java - hibernate java.lang.NullPointerException

Question

我已将 Set 嵌套到我的实体中。这是我的代码:

MyClassA:

@Entity
@Table(name = "aaa")
public class MyClassA {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "name", nullable = false)
    private String name;

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private Set<MyClassB> mycollection = new HashSet<MyClassB>();

    public MyClassA() {    
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Set<MyClassB> getMyClassB() {
        return mycollection;
    }

    public void setMyClassB(Set<MyClassB> mycollection) {
        this.mycollection = mycollection;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + id;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        result = prime * result + ((mycollection == null) ? 0 : mycollection.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        MyClassA other = (MyClassA) obj;
        if (id != other.id)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        if (mycollection == null) {
            if (other.mycollection != null)
                return false;
        } else if (!mycollection.equals(other.mycollection))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "MyClassA [id=" + id + ", name=" + name + ", mycollection=" + mycollection + "]";
    }       
}

MyClassB:

@Entity
@Table(name = "bbb")
public class MyClassB {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "name", nullable = false)
    private String name;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "elementname", nullable = false)
    private String elementname;                

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "type", nullable = false)
    private String type;

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private Set<MyClassC> mycollection = new HashSet<MyClassC>();

    public MyClassB() {    
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getElementname() {
        return elementname;
    }

    public void setElementname(String elementname) {
        this.elementname = elementname;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Set<MyClassC> getMyCollection() {
        return mycollection;
    }

    public void setMyCollection(Set<MyClassC> mycollection) {
        this.mycollection = mycollection;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((elementname == null) ? 0 : elementname.hashCode());
        result = prime * result + id;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
Line 79---> result = prime * result + ((mycollection == null) ? 0 : mycollection.hashCode());
        result = prime * result + ((type == null) ? 0 : type.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        MyClassB other = (MyClassB) obj;
        if (elementname == null) {
            if (other.elementname != null)
                return false;
        } else if (!elementname.equals(other.elementname))
            return false;
        if (id != other.id)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        if (mycollection == null) {
            if (other.mycollection != null)
                return false;
        } else if (!mycollection.equals(other.mycollection))
            return false;
        if (type == null) {
            if (other.type != null)
                return false;
        } else if (!type.equals(other.type))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "MyClassB [id=" + id + ", name=" + name + ", elementname=" + elementname + ", type=" + type + ", mycollection=" + mycollection + "]";
    }       
}

MyClassC:

@Entity
@Table(name = "ccc")
public class MyClassC {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "name", nullable = false)
    private String name;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "value", nullable = false)
    private String value;

    public MyClassC(){          
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + id;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        result = prime * result + ((value == null) ? 0 : value.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        MyClassC other = (MyClassC) obj;
        if (id != other.id)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        if (value == null) {
            if (other.value != null)
                return false;
        } else if (!value.equals(other.value))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "MyClassC [id=" + id + ", name=" + name + ", value=" + value + "]";
    }

}

当我试图在我的 Controller 中获取所有 MyClassA 对象时，出现以下异常:

2016-09-28 10:10:46 DEBUG DefaultHandlerExceptionResolver:134 - Resolving exception from handler [public org.springframework.http.ResponseEntity> com.example.controller.MyController.listAllMyClassA()]: java.lang.NullPointerException 2016-09-28 10:10:46 DEBUG DispatcherServlet:989 - Could not complete request java.lang.NullPointerException at org.hibernate.engine.internal.StatefulPersistenceContext.getLoadedCollectionOwnerOrNull(StatefulPersistenceContext.java:756) at org.hibernate.event.spi.AbstractCollectionEvent.getLoadedOwnerOrNull(AbstractCollectionEvent.java:75) at org.hibernate.event.spi.InitializeCollectionEvent.(InitializeCollectionEvent.java:36) at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1931) at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:559) at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:261) at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:555) at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:143) at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:316) at com.example.model.MyClassB.hashCode(MyClassB.java:79) at java.util.HashMap.hash(HashMap.java:338) at java.util.HashMap.put(HashMap.java:611) at java.util.HashSet.add(HashSet.java:219) at java.util.AbstractCollection.addAll(AbstractCollection.java:344) at org.hibernate.collection.internal.PersistentSet.endRead(PersistentSet.java:344) at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollection(CollectionLoadContext.java:251) at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:238) at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:211) at org.hibernate.loader.Loader.endCollectionLoad(Loader.java:1157) at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1126) at org.hibernate.loader.Loader.processResultSet(Loader.java:973) at org.hibernate.loader.Loader.doQuery(Loader.java:921) at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:355) at org.hibernate.loader.Loader.doList(Loader.java:2554) at org.hibernate.loader.Loader.doList(Loader.java:2540) at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2370) at org.hibernate.loader.Loader.list(Loader.java:2365) at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:126) at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1718) at org.hibernate.internal.CriteriaImpl.list(CriteriaImpl.java:380) at com.example.dao.MyClassADaoImpl.findAllGroupQuestions(MyClassADaoImpl.java:42) at com.example.service.MyClassAImpl.findAllGroupQuestions(MyClassAImpl.java:41) 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:497) at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317) at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207) at com.sun.proxy.$Proxy63.findAllGroupQuestions(Unknown Source) at gr.citystore.helios.controller.QuestionaireController.listAllGroupQuestions(QuestionaireController.java:212) 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:497) at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857) at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316) at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126) at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:168) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:96) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213) at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176) at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344) at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674) at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2500) at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2489) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745)

MyClassADaoImpl:

@SuppressWarnings("unchecked")
public List<MyClassA> findAllMyClassAs() {
    Criteria criteria = createEntityCriteria();
    criteria.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);
    return (List<MyClassA>) criteria.list();
}

最后，我的服务实现 MyClassAImpl:

public List<MyClassA> findAllMyClassAs() {
        return dao.findAllMyClassAs();
    }

我的 Hibernate 版本是 4.3.11.Final。如果您需要任何其他信息，请告诉我!谢谢

Answer 1

查看您的堆栈跟踪，我相信这个问题的根源在于您的 hashCode 方法:

com.example.model.MyClassB.hashCode(MyClassB.java:79) at

尝试从您的 hashCode 方法中删除 sets 属性。我不认为这对于计算类的哈希值是必要的。在大多数情况下，您使用业务键(即标识对象的唯一属性)。

https://docs.jboss.org/hibernate/stable/core.old/reference/en/html/persistent-classes-equalshashcode.html

注意安全! :)