Question

使用jsf会导致NullpointerException：

    WARNING: StandardWrapperValve[jsp]: PWC1406: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at javax.faces.webapp.UIComponentClassicTagBase.setJspId(UIComponentClassicTagBase.java:1858)
    at org.apache.jsp.jsf.list_jsp._jspx_meth_h_form_0(list_jsp.java:112)
    at org.apache.jsp.jsf.list_jsp._jspService(list_jsp.java:86)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:770)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:411)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:770)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:722)

在我的glassfish-server和我的动态web项目的lib文件夹中，如下所示罐子：

标准1.1.2.jar
JSTL-JSTL-1.2.jar
的jsp-API-2.1
JSF的参数impl-2.1.7.jar
JSF-API-2.2.0-m03.jar

我的豆子：

@Stateless
@Named 
public class StatelessBean {

    public int getNumberOfMovies() {
        return 42;
    }

    public int getNumberOfPersons() {
        return 42;
    }
}

我的jsf：

    <%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="f" uri="http://java.sun.com/jsf/core"%>
<%@ taglib prefix="h" uri="http://java.sun.com/jsf/html"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<link href="../css/basic.css" type="text/css" rel="stylesheet">
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Liste</title>
</head>
<body>
    <h:form>
        <h1>Stateless</h1>
        <h:outputText value="Anzahl der Filme: #{StatelessBean.getNumberOfMovies()}" />
        <h:outputText value="Anzahl der Personen: #{StatelessBean.getNumberOfPersons()}" />
    </h:form>   
</body>
</html>

这里提供的拳击手：stackoverflow没有帮助。

不知道如何解决这个问题。

Answer 1

您应该像这样更改您的视图代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:ui="http://java.sun.com/jsf/facelets">
    <h:head>
        <link href="css/basic.css" type="text/css" rel="stylesheet">
        <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
        <title>Liste</title>
    </h:head>
    <h:body>
        <h:form>
            <h1>Stateless</h1>
            <h:outputText value="Anzahl der Filme: #{statelessBean.getNumberOfMovies()}" />
            <h:outputText value="Anzahl der Personen: #{statelessBean.getNumberOfPersons()}" />
        </h:form>   
    </h:body>
</html>

这是JSF声明taglibs的方式。

您还需要更改web.xml中的某些配置，并将文件重命名为yourfile.xhtml：

<context-param>
    <param-name>javax.faces.DEFAULT_SUFFIX</param-name>
    <param-value>.xhtml</param-value>
</context-param>

<servlet>
    <servlet-name>Faces Servlet</servlet-name>
    <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
</servlet>

<!-- Use prefix mapping for Facelets pages, e.g. http://localhost:8080/webapp/yourfile.jspx -->
<servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>*.jspx</url-pattern>
</servlet-mapping>

要在EL表达式中使用bean，您需要像这样更改它：

@ManagedBean
@RequestScoped
public class StatelessBean {

    public int getNumberOfMovies() {
        return 42;
    }

    public int getNumberOfPersons() {
        return 42;
    }
}

更多信息：

Custom tags in JSF 2.0

Answer 2

尝试将调用更改为getNumberOfMovies。 JSF默默地将“get”和括号“（）”添加到html中的值。我们的想法是你编写getter和setter，然后命名属性，JSF调用适当的属性。

<h:outputText value="Anzahl der Filme: #{statelessBean.numberOfMovies}" />
        <h:outputText value="Anzahl der Personen: #{statelessBean.numberOfPersons}" />

但是，这会调用propertyNotFoundException。它也可能是你的空指针的原因，但我不确定。

javax.faces.webapp.UIComponentClassicTagBase.setJspId中的java.lang.NullPointerException

2 个答案: