JSF 2 managed bean does not get instantiated

问题

I am having this problem in this sample jsf project I created. Managed beans do not get instantiated. Bean class:

@ManagedBean(name="loginMB")
@RequestScoped
public class LoginMB extends AbstractMB {

    private static final long serialVersionUID = -8523135776442886000L;
    @ManagedProperty("#{userMB}")
    private UserMB userMB;

    //getters and setters 

   public String login() {      
        UserSupport userSupport = new UserSupportImpl();        
        User user = userSupport.isValidLogin(email, password);      
        if (user != null) {
            getUserMB().setUser(user);
            FacesContext context = FacesContext.getCurrentInstance();
            HttpServletRequest request = (HttpServletRequest) context
                    .getExternalContext().getRequest();
            request.getSession().setAttribute("user", user);
            return "loggedIn";
            //return "/pages/protected/index.xhtml";
        }
        displayErrorMessageToUser("Check your email/password");
        return null;
    }
}

ManagedBean annotation and RequestScope annotation have been imported from

import javax.faces.bean.*;

this is how i ve used above bean,

    <!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" 
xmlns:f="http://java.sun.com/jsf/core" 
xmlns:h="http://java.sun.com/jsf/html"
    xmlns:p="http://primefaces.org/ui">
<h:head>
</h:head>
<h:body>
    <p>#{bundle.loginHello}</p>
    <h:form>
        <p:growl showDetail="false" life="3000" />
        <h:panelGrid columns="2">
            <h:outputLabel value="#{bundle.loginUserName}" />
            <h:inputText value="#{loginMB.email}" label="Email" id="email" required="true">             
                <f:validateLength minimum="6" />
            </h:inputText>
            <h:outputLabel value="#{bundle.loginPassword}" />

            <h:inputSecret value="#{loginMB.password}" label="Password" id="senha" required="true" autocomplete="off" >         
                <f:validateLength minimum="6" />
            </h:inputSecret>


        </h:panelGrid>
        <p:commandButton action="#{loginMB.login}" value="Log in" ajax="false" />
    </h:form>
</h:body>
</html>

Other managed bean

@SessionScoped
@ManagedBean(name = "userMB")
public class UserMB implements Serializable {
    public static final String INJECTION_NAME = "#{userMB}";
    private static final long serialVersionUID = 1L;

    private User user;
        .......
}

Exception:

javax.el.PropertyNotFoundException: /login.xhtml @14,83 value="#{loginMB.email}": Target Unreachable, identifier 'loginMB' resolved to null
at com.sun.faces.facelets.el.TagValueExpression.getType(TagValueExpression.java:100)
at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:95)

faces-config.xml

<faces-config
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_2_1.xsd"
    version="2.1">

    <application>
        <resource-bundle>
            <base-name>messages</base-name>
            <var>bundle</var>
        </resource-bundle>
        <message-bundle>messages</message-bundle>
    </application>

    <navigation-rule>
        <from-view-id>/login.xhtml</from-view-id>
        <navigation-case>
            <from-action>#{loginMB.login}</from-action>
            <from-outcome>loggedIn</from-outcome>
            <to-view-id>/index.xhtml</to-view-id>
            <redirect />
        </navigation-case>      
    </navigation-rule>
    <!-- <managed-bean>
        <managed-bean-name>loginMB</managed-bean-name>
        <managed-bean-class> com.sample.jsfjpa.beans.LoginMB</managed-bean-class>
        <managed-bean-scope>request</managed-bean-scope>
    </managed-bean>
    <managed-bean>
        <managed-bean-name>userMB</managed-bean-name>
        <managed-bean-class> com.sample.jsfjpa.beans.UserMB</managed-bean-class>
        <managed-bean-scope>session</managed-bean-scope>
    </managed-bean> -->
</faces-config>

回答1:

Managed beans are not created unless you specifically invoke one of their properties or methods. That happens for all the scopes, except the @ApplicationScoped ones having @ManagedBean(eager=true) which are specifically created when JSF context loads.

Here you're referencing #{loginMB} from the view, but not #{userMB} so there's no chance to have it created.

In order to instance your @SessionScoped managed bean you can add following code in your login page:

<f:metadata>
    <f:event type="preRenderView" listener="#{userMB.initialize}" />
</f:metadata>

Which sets a listener that is executed before page rendering. You can invoke here just an empty method (to execute it JSF will construct your bean if not already created).

Starting from JSF 2.2 you can replace the preRenderView method for the new f:viewAction, which has some benefits (it's parameterless and it doesn't get invoked on postbacks ):

<f:metadata>
    <f:viewAction action="#{userMB.initialize}" />
</f:metadata>

来源：https://stackoverflow.com/questions/18592048/jsf-2-managed-bean-does-not-get-instantiated

标签

jsf-2

managed-bean