EL表达式中的首字母大写造成的bug

今天用EL表达式的${ }时出bug了。

org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/jsp/reader/show.jsp at line 1615: 16: ${reader.R_ID}<br/>17: Stacktrace:org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:584)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:481)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)javax.servlet.http.HttpServlet.service(HttpServlet.java:729)org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)javax.servlet.http.HttpServlet.service(HttpServlet.java:622)org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)javax.servlet.http.HttpServlet.service(HttpServlet.java:729)org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

javax.el.PropertyNotFoundException: Property 'R_ID' not found on type net.xcj.entity.Readerjavax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:259)javax.el.BeanELResolver$BeanProperties.access$300(BeanELResolver.java:212)javax.el.BeanELResolver.property(BeanELResolver.java:346)javax.el.BeanELResolver.getValue(BeanELResolver.java:92)org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:110)org.apache.el.parser.AstValue.getValue(AstValue.java:169)org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:944)org.apache.jsp.WEB_002dINF.jsp.reader.show_jsp._jspService(show_jsp.java:130)org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)javax.servlet.http.HttpServlet.service(HttpServlet.java:729)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)javax.servlet.http.HttpServlet.service(HttpServlet.java:729)org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)javax.servlet.http.HttpServlet.service(HttpServlet.java:622)org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)javax.servlet.http.HttpServlet.service(HttpServlet.java:729)org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

看了看，上面说Reader类中没找到R_ID，但是我去Reader中找，R_ID在那里静静地躺着。最后才发现，原来EL表达式，比如说${Reader.name}，它会根据name去Reader类里寻找这个name的get方法，此时会自动把name首字母大写并加上get前缀， 一旦找到与之匹配的方法，El表达式就会认为这就是要访问的属性，并返回属性的值EL表达式会根据name去Reader类里寻找这个name的get方法，此时会自动把name首字母大写并加上get前缀，    一旦找到与之匹配的方法，El表达式就会认为这就是要访问的属性，并返回属性的值。

一般按照规范来说，属性的首字母是小写的，不过我因为按数据库表来命名，首字母大写了，就遇见了这个bug，只需要把${reader.R_ID}改成${reader.r_ID}就行了。