La pagination s’effectue en Java Hibernate

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1- Qu'est-ce que la Pagination ?

La pagination est une technique permettant de diviser une liste de plusieurs enregistrements (record) en sous-listes. Par exemple, vous effectuez une recherche avec un mot clé sur Google et recevez des dizaines de milliers de résultats. Cependant, chaque page Google affiche seulement 10 résultats pour vous. D'autres résultats apparaîtront sur les pages suivantes.
L'application  Java utilise  Hibernate, une requête (query statement) peut renvoyer une liste de l'enregistrement (record) et vous vous posez certainement la question comment de retirer une partie de la liste (les enregistrements de la position N1 vers la position N2) et tenir les informations de la totalité des enrgistrement ainsi que le nombre total de pages.

Hibernate vs JPA

Malgré que  Hibernate et  JPA soient les deux technologies similaires, si vous sachiez de  Hibernate ce deviendra facile de travailler avec  JPA et à l'inverse. Pourtantm il y a également quelques différences. Une de ces différences est que  Hibernate fournit des techniques de pagination beaucoup mieux que  JPA. Dans ce poste, je vous donnerai des explications sur la pagination de  Hibernate 5. Il est à noter que cette technique n'est pas soutenue par  JPA.

2- Fonctionnalité de pagination de Hibernate

Tous ce que vous devez faire est de créer un objet  Query, et de fournir des paramètres  page, maxResult, maxNavigationResult afin de créer l'objet  PaginationResult.
PaginationResult est une classe utilitaire, elle supporte le requêtage et le renvoiement la liste des enregistrements correspondants aux paramètres ci-desus.
PaginationResult.java
package org.o7planning.tutorial.hibernate.pagination;

import java.util.ArrayList;
import java.util.List;

import org.hibernate.ScrollMode;
import org.hibernate.ScrollableResults;
import org.hibernate.query.Query;

public class PaginationResult<E> {

    private int totalRecords;
    private int currentPage;
    private List<E> list;
    private int maxResult;
    private int totalPages;

    private int maxNavigationPage;

    private List<Integer> navigationPages;

    // @page: 1, 2, ..
    public PaginationResult(Query<E> query, int page, int maxResult, int maxNavigationPage) {
        final int pageIndex = page - 1 < 0 ? 0 : page - 1;

        int fromRecordIndex = pageIndex * maxResult;
        int maxRecordIndex = fromRecordIndex + maxResult;

        ScrollableResults resultScroll = query.scroll(ScrollMode.SCROLL_INSENSITIVE  );

        List<E> results = new ArrayList<E>();

        boolean hasResult =   resultScroll.first();

        if (hasResult) {
        
            // Scroll to position:
             hasResult = resultScroll.scroll(fromRecordIndex);

            if (hasResult) {
                do {
                    E record = (E) resultScroll.get(0);
                    results.add(record);
                } while (resultScroll.next()//
                        && resultScroll.getRowNumber() >= fromRecordIndex
                        && resultScroll.getRowNumber() < maxRecordIndex);

            }
 
            // Go to Last record.
             resultScroll.last();
        }
 
        // Total Records
        this.totalRecords = resultScroll.getRowNumber() + 1;
        this.currentPage = pageIndex + 1;
        this.list = results;
        this.maxResult = maxResult;

        if (this.totalRecords % this.maxResult == 0) {
            this.totalPages = this.totalRecords / this.maxResult;
        } else {
            this.totalPages = (this.totalRecords / this.maxResult) + 1;
        }

        this.maxNavigationPage = maxNavigationPage;

        if (maxNavigationPage < totalPages) {
            this.maxNavigationPage = maxNavigationPage;
        }
        resultScroll.close();

        this.calcNavigationPages();
    }

    private void calcNavigationPages() {

        this.navigationPages = new ArrayList<Integer>();

        int current = this.currentPage > this.totalPages ? this.totalPages : this.currentPage;

        int begin = current - this.maxNavigationPage / 2;
        int end = current + this.maxNavigationPage / 2;
 
        // The first page
        navigationPages.add(1);
        if (begin > 2) {

    
            // Using for '...'
            navigationPages.add(-1);
        }

        for (int i = begin; i < end; i++) {
            if (i > 1 && i < this.totalPages) {
                navigationPages.add(i);
            }
        }

        if (end < this.totalPages - 2) {
 
            // Using for '...'
            navigationPages.add(-1);
        }
    
        // The last page.
        navigationPages.add(this.totalPages);
    }

    public int getTotalPages() {
        return totalPages;
    }

    public int getTotalRecords() {
        return totalRecords;
    }

    public int getCurrentPage() {
        return currentPage;
    }

    public List<E> getList() {
        return list;
    }

    public int getMaxResult() {
        return maxResult;
    }

    public List<Integer> getNavigationPages() {
        return navigationPages;
    }

}

Example :

Employee.java
package org.o7planning.tutorial.hibernate.entities;
 
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.UniqueConstraint;
 
@Entity
@Table(name = "EMPLOYEE", //
        uniqueConstraints = { @UniqueConstraint(columnNames = { "EMP_NO" }) })
public class Employee {
 
    @Id
    @Column(name = "EMP_ID")
    private Long empId;
 
    @Column(name = "EMP_NO", length = 20, nullable = false)
    private String empNo;
 
    @Column(name = "EMP_NAME", length = 50, nullable = false)
    private String empName;
 
    @Column(name = "JOB", length = 30, nullable = false)
    private String job;
 
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "MNG_ID")
    private Employee manager;
 
    @Column(name = "HIRE_DATE", nullable = false)
    @Temporal(TemporalType.DATE)
    private Date hideDate;
 
    @Column(name = "SALARY", nullable = false)
    private Float salary;
 
    @Lob
    @Column(name = "IMAGE", length = Integer.MAX_VALUE, nullable = true)
    private byte[] image;
 
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "DEPT_ID", nullable = false)
    private Department department;
 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "empId")
    private Set<Employee> employees = new HashSet<Employee>(0);
 
    // Getter & Setter
 
}
Department.java
package org.o7planning.tutorial.hibernate.entities;
 
import java.util.HashSet;
import java.util.Set;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;
 
@Entity
@Table(name = "DEPARTMENT", //
        uniqueConstraints = { @UniqueConstraint(columnNames = { "DEPT_NO" }) })
public class Department {
    @Id
    @Column(name = "DEPT_ID")
    private Integer deptId;
 
    @Column(name = "DEPT_NO", length = 20, nullable = false)
    private String deptNo;
    @Column(name = "DEPT_NAME", nullable = false)
    private String deptName;
 
    @Column(name = "LOCATION")
    private String location;
 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "department")
    private Set<Employee> employees = new HashSet<Employee>(0);
 
    public Department() {
    }  
 
    // Getter & Setter
}
EmployeeInfo.java
package org.o7planning.tutorial.hibernate.beans;

public class EmployeeInfo {

    private Long empId;

    private String empNo;

    private String empName;

    private String deptNo;

    private String deptName;

    public EmployeeInfo() {

    }

    // This constructor is used by Hibernate Query.
    public EmployeeInfo(Long empId, String empNo, String empName, String deptNo, String deptName) {
        this.empId = empId;
        this.empNo = empNo;
        this.empName = empName;
        this.deptNo = deptNo;
        this.deptName = deptName;
    }

    // Getter & Setter
}

Example 1 :

PaginationExample1.java
package org.o7planning.tutorial.hibernate.pagination;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class PaginationExample1 {

    public static void main(String[] args) {

        // Have sessionFactory object...
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        String sql = "Select e from " + Employee.class.getName() + " e " //
                + " Where e.empId > :empId ";
        Query<Employee> query = session.createQuery(sql, Employee.class);
        query.setParameter("empId", 100);

        int page = 1;
        int maxResult = 20;
        int maxNavigationResult = 10;

        PaginationResult<Employee> result = new PaginationResult<Employee>(query, page, maxResult, maxNavigationResult);

        // Result:
        List<Employee> emps = result.getList();
        int totalPages = result.getTotalRecords();
        int totalRecords = result.getTotalRecords();

        // 1 2 3 4 5 ... 11 12 13
        List<Integer> navPages = result.getNavigationPages();

    }

}

Example 2 :

PaginationExample2.java
package org.o7planning.tutorial.hibernate.pagination;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.beans.EmployeeInfo;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class PaginationExample2 {

    public static void main(String[] args) {

        // Get sessionFactory object...
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        String sql = "Select new " + EmployeeInfo.class.getName() //
                + " (e.empId,e.empNo,e.empName,d.deptNo,d.deptName) " //
                + " from " + Employee.class.getName() + " e " //
                + " Join e.department d " //
                + " Order by e.empNo ";
        Query<EmployeeInfo> query = session.createQuery(sql, EmployeeInfo.class);

        int page = 1;
        int maxResult = 20;
        int maxNavigationResult = 10;

        PaginationResult<EmployeeInfo> result
             = new PaginationResult<EmployeeInfo>(query, page, maxResult, maxNavigationResult);

        // Result:
        List<EmployeeInfo> emps = result.getList();
        int totalPages = result.getTotalRecords();
        int totalRecords = result.getTotalRecords();

        // 1 2 3 4 5 ... 11 12 13
        List<Integer> navPages = result.getNavigationPages();

    }

}
Et l'exemple .... d'un extrait du code JSP utilise  PaginationResult :
JSP Pagination
<c:if test="${paginationProducts.totalPages > 1}">
   <div class="page-navigator">
      <c:forEach items="${paginationProducts.navigationPages}" var = "page">
         <c:if test="${page != -1 }">
            <a href="productList?page=${page}" class="nav-item">${page}</a>
         </c:if>
         <c:if test="${page == -1 }">
            <span class="nav-item"> ... </span>
         </c:if>
      </c:forEach>
   </div>
</c:if>

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