java - 尝试让简单的 Struts2 w/Hibernate 示例工作时出错

Question

我在使用 Struts2 和 Hibernate 获取具有许多表关系的较大应用程序时遇到一些问题，因此我决定创建一个规模小得多的示例来解决这个问题，但我也无法使其正常工作。我的主要问题是，当涉及任何惰性实例化集时，我根本无法让两者一起工作。我试图找出如何使其在加载和不加载惰性数据的情况下工作，但在这种情况下，我已经加载了惰性数据，并且收到了“java.lang.StackOverflowError”。我有两个表，“部门”有两个条目，“员工”有三个条目；我正在使用 Struts2“xslt”结果类型。这是两个持久化类:

部门:

package com.test.model;
// Generated Apr 7, 2012 7:10:28 PM by Hibernate Tools 3.4.0.CR1

import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

/**
 * Departments generated by hbm2java
 */
@Entity
@Table(name="Departments"
    ,catalog="test"
)
public class Departments  implements java.io.Serializable {


     private Integer id;
     private String name;
     private Set<Employees> employeeses = new HashSet(0);

    public Departments() {
    }


    public Departments(String name) {
        this.name = name;
    }
    public Departments(String name, Set employeeses) {
       this.name = name;
       this.employeeses = employeeses;
    }

     @Id @GeneratedValue(strategy=IDENTITY)


    @Column(name="Id", unique=true, nullable=false)
    public Integer getId() {
        return this.id;
    }

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


    @Column(name="Name", nullable=false)
    public String getName() {
        return this.name;
    }

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

    @OneToMany(fetch=FetchType.LAZY, mappedBy="departments")
    public Set<Employees> getEmployeeses() {
        return this.employeeses;
    }

    public void setEmployeeses(Set employeeses) {
        this.employeeses = employeeses;
    }
}

员工:

package com.test.model;
// Generated Apr 7, 2012 7:10:28 PM by Hibernate Tools 3.4.0.CR1


import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

/**
 * Employees generated by hbm2java
 */
@Entity
@Table(name="Employees"
    ,catalog="test"
)
public class Employees  implements java.io.Serializable {


     private Integer id;
     private Departments departments;
     private String firstName;
     private String lastName;

    public Employees() {
    }

    public Employees(Departments departments, String firstName, String lastName) {
       this.departments = departments;
       this.firstName = firstName;
       this.lastName = lastName;
    }

     @Id @GeneratedValue(strategy=IDENTITY)


    @Column(name="Id", unique=true, nullable=false)
    public Integer getId() {
        return this.id;
    }

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

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="DepartmentsId", nullable=false)
    public Departments getDepartments() {
        return this.departments;
    }

    public void setDepartments(Departments departments) {
        this.departments = departments;
    }


    @Column(name="FirstName", nullable=false)
    public String getFirstName() {
        return this.firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }


    @Column(name="LastName", nullable=false)
    public String getLastName() {
        return this.lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

我在 DepartmentsManager 类中使用的 HQL 查询是:“from Departments d left join fetch d.employeeses”。

这是错误的堆栈跟踪:

Exception in thread "http-bio-8080-exec-4" java.lang.StackOverflowError at java.security.AccessController.doPrivileged(Native Method) at org.apache.commons.logging.LogFactory.getContextClassLoaderInternal(LogFactory.java:859) at org.apache.commons.logging.LogFactory.getFactory(LogFactory.java:423) at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:685) at com.opensymphony.xwork2.util.logging.commons.CommonsLoggerFactory.getLoggerImpl(CommonsLoggerFactory.java:29) at com.opensymphony.xwork2.util.logging.LoggerFactory.getLogger(LoggerFactory.java:42) at org.apache.struts2.views.xslt.AbstractAdapterNode.(AbstractAdapterNode.java:85) at org.apache.struts2.views.xslt.AbstractAdapterElement.(AbstractAdapterElement.java:41) at org.apache.struts2.views.xslt.BeanAdapter.(BeanAdapter.java:73) at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:525) at java.lang.Class.newInstance0(Class.java:372) at java.lang.Class.newInstance(Class.java:325) at org.apache.struts2.views.xslt.AdapterFactory.constructAdapterInstance(AdapterFactory.java:209) at org.apache.struts2.views.xslt.AdapterFactory.adaptNode(AdapterFactory.java:159) at org.apache.struts2.views.xslt.BeanAdapter.buildChildAdapters(BeanAdapter.java:135) at org.apache.struts2.views.xslt.AbstractAdapterNode.getChildAdapters(AbstractAdapterNode.java:128) at org.apache.struts2.views.xslt.AbstractAdapterNode.getChildNodes(AbstractAdapterNode.java:186) at org.apache.struts2.views.xslt.BeanAdapter.getChildNodes(BeanAdapter.java:88) at org.apache.struts2.views.xslt.AbstractAdapterNode.getFirstChild(AbstractAdapterNode.java:194) at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2SAX.parse(DOM2SAX.java:300) at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2SAX.parse(DOM2SAX.java:302)...[this line repeats ad nauseam]

有人可以给我指出正确的方向吗？

谢谢!

Answer 1

是的，这是一个想法:

您有一个 Departments 类(错误命名 - 使用单数 Department)。它有一组 Employee 实例。这是一种一对多的关系:一个部门可以有一名或多名员工。到目前为止，一切顺利。

您的Employees 类(更糟糕的命名 - 使用单数Employee)引用了其父部门。

你看到问题了吗？每次调用 Employee 构造函数时，您都可以调用 Department 构造函数，它会创建一组Employees。原始 Employee 的实例位于该 Set 中，它再次调用 Department 构造函数，令人作呕。

您需要打破循环:这是双向一对多:

http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/example-parentchild.html#example-parentchild-bidir