Java/JPA/Pageable ResultSet

Pageable Entity Manager

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 String getName() {
        return name;
    }
    
    public Collection<Professor> getProfessors() {
        return employees;
    }
    public String toString() {
        return "Department no: " + getId() + 
               ", name: " + getName();
    }
}

File: Professor.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
@Entity
public class Professor {
    @Id
    private int id;
    private String name;
    private long salary;
    @Temporal(TemporalType.DATE)
    private Date startDate;
    
    @ManyToOne
    private Professor manager;
    
    @OneToMany(mappedBy="manager")
    private Collection<Professor> directs;
    @ManyToOne
    private Department department;
    
    @ManyToMany 
    private Collection<Project> projects;
    public Professor() {
        projects = new ArrayList<Project>();
        directs = new ArrayList<Professor>();
    }
    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    public long getSalary() {
        return salary;
    }
    public Date getStartDate() {
        return startDate;
    }
    
    public Department getDepartment() {
        return department;
    }
    
    public Collection<Professor> getDirects() {
        return directs;
    }
    
    public Professor getManager() {
        return manager;
    }
    public Collection<Project> getProjects() {
        return projects;
    }
    
    public String toString() {
        return "Professor " + getId() + 
               ": name: " + getName() +
               ", salary: " + getSalary() +
               ", dept: " + ((getDepartment() == null) ? null : getDepartment().getName());
    }
}

File: ProfessorService.java
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.Query;
public class ProfessorService {
  protected EntityManager em;
  public ProfessorService(EntityManager em) {
    this.em = em;
  }
  
  private int currentPage;
  private int maxResults;
  private int pageSize;
  
  public int getPageSize() {
      return pageSize;
  }
  
  public int getMaxPages() {
      return maxResults / pageSize;
  }
  public void init(int pageSize) {
      this.pageSize = pageSize;
      maxResults = ((Long) em.createQuery("SELECT COUNT(e) FROM Professor e")
                                  .getSingleResult()).intValue();
      currentPage = 0;
  }
  
  public List getCurrentResults() {
      return em.createQuery("SELECT e FROM Professor e")
               .setFirstResult(currentPage * pageSize)
               .setMaxResults(pageSize)
               .getResultList();
  }
  
  public void next() {
      currentPage++;
  }
  
  public void previous() {
      currentPage--;
      if (currentPage < 0) {
          currentPage = 0;
      }
  }
  
  public int getCurrentPage() {
      return currentPage;
  }
  
  public void setCurrentPage(int currentPage) {
      this.currentPage = currentPage;
  }

}

File: Project.java

import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Project {
    @Id
    protected int id;
    protected String name;
    @ManyToMany(mappedBy="projects")
    private Collection<Professor> employees;
    public Project() {
        employees = new ArrayList<Professor>();
    }
    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    
    public Collection<Professor> getProfessors() {
        return employees;
    }
    
    public String toString() {
        return "Project id: " + getId() + ", name: " + getName();
    }
}

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 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.init(3);
    service.next();
    service.previous();
    for (Object o : service.getCurrentResults()) {
      System.out.print(o);
    }
    System.out.println("Page " + (service.getCurrentPage() + 1) + " of " + service.getMaxPages());
    if (service.getCurrentPage() == 0) {
      System.out.print("Previous disabled ");
    }
    if (service.getCurrentPage() + 1 == service.getMaxPages()) {
      System.out.print("Next disabled ");
    }
    util.checkData("select * from Professor");
    util.checkData("select * from Department");
    em.getTransaction().rumit();
    em.close();
    emf.close();
  }
}


File: persistence.xml
<persistence xmlns="http://java.sun.ru/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>