java - 为我的 EntityManager 获取空指针异常

Question

在以下方面使用 Wildfly 10:JSON 网络服务通过 DAO 对象使用 hibernate 访问 postgresql 数据库。

更具体地说，我的 POJO User.java:

@Entity (name="User")
@Table(name = "users")
public class User {


    @Id @GeneratedValue
    @Column(name="id")
    private int id;

    @Column(name="username")
    private String userName;

    @Column(name="password")
    private String password;

    @Column(name="email")
    private String emailAddress;

    public User(String userName, String password, String emailAddress) {
        super();
        this.userName = userName;
        this.password = password;
        this.emailAddress = emailAddress;
    }

    public User() {
        super();
    }

    public int getId() {
        return id;
    }

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

我的用户道:

@Stateless
public class UserDao {

    @PersistenceContext (unitName="librarysoftjpa")
    private EntityManager entityManager;

    public List<User> getAllUsers(){
List<User> allUsers=null;

        CriteriaBuilder criteriaBuilder = this.entityManager.getCriteriaBuilder();
        CriteriaQuery<User> criteria = criteriaBuilder.createQuery(User.class);
        criteria.from(User.class);

        TypedQuery<User>query = entityManager.createQuery(criteria);
        allUsers = query.getResultList();
        return allUsers;    
    }
}

我的网络服务:

@RequestScoped
@Path("/users")
@Produces("application/json")
@Consumes("application/json")
public class UserWebService {


    private UserDao userDao;


    public UserWebService(){
        this.userDao=new UserDao();
    }
@GET
    @Path("/all")
    public List<User> getAllUsers(){
        List<User>users=this.userDao.getAllUsers();
        return users;
    }
}

我的 persistence.xml:

<persistence version="2.1"
   xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="
        http://xmlns.jcp.org/xml/ns/persistence
        http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
   <persistence-unit name="librarysoftjpa" transaction-type="JTA">
    <jta-data-source>java:/PostGreLibrarySoftDS</jta-data-source>
    <class>org.declercq.librarysoftbackend.models.Permission</class>
    <class>org.declercq.librarysoftbackend.models.Role</class>
    <class>org.declercq.librarysoftbackend.models.User</class>
      <properties>
         <!-- Properties for Hibernate -->
         <property name="hibernate.hbm2ddl.auto" value="update" />
         <property name="hibernate.show_sql" value="true" />
         <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
         <property name="hibernate.format_sql" value="true"/>

      </properties>
   </persistence-unit>
</persistence>

所以我正在使用由 Wildfly 10 管理的容器管理的持久性。但是，在访问 Web 服务时，我的实体管理器出现空指针异常:

10:17:10,095 INFO  [org.wildfly.extension.undertow] (ServerService Thread Pool -- 62) WFLYUT0021: Registered web context: /librarysoftbackend
10:17:10,174 INFO  [org.jboss.as.server] (ServerService Thread Pool -- 34) WFLYSRV0010: Deployed "librarysoftbackend.war" (runtime-name : "librarysoftbackend.war")
10:17:10,341 INFO  [org.jboss.as] (Controller Boot Thread) WFLYSRV0060: Http management interface listening on http://127.0.0.1:9990/management
10:17:10,342 INFO  [org.jboss.as] (Controller Boot Thread) WFLYSRV0051: Admin console listening on http://127.0.0.1:9990
10:17:10,343 INFO  [org.jboss.as] (Controller Boot Thread) WFLYSRV0025: WildFly Full 10.1.0.Final (WildFly Core 2.2.0.Final) started in 14178ms - Started 422 of 670 services (404 services are lazy, passive or on-demand)
10:17:18,898 ERROR [io.undertow.request] (default task-3) UT005023: Exception handling request to /librarysoftbackend/rest/users/all: org.jboss.resteasy.spi.UnhandledException: java.lang.NullPointerException
    at org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:77)
    at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:220)
    at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:175)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:418)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:209)
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
    at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
    at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)
    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)
    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)
    at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
    at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:805)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
    at org.declercq.librarysoftbackend.dao.UserDao.getAllUsers(UserDao.java:64)
    at org.declercq.librarysoftbackend.rest.UserWebService.getAllUsers(UserWebService.java:69)
    at org.declercq.librarysoftbackend.rest.UserWebService$Proxy$_$$_WeldClientProxy.getAllUsers(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:139)
    at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:295)
    at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:249)
    at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:236)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:402)
    ... 43 more

更具体地说:

Caused by: java.lang.NullPointerException
    at org.declercq.librarysoftbackend.dao.UserDao.getAllUsers(UserDao.java:64)

指向:

CriteriaBuilder criteriaBuilder = this.entityManager.getCriteriaBuilder();

在 UserDao.java 中。

知道我在这里做错了什么吗？

更新:此处链接的主题可能是重复的，与此相关的百分比绝对为零。我的问题是容器管理的持久性上下文和在我的应用程序中注入(inject)实体管理器，而不是不知道如何初始化对象。

更新 2:在阅读 Adam Bien 的这篇文章后，我稍微更改了我的代码并通过添加注释 @Stateless 将我的 UserDao 视为一个 Bean:http://www.adam-bien.com/roller/abien/entry/ejb_3_persistence_jpa_for .基本上说 JPA 不再需要 DAO，EJB 更好。但是，同一位置上仍然存在空指针异常。 (也尝试了@Stateful，结果相同)。

更新 3:在 Wildfly 的 standalone.xml 中配置我的数据源:

<datasources>
                <datasource jndi-name="java:/PostGreLibrarySoftDS" pool-name="PostgrePool">
                    <connection-url>jdbc:postgresql://127.0.0.1:5432/librarysoft</connection-url>
                    <driver>postgres</driver>
                    <security>
                        <user-name>test</user-name>
                        <password>test</password>
                    </security>
                </datasource>
                <drivers>
                    <driver name="postgres" module="org.postgres">
                        <driver-class>org.postgresql.Driver</driver-class>
                    </driver>
                </drivers>

已解决。解决方案是将 @Stateless 符号添加到我的 UserDao 类，使其成为一个 bean。接下来，在 UserWebService 中，添加属性:

@EJB
private UserDao userDao;

在此处使用 @EJB 注入(inject) bean 是解决方案。

Answer 1

您的 UserDao 不受任何框架管理。请注意，在您提供的示例中，电影对象上有 @Stateful。这告诉你容器它应该注入(inject)依赖项:在你的例子中是 PersistenceManager。