Apache Mina Server 是一个网络通信应用框架，也就是说，它主要是对基于 TCP/IP、UDP/IP协议栈的通信框架（当然，也可以提供 JAVA 对象的序列化服务、虚拟机管道通信服务等），Mina 可以帮助我们快速开发高性能、高扩展性的网络通信应用，Mina 提供了事件驱动、异步（Mina 的异步 IO 默认使用的是 JAVA NIO 作为底层支持）操作的编程模型。
从官网文档“MINA based Application Architecture”中可以看到Mina作为一个通信层框架，在实际应用所处的位置，如图所示：
Mina位于用户应用程序和底层Java网络API（和in-VM通信）之间，我们开发基于Mina的网络应用程序，就无需关心复杂的通信细节。
应用整体架构
再看一下，Mina提供的基本组件，如图所示：
也就是说，无论是客户端还是服务端，使用Mina框架实现通信的逻辑分层在概念上统一的，即包含如下三层：
- I/O Service – Performs actual I/O
- I/O Filter Chain – Filters/Transforms bytes into desired Data Structures and vice-versa
- I/O Handler – Here resides the actual business logic
想要开发基于MIna的应用程序，你只需要做如下事情：
- Create an I/O service – Choose from already available Services (*Acceptor) or create your own
- Create a Filter Chain – Choose from already existing Filters or create a custom Filter for transforming request/response
- Create an I/O Handler – Write business logic, on handling different messages
下面看一下使用Mina的应用程序，在服务器端和客户端的架构细节：
服务器端架构
服务器端监听指定端口上到来的请求，对这些请求经过处理后，回复响应。它也会创建并处理一个链接过来的客户会话对象（Session）。服务器端架构如图所示：
对服务器端的说明，引用官网文档，如下所示：
- IOAcceptor listens on the network for incoming connections/packets
- For a new connection, a new session is created and all subsequent request from IP Address/Port combination are handled in that Session
- All packets received for a Session, traverses the Filter Chain as specified in the diagram. Filters can be used to modify the content of packets (like converting to Objects, adding/removing information etc). For converting to/from raw bytes to High Level Objects, PacketEncoder/Decoder are particularly useful
- Finally the packet or converted object lands in IOHandler. IOHandlers can be used to fulfill business needs.
客户端架构
客户端主要做了如下工作：
- 连接到服务器端
- 向服务器发送消息
- 等待服务器端响应，并处理响应
客户端架构，如图所示：
对客户端架构的说明，引用官网文档内容，如下所示：
- Client first creates an IOConnector (MINA Construct for connecting to Socket), initiates a bind with Server
- Upon Connection creation, a Session is created and is associated with Connection
- Application/Client writes to the Session, resulting in data being sent to Server, after traversing the Filter Chain
- All the responses/messages received from Server are traverses the Filter Chain and lands at IOHandler, for processing
应用实例开发
下面根据上面给出的架构设计描述，看一下Mina（版本2.0.7）自带的例子，如何实现一个简单的C/S通信的程序，非常容易。
服务端
首先，服务器端需要使用的组件有IoAdaptor、IoHandler、IoFilter，其中IoFilter可选.
我们基于Mina自带的例子进行了简单地修改，实现服务端IoHandler的代码如下所示：
package org.shirdrn.mina.server;
import org.apache.mina.core.service.IoHandlerAdapter;
import org.apache.mina.core.session.IdleStatus;
import org.apache.mina.core.session.IoSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TinyServerProtocolHandler extends IoHandlerAdapter {
private final static Logger LOGGER = LoggerFactory.getLogger(TinyServerProtocolHandler.class);
@Override
public void sessionCreated(IoSession session) {
session.getConfig().setIdleTime(IdleStatus.BOTH_IDLE, 10);
}
@Override
public void sessionClosed(IoSession session) throws Exception {
LOGGER.info("CLOSED");
}
@Override
public void sessionOpened(IoSession session) throws Exception {
LOGGER.info("OPENED");
}
@Override
public void sessionIdle(IoSession session, IdleStatus status) {
LOGGER.info("*** IDLE #" + session.getIdleCount(IdleStatus.BOTH_IDLE) + " ***");
}
@Override
public void exceptionCaught(IoSession session, Throwable cause) {
session.close(true);
}
@Override
public void messageReceived(IoSession session, Object message)
throws Exception {
LOGGER.info( "Received : " + message );
if(!session.isConnected()) {
session.close(true);
}
}
}
这个版本中，IoHandlerAdapter实现了IoHandler接口，里面封装了一组用于事件处理的空方法，其中包含服务端和客户端的事件。在实际应用中，客户端可以选择客户端具有的事件，服务器端选择服务器端具有的事件，然后分别对这两类事件进行处理（有重叠的事件，如连接事件、关闭事件、异常事件等）。
客户端的IoHandler的具体实现也是类似的，不过多累述。
下面看启动服务器的主方法类，代码如下所示：
package org.shirdrn.mina.server;
import java.net.InetSocketAddress;
import org.apache.mina.filter.codec.ProtocolCodecFilter;
import org.apache.mina.filter.codec.textline.TextLineCodecFactory;
import org.apache.mina.transport.socket.SocketAcceptor;
import org.apache.mina.transport.socket.nio.NioSocketAcceptor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TinyMinaServer {
private final static Logger LOG = LoggerFactory.getLogger(TinyMinaServer.class);
/** Choose your favorite port number. */
private static final int PORT = 8080;
public static void main(String[] args) throws Exception {
SocketAcceptor acceptor = new NioSocketAcceptor();
acceptor.setReuseAddress(true);
acceptor.getFilterChain().addLast("codec", new ProtocolCodecFilter(new TextLineCodecFactory()));
// Bind
acceptor.setHandler(new TinyServerProtocolHandler());
acceptor.bind(new InetSocketAddress(PORT));
LOG.info("Listening on port " + PORT);
LOG.info("Server started!");
for (;;) {
LOG.info("R: " + acceptor.getStatistics().getReadBytesThroughput() + ", W: " + acceptor.getStatistics().getWrittenBytesThroughput());
Thread.sleep(3000);
}
}
}
客户端
实现客户端IoHandler的代码如下所示：
package org.shirdrn.mina.client;
import org.apache.mina.core.service.IoHandlerAdapter;
import org.apache.mina.core.session.IdleStatus;
import org.apache.mina.core.session.IoSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TinyClientProtocolHandler extends IoHandlerAdapter {
private final static Logger LOGGER = LoggerFactory
.getLogger(TinyClientProtocolHandler.class);
@Override
public void sessionCreated(IoSession session) {
LOGGER.info("CLIENT::CREATED");
}
@Override
public void sessionClosed(IoSession session) throws Exception {
LOGGER.info("CLIENT::CLOSED");
}
@Override
public void sessionOpened(IoSession session) throws Exception {
LOGGER.info("CLIENT::OPENED");
}
@Override
public void sessionIdle(IoSession session, IdleStatus status) {
LOGGER.info("CLIENT::*** IDLE #"
+ session.getIdleCount(IdleStatus.BOTH_IDLE) + " ***");
}
@Override
public void exceptionCaught(IoSession session, Throwable cause) {
LOGGER.info("CLIENT::EXCEPTIONCAUGHT");
cause.printStackTrace();
}
public void messageSent(IoSession session, Object message) throws Exception {
LOGGER.info("CLIENT::MESSAGESENT: " + message);
}
}
下面看启动客户端的主方法类，代码如下所示：
package org.shirdrn.mina.client;
import java.net.InetSocketAddress;
import org.apache.mina.core.future.ConnectFuture;
import org.apache.mina.filter.codec.ProtocolCodecFilter;
import org.apache.mina.filter.codec.textline.TextLineCodecFactory;
import org.apache.mina.transport.socket.SocketConnector;
import org.apache.mina.transport.socket.nio.NioSocketConnector;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TinyMinaClient {
private final static Logger LOG = LoggerFactory.getLogger(TinyMinaClient.class);
/** Choose your favorite port number. */
private static final int PORT = 8080;
public static void main(String[] args) throws Exception {
SocketConnector connector = new NioSocketConnector();
// Connect
connector.getFilterChain().addLast("codec", new ProtocolCodecFilter(new TextLineCodecFactory()));
connector.setHandler(new TinyClientProtocolHandler());
for (int i = 0; i < 10; i++) {
ConnectFuture future = connector.connect(new InetSocketAddress(PORT));
LOG.info("Connect to port " + PORT);
future.awaitUninterruptibly();
future.getSession().write(String.valueOf(i));
Thread.sleep(1500);
}
}
}
我们只是发送了十个数字，每发一次间隔1500ms。
测试上述服务器端与客户端交互，首先启动服务器端，监听8080端口。
接着启动客户端，连接到服务器端8080端口，然后发送消息，服务器端接收到消息后，直接将到客户端的连接关闭掉。
参考链接
- http://mina.apache.org/mina-project/index.html
- http://mina.apache.org/mina-project/userguide/user-guide-toc.html
- http://mina.apache.org/mina-project/userguide/ch2-basics/application-architecture.html
- http://mina.apache.org/mina-project/userguide/ch2-basics/server-architecture.html
- http://mina.apache.org/mina-project/userguide/ch2-basics/client-architecture.html
参考文档
- 《Apache_Mina_Server_2.0中文参考手册V1.0.pdf》
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