类级别查询优化：
创建一个实体类：
package domain;import java.util.HashSet;import java.util.Set;//客户实体public class Customer { ???????private Long cust_id; ???private String cust_name; ???private String cust_source; ???private String cust_industry; ???private String cust_level; ???private String cust_linkman; ???private String cust_phone; ???private String cust_mobile; ???//使用set集合,表达一对多关系 ???private Set<LinkMan> linkMens = new HashSet<LinkMan>(); ???public Set<LinkMan> getLinkMens() { ???????return linkMens; ???} ???public void setLinkMens(Set<LinkMan> linkMens) { ???????this.linkMens = linkMens; ???} ???public Long getCust_id() { ???????return cust_id; ???} ???public void setCust_id(Long cust_id) { ???????this.cust_id = cust_id; ???} ???public String getCust_name() { ???????return cust_name; ???} ???public void setCust_name(String cust_name) { ???????this.cust_name = cust_name; ???} ???public String getCust_source() { ???????return cust_source; ???} ???public void setCust_source(String cust_source) { ???????this.cust_source = cust_source; ???} ???public String getCust_industry() { ???????return cust_industry; ???} ???public void setCust_industry(String cust_industry) { ???????this.cust_industry = cust_industry; ???} ???public String getCust_level() { ???????return cust_level; ???} ???public void setCust_level(String cust_level) { ???????this.cust_level = cust_level; ???} ???public String getCust_linkman() { ???????return cust_linkman; ???} ???public void setCust_linkman(String cust_linkman) { ???????this.cust_linkman = cust_linkman; ???} ???public String getCust_phone() { ???????return cust_phone; ???} ???public void setCust_phone(String cust_phone) { ???????this.cust_phone = cust_phone; ???} ???public String getCust_mobile() { ???????return cust_mobile; ???} ???public void setCust_mobile(String cust_mobile) { ???????this.cust_mobile = cust_mobile; ???} ???@Override ???public String toString() { ???????return "Customer [cust_id=" + cust_id + ", cust_name=" + cust_name + "]"; ???}}自定义工具类：
package utils;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class HibernateUtils { ???private static SessionFactory sf; ???????static{ ???????//1 创建,调用空参构造 ???????Configuration conf = new Configuration().configure(); ???????//2 根据配置信息,创建 SessionFactory对象 ????????sf = conf.buildSessionFactory(); ???} ???????//获得session => 获得全新session ???public static Session openSession(){ ???????????????//3 获得session ???????????????Session session = sf.openSession(); ???????????????????????????????return session; ???????????} ???//获得session => 获得与线程绑定的session ???public static Session getCurrentSession(){ ???????//3 获得session ???????Session session = sf.getCurrentSession(); ???????????????return session; ???} ???}测试类示例：
package lazy;import org.hibernate.Session;import org.hibernate.Transaction;import org.junit.Test;import domain.Customer;import utils.HibernateUtils;//懒加载|延迟加载public class Demo { ???????@Test ???// get方法 : 立即加载.执行方法时立即发送sql语句查询结果 ???public void fun1(){ ???????Session session = HibernateUtils.openSession(); ???????Transaction tx = session.beginTransaction(); ???????//---------------------------------------------------- ???????????????Customer c = session.get(Customer.class, 2l); ???????????????System.out.println(c); ???????//---------------------------------------------------- ???????tx.commit(); ???????session.close(); ???????????} ???????@Test ???// load方法(默认):是在执行时,不发送任何sql语句.返回一个对象.使用该对象时,才执行查询. ???// 延迟加载: 仅仅获得没有使用.不会查询.在使用时才进行查询. ???// 是否对类进行延迟加载: 可以在配置文件中通过在class元素上配置lazy属性来控制. ???????//lazy:true ?加载时,不查询.使用时才查询b ???????//lazy:false 加载时立即查询. ???public void fun2(){ ???????Session session = HibernateUtils.openSession(); ???????Transaction tx = session.beginTransaction(); ???????//---------------------------------------------------- ???????????????Customer c = session.load(Customer.class, 2l); ???????????????//---------------------------------------------------- ???????tx.commit(); ???????session.close(); ???????System.out.println(c); ???????????} ???}为了提高效率，建议使用延迟加载，要确保调用属性时候，session是打开的，否则会报出异常
关联级别优化：
配置文件：集合的属性配置
lazy属性: 决定是否延迟加载
true(默认值): 延迟加载,懒加载
false: 立即加载
extra: 极其懒惰
fetch属性: 决定加载策略.使用什么类型的sql语句加载集合数据
select(默认值): 单表查询加载
join: 使用多表查询加载集合
subselect:使用子查询加载集合
结论:为了提高效率.fetch的选择上应选择select. lazy的取值应选择 true. 全部使用默认值.
hibernate框架学习笔记12：查询优化
原文地址：https://www.cnblogs.com/xuyiqing/p/8454930.html