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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 import java.util.Collection ;
8 import java.util.Iterator ;
9
10 import javax.servlet.http.HttpServlet ;
11 import javax.servlet.http.HttpServletRequest ;
12 import javax.servlet.http.HttpServletResponse ;
13
14 import javax.servlet.ServletException ;
15
16 import javax.persistence.*;
17
18
21 public class ManyToManyServlet extends HttpServlet {
22 @PersistenceContext(name="example")
23 private EntityManager _entityManager;
24
25 public void init()
26 {
27 Student student = null;
28
29 try {
30 student = _entityManager.find(Student.class, new Long (1));
31 } catch (Throwable e) {
32 }
33
34 if (student == null) {
35 _entityManager.getTransaction().begin();
36
37 try {
38 Student harry = new Student("Harry Potter");
39 _entityManager.persist(harry);
40
41 Student ron = new Student("Ron Weasley");
42 _entityManager.persist(ron);
43
44 Student hermione = new Student("Hermione Granger");
45 _entityManager.persist(hermione);
46
47 Course darkArts = new Course("Defense Against the Dark Arts");
48 _entityManager.persist(darkArts);
49
50 Course potions = new Course("Potions");
51 _entityManager.persist(potions);
52
53 Course divination = new Course("Divination");
54 _entityManager.persist(divination);
55
56 Course arithmancy = new Course("Arithmancy");
57 _entityManager.persist(arithmancy);
58
59 Course transfiguration = new Course("Transfiguration");
60 _entityManager.persist(transfiguration);
61
62 Grade grade;
63
64 _entityManager.persist(new Grade(harry, darkArts, "A"));
65 _entityManager.persist(new Grade(harry, potions, "C-"));
66 _entityManager.persist(new Grade(harry, transfiguration, "B+"));
67 _entityManager.persist(new Grade(harry, divination, "B"));
68
69 _entityManager.persist(new Grade(ron, darkArts, "A-"));
70 _entityManager.persist(new Grade(ron, potions, "C+"));
71 _entityManager.persist(new Grade(ron, transfiguration, "B"));
72 _entityManager.persist(new Grade(ron, divination, "B+"));
73
74 _entityManager.persist(new Grade(hermione, darkArts, "A+"));
75 _entityManager.persist(new Grade(hermione, potions, "A-"));
76 _entityManager.persist(new Grade(hermione, transfiguration, "A+"));
77 _entityManager.persist(new Grade(hermione, arithmancy, "A+"));
78 } finally {
79 _entityManager.getTransaction().commit();
80 }
81 }
82 }
83
84 public void service(HttpServletRequest req, HttpServletResponse res)
85 throws java.io.IOException , ServletException
86 {
87 PrintWriter out = res.getWriter();
88
89 res.setContentType("text/html");
90
91 Query allStudent = _entityManager.createQuery("SELECT o FROM Student o");
92
93 List students = allStudent.getResultList();
94
95 for (int i = 0; i < students.size(); i++) {
96 Student student = (Student) students.get(i);
97
98 out.println("<h3>" + student.getName() + "</h3>");
99
100 Collection courses = student.getCourses();
101
102 out.println("<ul>");
103 Iterator iter = courses.iterator();
104 while (iter.hasNext()) {
105 Course course = (Course) iter.next();
106
107 out.println("<li>" + course.getName());
108 }
109 out.println("</ul>");
110 }
111 }
112 }
113 |
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