websocket实战（3） 错误处理及
回顾
websocket实战（1） 入门
WEBSocket实战（2） 信息处理发送、接收和编码
通过前面说明，已经轻松构建一个简单的websocket ServerEndPoint了。可以为EndPoint加上×××，编码器，为EndPoint提供支持。但是，作为一个服务器，遇到错误怎么办？websocket作为一个简单的容器组件，也具备简单配置管理功能。
1.错误处理
1.1@onError
其实很简单，就是在ServerEndPoint类中，添加一个方法，要求该方法被@onError修饰。
如下
@ServerEndpoint("/testendpoint")
public class TestEndpoint {
...
@OnError
public void error(Session session, Throwable t) {
t.printStackTrace();
...
}
}代码片段（代码没有意义，纯属测试）
@ServerEndpoint("/echo")
public class EchoEndpoint {
@OnMessage
public String onMessage(String message,Session session) {
System.out.println("Received : " + message);
int random = new Random().nextInt(5);
if(random==3){
throw new RuntimeException("自定义异常");
}else{
System.out.println("random="+random);
}
return message+"-"+session.getId();
}
@OnOpen
public void myOnOpen(Session session) {
session.getUserProperties().put("startTime",new Date());
System.out.println("WebSocket opened: " + session.getId());
}
@OnClose
public void myOnClose(CloseReason reason) {
System.out.println("Closing a WebSocket due to " + reason.getReasonPhrase());
}
@OnError
public void error(Session session, Throwable t) {
System.out.println("发生错误，请注意");
t.printStackTrace();
}
}如果遇到错误，将抛异常如下
发生错误，请注意(error方法中输出)
java.lang.RuntimeException: 自定义异常
at com.sample.websocket.endpoint.EchoEndpoint.onMessage(EchoEndpoint.java:21)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.Tomcat.websocket.pojo.PojoMessageHandlerWholeBase.onMessage(PojoMessageHandlerWholeBase.java:80)
at org.apache.tomcat.websocket.WsFrameBase.sendMessageText(WsFrameBase.java:393)
at org.apache.tomcat.websocket.WsFrameBase.processDataText(WsFrameBase.java:494)
at org.apache.tomcat.websocket.WsFrameBase.processData(WsFrameBase.java:289)
at org.apache.tomcat.websocket.WsFrameBase.processInputBuffer(WsFrameBase.java:130)
Closing a WebSocket due to An unrecoverable IOException occurred so the connection was closed（myOnClose调用输出）
at org.apache.tomcat.websocket.server.WsFrameServer.onDataAvailable(WsFrameServer.java:56)
....
1.2 Error Handing
主要错误有3种。
Deployment Errors （部署期间，比如tomcat启动）
Errors Originating in Websocket Application Code（websocket endpoint 发生错误）
Errors Originating in the Container and/or Underlying Connection（连接peer内部错误）
javax.websocket. CloseReason
CloseReason.CloseCode
public enum CloseCodes implements CloseReason.CloseCode {
...
CLOSED_ABNORMALLY(1006),
...
}
//1006是一个比较特殊的错误码
//其他错误码，参照Enum CloseCodesif the local
container determines the session has timed out, the local implementation must use the websocket protocol
close code 1006
2.配置管理
2.1 先从javax.websocket.Session说起
Session 代表一个有效连接。周期从（Open ->Close）
简单将Session的方法分为几类（当然你也许有更好的分类）
配置信息（其中有些配置信息来源于WebContainer）
Session状态信息
自定义存储信息
请求信息
Session的操作方法
测试代码
package com.sample.websocket.endpoint;
import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.NIO.ByteBuffer;
import java.util.Iterator;
import java.util.Set;
@ServerEndpoint("/config")
public class ReceiveEndpoint {
@OnMessage
public void textMessage(Session session, String msg) {
System.out.println("Text message: " + msg);
Set<Session> openSessions = session.getOpenSessions();
System.out.println(" session.OpenSessions.size" + openSessions.size());
}
@OnMessage
public void binaryMessage(Session session, ByteBuffer msg) {
System.out.println("Binary message: " + msg.toString());
}
@OnMessage
public void pongMessage(Session session, PongMessage msg) {
System.out.println("Pong message: " + msg.getApplicationData().toString());
}
@OnClose
public void nClose(Session session, CloseReason reason) {
System.out.println("Pong message: " + reason.getReasonPhrase()+"-->"+reason.getCloseCode());
}
@OnError
public void onError(Throwable t){
t.printStackTrace();
}
@OnOpen
public void onOpen(Session session){
System.out.println("session.getId()=" + session.getId());
Set<Session> openSessions = session.getOpenSessions();
System.out.println(" session.OpenSessions.size=" + openSessions.size());
session.getUserProperties().put("userName","Guest"+session.getId());
Iterator<Session> iterator = openSessions.iterator();
System.out.println("open session list===========");
while(iterator.hasNext()){
Session s = iterator.next();
String sid = s.getId();
System.out.println("session.id==>"+ sid);
Object user = s.getUserProperties().get("userName");
System.out.println("session."+sid+"username==>"+user);
}
System.out.println();
System.out.println();
WebSocketContainer wsc = session.getContainer();
System.out.println("WebSocketContainer Info==========");
System.out.println("webSocketContainer=" + wsc);
System.out.println("defaultAsyncTimeout->"+wsc.getDefaultAsyncSendTimeout());
System.out.println("defaultMaxBinaryMessageBufferSize-->"+wsc.getDefaultMaxBinaryMessageBufferSize());
System.out.println("defaultMaxSessionIdleTimeout-->"+wsc.getDefaultMaxSessionIdleTimeout());
System.out.println("installedExtensions.size==>" + wsc.getInstalledExtensions().size());
System.out.println();
System.out.println();
System.out.println("session parameter");
System.out.println("session.getMaxBinaryMessageBufferSize()==>"+session.getMaxBinaryMessageBufferSize());
System.out.println("session.getMaxIdleTimeout()==>"+session.getMaxIdleTimeout());
System.out.println("session.getNeGotiatedSubprotocol()==>"+session.getNegotiatedSubprotocol());
System.out.println("session.getProtocolVersion()==>"+session.getProtocolVersion());
System.out.println("session.getRequestURI()==>" + session.getRequestURI());
System.out.println();
System.out.println();
Set<MessageHandler> messageHandlers = session.getMessageHandlers();
Iterator<MessageHandler> messageHandlerIterator = messageHandlers.iterator();
System.out.println("MessageHandlers");
while(messageHandlerIterator.hasNext()){
MessageHandler handler = messageHandlerIterator.next();
System.out.println(handler.toString());
}
System.out.println("session.getUserPrincipal().getName()==>"+session.getUserPrincipal());
}
}输出结果如下
session.getId()=0
session.OpenSessions.size=0
open session list===========
WebSocketContainer Info==========
webSocketContainer=org.apache.tomcat.websocket.server.WsServerContainer@4d3De8ab
defaultAsyncTimeout->-1
defaultMaxBinaryMessageBufferSize-->8192
defaultMaxSessionIdleTimeout-->0
installedExtensions.size==>0
session parameter
session.getMaxBinaryMessageBufferSize()==>8192
session.getMaxIdleTimeout()==>0
session.getNegotiatedSubprotocol()==>
session.getProtocolVersion()==>13
session.getRequestURI()==>/wsexample/config
MessageHandlers
org.apache.tomcat.websocket.pojo.PojoMessageHandlerWholePong@6e710882
org.apache.tomcat.websocket.pojo.PojoMessageHandlerWholeBinary@3ee5c773
org.apache.tomcat.websocket.pojo.PojoMessageHandlerWholeText@1f69b445
session.getUserPrincipal().getName()==>null
Text message: Hello WebSocket!
session.OpenSessions.size=1
下面是我分析结果
1.session.id是从0递增的
2.session.getOpenSessions(),api定义是获取连接EndPoint的Session的数目,但实际上永远返回1
3.session.getOpenSessions() 在@OnOpen方法中调用返回0，在@OnMessage方法中调用返回1，即便打开了多个连接也是如此。在Tomcat7.72中如此。
4.定义了3个OnMessage修饰的方法，MessageHandler也是三个
5.几个参数从WebSocketContainer中的参数，与Session的参数一致。比如MaxBinaryMessageBufferSize等
6.即使在方法中修改了WebSocketContainer的配置参数值，session中对应的值也不会变。
session.getOpenSessions() API
Return a copy of the Set of all the open web socket sessions that represent connections to the same endpoint to which this session represents a connection. The Set includes the session this method is called on.
调整Session中的若干参数值
@OnOpen
public void onOpen(final Session session) {
session.setMaxIdleTimeout(TIMEOUT);
...
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