package example;
import java.io.PrintWriter;
import java.io.IOException;
import java.util.List;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
import javax.persistence.*;
/**
* A client to illustrate the query.
*/
public class ManyToOneServlet extends HttpServlet {
@PersistenceContext(name="example")
private EntityManager _entityManager;
public void init()
{
House house = null;
try {
house = _entityManager.find(House.class, new Long(1));
} catch (Throwable e) {
}
if (house == null) {
_entityManager.getTransaction().begin();
try {
House gryffindor = new House("Gryffindor");
_entityManager.persist(gryffindor);
House slytherin = new House("Slytherin");
_entityManager.persist(slytherin);
House ravenclaw = new House("Ravenclaw");
_entityManager.persist(ravenclaw);
House hufflepuff = new House("Hufflepuff");
_entityManager.persist(hufflepuff);
Student student;
student = new Student("Harry Potter", "M", gryffindor);
_entityManager.persist(student);
student = new Student("Ron Weasley", "M", gryffindor);
_entityManager.persist(student);
student = new Student("Hermione Granger", "F", gryffindor);
_entityManager.persist(student);
student = new Student("Draco Malfoy", "M", slytherin);
_entityManager.persist(student);
student = new Student("Millicent Bulstrode", "F", slytherin);
_entityManager.persist(student);
student = new Student("Penelope Clearwater", "F", ravenclaw);
_entityManager.persist(student);
} finally {
_entityManager.getTransaction().commit();
}
}
}
public void service(HttpServletRequest req, HttpServletResponse res)
throws java.io.IOException, ServletException
{
PrintWriter out = res.getWriter();
res.setContentType("text/html");
Query allStudent = _entityManager.createQuery("SELECT o FROM Student o");
List students = allStudent.getResultList();
for (int i = 0; i < students.size(); i++) {
Student student = (Student) students.get(i);
out.println(student.getName() + " lives in " +
student.getHouse().getName() + "<br>");
}
String sql = "SELECT s FROM Student s WHERE s.house.name=?1";
Query houseStudents = _entityManager.createQuery(sql);
houseStudents.setParameter(1, "Gryffindor");
students = houseStudents.getResultList();
out.println("<h3>Gryffindor Students</h3>");
for (int i = 0; i < students.size(); i++) {
Student student = (Student) students.get(i);
out.println(student.getName() + "<br>");
}
}
}