JPA Instances-Reprint

Specific examples

After completion of the project structure such as:

(Note: The location of the Persistence.xml file determines the root of persistence (persistence root). The root of the persistence is the jar file or the directory containing the Meta-inf directory (provided that Persistence.xml is located here). This persistence.xml file is generally placed in the Meta-inf under SRC. The name and position are not changed)

A), import the relevant jar package (see) and create the Meta-inf and Persistence.xml files.

The Persistence.xml is configured as follows: (my data is MySQL, different implementations of different databases and JPA will result in different configuration content)

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2. <persistence xmlns="http://java.sun.com/xml/ns/persistence"
4. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
6. xsi:schemalocation="Http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/ Persistence_version=1 ">
8. <persistence-unit name="MYSQLJPA" transaction-type="resource_local">
10. <properties>
12. <property name= "hibernate.dialect" value="Org.hibernate.dialect.MySQL5Dialect" / >
14. <property name= "hibernate.connection.driver_class" value="Com.mysql.jdbc.Driver" / >
16. <property name= "hibernate.connection.username" value="root" />
18. <property name= "hibernate.connection.password" value="123456" />
20. <property name= "hibernate.connection.url" value="JDBC:MYSQL://LOCALHOST:3306/DB1" />
22. <property name= "hibernate.max_fetch_depth" value="3" />
24. <property name= "hibernate.hbm2ddl.auto" value="Update" />
26. </Properties>
28. </persistence-unit>
30. </Persistence>

b), write the entity bean, as follows:

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2. Package Com.hmk.bean;
6. Import Javax.persistence.Column;
8. Import javax.persistence.Entity;
10. Import Javax.persistence.GeneratedValue;
12. Import Javax.persistence.Id;
16. @Entity
18. Public class Person {
20. private int id;
22. private String name;
26. @Id @GeneratedValue
28. public int getId () {
30. return ID;
32. }
34. public void setId (int id) {
36. this.id = ID;
38. }
40. @Column (length=12)
42. Public String GetName () {
44. return name;
46. }
48. public void SetName (String name) {
50. this.name = name;
52. }
56. }

c), write the JUnit test code as follows:

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2. Package junit.test;
8. Import Javax.persistence.EntityManager;
10. Import Javax.persistence.EntityManagerFactory;
12. Import javax.persistence.Persistence;
16. Import Org.junit.BeforeClass;
18. Import Org.junit.Test;
22. Import Com.hmk.bean.Person;
26. Public class Jpatest {
30. @BeforeClass
32. public static void Setupbeforeclass () throws Exception {
34. }
38. @Test public void CreateTable () {
40. //Can verify that the build table is correct
42. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
44. Factory.close ();
46. }
50. @Test public Void Save () {
52. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
54. Entitymanager em = Factory.createentitymanager ();
56. Em.gettransaction (). Begin ();
58. Person person = new Person (); //person to new state
60. Person.setname ("Zhang San");
62. Em.persist (person); //Persistent entities
64. Em.gettransaction (). commit ();
66. Em.close ();
68. Factory.close ();
70. }
72. //new, escrow, removal, removal
76. @Test public Void Update () {
78. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
80. Entitymanager em = Factory.createentitymanager ();
82. Em.gettransaction (). Begin ();
84. Person person = em.find (person.   class, 1);
86. Person.setname ("HMK"); //person is a managed state
88. Em.gettransaction (). commit ();
90. Em.close ();
92. Factory.close ();
94. }
98. @Test public void Update2 () {
100. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
102. Entitymanager em = Factory.createentitymanager ();
104. Em.gettransaction (). Begin ();
106. Person person = em.find (person.   class, 1);
108. Em.clear (); //Change all entities in the entity manager to the off-pipe State
110. Person.setname ("Hmk2");
112. Em.merge (person); //Turn off state into managed state, merge can automatically select INSERT or update data
114. Em.gettransaction (). commit ();
116. Em.close ();
118. Factory.close ();
120. }
124. @Test public void Remove () {
126. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
128. Entitymanager em = Factory.createentitymanager ();
130. Em.gettransaction (). Begin ();
132. Person person = em.find (person.   class, 1);
134. Em.remove (person); //Delete entity
136. Em.gettransaction (). commit ();
138. Em.close ();
140. Factory.close ();
142. }
146. @Test public Void Find () {
148. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
150. Entitymanager em = Factory.createentitymanager ();
152. Person person = em.find (person.  Class, 2); //A Get method similar to hibernate, returns NULL when no data is found
154. System.out.println (Person.getname ());
156. Em.close ();
158. Factory.close ();
160. }
162. @Test public void Find2 () {
164. Entitymanagerfactory factory = persistence.createentitymanagerfactory ("MYSQLJPA");
166. Entitymanager em = Factory.createentitymanager ();
168. Person person = em.getreference (person.  Class, 2); //Similar to Hibernate's Load method, lazy loading. An exception occurs when there is no corresponding data
170. System.out.println (Person.getname ()); //Real call to find data
172. Em.close ();
174. Factory.close ();
176. }
178. }

D), run the appropriate method in the JUnit test code.

JPA Instances-Reprint