How To Create Entity Manager
Create Entity Manager Factory : Entity Manager « JPA « Java
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Create Entity Manager Factory
File : Professor.java import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Professor { @Id private int id; private String name; private long salary; public Professor() { } public Professor( int id) { this.id = id; } public int getId() { return id; } public void setId( int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public long getSalary() { return salary; } public void setSalary( long salary) { this.salary = salary; } public String toString() { return "Professor id: " + getId() + " name: " + getName() + " salary: " + getSalary(); } } File : ProfessorService.java import java.util.Collection; import javax.persistence.EntityManager; import javax.persistence.Query; public class ProfessorService { protected EntityManager em; public ProfessorService(EntityManager em) { this.em = em; } public Professor createProfessor( int id, String name, long salary) { Professor emp = new Professor(id); emp.setName(name); emp.setSalary(salary); em.persist(emp); return emp; } public void removeProfessor( int id) { Professor emp = findProfessor(id); if (emp != null) { em.remove(emp); } } public Professor raiseProfessorSalary( int id, long raise) { Professor emp = em.find(Professor.class, id); if (emp != null) { emp.setSalary(emp.getSalary() + raise); } return emp; } public Professor findProfessor( int id) { return em.find(Professor.class, id); } public Collection<Professor> findAllProfessors() { Query query = em.createQuery("SELECT e FROM Professor e"); return (Collection<Professor>) query.getResultList(); } } File : JPAUtil.java import java.io.Reader; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.Statement; public class JPAUtil { Statement st; public JPAUtil() throws Exception{ Class.forName("org.hsqldb.jdbcDriver"); System.out.println("Driver Loaded."); String url = "jdbc:hsqldb:data/tutorial"; Connection conn = DriverManager.getConnection(url, "sa", ""); System.out.println("Got Connection."); st = conn.createStatement(); } public void executeSQLCommand(String sql) throws Exception { st.executeUpdate(sql); } public void checkData(String sql) throws Exception { ResultSet rs = st.executeQuery(sql); ResultSetMetaData metadata = rs.getMetaData(); for ( int i = 0; i < metadata.getColumnCount(); i++) { System.out.print("\t"+ metadata.getColumnLabel(i + 1)); } System.out.println("\n----------------------------------"); while (rs.next()) { for ( int i = 0; i < metadata.getColumnCount(); i++) { Object value = rs.getObject(i + 1); if (value == null) { System.out.print("\t "); } else { System.out.print("\t"+value.toString().trim()); } } System.out.println(""); } } } File : Main.java // create and persist an employee import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; public class Main { public static void main(String[] a) throws Exception { JPAUtil util = new JPAUtil(); EntityManagerFactory emf = Persistence.createEntityManagerFactory("ProfessorService"); EntityManager em = emf.createEntityManager(); ProfessorService service = new ProfessorService(em); em.getTransaction().begin(); Professor emp = service.createProfessor(158, "John Doe", 45000); em.getTransaction().commit(); System.out.println("Persisted " + emp); util.checkData("select * from Professor"); em.close(); emf.close(); } } File : persistence.xml <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0"> <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL"> <properties> <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/> <property name="hibernate.hbm2ddl.auto" value="update"/> <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/> <property name="hibernate.connection.username" value="sa"/> <property name="hibernate.connection.password" value=""/> <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/> </properties> </persistence-unit> </persistence>
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How To Create Entity Manager
Source: http://www.java2s.com/Code/Java/JPA/CreateEntityManagerFactory.htm
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