3. 服务器端WebSocket编程
Tomcat 7提供了WebSocket支持，这里就以Tomcat 7 为例，探索一下如何在服务器端进行WebSocket编程。需要加载的依赖包为 libcatalina.jar、libtomcat-coyote.jar
这里有两个重要的类 ：WebSocketServlet 和 StreamInbound， 前者是一个容器，用来初始化WebSocket环境；后者是用来具体处理WebSocket请求和响应的。
编写一个Servlet类，继承自WebSocket，实现其抽象方法即可，代码如下：
package websocket;
import java.util.concurrent.atomic.AtomicInteger;
import javax.servlet.http.HttpServletRequest;
import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;
public class HelloWebSocketServlet extends WebSocketServlet {
private static final long serialVersionUID = 1L;
private final AtomicInteger connectionIds = new AtomicInteger(0);
@Override
protected StreamInbound createWebSocketInbound(String arg0,
HttpServletRequest request) {
return new HelloMessageInbound(connectionIds.getAndIncrement(), request
.getSession().getId());
}
}
package websocket;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.nio.CharBuffer;
import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WsOutbound;
public class HelloMessageInbound extends StreamInbound {
private String WS_NAME;
private final String FORMAT = "%s : %s";
private final String PREFIX = "ws_";
private String sessionId = "";
public HelloMessageInbound(int id, String _sessionId) {
this.WS_NAME = PREFIX + id;
this.sessionId = _sessionId;
}
@Override
protected void onTextData(Reader reader) throws IOException {
char[] chArr = new char[1024];
int len = reader.read(chArr);
send(String.copyValueOf(chArr, 0, len));
}
@Override
protected void onClose(int status) {
System.out.println(String.format(FORMAT, WS_NAME, "closing ......"));
super.onClose(status);
}
@Override
protected void onOpen(WsOutbound outbound) {
super.onOpen(outbound);
try {
send("hello, my name is " + WS_NAME);
send("session id = " + this.sessionId);
} catch (IOException e) {
e.printStackTrace();
}
}
private void send(String message) throws IOException {
message = String.format(FORMAT, WS_NAME, message);
System.out.println(message);
getWsOutbound().writeTextMessage(CharBuffer.wrap(message));
}
@Override
protected void onBinaryData(InputStream arg0) throws IOException {
}
}
在Web.xml中进行Servlet配置：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> <display-name>websocket demo</display-name> <servlet> <servlet-name>wsHello</servlet-name> <servlet-class>websocket.HelloWebSocketServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>wsHello</servlet-name> <url-pattern>/websocket/say</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app>
