Struts 2 + Spring 2 + JPA + AJAX （二)

Domain

Our domain model will consist of just a simple "Person" class with a couple of fields.

   1. Create a new class named "Person" (File -> New -> Class), and enter "quickstart.model" for the package name.
   2. Add the fields "id" (int), "firstName" (String), and lastName ("String") with their setter/getter methods.
   3. Mark your class with the "@Entity" annotation, and the "id" field with the annotations "@Id" and "@GeneratedValue".

your class will look like:
Person.java

package quickstart.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Person {
    @Id
    @GeneratedValue
    private Integer id;
    private String lastName;
    private String firstName;

    public String getFirstName() {
        return firstName;
    }

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

    public String getLastName() {
        return lastName;
    }

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

    public Integer getId() {
        return id;
    }

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

@Entity will let the provider know that this class can be persisted. @Id marks the "id" field as the primary key for this class. @GeneratedValue will cause the id field to be generated by the provider (Hibernate). Classes and fields are by default mapped to tables and columns with the same name, see JPA's documentation for more details.
Person service.

We will now write the class that will take care of CRUD operations on "Person" objects.

   1. Create a new interface (File -> New -> Interface), enter "PersonService" for the name, and "quickstart.service" for the namespace. Set its content to:

PersonService.java

package quickstart.service;

import java.util.List;

import quickstart.model.Person;

public interface PersonService {
    public List<Person> findAll();

    public void save(Person person);

    public void remove(int id);

    public Person find(int id);
}

   1. Create a new class (File -> New -> Class), enter "PersonServiceImpl" for the name and "quickstart.service" for the namespace. Set its content to:

PersonServiceImpl.java

package quickstart.service;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import org.springframework.transaction.annotation.Transactional;

import quickstart.model.Person;

@Transactional
public class PersonServiceImpl implements PersonService {
    private EntityManager em;

    @PersistenceContext
    public void setEntityManager(EntityManager em) {
        this.em = em;
    }

    @SuppressWarnings("unchecked")
    public List<Person> findAll() {
        Query query = getEntityManager().createQuery("select p FROM Person p");
        return query.getResultList();
    }

    public void save(Person person) {
        if (person.getId() == null) {
            // new
            em.persist(person);
        } else {
            // update
            em.merge(person);
        }
    }

    public void remove(int id) {
        Person person = find(id);
        if (person != null) {
            em.remove(person);
        }
    }

    private EntityManager getEntityManager() {
        return em;
    }

    public Person find(int id) {
        return em.find(Person.class, id);
    }

}

@PersistenceContext will make Spring inject an EntityManager into the service when it is instantiated. The @PersistenceContext annotation can be placed on the field, or on the setter method. If the class is annotated as @Transactional, Spring will make sure that its methods run inside a transaction.