javax.el.PropertyNotFoundException:在com.example.Bean类型上找不到属性'foo'

Question

我有结果

Query query = session.createQuery("From Pool as p left join fetch p.poolQuestion as s");

查询,我想在JSP上显示它.

我有循环:

<c:forEach items="${pools}" var="pool"> 

    <p>${pool.name}</p>

</c:forEach>

我想显示poolQ​​uestion表(连接表)的结果.我想要显示的值是"回答".

我该怎么做？

<c:forEach items="${pools}" var="pool"> 
    <p>${pool.answer}</p>
    <p>${pool.name}</p>             
</c:forEach>

上面的代码不起作用.

错误是:

  org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/views/home.jsp at line 21

18:     <c:forEach items="${pools}" var="pool"> 
19:             
20:             <p>${pool.name}</p>
21:             <c:out value="${pool.poolQuestion.answer}"/>
22:             
23:     </c:forEach>
24: 

    SEVERE: Servlet.service() for servlet appServlet threw exception
javax.el.PropertyNotFoundException: Property 'answer' not found on type com.pool.app.domain.Pool
    at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:214)
    at javax.el.BeanELResolver$BeanProperties.access$400(BeanELResolver.java:191)
    at javax.el.BeanELResolver.property(BeanELResolver.java:300)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:81)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:54)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:123)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:938)
    at org.apache.jsp.WEB_002dINF.views.home_jsp._jspx_meth_c_005fforEach_005f0(home_jsp.java:119)
    at org.apache.jsp.WEB_002dINF.views.home_jsp._jspService(home_jsp.java:78)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1047)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:817)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:669)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:574)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:680)

该模型是:

public List<Pool> getAll(){

    Session session = sessionFactory.getCurrentSession();

    Query query = session.createQuery("From Pool as p left join fetch p.poolQuestions as s");

    return query.list();

控制器是:

List<Pool> pool = poolService.getAll();

model.addAttribute("pools", pool);

而观点是:

<c:forEach items="${pools}" var="pool"> 

    <p>${pool.name}</p>
    <c:out value="${pool.answer}"/>

</c:forEach>

PS.在${pool.name}显示正常

Answer 1

javax.el.PropertyNotFoundException:在com.example.Bean类型上找不到属性'foo'

这实际上意味着所提到的类com.example.Bean没有针对上述属性的公共(非静态!)getter方法foo.请注意,字段本身与此无关!

公共getter方法名称必须以get,后跟属性名称,该属性名称仅在属性名称的第一个字母处大写,如Foo.

public Foo getFoo() {
    return foo;
}

因此,您需要确保有一个getter方法与属性名称完全匹配,并且该方法是public(非 - static)并且该方法不接受任何参数并且它返回non void.如果你有一个它仍然无法正常工作,那么你很可能正在忙着编辑代码而不必坚定地清理构建,重建代码并重新部署/重新启动应用程序.你需要确保你已经这样做了.

对于boolean(不是Boolean!)属性,getter方法名称必须以is而不是get.

public boolean isFoo() {
    return foo;
}

无论类型如何,foo场本身的存在因此都不相关.它可以有不同的名称,或完全不存在,甚至可以static.下面的所有内容仍然可以访问${bean.foo}.

public Foo getFoo() {
    return bar;
}

public Foo getFoo() {
    return new Foo("foo");
}

public Foo getFoo() {
    return FOO_CONSTANT;
}

你看,这个领域并不重要,而是getter方法本身.请注意,属性名称本身不应在EL中大写.换句话说,${bean.Foo}它永远不会起作用${bean.foo}.

也可以看看:

• javax.el.PropertyNotFoundException:属性'foo'在类型java.lang.Boolean上不可读
• Java表达式语言如何解析布尔属性？(在JSF 1.2中)
• 识别并解决javax.el.PropertyNotFoundException:Target Unreachable
• Outcommented Facelets代码仍调用#{bean.action()}之类的EL表达式,并在#{bean.action}上导致javax.el.PropertyNotFoundException

Answer 2

我相信id访问器与bean命名约定不匹配,这就是抛出异常的原因.它们应该如下:

public Integer getId() { return id; }    
public void setId(Integer i){ id= i; }