JSF 表達式問題

我在UserBean中定義了一個方法：
public String verify(){
......
}index.jsp中用了這樣的表達式：
<h:commandButton value="送出"
action="#{user.verify}"/>可是運行時報空指針異常：
java.lang.NullPointerException
at vo.UserBean.verify(UserBean.java:31)31行就是定義方法的位置：public String verify()請各位指點！

解决方案 »

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user 是在jsf的配置文件中配置的类的别名，楼主是否有写呢？
写个类似的给楼主<managed-bean>
<managed-bean-name>user </managed-bean-name>
<managed-bean-class>
com.web.user
</managed-bean-class>
<managed-bean-scope>session</managed-bean-scope>
</managed-bean>
package vo;
public class UserBean {
private String name;
private String password;

public String getPassword() {
return password;
} public void setPassword(String password) {
this.password = password;
} public String getErrMessage() {
return errMessage;
} public void setErrMessage(String errMessage) {
this.errMessage = errMessage;
} private String errMessage; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
}
public String verify(){
if(!name.equals("chen")||!password.equals("123")){
errMessage="密碼或名稱錯誤！";
return "failure";
}
else{
return "success";
} }
}<?xml version="1.0" encoding="ISO-8859-1"?>
<faces-config>
<navigation-rule>
<from-view-id>index.jsp</from-view-id>
<navigation-case>
<from-outcome>success</from-outcome>
<to-view-id>welcome.jsp</to-view-id>
</navigation-case>
<navigation-case>
<from-outcome>failure</from-outcome>
            <to-view-id>index.jsp</to-view-id>
</navigation-case> </navigation-rule>
<managed-bean>
<managed-bean-name>user</managed-bean-name>
<managed-bean-class>
vo.UserBean
</managed-bean-class>
<managed-bean-scope>session</managed-bean-scope>
</managed-bean>
</faces-config><%@ page language="java" pageEncoding="GB2312"%>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>First JSF Project</title>
</head> <body>
<f:view>
<h:form>
<h3>
Please cint your name!
</h3>
<h:outputText value="#{user.errMessage}" /><p>
        NAME:<h:inputText value="#{user.name}" /><p>
       PWD:<h:inputSecret value="#{user.password}" /><p>
<h:commandButton value="Go" action="#{user.verify}" />
</h:form>
</f:view>
</body>
</html><%@ page language="java" pageEncoding="GB2312"%>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %><%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>"> <title>My JSF 'welcome.jsp' starting page</title>

<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head>

<body>
<f:view>
<h:outputText value="#{user.name}"/> 您好！
<h3>欢迎使用 JavaServer Faces！</h3>
</f:view>
</body>
</html>
package vo;
public class UserBean {
private String name;
private String password;public String getPassword() {
return password;
}public void setPassword(String password) {
this.password = password;
}public String getErrMessage() {
return errMessage;
}public void setErrMessage(String errMessage) {
this.errMessage = errMessage;
}private String errMessage;public String getName() {
return name;
}public void setName(String name) {
this.name = name;
}
public String verify(){
if(!name.equals("chen")||!password.equals("123")){
errMessage="密碼或名稱錯誤！";
return "failure";
}
else{
return "success";
}}
}
这是faces-config.xml:
<?xml version="1.0" encoding="ISO-8859-1"?>
<faces-config>
<navigation-rule>
<from-view-id>index.jsp</from-view-id>
<navigation-case>
<from-outcome>success</from-outcome>
<to-view-id>welcome.jsp</to-view-id>
</navigation-case>
<navigation-case>
<from-outcome>failure</from-outcome>
  <to-view-id>index.jsp</to-view-id>
</navigation-case></navigation-rule>
<managed-bean>
<managed-bean-name>user</managed-bean-name>
<managed-bean-class>
vo.UserBean
</managed-bean-class>
<managed-bean-scope>session</managed-bean-scope>
</managed-bean>
</faces-config>
这是index.jsp:
<%@ page language="java" pageEncoding="GB2312"%>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>First JSF Project</title>
</head><body>
<f:view>
<h:form>
<h3>
Please cint your name!
</h3>
<h:outputText value="#{user.errMessage}" /><p>
NAME:<h:inputText value="#{user.name}" /><p>
PWD:<h:inputSecret value="#{user.password}" /><p>
<h:commandButton value="Go" action="#{user.verify}" />
</h:form>
</f:view>
</body>
</html>
这是welcome.jsp:
<%@ page language="java" pageEncoding="GB2312"%>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %><%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>"><title>My JSF 'welcome.jsp' starting page</title><meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head>

<body>
<f:view>
<h:outputText value="#{user.name}"/> 您好！
<h3>欢迎使用 JavaServer Faces！</h3>
</f:view>
</body>
</html>
2011/02/14 11:14:13 com.sun.faces.application.ActionListenerImpl processAction
致命的: java.lang.NullPointerException
javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
at javax.faces.component.UICommand.broadcast(UICommand.java:387)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:475)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:756)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:265)
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.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:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
at vo.UserBean.verify(UserBean.java:31)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.el.parser.AstValue.invoke(AstValue.java:191)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
at org.apache.jasper.el.JspMethodExpression.invoke(JspMethodExpression.java:68)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
... 20 more
2011/02/14 11:14:13 com.sun.faces.lifecycle.InvokeApplicationPhase execute
警告: #{user.verify}: java.lang.NullPointerException
javax.faces.FacesException: #{user.verify}: java.lang.NullPointerException
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
at javax.faces.component.UICommand.broadcast(UICommand.java:387)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:475)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:756)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:265)
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.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:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)
Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
... 19 more
Caused by: java.lang.NullPointerException
at vo.UserBean.verify(UserBean.java:31)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.el.parser.AstValue.invoke(AstValue.java:191)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
at org.apache.jasper.el.JspMethodExpression.invoke(JspMethodExpression.java:68)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
... 20 more
2011/02/14 11:14:13 com.sun.faces.lifecycle.Phase doPhase
致命的: JSF1054: (Phase ID: INVOKE_APPLICATION 5, View ID: /index.jsp) Exception thrown during phase execution: javax.faces.event.PhaseEvent[source=com.sun.faces.lifecycle.LifecycleImpl@ae97c4]
2011/02/14 11:14:13 org.apache.catalina.core.StandardWrapperValve invoke
致命的: サーブレット Faces Servlet のServlet.service()が例外を投げました
java.lang.NullPointerException
at vo.UserBean.verify(UserBean.java:31)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.el.parser.AstValue.invoke(AstValue.java:191)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
at org.apache.jasper.el.JspMethodExpression.invoke(JspMethodExpression.java:68)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
at javax.faces.component.UICommand.broadcast(UICommand.java:387)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:475)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:756)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:265)
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.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:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)
if(!name.equals("chen")||!password.equals("123"))
-->
if(!"chen".equals(name)||!"123".equals(password))