El表达式取值机制问题之错误说明： at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:237)

首先贴出报错信息：

十二月 14, 2017 10:54:42 下午 org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet jsp threw exception
javax.el.PropertyNotFoundException: Property 'classroomid' not found on type cn.toohoo.classroom.dto.Classroom
    at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:237)
    at javax.el.BeanELResolver$BeanProperties.access$400(BeanELResolver.java:214)
    at javax.el.BeanELResolver.property(BeanELResolver.java:325)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:85)
    at org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:104)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:183)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:1026)
    at org.apache.jsp.admin.classroom.listclassroom_jsp._jspx_meth_c_005fforEach_005f0(listclassroom_jsp.java:356)
    at org.apache.jsp.admin.classroom.listclassroom_jsp._jspx_meth_c_005fif_005f0(listclassroom_jsp.java:314)
    at org.apache.jsp.admin.classroom.listclassroom_jsp._jspService(listclassroom_jsp.java:218)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at cn.toohoo.classroom.servlet.ClassroomServlet.listClassroom(ClassroomServlet.java:194)
    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:601)
    at cn.toohoo.baseservlet.BaseServlet.service(BaseServlet.java:44)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    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:99)
    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:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
java.lang.reflect.InvocationTargetException
    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:601)
    at cn.toohoo.baseservlet.BaseServlet.service(BaseServlet.java:44)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

    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:99)

    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:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.jasper.JasperException: An exception occurred processing JSP page /admin/classroom/listclassroom.jsp at line 131

128:                                <c:forEach var="Classroom" items="${requestScope.pageBean.pageData}" varStatus="vs">
129:                                    <tr>
130:                                      <td>${vs.count }</td>
131:                                      <td>${Classroom.classroomid }</td>
132:                                      <td>${Classroom.classroomname }</td>
133:                                      <td>${Classroom.classroomtype }</td>
134:                                      <td>${Classroom.classroomcapacity }</td>


Stacktrace:

    at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at cn.toohoo.classroom.servlet.ClassroomServlet.listClassroom(ClassroomServlet.java:194)
    ... 22 more
Caused by: javax.el.PropertyNotFoundException: Property 'classroomid' not found on type cn.toohoo.classroom.dto.Classroom
    at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:237)
    at javax.el.BeanELResolver$BeanProperties.access$400(BeanELResolver.java:214)
    at javax.el.BeanELResolver.property(BeanELResolver.java:325)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:85)
    at org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:104)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:183)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:1026)
    at org.apache.jsp.admin.classroom.listclassroom_jsp._jspx_meth_c_005fforEach_005f0(listclassroom_jsp.java:356)
    at org.apache.jsp.admin.classroom.listclassroom_jsp._jspx_meth_c_005fif_005f0(listclassroom_jsp.java:314)
    at org.apache.jsp.admin.classroom.listclassroom_jsp._jspService(listclassroom_jsp.java:218)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    ... 32 more

然后按照报错信息

javax.el.PropertyNotFoundException: Property 'classroomid' not found on type cn.toohoo.classroom.dto.Classroom

到Classroom实体类查找

    private String classroomid;
    private String classroomname;
    private String classroomtype;
    private String classroomcapacity;
    public String getClassroomId() {
        return classroomid;
    }
    public void setClassroomId(String classroomid) {
        this.classroomid = classroomid;
    }
    public String getClassroomname() {
        return classroomname;
    }
    public void setClassroomname(String classroomname) {
        this.classroomname = classroomname;
    }

是存在  private String classroomid; 的呀，然后纳闷，然后各种修改，

。。。。。。。。。。。。。。。

最后，回到jsp

                           <c:if test="${not empty requestScope.pageBean.pageData}">
                               <c:forEach var="Classroom" items="${requestScope.pageBean.pageData}" varStatus="vs">
                                   <tr>
                                     <td>${vs.count }</td>
                                     <td>${Classroom.classroomid }</td>
                                     <td>${Classroom.classroomname }</td>
                                     <td>${Classroom.classroomtype }</td>
                                     <td>${Classroom.classroomcapacity }</td>
                                     <td>
                                           <a href="<c:url value='/ClassroomServlet?method=queryClassroom&classroomid=${Classroom.classroomid }'/>">修改</a>
                                          <a href="<c:url value='/ClassroomServlet?method=deleteClassroom&classroomid=${Classroom.classroomid }'/>">删除</a>
                                       </td>
                                   </tr>
                              </c:forEach>
                      </c:if>

索性将含有${Classroom.classroomid }的行去掉

改成

                           <c:if test="${not empty requestScope.pageBean.pageData}">
                               <c:forEach var="Classroom" items="${requestScope.pageBean.pageData}" varStatus="vs">
                                   <tr>
                                     <td>${vs.count }</td>
                                     
                                     <td>${Classroom.classroomname }</td>
                                     <td>${Classroom.classroomtype }</td>
                                     <td>${Classroom.classroomcapacity }</td>
                                     <td>
                                          
                                       </td>
                                   </tr>
                              </c:forEach>
                      </c:if>

网页一访问通过了

为什么${Classroom.classroomname }可以通过而${Classroom.classroomid }却不可以通过呢，继续检查Classroom实体类

回到jsp将${Classroom.classroomid }改成${Classroom.classroomId }

重新部署，访问通过，好家伙

总结：myeclipse的报错还是要很认真分析的，还有这个错误让我对EL表达式的取值方法了解更深了，就是通过对外的公共方法来取值的，所以说名字一定要正确，同时对于这次myeclipse生成的代码我真的是郁闷爆了，认真检查！汲取教训。