Mybatis(一）通过XML配置

安装

如果使用 Maven 来构建项目，则需将下面的 dependency 代码置于 pom.xml 文件中：

<dependency>
  <groupId>org.mybatisgroupId>
  <artifactId>mybatisartifactId>
  <version>x.x.xversion>
dependency>

我的version版本是3.5.3

接着导入MySQL

<dependency>
	<groupId>mysqlgroupId>
	<artifactId>mysql-connector-javaartifactId>
	<version>8.0.18version>			
dependency>		

导入单元测试Junit

<dependency>
	<groupId>junitgroupId>
	<artifactId>junitartifactId>
	<version>4.12version>			
dependency>		

maven项目中配置JDK1.8的插件

<build>
       <plugins>
           <plugin>
             <groupId>org.apache.maven.pluginsgroupId>
             <artifactId>maven-compiler-pluginartifactId>
             <configuration>
               <source>1.8source>
               <target>1.8target>
               <encoding>utf-8encoding>
             configuration>
           plugin>
       plugins>
   build>

在数据库中创建表

use test;
CREATE TABLE category_ (
  id int(11) NOT NULL AUTO_INCREMENT,
  name varchar(32) DEFAULT NULL,
  PRIMARY KEY (id)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

maven 项目结构图

数据库配置文件db.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/test?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=utf-8
username=root
password=root

mybatis的配置文件 mybatis.cfg.xml

<configuration>

	<properties resource="db.properties">properties>
	
	<typeAliases>
		<package name="pojo"/>
	typeAliases>
	
	<environments default="development">
	
		<environment id="development">
		
			<transactionManager type="JDBC"/>
			
			<dataSource type="POOLED">
			
				<property name="driver" value="${driver}"/>
				
				<property name="url" value="${url}"/>
				
				<property name="username" value="${username}"/>
				
				<property name="password" value="${password}"/>
			dataSource>
		environment>
	environments>
	
	<mappers>
	
		<mapper resource="pojo/Category.xml"/>
	mappers>
configuration>

创建实体类Category

package pojo;

public class Category {
	private int id;
	private String name;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

SQL语句映射文件Category.xml

namespace 说明
对命名空间的一点说明

<mapper namespace="pojo">


	<select id="list" resultType="Category">
		select * from category_
	select>
	<select id="one" parameterType="int" resultType="Category">
		select * from category_ where id=#{id}
	select>
	
	<insert id="save" parameterType="Category">
		insert into category_ values(null,#{name})
	insert>
	
	<delete id="delete" parameterType="int">
		delete from category_ where id=#{id}
	delete>
	
	<update id="update" parameterType="Category">
		update category_ set name=#{name} where id=#{id}
	update>
mapper>

测试数据

package test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import pojo.Category;

public class TestCase {
	SqlSessionFactory sf;
	SqlSession ss;
	@Before
	public void before() throws IOException {
		String resource="mybatis.cfg.xml";
		//配置文件mybatis-config.xml，得到SqlSessionFactory
		InputStream inputStream=Resources.getResourceAsStream(resource); 
		sf=new SqlSessionFactoryBuilder().build(inputStream);
		//通过SqlSessionFactory获得SqlSession
		ss=sf.openSession();
	}
	/*
	 *查询所有
	 */
	@Test
	public void test() {
		List<Category>list=ss.selectList("list");
		for (Category category : list) {
			System.out.println(category.getName());
		}
	}
	/*
	 *新增数据
	 */
	@Test
	public void save() {
		Category c=new Category();
		c.setName("category 1");
		int count=ss.insert("save",c);
		System.out.println(count);//返回新增的数据的个数
	}
	/*
	 *修改数据
	 */
	@Test
	public void update(){
		Category c=ss.selectOne("one", 1);
		c.setName("分类1");
		int count=ss.update("update", c);
		System.out.println(count);//返回更新的数据的个数
	}
	/*
	 *删除数据
	 */
	@Test
	public void delete(){
		Category c=ss.selectOne("one", 1);
		int count=ss.delete("delete",c);
		System.out.println(count);//返回删除数据的个数
	}
	//SqlSession的关闭
	@After
	public void after() {
	// 提交事务
		ss.commit();
		// 关闭Session
		ss.close();
	}
}

基本原理

应用程序找Mybatis要数据
mybatis从数据库中找来数据
通过mybatis-cfg.xml 定位哪个数据库
通过Category.xml执行对应的select，update,insert,delete语句
基于Category.xml把返回的数据库记录封装在Category对象中
返回数据