JPA CRUD example
Here is the class that we will be using as the Entity Class….
package employeeDB;import javax.persistence.*;
@Entity
publicclass Employee {
@Id String name;
Double salary;
public Employee()
{
}
public Employee (String name, Double Salary)
{
this.name=name;
this.salary=Salary;
}
publicvoid setSalary(Double Salary)
{
this.salary=Salary;
}
publicString toString()
{
return"Name: "+name+"\nSalary: "+salary ;
}
}
Example Program
package employeeDB;
import javax.persistence.*;
import java.util.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {
/**
* Displays all Employees in the Database
*/
private static void displayAll()
{
em.getTransaction().begin();
TypedQuery e=em.createQuery(displayAllQuery, Employee.class);
List <Employee> employees=e.getResultList();
if(employees.size()>0)
{
for(Employee temp:employees)
{
System.out.println(temp);
System.out.println();
}
System.out.println(employees.size()+" Employee Records Available...!");
}
else
System.out.println("Database is Empty!");
em.getTransaction().commit();
}
/**
* Insets an Employee into the Database.
*/
private static void insert()
{
System.out.print("Enter the number of Employees to be inserted: ");
n=input.nextInt();
em.getTransaction().begin();
for(int i=0;i<n;i++)
{
System.out.println("Enter the details of Employee "+(i+1)+": ");
System.out.print("Name: ");
//I use BufferedReader to read String and hence I need to
// Catch the IOException that it may throw
try
{
name=bufferedReader.readLine();
}
catch (IOException e)
{
e.printStackTrace();
}
System.out.print("Salary: ");
Salary=input.nextDouble();
Employee emp=new Employee(name,Salary);
em.persist(emp); //Store emp into Database
}
em.getTransaction().commit();
System.out.println("\n"+n+" employee record(s) Created!\n");
TypedQuery count=em.createQuery(countQuery,Employee.class);
System.out.println("\n"+count.getSingleResult()+" employee record(s) Available in Database!\n");
}
/**
* Deletes the specified Employee from the database
*@param name
*/
private static void delete(String name)
{
em.getTransaction().begin();
Employee e=(Employee) em.find(Employee.class, name); //Find Object to be deleted
em.remove(e); //Delete the Employee from database
System.out.printf("Employee %s removed from Database....",e.name);
em.getTransaction().commit();
//Display Number of Employees left
TypedQuery count=em.createQuery(countQuery,Employee.class);
System.out.println("\n"+count.getSingleResult()+" employee record(s) Available in Database!\n");
}
/**
* Changes salary of the specified employee to passed salary
*@param name
*@param Salary
*/
private static void modify(String name,Double Salary)
{
em.getTransaction().begin();
Employee e=(Employee) em.find(Employee.class, name); //Find Employee to be modified
e.setSalary(Salary); //Modify the salary
em.getTransaction().commit();
System.out.println("Modification Successful!\n");
}
public static void main(String arg[])
{
System.out.println("Welcome to the Employee Database System!\n\n");
do{
System.out.print("Menu: \n 1. View DB\n2. Insert \n3. Delete \n4. Modify\n5. Exit\nEnter Choice...");
int ch=input.nextInt();
try{
switch(ch)
{
case 1:
displayAll();
break;
case 2:
insert();
break;
case 3:
System.out.print("Name of Employee to be Deleted2: ");
name=bufferedReader.readLine();
delete(name);
break;
case 4:
System.out.print("Name of Employee to be Modified: ");
name=bufferedReader.readLine();
System.out.print("New Salary: ");
Salary=input.nextDouble();
modify(name,Salary);
break;
case 5:
if(em!=null) em.close(); //Close EntityManager
if(emf!=null) emf.close(); //Close EntityManagerFactory
exit=true;
break;
}
}
catch (IOException e)
{
e.printStackTrace();
}
}while(!exit);
}
static EntityManagerFactory emf=Persistence.createEntityManagerFactory("empDB.odb");
static EntityManager em=emf.createEntityManager();
static Scanner input=new Scanner(System.in);
static BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
static int n;
static String name;
static Double Salary;
static boolean exit=false;
//Query Repository
static String countQuery="Select count(emp) from Employee emp";
static String displayAllQuery="Select emp from Employee emp";
}
Related Article:
Reference: Java Persistence API: a quick intro… from our JCG partner Steve Robinson at Footy 'n' Tech blog
