java - Hibernate中的操作流程是怎样的？

Question

我编写了一个简单的 Hibernate 程序，但我对流程和构造函数的使用感到困惑。

这是主要的 POJO 类:

package mypack;

import org.apache.log4j.Logger;

public class Emp {

    String name,job;
    int id,salary;

    public Emp()
    {
        super();
        System.out.println("Inside Default constructor"+this);

    }

    public Emp(String name, String job, int salary) {
        super();
        System.out.println("Inside parameterised constructor"+this);
        this.name = name;
        this.job = job;
        this.salary = salary;
    }

    public String getName() {
        System.out.println("Inside Get name"+this);
        return name;
    }

    public void setName(String name) {
        System.out.println("Inside set name"+this);
        this.name = name;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public int getId() {
        return id;
    }

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

    public int getSalary() {
        return salary;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }
}

这是ObjectSaver类:

package mypack;

import org.hibernate.*;

public class ObjSaver {

    public static void main(String[] args) {

    Emp e1=new Emp("A","job1",45000);
    Emp e2=new Emp("B","Job2",45035);
    Emp e3=new Emp("C","Job3",44585);
    Emp e4=new Emp("4","Job4",44582545);

    System.out.println("Saving Emp Objects");
    Session session=Myfactory.getSession();
    System.out.println("session obtained");
    Transaction t1=session.beginTransaction();
    System.out.println("Transaction begin");
    session.save(e1);
    session.save(e2);
    session.save(e3);
    session.save(e4);
    t1.commit();
    session.close();

    System.out.println("Successfully Saved");
    }

}

MyFactory 类:

package mypack;

import org.hibernate.*;
import org.hibernate.cfg.Configuration;

public class Myfactory 
{
    private static SessionFactory factory;
    static
    {
        System.out.println("Loading configuration...");
        Configuration cfg=new Configuration().configure();
        //Configuration cfg=new Configuration().configure("hibernate.cfg.xml");
        System.out.println("Configuration loaded");
         factory = cfg.buildSessionFactory();
        System.out.println("SessionFactory Created");

    }

    public static  Session getSession()
    {
        System.out.println("returning session");
        return factory.openSession();
    }
}

映射文件:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 
 <hibernate-mapping>


 <class name="mypack.Emp" table="Employee">

 <id name="id"  type="int">
 <generator class="increment"/>
 </id>

 <property name="name"/>
 <property name="job"/>
 <property name="salary"/>

 </class>

 </hibernate-mapping>

输出:

Inside parameterised constructormypack.Emp@1bab50a
Inside parameterised constructormypack.Emp@c3c749
Inside parameterised constructormypack.Emp@150bd4d
Inside parameterised constructormypack.Emp@1bc4459
Saving Emp Objects
Loading configuration...
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Configuration loaded
Inside Default constructormypack.Emp@fdb00d
Inside Default constructormypack.Emp$$EnhancerByCGLIB$$aa36f81a@17a4989
Inside Default constructormypack.Emp@659db7
Inside Get namemypack.Emp@659db7
Inside set namemypack.Emp@659db7
SessionFactory Created
returning session
session obtained
Transaction begin
Inside Get namemypack.Emp@1bab50a
Inside Get namemypack.Emp@c3c749
Inside Get namemypack.Emp@150bd4d
Inside Get namemypack.Emp@1bc4459
Inside Get namemypack.Emp@1bab50a
Inside Get namemypack.Emp@c3c749
Inside Get namemypack.Emp@150bd4d
Inside Get namemypack.Emp@1bc4459
Inside Get namemypack.Emp@150bd4d
Inside Get namemypack.Emp@c3c749
Inside Get namemypack.Emp@1bc4459
Inside Get namemypack.Emp@1bab50a
Hibernate: insert into Employee (name, job, salary, id) values (?, ?, ?, ?)
Hibernate: insert into Employee (name, job, salary, id) values (?, ?, ?, ?)
Hibernate: insert into Employee (name, job, salary, id) values (?, ?, ?, ?)
Hibernate: insert into Employee (name, job, salary, id) values (?, ?, ?, ?)
Successfully Saved

为什么默认构造函数运行了3次？为什么 setter 和 getter 在默认构造函数之后运行？谁能解释一下流程？

Answer 1

Hibernate 需要所有持久类的无参构造函数。 因为 Hibernate 使用 Java Reflection 为您创建对象，而 Java Reflection 会调用默认构造函数，因此您使用 save 方法保存的每个对象都会调用您的默认构造函数。

Hibernate 每当您从数据库读取数据时，Hibernate 都会使用 setter 方法来初始化实体，并在您持久化到数据库时，使用 getter 方法来获取要持久化的实际值。

由于您只是坚持，所以应该只调用 getter。