org.hibernate.LazyInitializationException：无法初始化代理 - 没有会话 5答案

【问题标题】：org.hibernate.LazyInitializationException: could not initialize proxy - no Session 5org.hibernate.LazyInitializationException：无法初始化代理 - 没有会话 5
【发布时间】：2015-11-09 01:41:34
【问题描述】：

我有一些错误要解决，这里是错误：

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
at model.Teacher_$$_jvstd69_0.toString(Teacher_$$_jvstd69_0.java)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getFormattedValue(HtmlBasicRenderer.java:517)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getFormattedValue(HtmlBasicRenderer.java:540)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:357)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1903)
at org.primefaces.component.column.Column.renderChildren(Column.java:344)
at org.primefaces.component.datatable.DataTableRenderer.encodeCell(DataTableRenderer.java:1019)
at org.primefaces.component.datatable.DataTableRenderer.encodeRow(DataTableRenderer.java:967)
at org.primefaces.component.datatable.DataTableRenderer.encodeRows(DataTableRenderer.java:878)
at org.primefaces.component.datatable.DataTableRenderer.encodeTbody(DataTableRenderer.java:825)
at org.primefaces.component.datatable.DataTableRenderer.encodeTbody(DataTableRenderer.java:788)
at org.primefaces.component.datatable.DataTableRenderer.encodeRegularTable(DataTableRenderer.java:281)
at org.primefaces.component.datatable.DataTableRenderer.encodeMarkup(DataTableRenderer.java:243)
at org.primefaces.component.datatable.DataTableRenderer.encodeEnd(DataTableRenderer.java:85)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1903)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1899)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1899)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:451)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
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.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
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:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:617)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

它发生在我从 Hibernate 工具生成的关系 2 表之后

表学生

    @Entity
@Table(name = "student", schema = "public")
public class Student implements java.io.Serializable {

    private static final long serialVersionUID = 3484556118289412550L;
    private int stuId;
    private Teacher teacher;
    private String stuName;
    private Integer stuAge;

    public Student() {
    }

    public Student(int stuId) {
        this.stuId = stuId;
    }

    public Student(int stuId, Teacher teacher, String stuName, Integer stuAge) {
        this.stuId = stuId;
        this.teacher = teacher;
        this.stuName = stuName;
        this.stuAge = stuAge;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "stu_id", unique = true, nullable = false)
    public int getStuId() {
        return this.stuId;
    }

    public void setStuId(int stuId) {
        this.stuId = stuId;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "stu_teachid")
    public Teacher getTeacher() {
        return this.teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    @Column(name = "stu_name", length = 40)
    public String getStuName() {
        return this.stuName;
    }

    public void setStuName(String stuName) {
        this.stuName = stuName;
    }

    @Column(name = "stu_age")
    public Integer getStuAge() {
        return this.stuAge;
    }

    public void setStuAge(Integer stuAge) {
        this.stuAge = stuAge;
    }

}

老师

@Entity
@Table(name = "teacher", schema = "public")
public class Teacher implements java.io.Serializable {

    private static final long serialVersionUID = 3863374948774698083L;
    private int teachId;
    private String teachName;
    private Set<Student> students = new HashSet<Student>(0);

    public Teacher() {
    }

    public Teacher(int teachId) {
        this.teachId = teachId;
    }

    public Teacher(int teachId, String teachName, Set<Student> students) {
        this.teachId = teachId;
        this.teachName = teachName;
        this.students = students;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "teach_id", unique = true, nullable = false)
    public int getTeachId() {
        return this.teachId;
    }

    public void setTeachId(int teachId) {
        this.teachId = teachId;
    }

    @Column(name = "teach_name", length = 40)
    public String getTeachName() {
        return this.teachName;
    }

    public void setTeachName(String teachName) {
        this.teachName = teachName;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "teacher")
    public Set<Student> getStudents() {
        return this.students;
    }

    public void setStudents(Set<Student> students) {
        this.students = students;
    }

}

我的 applicationContext.xml

<context:component-scan base-package="controller"></context:component-scan>
    <context:component-scan base-package="dao"></context:component-scan>
    <context:component-scan base-package="model"></context:component-scan>
    <context:component-scan base-package="service"></context:component-scan>

    <!-- Enable Spring Annotation Configuration -->
    <context:annotation-config />
    <context:spring-configured />

    <!-- Create Data Source bean -->
    <bean id="DataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName" value="org.postgresql.Driver" />
        <property name="url" value="jdbc:postgresql://localhost:5432/university" />
        <property name="username" value="postgres" />
        <property name="password" value="1234" />
    </bean>
    <!-- Define SessionFactory bean -->
    <bean id="SessionFactory"
        class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="DataSource" />
        <property name="annotatedClasses">
            <list>
                <value>model.Student</value>
                <value>model.Teacher</value>
            </list>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</prop>
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.format_sql">true</prop>
                <prop key="hibernate.use_sql_comments">true</prop>
                <prop key="hibernate.temp.use_jdbc_metadata_defaults">false</prop>
            </props>
        </property>
    </bean>

    <!-- Detect @Transactional Annotation -->
    <tx:annotation-driven transaction-manager="txManager" />


    <!-- Transaction Manager is defined -->
    <bean id="txManager"
        class="org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name="sessionFactory" ref="SessionFactory" />
    </bean>

如何解决这个问题？

【问题讨论】：

标签： java hibernate jsf-2

【解决方案1】：

将一组学生的映射从 LAZY 更改为 EAGER

【讨论】：

实际上你最好不要使用急切的抓取。这是一个很好的秘诀，可以在以后用它击中自己的脚。

【解决方案2】：

有三种方法可以避免延迟初始化异常：

在映射文件中将惰性属性设置为 false。我不推荐这种方法，因为它会增加数据库负载，因此会降低性能。
保持会话打开。在处理数据之前不要关闭会话。如果在请求期间会话处于打开状态，您可以获得关联的图表，但您需要确保该操作在同一事务中进行。
急切地获取关联。在 HQL 查询中使用关键字“fetch”来检索关联。从我的角度来看，这是避免延迟初始化问题的最佳解决方案。在 HQL 中，只需在 from 子句中添加 fetch 关键字即可急切地获取关联。

【讨论】：

谢谢你的解释:)