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：

 1 package com.entity; 2 /** 3  * @author:秦林森 4  */ 5  6 import javax.persistence.criteria.CriteriaBuilder; 7  8 public class Page { 9     /**10      *  其中currentPage,perPageRows这两个参数是做分页查询必须具备的参数11      *  原因是：hibernate中的Criteria或则是Query这两个接口：都有setFirstResult(Integer firstResult)12      *  和setMaxResult(Integer maxResult),13      *  这里的firstResult就是每页的开始的索引数：14      *  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)15      *  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：16      *  (currentPage-1)*perPageRows 1-1=(currentPge-1)*perPageRows.17      *18      *  maxResult就是每页能查询的最大记录数：也就是perPageRows.19      *20      *  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。21      */22     private Integer currentPage;//当前页23     private Integer perPageRows;//每页的记录数24     private Integer totalRows;//总记录数：25     private Integer totalPages;//总页数：26     public Integer getCurrentPage() {27         return currentPage;28     }29 30     public void setCurrentPage(Integer currentPage) {31         this.currentPage = currentPage;32     }33 34     public Integer getPerPageRows() {35         return perPageRows;36     }37 38     public void setPerPageRows(Integer perPageRows) {39         this.perPageRows = perPageRows;40     }41 42     public Integer getTotalRows() {43         return totalRows;44     }45 46     public void setTotalRows(Integer totalRows) {47         this.totalRows = totalRows;48     }49 50     public Integer getTotalPages() {51         return totalPages;52     }53 54     public void setTotalPages(Integer totalPages) {55         this.totalPages = totalPages;56     }57 }

 

下面用Hibernate的Criteira接口进行查询：

对应的实体类Employee的代码如下：

 

 1 package com.entity; 2  3 import javax.persistence.*; 4  5 @Entity 6 @Table(name = "EMPLOYEE") 7 public class Employee { 8     @Id 9     @GeneratedValue(strategy = GenerationType.IDENTITY)10     private int id;11     @Column(name = "first_name")12     private String firstName;13     @Column(name = "last_name")14     private String lastName;15     @Column(name = "salary")16     private int salary;17     //a constructor with no arguments18 19 20     public Employee() {21     }22 23     public int getId() {24         return id;25     }26 27     public void setId(int id) {28         this.id = id;29     }30 31     public String getFirstName() {32         return firstName;33     }34 35     public void setFirstName(String firstName) {36         this.firstName = firstName;37     }38 39     public String getLastName() {40         return lastName;41     }42 43     public void setLastName(String lastName) {44         this.lastName = lastName;45     }46 47     public int getSalary() {48         return salary;49     }50 51     public void setSalary(int salary) {52         this.salary = salary;53     }54 }

 

 //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：

 1 package com.util; 2 import org.hibernate.SessionFactory; 3 import org.hibernate.boot.Metadata; 4 import org.hibernate.boot.MetadataSources; 5 import org.hibernate.boot.registry.StandardServiceRegistry; 6 import org.hibernate.boot.registry.StandardServiceRegistryBuilder; 7 import org.hibernate.cfg.Configuration; 8 import org.hibernate.service.ServiceRegistry; 9 public class HibernateUtil {10     private static final SessionFactory sessionFactory;11 12     private static ServiceRegistry serviceRegistry;13 14     static {15         try {16             StandardServiceRegistry standardRegistry =17                     new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();18             Metadata metaData =19                     new MetadataSources(standardRegistry).getMetadataBuilder().build();20             sessionFactory = metaData.getSessionFactoryBuilder().build();21         } catch (Throwable th) {22 23             System.err.println("Enitial SessionFactory creation failed"   th);24             throw new ExceptionInInitializerError(th);25 26         }27     }28     public static SessionFactory getSessionFactory() {29 30         return sessionFactory;31 32     }33 }

 

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。

 

来源：https://www.icode9.com/content-4-374401.html