首先看下这个错误：
java.util.ConcurrentModificationException: null
at java.util.HashMap$HashIterator.nextNode(Unknown Source) ~[na:1.8.0_51]
at java.util.HashMap$EntryIterator.next(Unknown Source) ~[na:1.8.0_51]
at java.util.HashMap$EntryIterator.next(Unknown Source) ~[na:1.8.0_51]
at com.mayocase.handler.MyAuthenctiationSuccessHandler.onAuthenticationSuccess(MyAuthenctiationSuccessHandler.java:77) ~[classes/:na]
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.successfulAuthentication(AbstractAuthenticationProcessingFilter.java:326) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:240) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:124) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:82) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at com.mayocase.filter.MySecurityContextPersistenceFilter.doFilter(MySecurityContextPersistenceFilter.java:31) ~[classes/:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) ~[spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.28.jar:8.5.28]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_51]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_51]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.28.jar:8.5.28]
at java.lang.Thread.run(Unknown Source) [na:1.8.0_51]然后看下代码：
public static HashMap<String, HttpSession> sessionMap = new HashMap<String, HttpSession>();
// 2.先判断用户是否重复登录
for (Entry<String, HttpSession> entry : sessionMap.entrySet()) {
HttpSession session = entry.getValue();
// 2.1 判断session中所包含的用户名称是否有当前登录用户
String username = SessionUtil.getUserName(session);
if (currentuser.equals(username)) {
System.out.println("用户：" + currentuser + "已经在其它地方登录过，将踢除！");
SessionUtil.expireSession(session);
logger.info(entry.getKey());
sessionMap.remove(entry.getKey());//就是这个地方引起的错误
}
}解决方法，修改代码为：
public static HashMap<String, HttpSession> sessionMap = new HashMap<String, HttpSession>();
// 2.先判断用户是否重复登录
Iterator<Entry<String, HttpSession>> iterator = sessionMap.entrySet().iterator();
while(iterator.hasNext()) {
Map.Entry<String, HttpSession> entry = iterator.next();
HttpSession session = entry.getValue();
// 2.1 判断session中所包含的用户名称是否有当前登录用户
String username = SessionUtil.getUserName(session);
if (currentuser.equals(username)) {
System.out.println("用户：" + currentuser + "已经在其它地方登录过，将踢除！");
SessionUtil.expireSession(session);
logger.info(entry.getKey());
iterator.remove();
}
}