小贝子编程

Java EE and JSF NullPointerException



我正在尝试创建一个超级简单的web应用程序，该应用程序使用在Apache TomEE上运行的Java EE进行登录。在这样做的时候，我在一个我认为非常简单的页面上遇到了一个java.lang.NullPointerException的javax.servlet.ServletException。

一些系统和库信息：

- CentOS 6.5
- Eclipse Kepler IDE for Java EE Developers
- JRE System Library [java-1.7.0-openjdk-1.7.0.45.x86_64]
- Apache Tomcat v7.0
- Apache TomEE 1.6.0 JAX-RS
- JSF Mojara 2.2 (javax.faces.jar)
- log4j 1.2.17 (log4j-1.2.17.jar)

愚蠢的简单页面(home.xhtml)：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.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">
<h:head>
<title>LogTest Home</title>
</h:head>
<h:body>
<h1>Testing:</h1>
<h:outputText value="#{logTest.foo()}"/>
</h:body>
</html>

backingbean(logTest.java)：

package test.pack;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import org.apache.log4j.Logger;
@ManagedBean(name="logTest")
@SessionScoped
public class logTest {
private static final Logger LOGGER = Logger.getLogger(logTest.class);
private String statusMsg = "Default status";
public String getStatusMsg() {
return statusMsg;
}
public void setStatusMsg(String statusMsg) {
this.statusMsg = statusMsg;
}
public String foo() {
LOGGER.info("Currently executing method foo()");
setStatusmsg("Hello foo()!");
return "foo() executed successfully!";
}
}

/WEB-INF/classes目录中的log4j.properties文件

log4j.rootLogger = TRACE, toConsole, toFile
#Test File Logs
log4j.appender.toFile=org.apache.log4j.DailyRollingFileAppender
log4j.appender.toFile=/opt/tommee/logs/log4jWebapp.log
log4j.appender.toFile.DatePattern='.'yyyy-MM-dd
log4j.appender.toFile.layout=org.apache.log4j.PatternLayout
log4j.appender.toFile.layout.ConversionPattern=%d %5p [%t] - %c%M - %m%n
#Test Console Logs
log4j.appender.toConsole=org.apache.log4j.ConsoleAppender
log4j.appender.toConsole.layout=org.apache.log4j.PatternLayout
log4j.appender.toConsole.layout.ConversionPattern=%d %5p [%t] - %c%M - %m%n

部署描述符(web.xml)

<?xml version"1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://wwww.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaaee/web-app_3_0.xsd"
version="3.0">
<display-name>log4jTEst</display-name>
<welcome-file-list>
<welcome-filee>faces/home.xhtml</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>Faces Servlet</servlet-name>
<servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>/faces/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>*.jsf</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>*.faces</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>*.xhtml</url-pattern>
</servlet-mapping>
<context-param>
<description>State saving method: 'client' or 'server' (=default). See JSF Specification 2.5.2</description>
<param-name>javax.faces.STATE_SAVING_METHOD</param-name>
<param-value>client</param-value>
</context-param>
<context-param>
<param-name>javax.servlet.jsp.jstl.fmt.localizationContext</param-name>
<param-value>resources.application</param-value>
</context-param>
<listener>
<listener-class>com.sun.faces.config.ConfigureListener</listener-class>
</listener>
</web-app>

现在，当我在我设置的服务器上运行此程序时，我会从Eclipse浏览器中得到：

HTTP Status 500-
type - Exception report
message
description - The server encountered an internal error that prevented it from fulfilling this request.
exception -
javax.servlet.ServletException
javax.faces.webapp.FacesServlet.service(FacesServlet.java:659)
org.apachee.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
root cause -
java.lang.NullPointerException
javax.el.CompositeELResolver.invoke(CompositeELResolver.java:255)
javax.el.CompositeELResolver.invoke(CompositeELResolver.java:255)
org.apachee.el.parser.AstValue.getValue(AstValue.java:173)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.jaava:109)
javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
javax.faces.component.UIOutput.getValue(UIOutput.java:174)
com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
javax.faces.component.UIComponentBase.encodeEnd(UIComponent.java:924)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1863)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1859)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1859)
com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:443)
com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
note - the full stack trace of the root cause is available in the Apache Tomcat (TomEE)/7.00.47 (1.6.0) logs

以下是启动后的服务器日志：

Feb 10, 2014 4:40:29 PM com.sun.faces.application.view.FaceletViewHandlingStrategy handleRenderException
SEVERE: Error Rendering View[/home.xhtml]
java.lang.NullPointerException
javax.el.CompositeELResolver.invoke(CompositeELResolver.java:255)
javax.el.CompositeELResolver.invoke(CompositeELResolver.java:255)
org.apachee.el.parser.AstValue.getValue(AstValue.java:173)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.jaava:109)
javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
javax.faces.component.UIOutput.getValue(UIOutput.java:174)
com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
javax.faces.component.UIComponentBase.encodeEnd(UIComponent.java:924)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1863)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1859)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1859)
com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:443)
com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
org.apache.catalina.core.StandardContextValve.invoke(StadnardContextValve.java:123)
org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
java.lang.Thread.run(Thread.java:744)
Feb 10, 2014 4:40:29 PM org.apache.catalina.core.StandaardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Faces Servlet] in context with hpath [/log4jTest] threw exception [null] with root cause
java.lang.NullPointerExpression
javax.el.CompositeELResolver.invoke(CompositeELResolver.java:255)
javax.el.CompositeELResolver.invoke(CompositeELResolver.java:255)
org.apachee.el.parser.AstValue.getValue(AstValue.java:172)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.jaava:109)
javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
javax.faces.component.UIOutput.getValue(UIOutput.java:174)
com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
javax.faces.component.UIComponentBase.encodeEnd(UIComponent.java:924)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1863)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1859)
javax.faces.component.UIComponent.encodeALL(UIComponent.java:1859)
com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:443)
com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
org.apache.catalina.core.StandardContextValve.invoke(StadnardContextValve.java:123)
org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
java.lang.Thread.run(Thread.java:744)

所以，我需要一些东西：A-为了解决这个nullPointerException(我认为这是由于我自己对JavaEE缺乏了解，因此对平台的一些滥用。B-关于我如何正确或不正确地使用JavaEE的信息，以及可以帮助我改进的信息/资源。主要是对这个简单应用程序的更正。

对我来说，在写下这个帮助请求时，我偶然发现了一个关于设置日志的问题的答案。显然，我现在已经开始工作了，这很好，但通过我的调整，上面的问题一直存在。

感谢您的阅读，我感谢您的建议、更正和支持！

因此，当您的页面上有<h:outputText value="#{logTest.foo()}"/>时，处理器读取的是：

  1. 在托管bean中可能有一个名为foo的变量
  2. 根据JavaBean方法命名标准，该托管bean中将有一个名为getFoo()的方法

您的类在这两方面都失败，因此出现错误。

<h:outputText/>需要一个值绑定，即类上实际属性的getter，而不是一个只返回值(不带参数)的方法。因此，预期是：

public class logTest {
private static final Logger LOGGER = Logger.getLogger(logTest.class);
private String statusMsg = "Default status";
private String foo = "TheFoo" //There should be a named variable
public String getStatusMsg() {
return statusMsg;
}
public void setStatusMsg(String statusMsg) {
this.statusMsg = statusMsg;
}
public String getFoo(){
LOGGER.info("Currently executing method getFoo()");
return this.foo;
}
public String foo() {
LOGGER.info("Currently executing method foo()");
setStatusmsg("Hello foo()!");
return "foo() executed successfully!";
}
}

更多信息：

  • 值和方法表达式

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