DAO 方法全部 return NullPointerException

Question

我正在开发一个用于考试的小网络应用程序，但我遇到了 Dao 方法的几个问题，它们都是 return NullPointerException。

这是外观：

@Stateless(name = "administratorFacade")
    public class AdministratorFacade {

    @PersistenceContext(unitName = "clinic-unit")
    private EntityManager em;

    public Administrator getAdministrator(String username){
        AdministratorDaoJPA administratorDao = new AdministratorDaoJPA();
        Administrator administrator = administratorDao.findByUsername(username);
        return administrator;
    } //An example of method that uses DAO

这是 DAO：

public class AdministratorDaoJPA implements AdministratorDao {

    @PersistenceContext(unitName = "clinic-unit", type = PersistenceContextType.EXTENDED)
        private EntityManager em;

        @Override
        public Administrator findByUsername(String username){
            Query query = em.createQuery("SELECT a FROM Administrator a WHERE a.username=?");
            return (Administrator)query.setParameter(1,username).getSingleResult();
        }

还有 Administrator.java:

@Entity
@NamedQuery(name="allAdministrators", query="SELECT a FROM Administrator a")
public class Administrator {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column(unique = true, nullable = false)
    private String username;
    @Column(nullable = false)
    private String name;
    @Column(nullable = false)
    private String surname;
    @Column(nullable = false)
    private String pwd;

    public Administrator(){}

    public Administrator(String username, String name, String surname, String pwd) {
        this.username=username;
        this.name = name;
        this.surname=surname;
        this.pwd = pwd;
    }


    public String getUsername() {
        return this.username;
    }


    public void setUsername(String username) {
        this.username = username ;

    }

    public String getName() {
        return this.name;
    }

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

    public String getPwd() {
        return this.pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public String getSurname() {
        return surname;
    }


    public void setSurname(String surName) {
        this.surname = surName;
    }
    @Override
    public boolean equals(Object o) {
        Administrator adm = (Administrator) o;
        return adm.getUsername().equals(this.getUsername());
    }

    @Override
    public int hashCode() {
        return this.getUsername().hashCode();
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder();
        sb.append("Adinistrator"); 
        sb.append("{id='").append(id); 
        sb.append(", name='").append(name);
        sb.append(", surname='").append(surname);
        sb.append(", username='").append(username);
        sb.append("}\n");
        return sb.toString();
    }
}

最后 persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
    xmlns="http://java.sun.com/xml/ns/persistence" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
    http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

    <persistence-unit name="clinic-unit" transaction-type="JTA">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <jta-data-source>PostgreSQL Database</jta-data-source>

        <class>it.clinic.model.Indicator</class>
        <class>it.clinic.model.Administrator</class>
        <class>it.clinic.model.Exam</class>
        <class>it.clinic.model.ExamTypology</class>
        <class>it.clinic.model.Medic</class>
        <class>it.clinic.model.Patient</class>
        <class>it.clinic.model.Prerequisite</class>

        <properties>
             <!-- ad ogni esecuzione viene creato lo schema, cancellando il contenuto delle tabelle  
             <property name="hibernate.hbm2ddl.auto" value="create"/>  -->

              <!-- SQL dialect -->
             <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>

             <!--- Per avere info sulle istruzioni SQL inviate al db -->
             <property name="hibernate.show_sql" value="true" />
             <property name="hibernate.format_sql" value="true" />
             <property name="hibernate.hbm2ddl.auto" value="update"/>
             <property name="hibernate.archive.autodetection" value="class"/>

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

堆栈跟踪：

java.lang.NullPointerException it.clinic.persistence.ExamTypologyDaoJPA.findAll(ExamTypologyDaoJPA.java:54) it.clinic.facade.AdministratorFacade.getAllExamTypologies(AdministratorFacade.java:53) sun.reflect.NativeMethodAccessorImpl.invoke0(本机方法) sun.reflect.NativeMethodAccessorImpl.调用(NativeMethodAccessorImpl.java:62) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.apache.openejb.core.interceptor.ReflectionInvocationContext$Invocation.invoke(ReflectionInvocationContext.java:205) org.apache.openejb.core.interceptor.ReflectionInvocationContext.proceed(ReflectionInvocationContext.java:186) org.apache.openejb.monitoring.StatsInterceptor.record(StatsInterceptor.java:181) org.apache.openejb.monitoring.StatsInterceptor.invoke(StatsInterceptor.java:100) sun.reflect.NativeMethodAccessorImpl.invoke0(本机方法) sun.reflect.NativeMethodAccessorImpl.调用(NativeMethodAccessorImpl.java:62) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.apache.openejb.core.interceptor.ReflectionInvocationContext$Invocation.invoke(ReflectionInvocationContext.java:205) org.apache.openejb.core.interceptor.ReflectionInvocationContext.proceed(ReflectionInvocationContext.java:186) org.apache.openejb.core.interceptor.InterceptorStack.invoke(InterceptorStack.java:85) org.apache.openejb.core.stateless.StatelessContainer._invoke(StatelessContainer.java:236) org.apache.openejb.core.stateless.StatelessContainer.invoke(StatelessContainer.java:203) org.apache.openejb.core.ivm.EjbObjectProxyHandler.synchronizedBusinessMethod(EjbObjectProxyHandler.java:265) org.apache.openejb.core.ivm.EjbObjectProxyHandler.businessMethod(EjbObjectProxyHandler.java:260) org.apache.openejb.core.ivm.EjbObjectProxyHandler._invoke(EjbObjectProxyHandler.java:89) org.apache.openejb.core.ivm.BaseEjbProxyHandler.invoke(BaseEjbProxyHandler.java:347) it.clinic.facade.AdministratorFacade$$LocalBeanProxy.getAllExamTypologies(it/clinic/facade/AdministratorFacade.java) it.clinic.controller.ExamTypologyController.examTypologiesList(ExamTypologyController.java:35) sun.reflect.NativeMethodAccessorImpl.invoke0(本机方法) sun.reflect.NativeMethodAccessorImpl.调用(NativeMethodAccessorImpl.java:62) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.apache.tomee.catalina.JavaeeInstanceManager.postConstruct(JavaeeInstanceManager.java:163) org.apache.tomee.mojarra.TomEEInjectionProvider.invokePostConstruct(TomEEInjectionProvider.java:57) com.sun.faces.mgbean.BeanBuilder.invokePostConstruct(BeanBuilder.java:221) com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:103) com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:409) com.sun.faces.mgbean.BeanManager.create(BeanManager.java:269) com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:257) com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:117) com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176) com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203) com.sun.faces.el.ChainTypeCompositeELResolver.getValue(ChainTypeCompositeELResolver.java:90) org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:96) org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:80) org.apache.el.parser.AstValue.getValue(AstValue.java:137) org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184) org.apache.jasper.el.JspValueExpression.getValue(JspValueExpression.java:115) org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:151) javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:256) org.apache.jsp.ExamTypologies_jsp._jspx_meth_c_005fforEach_005f0(ExamTypologies_jsp.java:280) org.apache.jsp.ExamTypologies_jsp._jspService(ExamTypologies_jsp.java:232) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) com.sun.faces.context.ExternalContextImpl.dispatch(ExternalContextImpl.java:642) com.sun.faces.application.view.JspViewHandlingStrategy.executePageToBuildView(JspViewHandlingStrategy.java:363) com.sun.faces.application.view.JspViewHandlingStrategy.buildView(JspViewHandlingStrategy.java:153) com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:99) com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219) javax.faces.webapp.FacesServlet.service(FacesServlet.java:647) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) org.apache.openejb.server.httpd.WebBeansFilter.doFilter(WebBeansFilter.java:52)

我将 JPA 与 Tomee 和 JSF 2.2 一起使用。我希望你能帮助我完成这个:)

Answer 1

您正在使用

new AdministratorDaoJPA()

获取你的 DAO。所以容器不能向那个对象注入任何东西，因此 entityManager 字段有它的默认值：null.

要进行注入，您必须让容器创建并注入对象。

您的门面中也不需要实体管理器，因此将它注入那里毫无意义。您需要注入的是 DAO:

@Inject
private AdministratorDaoJPA administratorDao;

DAO 方法全部 return NullPointerException

DAO methods all return NullPointerException

java

jpa

nullpointerexception

apache-tomee