Department.java Source code

Introduction

Here is the source code for Department.java

Source

    File:Department.java

    import java.util.ArrayList;
    import java.util.Collection;

    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.OneToMany;

@Entity
public class Department {
    @Id
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    private Collection<Professor> employees;

    public Department() {
        employees = new ArrayList<Professor>();
    }
    
    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 Collection<Professor> getProfessors() {
        return employees;
    }

    public String toString() {
        return "Department no: " + getId() + 
               ", name: " + getName();
    }
}

    File:Professor.java

    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.ManyToOne;

@Entity
public class Professor {
    @Id
    private int id;
    private String name;
    
    @ManyToOne
    private Department department;
    

    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 Department getDepartment() {
        return department;
    }
    
    public void setDepartment(Department dept) {
        this.department = dept;
    }
    
    public String toString() {
        return "Professor " + getId() + 
               ": name: " + getName() +
               ", dept: " + ((getDepartment() == null) ? null : getDepartment().getName());
    }
}

    File:ProfessorService.java

    import java.util.Collection;

    import javax.persistence.EntityManager;

public class ProfessorService {
  protected EntityManager em;

  public ProfessorService(EntityManager em) {
    this.em = em;
  }

  public Professor createProfessor(int empId, String empName, int deptId) {
    Department dept = em.getReference(Department.class, deptId);
    Professor emp = new Professor();
    emp.setId(empId);
    emp.setName(empName);
    emp.setDepartment(dept);
    dept.getProfessors().add(emp);
    em.persist(emp);
    return emp;
  }

  public Collection<Professor> findAllProfessors() {
    return (Collection<Professor>) em.createQuery("SELECT e FROM Professor e").getResultList();
  }

  public Collection<Department> findAllDepartments() {
    return (Collection<Department>) em.createQuery("SELECT d FROM Department d").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

    import java.util.Collection;
    import java.util.Iterator;

    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();

            service.createProfessor(1, "empName", 1);

            util.checkData("select * from Professor");

            em.getTransaction().commit();
            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>