JPA入门(一)

1.POJO 

Employee.java

package pojo;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name="T_EMPLOYEE")
public class Employee {
    @Id
    private String id;
    private String name;
    private double salary;

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public double getSalary() {
        return salary;
    }

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

	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", salary=" + salary
				+ "]";
	}

}

 

2.Dao 

EmployeeDao.java

package dao;
import javax.persistence.EntityManager;

import pojo.Employee;

public class EmployeeDao {
    private EntityManager em=null;
    
	public EmployeeDao(EntityManager em) {
		this.em = em;
	}

	public Employee createEmployee(String id,String name,double salary){
        Employee emp = new Employee();
        emp.setId(id);
        emp.setName(name);
        emp.setSalary(salary);
        em.persist(emp);
        return emp;
    }
    
    public void removeEmployee(String id){
        Employee emp = findEmployee(id);
        if(emp==null){
            throw new RuntimeException("The employee whose id is "+ id+" is not existed");
        }
        em.remove(emp);                        
    }
    
    public Employee findEmployee(String id){
        return em.find(Employee.class,id);
    }
    
    public Employee updateEmployee(String id,String name,double salary){
        Employee emp=findEmployee(id);
        if(emp==null){
            throw new RuntimeException("The employee whose id is "+ id+" is not existed");
        }
        emp.setName(name);
        emp.setSalary(salary);
        return emp;
    }
    
}

 

3.Configuration file

persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
	xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
               http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
	<persistence-unit name="emp" transaction-type="RESOURCE_LOCAL">
		<provider>org.hibernate.ejb.HibernatePersistence</provider>
		<properties>
			<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
			<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF-8" />
			<property name="javax.persistence.jdbc.user" value="root" />
			<property name="javax.persistence.jdbc.password" value="root" />
		</properties>
	</persistence-unit>
</persistence>

 

4. Test class

Main.java

package test;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import pojo.Employee;
import dao.EmployeeDao;
public class Main {

	public static void main(String[] args) {
	    EntityManagerFactory emf=Persistence.createEntityManagerFactory("emp");
	    EntityManager em=emf.createEntityManager();
	    
	    EmployeeDao employeeDao = new EmployeeDao(em);
	    
	    // create employee 
	    em.getTransaction().begin();
	    employeeDao.createEmployee("1", "xiao", 100);
	    em.getTransaction().commit();
	    
	    // update employee
	    em.getTransaction().begin();
	    employeeDao.updateEmployee("1", "xiao", 1000);
	    em.getTransaction().commit();
	    
	    // select employee
	    Employee e=employeeDao.findEmployee("1");
	    System.out.println(e);
	    
	    // remove employee
	    em.getTransaction().begin();
	    employeeDao.removeEmployee("1");
	    em.getTransaction().commit();
	}
}