使用struts和hibernate在jsp中顯示數據

Question

我被困在一個有問題的項目中。問題很簡單，但我不知道解決方案。這是我的問題：

我有一個Employee類與Hibernate，Employee Table映射。

Class Employee 
    int empId; 
    int empName; 

然後我有一個Assignment類與Hibernate，Assignment Table映射。對於每位員工，我有一份記錄在我的Assignment班以及一名員工的主管編號。主管也在Employee類中定義。現在

Class Assignment 
int empId; 
int supervisorId; //empId of the Supervisor in the Employee Table. 

，在我的動作類，我產生一個迭代器首先具有分配類的一個對象，我在我的JSP像下面顯示的：

<s:iterator value="assignmentList"> 
    <s:property value="empId"/> 
    <s:property value="supervisorId"/> 
    //Now here i want to display the empName of both the Employee and Supervisor. 
    //How can i pass the <s:property value="empId"/> and <s:property value="supervisorId"/> values to an action to get the Employee Class Objects so that i can display the employee names. 

我認爲它是一個簡單的問題加入兩個表，但不知道，如何在struts2中實現它。請幫忙。

編輯

這是我修改後的代碼

Employee類

@Entity 
    @Table(name="usertable") 
    public class User implements java.io.Serializable{ 

    private int id; 
    private String empName; 
    private String firstName; 
    private Assignment assignment; 

public Employee(){ 
} 

@Id 
    @GeneratedValue 
    @Column(name="id") 
    public int getId() { 
     return id; 
    } 
    @Column(name="empname") 
    public String getEmpname() { 
     return empName; 
    } 

    @OneToOne(fetch = FetchType.EAGER, mappedBy = "usertable", cascade = CascadeType.ALL) 
    public Assignment getAssignment() { 
     return assignment; 
    } 

    public void setAssignment(Assignment assignment) { 
     this.assignment = assignment; 
    } 
} 

分配類

@Entity 
@Table(name="assignment") 
public class Assignment implements java.io.Serializable{ 

private int id; 
private Employee employee; 

@Id 
@GeneratedValue 
@Column(name="id") 
public int getId() { 
    return id; 
} 
public void setId(int id) { 
    this.id = id; 
} 
@OneToOne(fetch = FetchType.EAGER) 
@JoinColumn(name = "id") 
public Employee getEmployee() { 
    return employee; 
} 
public void setEmployee(Employee employee) { 
    this.employee = employee; 
} 

} 

保存方法在Action類

SessionFactory sf = HibernateUtil.getSessionFactory(); 
Session session = sf.openSession(); 
session.beginTransaction(); 
     Employee emp=new Employee(); 
    Assignment assgn =new Assignment(); 
    emp.setAssignment(assgn); 
    assgn.setEmployee(emp); 
    session.save(assgn); 
    session.save(emp); 

    session.getTransaction().commit(); 
    session.close(); 

我的Util類：

public class HibernateUtil { 

private static final SessionFactory sessionFactory; 

static { 
    try { 
     // Create the SessionFactory from hibernate.cfg.xml 
     sessionFactory = new AnnotationConfiguration().configure() 
       .buildSessionFactory(); 
    } catch (Throwable ex) { 
     System.err.println("Initial SessionFactory creation failed." + ex); 
     throw new ExceptionInInitializerError(ex); 
    } 
} 

public static SessionFactory getSessionFactory() { 
    return sessionFactory; 
} 

}

當我在我的動作類運行的保存方法，我得到這個異常：

Struts has detected an unhandled exception: 

Messages: 
File: org/hibernate/cfg/OneToOneSecondPass.java 
Line number: 135 

java.lang.NullPointerException 
org.hibernate.cfg.OneToOneSecondPass.doSecondPass(OneToOneSecondPass.java:135) 
org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1163) 
org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:296) 
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1319) 
common.HibernateUtil.(HibernateUtil.java:14) 
backEnd.admin.saveemployee(admin.java:137) 
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
java.lang.reflect.Method.invoke(Method.java:597) 

現在該怎麼解決這個？我正在使用Hibernate註釋版本3.2.1。請幫忙。

Answer 1

您需要在此處配置一對一（或一對多，取決於您的型號）映射。既然你提到你對每個員工都有一個賦值記錄，所以這意味着Employee bean應該有一個對其相關賦值bean的引用。

我假設你正在使用註解配置休眠所以在你的Employee類一些細微的變化應該做的伎倆

//Injecting the assignment bean inside the employee bean  
private Assignement employeeAssignement; 

//Lazy type fetching means to get the assignemnt tuple only when it is needed 
@OneToOne(fetch = FetchType.LAZY, mappedBy = "Employee", cascade = CascadeType.ALL) 
public Assignment getEmployeeAssignment() { 
    return this.employeeAssignement; 
} 

public void setEmployeeAssignement(EmployeeAssignement employeeAssignement) { 
    this.employeeAssignement = employeeAssignement; 
} 

而且其良好的做法，以保持一個單獨的bean從您的實體bean是顯示目的與數據庫映射。 建立一個bean，說EmployeeDetailBean並指定你想在JSP上顯示的字段。

public class EmployeeDetailBean{ 
//The fields you want to display on the JSP 
...... 
//valid getter/setter 
} 

設置這些字段時，你的動作類叫做，創建的getter/setter方法這個bean和遍歷這個bean一旦你的JSP被調用，就像你迭代在您的文章中提到的其他豆。