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 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。
