为我的 EntityManager 获取空指针异常

问题描述 投票：0回答：2

使用 Wildfly 10 进行以下工作：JSON Web 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UserDao：

@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>

所以我正在使用容器管理的持久性，由 Wildfly 10 管理。 但是，当访问 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)

这指向：

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重复，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并在我的应用程序中注入实体管理器，而不是不知道如何初始化对象。

UPDATE2：在阅读 Adam Bien 的这篇文章后，我稍微更改了代码，并通过添加注释 @Stateless 将我的 UserDao 视为 Bean： http://www.adam-bien.com/roller/abien/entry/ejb_3_persistence_jpa_for 。基本上表明 JPA 不再需要 DAO，EJB 更好。但是，在同一位置仍然出现空指针异常。 （也尝试过@Stateful，相同的结果）。

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。 解决方案是向我的 UserDao 类添加 @Stateless 符号，使其成为一个 bean。 接下来，在 UserWebService 中添加属性：

@EJB
private UserDao userDao;

用 

@EJB
在这里注入 Bean 就是解决方案。

java postgresql hibernate wildfly entitymanager
2个回答
0
投票

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
。这告诉您容器应该注入依赖项：在您的情况下为 PersistenceManager。

0
投票

在您的 

UserWebService
资源中，您正在实例化您的 
UserDao
，如下所示：

public UserWebService(){
     this.userDao=new UserDao();
}

您的 

UserDao
是一个 
@Stateless
EJB（具有本地无界面视图）。

因此，让 EJB 容器注入 

UserDao
EJB，如下所示：

@EJB
private UserDao userDao;

您现在可以删除 

UserWebService
构造函数。

我希望这有帮助。

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