Hibernate实现分页查询
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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 arguments 18 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。
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