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1 package example;
2
3 import java.io.PrintWriter  ;
4 import java.io.IOException ;
5
6 import java.util.List ;
7
8 import javax.servlet.http.HttpServlet ;
9 import javax.servlet.http.HttpServletRequest ;
10 import javax.servlet.http.HttpServletResponse ;
11
12 import javax.servlet.ServletException ;
13
14 import javax.persistence.*;
15
16
19 public class OneToManyServlet extends HttpServlet {
20 @PersistenceContext
21 private EntityManager _entityManager;
22
23 public void init()
24 {
25 House house = null;
26
27 try {
28 house = _entityManager.find(House.class, new Long (1));
29 } catch (Throwable e) {
30 }
31
32 if (house == null) {
33 _entityManager.getTransaction().begin();
34
35 try {
36 House gryffindor = new House("Gryffindor");
37 _entityManager.persist(gryffindor);
38
39 House slytherin = new House("Slytherin");
40 _entityManager.persist(slytherin);
41
42 House ravenclaw = new House("Ravenclaw");
43 _entityManager.persist(ravenclaw);
44
45 House hufflepuff = new House("Hufflepuff");
46 _entityManager.persist(hufflepuff);
47
48 Student student;
49
50 student = new Student("Harry Potter", "M", gryffindor);
51 _entityManager.persist(student);
52
53 student = new Student("Ron Weasley", "M", gryffindor);
54 _entityManager.persist(student);
55
56 student = new Student("Hermione Granger", "F", gryffindor);
57 _entityManager.persist(student);
58
59 student = new Student("Draco Malfoy", "M", slytherin);
60 _entityManager.persist(student);
61
62 student = new Student("Millicent Bulstrode", "F", slytherin);
63 _entityManager.persist(student);
64
65 student = new Student("Penelope Clearwater", "F", ravenclaw);
66 _entityManager.persist(student);
67 } finally {
68 _entityManager.getTransaction().commit();
69 }
70 }
71 }
72
73 public void service(HttpServletRequest req, HttpServletResponse res)
74 throws java.io.IOException , ServletException
75 {
76 PrintWriter out = res.getWriter();
77
78 res.setContentType("text/html");
79
80 String sql = "SELECT h FROM House h";
81
82 Query allHouse = _entityManager.createQuery("SELECT o FROM House o");
83
84 List houses = allHouse.getResultList();
85
86 for (int i = 0; i < houses.size(); i++) {
87 House house = (House) houses.get(i);
88
89 out.println("<h3>" + house.getName() + "</h3>");
90
91 for (Student student : house.getStudents()) {
92 out.println(student.getName() + "<br>");
93 }
94 }
95 }
96 }
97 |
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Java API By Example, From Geeks To Geeks.