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

Question

我有以下结果

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>

并且我想显示poolQ​​uestion表（即Join表）的结果。我要显示的值是“答案”。

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);

并且视图是：

<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：在类型com.example.Bean上找不到属性’foo’

从字面上看，这意味着所提到的类com.example.Bean没有针对所提到的property的公共（非静态！）getter方法foo。请注意，此处的字段本身无关紧要！

公共获取方法的名称必须以开头get，然后是属性名称，该属性名称仅在属性名称的第一个字母处大写，例如Foo。

public Foo getFoo() {
    return foo;
}

因此，你需要确保有一个getter方法精确匹配属性名称，并且该方法是public（ 非 -
static），并且该方法不带任何参数，它返回非void。如果您只有一个，但仍然无法正常工作，则很可能是您忙于来回编辑代码，而没有牢固地清理构建，重新构建代码以及重新部署/重新启动应用程序。您需要确保已这样做。

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

public boolean isFoo() {
    return foo;
}

因此，无论类型如何，foo字段本身的存在 都不
重要。它可以具有不同的名称，也可以完全不存在，甚至可以是static。以下所有内容仍应可通过访问${bean.foo}。

public Foo getFoo() {
    return bar;
}



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



public Foo getFoo() {
    return FOO_CONSTANT;
}

您会看到，该字段不是重要的，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，${bean.Foo}它将永远不会起作用${bean.foo}。