Hibernate二次学习二----------session.flush、session.doWork

2022-11-20 22:34:29

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1. session

Hibernate是对JDBC的轻量级封装，将JDBC的Connection封装到了Session中，因此Hibernate对数据库的操作大多都是通过session实现的。

2. session.flush

在获取Session对象时，Hibernate默认关闭了自动提交事务。

Hibernate执行SQL时，会将所有SQL存入Session的缓存中，提交事务时，再在数据库中执行SQL
private SessionFactory sessionFactory;

private Session session;

private Transaction transaction;

@Test

public void testSaveStudent() {

	// 生成学生对象

	Student s = new Student(3, "张三丰", "男", new Date(), "武当山");

	session.save(s);

}

Before

public void init() {

	// 创建会话工厂对象

	sessionFactory = new Configuration().configure().buildSessionFactory();

	// 创建会话对象

	session = sessionFactory.openSession();

	// 开始事务

	transaction = session.beginTransaction();

}

@After

public void destory () {

	// 提交事务

	transaction.commit();

	// 关闭会话

	session.close();

	// 关闭会话工厂

	sessionFactory.close();

}
若不开启事务或开启事务不提交，则SQL语句就不能在数据库中执行，此时可以通过session.flush()方法，强制将缓存中的SQL语句刷新到数据库
private SessionFactory sessionFactory;

private Session session;

/**

 * 不开启事务，数据无法保存到数据库

 */

@Test

public void testSaveStudentNoTransaction() {

	// 生成学生对象

	Student s = new Student(5, "张三丰", "男", new Date(), "武当山");

	session.save(s);

}

/**

 * 不开启事务，使用session.flush()强制同步数据到数据库

 */

@Test

public void testSaveStudentByflush() {

	// 生成学生对象

	Student s = new Student(5, "张三丰", "男", new Date(), "武当山");

	session.save(s);

	session.flush();// 当不使用事务时，需使用flush方法，强制提交

}

/**

 * 开启事务，但不使用commit提交，而是使用session.flush()强制提交

 */

@Test

public void testSaveStudentTransaction() {

	// 开启事务

	session.beginTransaction();

	// 生成学生对象

	Student s = new Student(6, "张三丰", "男", new Date(), "武当山");

	session.save(s);

	session.flush();// 不提交事务时，直接使用flush方法，也可强制提交

}

Before

public void init() {

	// 创建会话工厂对象

	sessionFactory = new Configuration().configure().buildSessionFactory();

	// 创建会话对象

	session = sessionFactory.openSession();

}

@After

public void destory () {

	// 关闭会话

	session.close();

	// 关闭会话工厂

	sessionFactory.close();

}

3. session.doWork

Hibernate使用面向对象的思想来进行数据库操作，推荐使用的也是封装的HQL语句，但有时项目需要进行jdbc操作，此时可以使用session.doWork()，在匿名内部类中获取Connection，进行jdbc操作。
/**

 * 使用session.doWork()实现jdbc操作

 */

@Test

public void testSessionDowork() {

	final List<String> list = new ArrayList<String>();

	session.doWork(new Work() { // 使用dowork方法进行jdbc操作

		@Override

		public void execute(Connection connection) throws SQLException {

			String sql = "select sname from student";

			PreparedStatement ps = (PreparedStatement) connection.prepareStatement(sql);

			ResultSet rs = ps.executeQuery();

			try {

				while (rs.next()) {

					String name = rs.getString(1);

					list.add(name);

				}

			} finally {

				if (rs != null) {

					rs.close();

				}

				if (ps != null) {

					ps.close();

				}

				// 此时connection被session管理，不能手动关闭

				/*if (connection != null) {

					connection.close();

				}*/

			}

		}

	});

	for (int i = 0; i < list.size(); i++) {

		System.out.println(list.get(i));

	}

}

Before

public void init() {

	// 创建会话工厂对象

	sessionFactory = new Configuration().configure().buildSessionFactory();

	// 创建会话对象

	session = sessionFactory.openSession();

}

@After

public void destory () {

	// 关闭会话

	session.close();

	// 关闭会话工厂

	sessionFactory.close();

}

4. 完整代码

pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

	<modelVersion>4.0.0</modelVersion>

	<groupId>org.imooc</groupId>

	<artifactId>Hibernate_001</artifactId>

	<version>0.0.1-SNAPSHOT</version>

	<packaging>jar</packaging>

	<properties>

		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

	</properties>

	<dependencies>

		<!-- junit -->

		<dependency>

			<groupId>junit</groupId>

			<artifactId>junit</artifactId>

			<version>4.12</version>

			<scope>test</scope>

		</dependency>

		<!-- Hibernate -->

		<dependency>

		    <groupId>org.hibernate</groupId>

		    <artifactId>hibernate-core</artifactId>

		    <version>5.1.5.Final</version>

		</dependency>

		<!-- mysql-connector-java -->

		<dependency>

		    <groupId>mysql</groupId>

		    <artifactId>mysql-connector-java</artifactId>

		    <version>5.1.22</version>

		</dependency>

	</dependencies>

	<build>

		<plugins>

			<plugin>

				<groupId>org.apache.maven.plugins</groupId>

				<artifactId>maven-compiler-plugin</artifactId>

				<version>3.6.1</version>

				<configuration>

					<target>1.7</target>

					<source>1.7</source>

					<encoding>UTF-8</encoding>

				</configuration>

			</plugin>

		</plugins>

	</build>

</project>
Student.java
package com.imooc.hibernate.model;

import java.util.Date;

public class Student {

	private int sid; // 学号

	private String sname; // 姓名

	private String gender; // 性别

	private Date birthday; // 出生日期

	private String address; // 地址

	public Student() {

	}

	public Student(int sid, String sname, String gender, Date birthday, String address) {

		this.sid = sid;

		this.sname = sname;

		this.gender = gender;

		this.birthday = birthday;

		this.address = address;

	}

	public int getSid() {

		return sid;

	}

	public void setSid(int sid) {

		this.sid = sid;

	}

	public String getSname() {

		return sname;

	}

	public void setSname(String sname) {

		this.sname = sname;

	}

	public String getGender() {

		return gender;

	}

	public void setGender(String gender) {

		this.gender = gender;

	}

	public Date getBirthday() {

		return birthday;

	}

	public void setBirthday(Date birthday) {

		this.birthday = birthday;

	}

	public String getAddress() {

		return address;

	}

	public void setAddress(String address) {

		this.address = address;

	}

	@Override

	public String toString() {

		return "Student [sid=" + sid + ", sname=" + sname + ", gender="

				+ gender + ", birthday=" + birthday + ", address=" + address + "]";

	}

}
student.hbm.xml
<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC

	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

	"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

	<class name="com.imooc.hibernate.model.Student">

		<id name="sid" type="int">

			<column name="SID"/>

			<generator class="assigned"/> <!-- 主键生成策略 -->

		</id>

		<property name="sname" type="java.lang.String">

			<column name="SNAME"/>

		</property>

		<property name="gender" type="java.lang.String">

			<column name="GENDER"></column>

		</property>

		<property name="birthday" type="java.util.Date">

			<column name="BIRTHDAY"/>

		</property>

		<property name="address" type="java.lang.String">

			<column name="ADDRESS"></column>

		</property>

	</class>

</hibernate-mapping>
hibernate.cfg.xml
<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-configuration PUBLIC

	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

	<session-factory>

		<!-- 数据库连接名 -->

		<property name="connection.username">root</property>

		<!-- 数据库连接密码 -->

		<property name="connection.password">20121221</property>

		<!-- 数据库驱动 -->

		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>

		<!-- 数据库连接url -->

		<property name="connection.url">

			jdbc:mysql://localhost:3306/hibernate?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8

		</property>

		<!-- 方言 -->

		<property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>

		<!-- 展示SQL -->

		<property name="show_sql">true</property>

		<!-- 格式化SQL -->

		<property name="format_sql">false</property>

		<!-- 建表策略 -->

		<property name="hbm2ddl.auto">update</property>

		<!-- 指定映射文件 -->

		<mapping resource="hbm/student.hbm.xml"/>

	</session-factory>

</hibernate-configuration>
StudentTest.java
package com.imooc.hibernate.test;

import java.sql.Connection;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.util.ArrayList;

import java.util.Date;

import java.util.List;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.hibernate.jdbc.Work;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

import com.imooc.hibernate.model.Student;

import com.mysql.jdbc.PreparedStatement;

public class StudentTest {

	private SessionFactory sessionFactory;

	private Session session;

	/**

	 * 不开启事务，数据无法保存到数据库

	 */

	@Test

	public void testSaveStudentNoTransaction() {

		// 生成学生对象

		Student s = new Student(5, "张三丰", "男", new Date(), "武当山");

		session.save(s);

	}

	/**

	 * 不开启事务，使用session.flush()强制同步数据到数据库

	 */

	@Test

	public void testSaveStudentByflush() {

		// 生成学生对象

		Student s = new Student(5, "张三丰", "男", new Date(), "武当山");

		session.save(s);

		session.flush();// 当不使用事务时，需使用flush方法，强制提交

	}

	/**

	 * 开启事务，但不使用commit提交，而是使用session.flush()强制提交

	 */

	@Test

	public void testSaveStudentTransaction() {

		// 开启事务

		session.beginTransaction();

		// 生成学生对象

		Student s = new Student(6, "张三丰", "男", new Date(), "武当山");

		session.save(s);

		session.flush();// 不提交事务时，直接使用flush方法，也可强制提交

	}

	/**

	 * 使用session.doWork()实现jdbc操作

	 */

	@Test

	public void testSessionDowork() {

		final List<String> list = new ArrayList<String>();

		session.doWork(new Work() { // 使用dowork方法进行jdbc操作

			@Override

			public void execute(Connection connection) throws SQLException {

				String sql = "select sname from student";

				PreparedStatement ps = (PreparedStatement) connection.prepareStatement(sql);

				ResultSet rs = ps.executeQuery();

				try {

					while (rs.next()) {

						String name = rs.getString(1);

						list.add(name);

					}

				} finally {

					if (rs != null) {

						rs.close();

					}

					if (ps != null) {

						ps.close();

					}

					// 此时connection被session管理，不能手动关闭

					/*if (connection != null) {

						connection.close();

					}*/

				}

			}

		});

		for (int i = 0; i < list.size(); i++) {

			System.out.println(list.get(i));

		}

	}

	@Before

	public void init() {

		// 创建会话工厂对象

		sessionFactory = new Configuration().configure().buildSessionFactory();

		// 创建会话对象

		session = sessionFactory.openSession();

	}

	@After

	public void destory () {

		// 关闭会话

		session.close();

		// 关闭会话工厂

		sessionFactory.close();

	}

}

5. 总结

使用Hibernate时，若需使用jdbc进行操作，则使用session.doWork()

若需提前提交session缓存中的SQL，则使用session.flush()

eg:
    Transaction tx = session.beginTransaction();

    for (int i = 0; i < 100000; i++) {

        Student s = new Student(...);

        session.save(s);

        if (i % 20 == 0) { // 防止session内存溢出

            session.flush();

            session.clear();

        }

    }

    tx.commit();

    session.close();

参考：Hibernate初探之单表映射

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