JSF and ManagedBean : NullPointerException

Question

我正在设计一个带有托管bean的JSF应用程序。目前，我一直在尝试创建一个简单的登录页面(用户名和密码是硬编码的时刻):

<h:form class="form-signin">
    <h2 class="form-signin-heading">Please sign in</h2><hr />
    <input name="username" type="text" class="input-block-level" placeholder="Username" />
    <input name="password" type="password" class="input-block-level" placeholder="Password" />
    <h:commandButton action="#{userController.login}" class="btn btn-block btn-primary" type="submit" value="Sign in" />
</h:form>

这里是控制器(UserController.java):

@ManagedBean(name="userController")
@ApplicationScoped
public class UserController {
    @EJB
    private UserService userService;
    public UserService getUserService() {
        return userService;
    }
    public void setUserService(UserService userService) {
        this.userService = userService;
    }
    public UserController() {
    }
    public void login() throws IOException {
        Boolean login = userService.login("admin", "p4ssw0rd");
        ExternalContext externalContext = FacesContext.getCurrentInstance().getExternalContext();
        if (login == true) { 
            externalContext.redirect("dashboard.xhtml");
        } else {
            externalContext.redirect("login.xhtml");
        }
    }
}

UserService.java文件:

@Stateless
public class UserService {
    @PersistenceContext
    private EntityManager em;
    public static String md5(String input) {
        // Removed for clarity...
    }
    public Boolean login(String username, String password) {
        //String hash = md5(password);
        return Boolean.TRUE; // As you can see, nothing can fail for the moment
    }
}

当我提交登录表单时，出现了一个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:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:794)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1259)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:409)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1008)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1852)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.NullPointerException
    at com.myname.myproject.managedbean.UserController.login(UserController.java:33)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.apache.el.parser.AstValue.invoke(AstValue.java:278)
    at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:274)
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
    ... 24 more

在UserController.java中，如果我替换这一行:

Boolean login = userService.login("admin", "p4ssw0rd");

By this:

Boolean login = true; // Or false (I've tested twice)

一切正常，所以Java似乎没有找到UserService…

谢谢你的帮助，我完全迷路了。

Answer 1

您是否检查了在名为UserController的托管bean中放置getter和setter ?

如果不这样做，即使代码编译正确，依赖注入也不会被正确持有。

Answer 2

我认为问题出在EJB上。如果它是无接口bean，则应该注释@LocalBean，否则应该实现接口。试试这样做:

@Stateless
public class UserService implements UserServiceLocal {
    @Override
    public boolean login () {
        //dummy implementation
        return true;
    }
}

where UserServiceLocal is:

@Local
public interface UserServiceLocal {
    public boolean login();
}

用法:

@ManagedBean(name="userController")
@ApplicationScoped
public class UserController {
    @EJB
    private UserServiceLocal userService;
    public void login() {
       userService.login();
    }
}

Answer 3

关于为什么应该实现接口的问题，请参阅EJB's -何时使用远程和/或本地接口?EJB(企业java bean)可以有一个接口(可以用@Remote进行注释，这意味着实现它的bean在分布式环境中运行)，或者用@Local进行注释，这意味着bean在相同的JVM中运行。相反，无接口bean是不实现任何接口的bean。因此，您应该指示JVM将其视为bean而不是POJO(普通的旧java对象);这可以通过在应该是bean/EJB的类上添加@LocalBean注释来实现。