当我尝试保留时出现java.lang.NullPointerException

Question

当我尝试访问映射到“ UserManagedBean”的“用户” jsp页面时，我正在mave，jsf，spring，jpa / hibernate中编写应用程序，但出现异常：

GRAVE: 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:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
    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:312)
    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 com.java.projet.managed.bean.UserManagedBean.addUser(UserManagedBean.java:47)
    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 com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
    ... 20 more
24 oct. 2013 19:54:48 com.sun.faces.lifecycle.InvokeApplicationPhase execute
ATTENTION: #{userMB.addUser}: java.lang.NullPointerException
javax.faces.FacesException: #{userMB.addUser}: java.lang.NullPointerException
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
    at javax.faces.component.UICommand.broadcast(UICommand.java:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
    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:312)
    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 com.java.projet.managed.bean.UserManagedBean.addUser(UserManagedBean.java:47)
    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 com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
    ... 20 more
24 oct. 2013 19:54:48 org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: "Servlet.service()" pour la servlet Faces Servlet a généré une exception
java.lang.NullPointerException
    at com.java.projet.managed.bean.UserManagedBean.addUser(UserManagedBean.java:47)
    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 com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98)
    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:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
    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:312)
    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)

这是我的UserManagedBean.java的代码

@ManagedBean(name = "userMB")
@RequestScoped
public class UserManagedBean implements Serializable {

    private static final long serialVersionUID = 1L;
    private static final String SUCCESS = "success";
    private static final String ERROR = "error";

    // Spring User Service is injected...
    @ManagedProperty(value = "#{UserService}")
    private IUserService userService;

    List<User> userList;

    private int id;
    private String name;
    private String surname;

    /**
     * Add User
     * 
     * @return String - Response Message
     */
    public String addUser() {
        try {
            User user = new User();
            user.setId(getId());
            user.setName(getName());
            user.setSurname(getSurname());
            userService.addUser(user);
            return SUCCESS;
        } catch (DataAccessException e) {
            e.printStackTrace();
        }
        return ERROR;
    }

    /**
     * Reset Fields
     * 
     */
    public void reset() {
        this.setId(0);
        this.setName("");
        this.setSurname("");
    }

    /**
     * Get User List
     * 
     * @return List - User List
     */
    public List<User> getUserList() {
        userList = new ArrayList<User>();
        userList.addAll(getUserService().getUsers());
        return userList;
    }

    /**
     * Get User Service
     * 
     * @return IUserService - User Service
     */
    public IUserService getUserService() {
        return userService;
    }

    /**
     * Set User Service
     * 
     * @param IUserService
     *            - User Service
     */
    public void setUserService(IUserService userService) {
        this.userService = userService;
    }

    /**
     * Set User List
     * 
     * @param List
     *            - User List
     */
    public void setUserList(List<User> userList) {
        this.userList = userList;
    }

    /**
     * Get User Id
     * 
     * @return int - User Id
     */
    public int getId() {
        return id;
    }

    /**
     * Set User Id
     * 
     * @param int - User Id
     */
    public void setId(int id) {
        this.id = id;
    }

    /**
     * Get User Name
     * 
     * @return String - User Name
     */
    public String getName() {
        return name;
    }

    /**
     * Set User Name
     * 
     * @param String
     *            - User Name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * Get User Surname
     * 
     * @return String - User Surname
     */
    public String getSurname() {
        return surname;
    }

    /**
     * Set User Surname
     * 
     * @param String
     *            - User Surname
     */
    public void setSurname(String surname) {
        this.surname = surname;
    }

}

UserDAO.java

public class UserDAO implements IUserDAO {

    @PersistenceContext
    private EntityManager em;

    public void addUser(User user) {
        this.em.persist(user);
    }

    public void updateUser(User user) {
        this.em.merge(user);

    }

    public void deleteUser(User user) {

        this.em.remove(user);
    }

    public User getUserById(int id) {

        // List list = em.createQuery("from User where id=?").setParameter(0,
        // id)).list();
        User instance = em.find(User.class, id);
        return instance;

    }

    public List<User> getUsers() {
        try {
            // process query
            Query query = em.createQuery("select u from User u ");
            List<User> results = (List<User>) query.getResultList();
            // log.trace("find all not deleted users successful");
            return results;
        } catch (RuntimeException re) {
            // log.error("find all not deleted users failed", re);
            return new ArrayList<User>();
        }
    }

}

User.java

@Entity
@Table(name = "User")
public class User {
    private int id;
    private String name;
    private String surname;

    public User() {
    }

    public User(int id, String name, String surname) {

        this.id = id;
        this.name = name;
        this.surname = surname;
    }

    @Id
    @Column(name = "ID", unique = true, nullable = false)
    public int getId() {
        return this.id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Column(name = "NAME", unique = true, nullable = false)
    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Column(name = "SURNAME", unique = true, nullable = false)
    public String getSurname() {
        return this.surname;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }

}

UserService.java

@Transactional(readOnly = true)
public class UserService implements IUserService  {

   IUserDAO userDAO;


    @Transactional(readOnly = false)
    public void addUser(User user) {
        // TODO Auto-generated method stub
         getUserDAO().addUser(user);

    }

     @Transactional(readOnly = false)
    public void updateUser(User user) {
        // TODO Auto-generated method stub
         getUserDAO().deleteUser(user);

    }

     @Transactional(readOnly = false)
    public void deleteUser(User user) {
         getUserDAO().updateUser(user);

    }

    public User getUserById(int id) {
        // TODO Auto-generated method stub
        return  getUserDAO().getUserById(id);
    }

    public List<User> getUsers() {
        return  getUserDAO().getUsers();
    }

    public IUserDAO getUserDAO() {
        return userDAO;
    }

    public void setUserDAO(IUserDAO userDAO) {
        this.userDAO = userDAO;
    }


}

db.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd  
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd"
    default-autowire="byName">

    <!-- Scans within the base package of the application for @Components to 
        configure as beans -->
    <bean id="placeholderConfig"
        class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="location" value="classpath:db.properties" />
    </bean>

    <bean id="entityManagerFactory"
        class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="showSql" value="true" />
                <property name="generateDdl" value="true" />
                <property name="databasePlatform" value="${db.dialect}" />
            </bean>
        </property>
    </bean>

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName" value="${db.driver}" />
        <property name="url" value="${db.url}" />
        <property name="username" value="${db.username}" />
        <property name="password" value="${db.password}" />
    </bean>
    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    </bean>
    <tx:annotation-driven />
    <bean
        class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />
</beans>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Use this definition if using a Java EE 6 container This also stops Eclipse 
    from complaining that 3.0 is not a valid version <web-app version="3.0" 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-app_3_0.xsd"> -->
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">

    <!-- The definition of the Root Spring Container shared by all Servlets 
        and Filters -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/spring/root-context.xml</param-value>
    </context-param>

    <!-- Creates the Spring Container shared by all Servlets and Filters -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <!-- Processes application requests -->
    <servlet>
        <servlet-name>appServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring/app/servlet-context.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>appServlet</servlet-name>
        <url-pattern>/spring/</url-pattern>
    </servlet-mapping>

    <context-param>
        <param-name>facelets.DEVELOPMENT</param-name>
        <param-value>true</param-value>
    </context-param>

    <!-- Welcome Page -->
    <welcome-file-list>
        <welcome-file>/pages/index.html</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>*.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>


</web-app>

Answer 1

从UserManagedBean.java：

public String addUser() {
    try {
        User user = new User();
        user.setId(getId());
        user.setName(getName());
        user.setSurname(getSurname());
        userService.addUser(user);
        return SUCCESS;
    } catch (DataAccessException e) {
        e.printStackTrace();
    }
    return ERROR;
}

您可以验证此方法中的userService实例不为null吗？ 您调试方法了吗？ 也许注入的豆无法正常工作。

Answer 2

ID，名称和姓氏未在userManagedBean中初始化。 调用addUser时，将创建一个新用户。 然后，尝试使用来自userManagedBean的变量设置变量，这些变量也不会初始化。

Answer 3

您的Spring bean（UserService）不会注入到您的JSF受管bean（UserManagedBean）中。 检查以下内容：

1. 必须在faces-config.xml中配置SpringBeanFacesELResolver
2. 必须通过以下任一方式在您的Spring上下文中存在UserService类的实例（名称为“ UserService”！）：
   • 在application-context.xml中手动声明它
   • 或使用@Service批注进行标记并使用组件扫描