Hibernate使用
hibernate是一个ORM框架。
ORM的全拼是Object Relational Mapping，译为“对象关系映射”，是一种程序技术，用于实现面向对象编程语言里不同类型系统的数据之间的转换。从效果上来说，它其实是创建了一个可以在编程语言里使用的“虚拟对象数据库”。
使用较多的ORM框架有：
JPA---- Java Persistence API.JPA通过JDK 5.0注解或XML描述对象－关系表的映射关系（只有接口规范） Hibernate---- 最流行ORM框架，通过对象-关系映射配置，可以完全脱离底层SQL MyBatis---- 本是apache的一个开源项目 iBatis，支持普通 SQL查询，存储过程和高级映射的优秀持久层框架 Apache---- DBUtils Spring---- JDBCTemplate
接下来，我们通过一个案例演示hibernate的使用。先在项目中导入hibernate所需的一系列jar包：
接着，在源代码根路径下创建并配置hibernate.cfg.xml文件：
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.url">jdbc:mysql://localhost:3306/b0307</property>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.username">root</property>
<property name="connection.password">2018</property>
<property name="hibernate.show_sql">true</property>
<property name="hibernate.format_sql">true</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.current_session_context_class">thread</property>
<mapping resource="com/itszt/domain/Emp.hbm.xml"></mapping>
</session-factory>
</hibernate-configuration>
然后，映射数据库中的一个表，并据此创建映射的类Emp，并配置该类基于hibernate的配置文件Emp.hbm.xml：
package com.itszt.domain;
/**
* 测试用的实体类
*/
public class Emp {
private int uid;
private String name;
public Emp(int uid, String name) {
this.uid = uid;
this.name = name;
}
@Override
public String toString() {
return "Emp{" +
"uid=" + uid +
", name='" + name + '\'' +
'}';
}
public int getUid() {
return uid;
}
public void setUid(int uid) {
this.uid = uid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Emp() {
}
}
Emp.hbm.xml配置文件：
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.itszt.domain">
<class name="Emp" table="emp">
<id name="uid" column="uid">
<generator class="native"></generator>
</id>
<property name="name" column="name"></property>
</class>
<query name="queryTest1">
SELECT new Emp(uid,name) FROM Emp WHERE uid=? order by uid desc
</query>
<query name="queryTest2">
FROM Emp order by uid desc
</query>
<query name="queryTest3">
<![CDATA[
FROM Emp WHERE uid > ? and uid < ?
]]>
</query>
</hibernate-mapping>
测试类：
import com.itszt.domain.Emp;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
/**
* 测试类
*/
public class Test {
public static void main(String[] args) {
Configuration configuration=new Configuration().configure("hibernate.cfg.xml");
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
Emp emp = new Emp();
emp.setUid(2);
emp.setName("小马222");
Transaction transaction = session.beginTransaction();
//演示操作增删改查
// session.save(emp);
// session.delete(emp);
// session.update(emp);
Emp emp1 = (Emp) session.get(Emp.class, 2);
System.out.println("emp1 = " + emp1);
transaction.commit();
session.close();
sessionFactory.close();
}
}
此外，我们再创建一个工具类UtilHibernate，用来基于hibernate生成一个session：
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
/**
* 工具类
*/
public class UtilHibernate {
private static Configuration configuration;
private static SessionFactory sessionFactory;
//什么是要重复调用的
//什么是要初始加载一次的
static {
try {
configuration=new Configuration().configure();
sessionFactory = configuration.buildSessionFactory();
//JVM的关闭钩子，在JVM退出时close我们的sessionFactory
Runtime.getRuntime().addShutdownHook(new Thread(){
@Override
public void run() {
super.run();
System.out.println("Execute Hook.....");
if (sessionFactory != null) {
sessionFactory.close();
}
}
});
} catch (HibernateException e) {
throw new ExceptionInInitializerError("hibernate加载失败！！");
}
}
public static Session openNew(){
return sessionFactory.openSession();
}
public static Session getCurrent(){
return sessionFactory.getCurrentSession();
}
public static void release(Session session){
if (session != null) {
if (session.isOpen()) {
session.close();
}
}
}
}
接下来，通过该工具类，再分别通过query查询，hql，以及criteria来测试各自的用法：
TestQuery.java
import com.itszt.domain.Emp;
import org.hibernate.Session;
import org.hibernate.Transaction;
/**
* 测试查询
*/
public class TestQuery {
public static void main(String[] args) {
Session session1 = UtilHibernate.getCurrent();
Transaction transaction = session1.beginTransaction();
//饿加载:只要查询，马上就执行sql然后把结果取回
Emp emp1= (Emp) session1.get(Emp.class, 2);
System.out.println("emp1 = " + emp1);
transaction.commit();
UtilHibernate.release(session1);
Session session2 = UtilHibernate.getCurrent();
Transaction transaction2 = session2.beginTransaction();
//懒加载：等到使用该对象的时候再执行sql然后把结果取回
Emp emp2= (Emp) session2.load(Emp.class, 2);
System.out.println("emp2 = " + emp2);
transaction2.commit();
UtilHibernate.release(session2);
//退出JVM。。。
System.exit(0);
}
}
-----------------------------------------------------
TestHQL.java
import com.itszt.domain.Emp;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import java.util.Arrays;
import java.util.List;
/**
* HQL查询语言
*/
public class TestHQL {
//：role形式的参数设置查询
public static void main(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("SELECT new Emp(uid,name) FROM Emp WHERE uid=:uid AND name=:name");
// query.setParameter("uid",8);
// query.setParameter("name","测试角色2222222");
Emp emp=new Emp(2,"小马222");
query.setProperties(emp);
Object result = query.uniqueResult();
System.out.println("result = " + result);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
public static void main4(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("SELECT new Emp(uid,name) FROM Emp WHERE uid=?");
query.setParameter(0,2);
Emp emp= (Emp) query.uniqueResult();
System.out.println("emp = " + emp);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
//查询其中的几列
public static void main3(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("SELECT uid,name FROM Emp WHERE uid=?");
query.setParameter(0,2);
Object[] results= (Object[]) query.uniqueResult();
System.out.println("results = " + Arrays.toString(results));
Query query1 = session.createQuery("SELECT COUNT (*) FROM Emp");
Long num = (Long) query1.uniqueResult();
System.out.println("num = " + num);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
//查询单个数据，设置查询条件，返回单个对象
public static void main2(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("FROM Emp WHERE uid=?");
query.setParameter(0,2);
Emp emp= (Emp) query.uniqueResult();
System.out.println("emp = " + emp);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
//查询全部数据 ，返回一个list
public static void main1(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Query query = session.createQuery("FROM Emp");
List<Emp> list = query.list();
System.out.println("list = " + list);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
}
--------------------------------------------
TestHQL2.java
import com.itszt.domain.Emp;
import org.hibernate.Query;
import org.hibernate.SQLQuery;
import org.hibernate.Session;
import org.hibernate.Transaction;
import java.util.Arrays;
import java.util.List;
/**
* HQL查询语言2
*/
@SuppressWarnings("ALL")
public class TestHQL2 {
//原生SQL查询
public static void main(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
SQLQuery sqlQuery = session.createSQLQuery("SELECT * FROM emp");
sqlQuery.addEntity(Emp.class);
List<Emp> emp = (List<Emp>) sqlQuery.list();
System.out.println("emp = " + emp);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
//原生SQL查询
public static void main2(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
SQLQuery sqlQuery = session.createSQLQuery("SELECT * FROM emp");
List<Object[]> list = sqlQuery.list();
for (Object[] o : list) {
System.out.println("o = " + Arrays.toString(o));
}
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
//将SQL写在配置文件里
public static void main1(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Query query = session.getNamedQuery("queryTest1");
query.setParameter(0,8);
Emp emp= (Emp) query.uniqueResult();
System.out.println("emp = " + emp);
Query queryTest2 = session.getNamedQuery("queryTest2");
List list = queryTest2.list();
System.out.println("list = " + list);
Query queryTest3 = session.getNamedQuery("queryTest3");
queryTest3.setParameter(0,2);
queryTest3.setParameter(1,6);
List list2 = queryTest3.list();
System.out.println("list2 = " + list2);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
}
------------------------------------------------------
TestCriteria.java
import com.itszt.domain.Emp;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Restrictions;
import java.util.List;
/**
* 测试Criteria方式
*/
public class TestCriteria {
public static void main(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Criteria criteria = session.createCriteria(Emp.class);
//基本比较
//criteria.add(Restrictions.lt("uid",5));
// criteria.add(Restrictions.lt("uid",3));
// criteria.add(Restrictions.gt("uid",1));
//分页---------
criteria.setFirstResult(0);
criteria.setMaxResults(5);
//分页---------
List<Emp> emps= criteria.list();
System.out.println("emps = " + emps);
//聚合
/*criteria.setProjection(Projections.sum("uid"));
Long result= (Long) criteria.uniqueResult();
System.out.println("result = " + result);*/
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
public static void main1(String[] args) {
Session session = UtilHibernate.getCurrent();
Transaction transaction = session.beginTransaction();
Criteria criteria = session.createCriteria(Emp.class);
criteria.add(Restrictions.eq("uid",6));
Emp emp = (Emp) criteria.uniqueResult();
System.out.println("emp = " + emp);
transaction.commit();
UtilHibernate.release(session);
System.exit(0);
}
}
