用Hibernate实现分页查询

分页查询就是把数据库中某张表的记录数进行分页查询，在做分页查询时会有一个Page类，下面是一个Page类，我对其做了详细的注解：

package com.entity;
/**
 * @author:秦林森
 */

import javax.persistence.criteria.CriteriaBuilder;

public class Page {
    /**
     *  其中currentPage,perPageRows这两个参数是做分页查询必须具备的参数
     *  原因是：hibernate中的Criteria或则是Query这两个接口：都有setFirstResult(Integer firstResult)
     *  和setMaxResult(Integer maxResult),
     *  这里的firstResult就是每页的开始的索引数：
     *  每页开始的索引数的计算公式是：（currentPage-1）*perPageRows+1,(这是相对索引从1开始的)
     *  但是Hibernate中的firstResult的索引是从0开始的，所以在hibernate中每页开始的索引数的计算公式是：
     *  (currentPage-1)*perPageRows+1-1=(currentPge-1)*perPageRows.
     *
     *  maxResult就是每页能查询的最大记录数：也就是perPageRows.
     *
     *  Math.ceil(totalRows/perPageRows)==totalPages;//这是根据总记录数和每页的记录数算出总页数的计算公式。
     */
    private Integer currentPage;//当前页
    private Integer perPageRows;//每页的记录数
    private Integer totalRows;//总记录数：
    private Integer totalPages;//总页数：
    public Integer getCurrentPage() {
        return currentPage;
    }

    public void setCurrentPage(Integer currentPage) {
        this.currentPage = currentPage;
    }

    public Integer getPerPageRows() {
        return perPageRows;
    }

    public void setPerPageRows(Integer perPageRows) {
        this.perPageRows = perPageRows;
    }

    public Integer getTotalRows() {
        return totalRows;
    }

    public void setTotalRows(Integer totalRows) {
        this.totalRows = totalRows;
    }

    public Integer getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(Integer totalPages) {
        this.totalPages = totalPages;
    }
}

下面用Hibernate的Criteira接口进行查询：

对应的实体类Employee的代码如下：

package com.entity;

import javax.persistence.*;

@Entity
@Table(name = "EMPLOYEE")
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    @Column(name = "first_name")
    private String firstName;
    @Column(name = "last_name")
    private String lastName;
    @Column(name = "salary")
    private int salary;
    //a constructor with no arguments


    public Employee() {
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getSalary() {
        return salary;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }
}

 //创建EMPLOYEE表的sql语句是：

create table EMPLOYEE (
   id INT NOT NULL auto_increment,
   first_name VARCHAR(20) default NULL,
   last_name  VARCHAR(20) default NULL,
   salary     INT  default NULL,
   PRIMARY KEY (id)
);

首先在写一个配置文件：hibernate.cfg.xml用于连接数据库；

hibernate.cfg.xml的代码如下：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-5.0.dtd">

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">130850a,</property>
        <property name="hibernate.connection.pool_size">10</property>
        <property name="show_sql">true</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.current_session_context_class">thread</property>

        <mapping class="com.entity.Employee" />

    </session-factory>
</hibernate-configuration>

在写一个用于启动Hibernate的util类：HibernateUtil的代码如下：

package com.util;
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
public class HibernateUtil {
    private static final SessionFactory sessionFactory;

    private static ServiceRegistry serviceRegistry;

    static {
        try {
            StandardServiceRegistry standardRegistry =
                    new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
            Metadata metaData =
                    new MetadataSources(standardRegistry).getMetadataBuilder().build();
            sessionFactory = metaData.getSessionFactoryBuilder().build();
        } catch (Throwable th) {

            System.err.println("Enitial SessionFactory creation failed" + th);
            throw new ExceptionInInitializerError(th);

        }
    }
    public static SessionFactory getSessionFactory() {

        return sessionFactory;

    }
}

最后是分页查询的代码，代码如下：

package com.hibDemo;

import com.entity.Employee;
import com.entity.Page;
import com.util.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

import java.util.List;

public class PaginationQuery {

    public void paginationByCriteria(){
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
        Session session = sessionFactory.getCurrentSession();
        Transaction tx=null;
        try {
            //do some work
            tx=session.beginTransaction();
            Page page = new Page();
            /**
             * 假设现在查询的是第一页，每页查询的最大记录数是3.
             */
            page.setCurrentPage(1);
            page.setPerPageRows(3);
            Criteria criteria = session.createCriteria(Employee.class);
            Integer currentPage = page.getCurrentPage();//得到当前页
            Integer perPageRows = page.getPerPageRows();//得到每页的记录数：
            /**
             * 在Page类中我已说明了：每页开始的索引数在hibernate中的计算公式是：(currentPage-1)*perPageRows
             */
            criteria.setFirstResult((currentPage-1)*perPageRows);
            criteria.setMaxResults(perPageRows);
            List<Employee> employees = criteria.list();
            for(Employee employee:employees){
                System.out.println("*********************");
                System.out.println("id="+employee.getId()+" firstName="+employee.getFirstName()+" lastName="+employee.getLastName());
            }
            tx.commit();

        } catch (Exception e) {
            if(tx!=null){
                tx.rollback();
            }
            e.printStackTrace();
        } finally {
            session.close();//关闭流，一定要关闭，不然会影响运行速度。
        }
    }
    public static void main(String[] args) {
        PaginationQuery paginationQuery = new PaginationQuery();
        paginationQuery.paginationByCriteria();
    }
}

总结：这个Page类为Hibernate中setFirstResult,和setMaxResult服务的，抓住这个就可以了。代码可以随便写。