Question

我已将Set设置为我的实体。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 + "]";
    }

}

当我试图获取所有MyClassA对象时，在我的控制器中，我得到以下异常：

2016-09-28 10:10:46 DEBUG DefaultHandlerExceptionResolver：134 - 解决处理程序中的异常[public org.springframework.http.ResponseEntity＆gt; com.example.controller.MyController.listAllMyClassA（）]：java.lang.NullPointerException 2016-09-28 10:10:46 DEBUG DispatcherServlet：989 - 无法完成请求显示java.lang.NullPointerException at org.hibernate.engine.internal.StatefulPersistenceContext.getLoadedCollectionOwnerOrNull（StatefulPersistenceContext.java:756） at org.hibernate.event.spi.AbstractCollectionEvent.getLoadedOwnerOrNull（AbstractCollectionEvent.java:75）在org.hibernate.event.spi.InitializeCollectionEvent。（InitializeCollectionEvent.java:36）在org.hibernate.internal.SessionImpl.initializeCollection（SessionImpl.java:1931）在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）在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）在java.util.HashMap.hash（HashMap.java:338）在java.util.HashMap.put（HashMap.java:611）在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）在org.hibernate.loader.Loader.endCollectionLoad（Loader.java:1157）在org.hibernate.loader.Loader.initializeEntitiesAndCollections（Loader.java:1126）在org.hibernate.loader.Loader.processResultSet（Loader.java:973）在org.hibernate.loader.Loader.doQuery（Loader.java:921）在org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections（Loader.java:355）在org.hibernate.loader.Loader.doList（Loader.java:2554）在org.hibernate.loader.Loader.doList（Loader.java:2540）在org.hibernate.loader.Loader.listIgnoreQueryCache（Loader.java:2370）在org.hibernate.loader.Loader.list（Loader.java:2365）在org.hibernate.loader.criteria.CriteriaLoader.list（CriteriaLoader.java:126）在org.hibernate.internal.SessionImpl.list（SessionImpl.java:1718）在org.hibernate.internal.CriteriaImpl.list（CriteriaImpl.java:380）在com.example.dao.MyClassADaoImpl.findAllGroupQuestions（MyClassADaoImpl.java:42）在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）在java.lang.reflect.Method.invoke（Method.java:497）在org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection（AopUtils.java:317）在org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint（ReflectiveMethodInvocation.java:190）在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）在org.springframework.aop.framework.ReflectiveMethodInvocation.proceed（ReflectiveMethodInvocation.java:179）在org.springframework.aop.framework.JdkDynamicAopProxy.invoke（JdkDynamicAopProxy.java:207）在com.sun.proxy。$ Proxy63.findAllGroupQuestions（未知来源） 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）在java.lang.reflect.Method.invoke（Method.java:497）在org.springframework.web.method.support.InvocableHandlerMethod.doInvoke（InvocableHandlerMethod.java:221）在org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest（InvocableHandlerMethod.java:137）在org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle（ServletInvocableHandlerMethod.java:110）在org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod（RequestMappingHandlerAdapter.java:776）在org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal（RequestMappingHandlerAdapter.java:705）在org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle（AbstractHandlerMethodAdapter.java:85）在org.springframework.web.servlet.DispatcherServlet.doDispatch（DispatcherServlet.java:959）在org.springframework.web.servlet.DispatcherServlet.doService（DispatcherServlet.java:893）在org.springframework.web.servlet.FrameworkServlet.processRequest（FrameworkServlet.java:966）在org.springframework.web.servlet.FrameworkServlet.doGet（FrameworkServlet.java:857）在javax.servlet.http.HttpServlet.service（HttpServlet.java:622）在org.springframework.web.servlet.FrameworkServlet.service（FrameworkServlet.java:842）在javax.servlet.http.HttpServlet.service（HttpServlet.java:729）在org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:291）在org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:206）在org.apache.tomcat.websocket.server.WsFilter.doFilter（WsFilter.java:52）在org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:239）在org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:206）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:316）在org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke（FilterSecurityInterceptor.java:126）在org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter（FilterSecurityInterceptor.java:90）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.access.ExceptionTranslationFilter.doFilter（ExceptionTranslationFilter.java:114）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.session.SessionManagementFilter.doFilter（SessionManagementFilter.java:122）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter（AnonymousAuthenticationFilter.java:111）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter（SecurityContextHolderAwareRequestFilter.java:168）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter（RequestCacheAwareFilter.java:48）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter（AbstractAuthenticationProcessingFilter.java:205）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.authentication.logout.LogoutFilter.doFilter（LogoutFilter.java:120）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.csrf.CsrfFilter.doFilterInternal（CsrfFilter.java:96）在org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:107）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal（HeaderWriterFilter.java:64）在org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:107）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter（SecurityContextPersistenceFilter.java:91）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal（WebAsyncManagerIntegrationFilter.java:53）在org.springframework.web.filter.OncePerRequestFilter.doFilter（OncePerRequestFilter.java:107）在org.springframework.security.web.FilterChainProxy $ VirtualFilterChain.doFilter（FilterChainProxy.java:330）在org.springframework.security.web.FilterChainProxy.doFilterInternal（FilterChainProxy.java:213）在org.springframework.security.web.FilterChainProxy.doFilter（FilterChainProxy.java:176）在org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate（DelegatingFilterProxy.java:344）在org.springframework.web.filter.DelegatingFilterProxy.doFilter（DelegatingFilterProxy.java:261）在org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:239）在org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:206）在org.apache.catalina.core.StandardWrapperValve.invoke（StandardWrapperValve.java:212）在org.apache.catalina.core.StandardContextValve.invoke（StandardContextValve.java:106）在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）在org.apache.catalina.valves.AbstractAccessLogValve.invoke（AbstractAccessLogValve.java:616）在org.apache.catalina.core.StandardEngineValve.invoke（StandardEngineValve.java:88）在org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:521）在org.apache.coyote.http11.AbstractHttp11Processor.process（AbstractHttp11Processor.java:1096） at org.apache.coyote.AbstractProtocol $ AbstractConnectionHandler.process（AbstractProtocol.java:674）在org.apache.tomcat.util.net.AprEndpoint $ SocketProcessor.doRun（AprEndpoint.java:2500）在org.apache.tomcat.util.net.AprEndpoint $ SocketProcessor.run（AprEndpoint.java:2489）在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）在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，请告诉我们！感谢

Answer 1

查看你的stacktrace，我相信这个问题的根源在你的hashCode方法中：

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

尝试从hashCode方法中删除sets属性。我不认为这是计算类的哈希值所必需的。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

安全！：）

Hibernate java.lang.NullPointerException

1 个答案: