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

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目录

• 1. session
• 2. session.flush
• 3. session.doWork
• 4. 完整代码
• 5. 总结

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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