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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 CreateServlet extends HttpServlet {
20 @PersistenceContext(name="example")
21 private EntityManager _entityManager;
22
23 public void init()
24 {
25 Course course = null;
26
27 try {
28 course = _entityManager.find(Course.class, new Integer (1));
29 } catch (Throwable e) {
30 }
31
32 if (course == null) {
33 _entityManager.getTransaction().begin();
34
35 try {
36 course = new Course("Potions", "Severus Snape");
37 _entityManager.persist(course);
38
39 course = new Course("Transfiguration", "Minerva McGonagall");
40 _entityManager.persist(course);
41
42 course = new Course("Defense Against the Dark Arts", "Remus Lupin");
43 _entityManager.persist(course);
44 } finally {
45 _entityManager.getTransaction().commit();
46 }
47 }
48 }
49
50 public void service(HttpServletRequest req, HttpServletResponse res)
51 throws java.io.IOException , ServletException
52 {
53 PrintWriter out = res.getWriter();
54
55 res.setContentType("text/html");
56
57 Query courseQuery = _entityManager.createQuery("SELECT o FROM Course o");
58
59 out.println("<h3>Initial Classes</h3>");
60
61 displayCourses(out, courseQuery);
62
63 Course divination = null;
64 Course creatures = null;
65
66 _entityManager.getTransaction().begin();
67
68 try {
69 divination = new Course("Divination", "Sybil Trelawney");
70
71 _entityManager.persist(divination);
73
74 creatures = new Course("Care of Magical Creatures", "Rubeus Hagrid");
75
76 _entityManager.persist(creatures);
78
79 out.println("<h3>Adding some classes</h3>");
80 displayCourses(out, courseQuery);
81 } finally {
82 String sql = "SELECT o FROM Course o WHERE o.course=?1";
84
85 Query findQuery = _entityManager.createQuery(sql);
86
87 findQuery.setParameter(1, "Divination");
88 divination = (Course) findQuery.getSingleResult();
89
90 if (divination != null)
91 _entityManager.remove(divination);
92
93 findQuery.setParameter(1, "Care of Magical Creatures");
94 creatures = (Course) findQuery.getSingleResult();
95
96 if (creatures != null)
97 _entityManager.remove(creatures);
98
99 _entityManager.getTransaction().commit();
100 }
101
102 out.println("<h3>Removing the new classes</h3>");
103 displayCourses(out, courseQuery);
104 }
105
106 private void displayCourses(PrintWriter out, Query query)
107 throws IOException
108 {
109 List list = query.getResultList();
110
111 for (int i = 0; i < list.size(); i++) {
112 Course course = (Course) list.get(i);
113
114 out.println(course.getCourse() + " is taught by " +
115 course.getTeacher() + "<br>");
116 }
117 }
118 }
119 |
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