列出的所有网址,如果访问不了,请翻墙.....
SCTP由操作系统实现,但目前Windows7(Window8和Windows10未做测试),Mac OS X10.10.3 都没实现, 所以本次测试的运行环境为:
Centos6.5 64位
jdk1.8.0_40
(默认也没实现), 需要安装SCTP内核包.
安装方式:
http://lksctp.sourceforge.net/(或http://sourceforge.net/projects/lksctp/files/lksctp-tools/lksctp-tools-1.0.16.tar.gz/download) 提供了SCTP在linux中的实现模块
下载完毕后解压. 切换到解压后的目录
运行bootstrap(./bootstrap). 会自动生成configure
运行configure并设置参数(./configure --prefix=/usr/local), 再执行 make && make install
安装完毕后, 拷贝 /usr/local/lib/libsctp.so.1 到 /usr/java/$JAVA_HOME/lib/amd64/ 中. 如果不将此文件拷贝过去,启动时会报如下错误:
java.lang.UnsupportedOperationException: libsctp.so.1: cannot open shared object file: No such file or directory
- 还要临时禁用一下selinux, 输入 echo 0 > /selinux/enforce 如果不禁用,启动时会报如下错误:
java.net.SocketException: Permission denied
at sun.nio.ch.Net.localInetAddress(Native Method)
对于该错误可参见 https://bugs.openjdk.java.net/browse/JDK-7045222
对于selinux可参见 http://cnzhx.net/blog/turn-off-selinux/
项目结构如下图:
其中要引入rt.jar包,java的sctp类在里面.
具体代码如下:
DaytimeServer.java
package com.test;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import com.sun.nio.sctp.MessageInfo;
import com.sun.nio.sctp.SctpChannel;
import com.sun.nio.sctp.SctpServerChannel;
public class DaytimeServer {
static int SERVER_PORT = 3456;
static int US_STREAM = 0;
static int FR_STREAM = 1;
static SimpleDateFormat USformatter = new SimpleDateFormat("h:mm:ss a EEE d MMM yy, zzzz", Locale.US);
static SimpleDateFormat FRformatter = new SimpleDateFormat("h:mm:ss a EEE d MMM yy, zzzz", Locale.FRENCH);
public static void main(String[] args) throws IOException {
SctpServerChannel ssc = SctpServerChannel.open();
InetSocketAddress serverAddr = new InetSocketAddress("192.168.52.199",SERVER_PORT);
ssc.bind(serverAddr);
ByteBuffer buf = ByteBuffer.allocateDirect(60);
CharBuffer cbuf = CharBuffer.allocate(60);
Charset charset = Charset.forName("ISO-8859-1");
CharsetEncoder encoder = charset.newEncoder();
while (true) {
SctpChannel sc = ssc.accept();
/* get the current date */
Date today = new Date();
cbuf.put(USformatter.format(today)).flip();
encoder.encode(cbuf, buf, true);
buf.flip();
/* send the message on the US stream */
MessageInfo messageInfo = MessageInfo.createOutgoing(null, US_STREAM);
sc.send(buf, messageInfo);
/* update the buffer with French format */
cbuf.clear();
cbuf.put(FRformatter.format(today)).flip();
buf.clear();
encoder.encode(cbuf, buf, true);
buf.flip();
/* send the message on the French stream */
messageInfo.streamNumber(FR_STREAM);
sc.send(buf, messageInfo);
cbuf.clear();
buf.clear();
sc.close();
}
}
}
DaytimeClient.java
package com.test;
import java.io.IOException;
import java.io.PrintStream;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import com.sun.nio.sctp.AbstractNotificationHandler;
import com.sun.nio.sctp.AssociationChangeNotification;
import com.sun.nio.sctp.AssociationChangeNotification.AssocChangeEvent;
import com.sun.nio.sctp.HandlerResult;
import com.sun.nio.sctp.MessageInfo;
import com.sun.nio.sctp.SctpChannel;
import com.sun.nio.sctp.ShutdownNotification;
public class DaytimeClient {
static int SERVER_PORT = 3456;
static int US_STREAM = 0;
static int FR_STREAM = 1;
public static void main(String[] args) throws IOException {
InetSocketAddress serverAddr = new InetSocketAddress("192.168.52.199", SERVER_PORT);
ByteBuffer buf = ByteBuffer.allocateDirect(60);
Charset charset = Charset.forName("ISO-8859-1");
CharsetDecoder decoder = charset.newDecoder();
SctpChannel sc = SctpChannel.open(serverAddr, 0, 0);
/* handler to keep track of association setup and termination */
AssociationHandler assocHandler = new AssociationHandler();
/* expect two messages and two notifications */
MessageInfo messageInfo = null;
do {
messageInfo = sc.receive(buf, System.out, assocHandler);
buf.flip();
if (buf.remaining() > 0 && messageInfo.streamNumber() == US_STREAM) {
System.out.println("(US) " + decoder.decode(buf).toString());
} else if (buf.remaining() > 0 && messageInfo.streamNumber() == FR_STREAM) {
System.out.println("(FR) " + decoder.decode(buf).toString());
}
buf.clear();
} while (messageInfo != null);
sc.close();
}
static class AssociationHandler extends AbstractNotificationHandler<PrintStream>
{
public HandlerResult handleNotification(AssociationChangeNotification not, PrintStream stream) {
System.out.println(">>>> "+not.event());
if (not.event().equals(AssocChangeEvent.COMM_UP)) {
int outbound = not.association().maxOutboundStreams();
int inbound = not.association().maxInboundStreams();
stream.printf("New association setup with %d outbound streams" + ", and %d inbound streams.\n", outbound, inbound);
}
return HandlerResult.CONTINUE;
}
public HandlerResult handleNotification(ShutdownNotification not,PrintStream stream) {
stream.printf("The association has been shutdown.\n");
return HandlerResult.RETURN;
}
}
}
代码很简单,具体细节参见java API的sctp.
运行测试:
将工程以JAR file 的方式导出sctpTest.jar, 上传到centos中
以后台方式运行server端: java -cp sctpTest.jar com.test.DaytimeServer &
运行客户端: java -cp sctpTest.jar com.test.DaytimeClient
结果如下:
