md5加密用户登陆遇到的问题及解决办法

有个项目的登陆模块使用到了cas，应需求要求，用户名和密码传输时使用了md5加密模式，加密的密码可以直接保存在数据库，但是加密的用户名则必须解密出来才行，于是后台的java代码中便写了针对用户名的解密代码。
而前台，是在输完用户名和密码后，点击登陆按钮的时候调用相应的方法进行加密并发请求传输。
但是测试过程中却发现了一个问题，就是在有的时候输完用户名、密码和验证码以后回车，后台会报如下的数组下标越界的异常：

java.lang.ArrayIndexOutOfBoundsException: 5
at org.jasig.cas.util.Base64Util.decode(Base64Util.java:41)
at org.jasig.cas.authentication.MyAcceptUsersAuthenticationHandler.authenticateUsernamePasswordInternal(MyAcceptUsersAuthenticationHandler.java:32)
at org.jasig.cas.authentication.handler.support.AbstractUsernamePasswordAuthenticationHandler.doAuthentication(AbstractUsernamePasswordAuthenticationHandler.java:71)
at org.jasig.cas.authentication.handler.support.AbstractPreAndPostProcessingAuthenticationHandler.authenticate_aroundBody2(AbstractPreAndPostProcessingAuthenticationHandler.java:85)
at org.jasig.cas.authentication.handler.support.AbstractPreAndPostProcessingAuthenticationHandler.authenticate_aroundBody3$advice(AbstractPreAndPostProcessingAuthenticationHandler.java:57)
at org.jasig.cas.authentication.handler.support.AbstractPreAndPostProcessingAuthenticationHandler.authenticate(AbstractPreAndPostProcessingAuthenticationHandler.java:1)
at org.jasig.cas.authentication.AuthenticationManagerImpl.authenticateAndObtainPrincipal(AuthenticationManagerImpl.java:93)
at org.jasig.cas.authentication.AbstractAuthenticationManager.authenticate_aroundBody0(AbstractAuthenticationManager.java:57)
at org.jasig.cas.authentication.AbstractAuthenticationManager.authenticate_aroundBody1$advice(AbstractAuthenticationManager.java:57)
at org.jasig.cas.authentication.AbstractAuthenticationManager.authenticate(AbstractAuthenticationManager.java:1)
at sun.reflect.GeneratedMethodAccessor73.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
at org.perf4j.aop.AbstractTimingAspect$1.proceed(AbstractTimingAspect.java:47)
at org.perf4j.aop.AgnosticTimingAspect.runProfiledMethod(AgnosticTimingAspect.java:53)
at org.perf4j.aop.AbstractTimingAspect.doPerfLogging(AbstractTimingAspect.java:45)
at sun.reflect.GeneratedMethodAccessor38.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
at com.github.inspektr.audit.AuditTrailManagementAspect.handleAuditTrail(AuditTrailManagementAspect.java:126)
at sun.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at com.sun.proxy.$Proxy24.authenticate(Unknown Source)
at org.jasig.cas.CentralAuthenticationServiceImpl.createTicketGrantingTicket_aroundBody10(CentralAuthenticationServiceImpl.java:477)
at org.jasig.cas.CentralAuthenticationServiceImpl.createTicketGrantingTicket_aroundBody11$advice(CentralAuthenticationServiceImpl.java:57)
at org.jasig.cas.CentralAuthenticationServiceImpl.createTicketGrantingTicket(CentralAuthenticationServiceImpl.java:1)
at sun.reflect.GeneratedMethodAccessor72.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
at org.perf4j.aop.AbstractTimingAspect$1.proceed(AbstractTimingAspect.java:47)
at org.perf4j.aop.AgnosticTimingAspect.runProfiledMethod(AgnosticTimingAspect.java:53)
at org.perf4j.aop.AbstractTimingAspect.doPerfLogging(AbstractTimingAspect.java:45)
at sun.reflect.GeneratedMethodAccessor38.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
at com.github.inspektr.audit.AuditTrailManagementAspect.handleAuditTrail(AuditTrailManagementAspect.java:126)
at sun.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at com.sun.proxy.$Proxy25.createTicketGrantingTicket(Unknown Source)
at org.jasig.cas.authentication.ImageVaditeAuthenticationViaFormAction.submit(ImageVaditeAuthenticationViaFormAction.java:124)
at sun.reflect.GeneratedMethodAccessor71.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:851)
at ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1253)
at ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68)
at ognl.OgnlRuntime.callMethod(OgnlRuntime.java:1329)
at ognl.ASTMethod.getValueBody(ASTMethod.java:90)
at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
at ognl.SimpleNode.getValue(SimpleNode.java:258)
at ognl.ASTChain.getValueBody(ASTChain.java:141)
at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
at ognl.SimpleNode.getValue(SimpleNode.java:258)
at ognl.Ognl.getValue(Ognl.java:494)
at org.springframework.binding.expression.ognl.OgnlExpression.getValue(OgnlExpression.java:85)
at org.springframework.webflow.action.EvaluateAction.doExecute(EvaluateAction.java:75)
at org.springframework.webflow.action.AbstractAction.execute(AbstractAction.java:188)
at org.springframework.webflow.execution.AnnotatedAction.execute(AnnotatedAction.java:145)
at org.springframework.webflow.execution.ActionExecutor.execute(ActionExecutor.java:51)
at org.springframework.webflow.engine.ActionState.doEnter(ActionState.java:101)
at org.springframework.webflow.engine.State.enter(State.java:194)
at org.springframework.webflow.engine.Transition.execute(Transition.java:227)
at org.springframework.webflow.engine.impl.FlowExecutionImpl.execute(FlowExecutionImpl.java:393)
at org.springframework.webflow.engine.impl.RequestControlContextImpl.execute(RequestControlContextImpl.java:214)
at org.springframework.webflow.engine.TransitionableState.handleEvent(TransitionableState.java:119)
at org.springframework.webflow.engine.Flow.handleEvent(Flow.java:555)
at org.springframework.webflow.engine.impl.FlowExecutionImpl.handleEvent(FlowExecutionImpl.java:388)
at org.springframework.webflow.engine.impl.RequestControlContextImpl.handleEvent(RequestControlContextImpl.java:210)
at org.springframework.webflow.engine.ViewState.handleEvent(ViewState.java:232)
at org.springframework.webflow.engine.ViewState.resume(ViewState.java:196)
at org.springframework.webflow.engine.Flow.resume(Flow.java:545)
at org.springframework.webflow.engine.impl.FlowExecutionImpl.resume(FlowExecutionImpl.java:261)
at org.springframework.webflow.executor.FlowExecutorImpl.resumeExecution(FlowExecutorImpl.java:169)
at org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:183)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.jasig.cas.web.init.SafeDispatcherServlet.service_aroundBody2(SafeDispatcherServlet.java:128)
at org.jasig.cas.web.init.SafeDispatcherServlet.service_aroundBody3$advice(SafeDispatcherServlet.java:57)
at org.jasig.cas.web.init.SafeDispatcherServlet.service(SafeDispatcherServlet.java:1)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at com.github.inspektr.common.web.ClientInfoThreadLocalFilter.doFilter(ClientInfoThreadLocalFilter.java:63)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:259)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.jasig.cas.util.CookieFilter.doFilter(CookieFilter.java:57)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:409)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1044)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

debug之后发现了问题所在：
正常情况下，登陆时前台传递的用户名和密码应该是md5加密后的数据，但是在上面那种情况下传递的却并没有加密，在input中输入了什么，传递的依然还是什么。
这也就是说，回车之后根本就没有走md5加密数据的方法，因此，不是md5加密的，却用了md5加密的方式解密，程序便出现如上的异常。
最终的解决办法是在登陆界面的那些input中加上如下属性：

onkeypress="if(event.keyCode == 13) return false;"

也就是禁用了input上的enter键，在input上回车就不会再发请求到后台，也就不会再出现上述的问题。
参考文档：event.keyCode用法及列表