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怎么在java中使用WebSocket实现一个聊天消息推送功能？相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。
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环境：
JDK.1.7.0_51
apache-tomcat-7.0.53
java jar包：tomcat-coyote.jar、tomcat-juli.jar、websocket-api.jar
ChatAnnotation消息发送类：
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import com.util.HTMLFilter;
/**
* WebSocket 消息推送服务类
* @author 胡汉三
*
* 2014-11-18 下午7:53:13
*/
@ServerEndpoint(value = "/websocket/chat")
public class ChatAnnotation {
private static final Log log = LogFactory.getLog(ChatAnnotation.class);
private static final String GUEST_PREFIX = "Guest";
private static final AtomicInteger connectionIds = new AtomicInteger(0);
private static final Map connections = new HashMap();
private final String nickname;
private Session session;
public ChatAnnotation() {
nickname = GUEST_PREFIX + connectionIds.getAndIncrement();
}
@OnOpen
public void start(Session session) {
this.session = session;
connections.put(nickname, this);
String message = String.format("* %s %s", nickname, "has joined.");
broadcast(message);
}
@OnClose
public void end() {
connections.remove(this);
String message = String.format("* %s %s",
nickname, "has disconnected.");
broadcast(message);
}
/**
* 消息发送触发方法
* @param message
*/
@OnMessage
public void incoming(String message) {
// Never trust the client
String filteredMessage = String.format("%s: %s",
nickname, HTMLFilter.filter(message.toString()));
broadcast(filteredMessage);
}
@OnError
public void onError(Throwable t) throws Throwable {
log.error("Chat Error: " + t.toString(), t);
}
/**
* 消息发送方法
* @param msg
*/
private static void broadcast(String msg) {
if(msg.indexOf("Guest0")!=-1){
sendUser(msg);
} else{
sendAll(msg);
}
}
/**
* 向所有用户发送
* @param msg
*/
public static void sendAll(String msg){
for (String key : connections.keySet()) {
ChatAnnotation client = null ;
try {
client = (ChatAnnotation) connections.get(key);
synchronized (client) {
client.session.getBasicRemote().sendText(msg);
}
} catch (IOException e) {
log.debug("Chat Error: Failed to send message to client", e);
connections.remove(client);
try {
client.session.close();
} catch (IOException e1) {
// Ignore
}
String message = String.format("* %s %s",
client.nickname, "has been disconnected.");
broadcast(message);
}
}
}
/**
* 向指定用户发送消息
* @param msg
*/
public static void sendUser(String msg){
ChatAnnotation c = (ChatAnnotation)connections.get("Guest0");
try {
c.session.getBasicRemote().sendText(msg);
} catch (IOException e) {
log.debug("Chat Error: Failed to send message to client", e);
connections.remove(c);
try {
c.session.close();
} catch (IOException e1) {
// Ignore
}
String message = String.format("* %s %s",
c.nickname, "has been disconnected.");
broadcast(message);
}
}
} HTMLFilter工具类：
/**
* HTML 工具类
*
* @author 胡汉三
*/
public final class HTMLFilter {
public static String filter(String message) {
if (message == null)
return (null);
char content[] = new char[message.length()];
message.getChars(0, message.length(), content, 0);
StringBuilder result = new StringBuilder(content.length + 50);
for (int i = 0; i < content.length; i++) {
switch (content[i]) {
case '<':
result.append("<");
break;
case '>':
result.append(">");
break;
case '&':
result.append("&");
break;
case '"':
result.append(""");
break;
default:
result.append(content[i]);
}
}
return (result.toString());
}
}页面：