一个简单的mybatis入门demo

悠悠 2022-04-08 15:37 419阅读 0赞

### 数据库方面 ###

直接上建库、建表和插数据sql脚本

create database mybatis default character set utf8 collate utf8_general_ci;
    use mybatis;
    create table country 
    (id int primary key auto_increment,
     countryname varchar(255) null,
     countrycode varchar(255) null
    );
    show tables from mybatis;
    desc country;
    insert country(countryname, countrycode) values('中国', 'CN'),('美国', 'US'),('俄罗斯','RU'),('英国', 'GB'),('法国', 'FR'),('中国香港', 'HK');

### Java工程 ###

工程结构如下，使用maven管理jar包依赖

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21hZ2kxMjAx_size_16_color_FFFFFF_t_70][]

pom.xml文件内容

<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>simple</groupId>
      <artifactId>mybatis-demo</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      
      
      <properties>
      	<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      </properties>
      
      
      <dependencies>
      	
    	<dependency>
    	    <groupId>org.mybatis</groupId>
    	    <artifactId>mybatis</artifactId>
    	    <version>3.4.6</version>
    	</dependency>
    	
    	<dependency>
    		<groupId>mysql</groupId>
    		<artifactId>mysql-connector-java</artifactId>
    		<version>5.1.46</version>
    	</dependency>
    	
    	
    	<dependency>
    	    <groupId>org.slf4j</groupId>
    	    <artifactId>slf4j-api</artifactId>
    	    <version>1.7.25</version>
    	</dependency>
    	
    	<dependency>
    	    <groupId>org.slf4j</groupId>
    	    <artifactId>slf4j-log4j12</artifactId>
    	    <version>1.7.25</version>
    	</dependency>
    	
    	<dependency>
    	    <groupId>log4j</groupId>
    	    <artifactId>log4j</artifactId>
    	    <version>1.2.17</version>
    	</dependency>
    	
    	<dependency>
    		<groupId>junit</groupId>
    		<artifactId>junit</artifactId>
    		<version>4.12</version>
    		<scope>test</scope>
    	</dependency>
      </dependencies>
      
      
      <build>
      	<plugins>
      		<plugin>
      			<groupId>org.apache.maven.plugins</groupId>
      			<artifactId>maven-compiler-plugin</artifactId>
      			<configuration>
      				<source>1.8</source>
      				<targen>1.8</targen>
      			</configuration>
      		</plugin>
      	</plugins>
      </build>
    </project>

mybatis-config.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
      PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
      "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
    	
    	<properties resource="jdbc.properties"></properties>
    
    	<settings>
    		
    		<setting name="mapUnderscoreToCamelCase" value="true" />
    		
    		<setting name="logImpl" value="LOG4J" />
    	</settings>
    	
    	
    	<typeAliases>
    		<package name="cn.mybatis.mapper.model" />
    	</typeAliases>
    	
    	
    	<environments default="development">
    		<environment id="development">
    			<transactionManager type="JDBC" />
    			<dataSource type="POOLED">
    				
    				<property name="driver" value="${jdbc.driverClass}" />
    				<property name="url" value="${jdbc.url}" />
    				<property name="username" value="${jdbc.username}" />
    				<property name="password" value="${jdbc.password}" />
    			</dataSource>
    		</environment>
    	</environments>
    	
    	
    	<mappers>
    		<mapper resource="cn/mybatis/model/mapper/CountryMapper.xml" />
    	</mappers>
    </configuration>

jdbc.properties

jdbc.driverClass=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/mybatis
    jdbc.username=root
    jdbc.password=mysql

log4j.properties

#全局配置
    log4j.rootLogger=ERROR, stdout
    #mybatis日志配置
    log4j.logger.cn.mybatis.mapper=TRACE
    #控制台输出配置
    log4j.appender.stdout=org.apache.log4j.ConsoleAppender
    log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
    log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

Country.java

package cn.mybatis.mapper.model;
    
    public class Country {
    
    	private int id;
    	private String countryname;
    	private String countrycode;
    	
    	public int getId() {
    		return id;
    	}
    	public void setId(int id) {
    		this.id = id;
    	}
    	public String getCountryname() {
    		return countryname;
    	}
    	public void setCountryname(String countryname) {
    		this.countryname = countryname;
    	}
    	public String getCountrycode() {
    		return countrycode;
    	}
    	public void setCountrycode(String countrycode) {
    		this.countrycode = countrycode;
    	}
    	
    }

Main.java

package cn.mybatis.mapper.app;
    
    import java.io.IOException;
    import java.io.Reader;
    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 cn.mybatis.mapper.model.Country;
    
    public class Main {
    
    	private static SqlSessionFactory sqlSessionFactory;
    	
    	/**
    	 * 初始化sqlSessionFactory
    	 */
    	public static void init() {
    		try {
    			Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
    			sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    			reader.close();
    		} catch (IOException ignore) {
    			ignore.printStackTrace();
    		}
    	}
    	
    	public static void main(String[] args) {
    		
    		// 连接数据库
    		init();
    		
    		SqlSession sqlSession = sqlSessionFactory.openSession();
    		try {
    			List<Country> countryList = sqlSession.selectList("selectAll");
    			printCountryList(countryList);
    		} finally {
    			sqlSession.close();
    		}
    	}
    	
    	/**
    	 * 打印country信息
    	 * @param countryList 
    	 */
    	private static void printCountryList(List<Country> countryList) {
    		for (Country country : countryList) {
    			System.out.printf("%-4d%4s%4s\n", country.getId(), country.getCountryname(), country.getCountrycode());
    		}
    	}
    }

代码解读：

*  通过Resources工具类将mybatis-config.xml配置文件读入Reader
 *  再通过SqlSessionFactoryBuilder建造类使用Reader创建SqlSessionFactory工厂对象。在创建SqlSessionFactory对象的过程中，首先解析mybatis-config.xml配置文件，读取配置文件中的mappers配置后会读取全部的Mapper.xml进行具体方法的解析，在这些解析完成后，SqlSessionFactory就包含了所有的属性配置和执行SQL的信息。
 *  通过SqlSessionFactory工厂对象获取一个SqlSession
 *  通过SqlSession的selectList方法查找到CountryMapper.xml中id="selectAll" 的方法，执行SQL进行查询
 *  mybatis底层使用jdbc执行SQL，获得查询结果集ResultSet后，根据resultType的配置将结果映射为Country类型的集合，返回查询结果。

CountryMapperTest.java

package cn.mybatis.mapper;
    
    import java.io.IOException;
    import java.io.Reader;
    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.BeforeClass;
    import org.junit.Test;
    
    import cn.mybatis.mapper.model.Country;
    
    public class CountryMapperTest {
    
    	private static SqlSessionFactory sqlSessionFactory;
    	
    	@BeforeClass
    	public static void inti() {
    		try {
    			Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
    			sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    			reader.close();
    		} catch (IOException ignore) {
    			ignore.printStackTrace();
    		}
    	}
    	
    	@Test
    	public void testSelectAll() {
    		SqlSession sqlSession = sqlSessionFactory.openSession();
    		try {
    			List<Country> countryList = sqlSession.selectList("selectAll");
    			printCountryList(countryList);
    		} finally {
    			sqlSession.close();
    		}
    	}
    	
    	private void printCountryList(List<Country> countryList) {
    		for (Country country : countryList) {
    			System.out.printf("%-4d%4s%4s\n", country.getId(), country.getCountryname(), country.getCountrycode());
    		}
    	}
    }

CountryMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
    <mapper namespace="cn.mybatis.mapper.model.CountryMapper">
    	
    	<select id="selectAll" resultType="Country">
    		select id, countryname, countrycode from country
    	</select>
    </mapper>

至此，所有的文件都添加完成

### 测试 ###

测试时，可以使用Main.java 的main方法直接测试，也可以使用Junit进行测试

控制台可以看到如下信息，证明整个程序调通

DEBUG [main] - ==>  Preparing: select id, countryname, countrycode from country 
    DEBUG [main] - ==> Parameters: 
    TRACE [main] - <==    Columns: id, countryname, countrycode
    TRACE [main] - <==        Row: 1, 中国, CN
    TRACE [main] - <==        Row: 2, 美国, US
    TRACE [main] - <==        Row: 3, 俄罗斯, RU
    TRACE [main] - <==        Row: 4, 英国, GB
    TRACE [main] - <==        Row: 5, 法国, FR
    TRACE [main] - <==        Row: 6, 中国香港, HK
    DEBUG [main] - <==      Total: 6
    1     中国  CN
    2     美国  US
    3    俄罗斯  RU
    4     英国  GB
    5     法国  FR
    6   中国香港  HK

附：测试过程中，可能会存在部分依赖jar包下载失败的情况，如果工程如法下载到jar包，可以手动下载该jar包，并放到maven库中对应的位置，以支持文件编译和程序运行。

代码工程 下载路径 [https://download.csdn.net/download/magi1201/10859774][https_download.csdn.net_download_magi1201_10859774]

上面，一个简单的mybatis示例，作为学习记录。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21hZ2kxMjAx_size_16_color_FFFFFF_t_70]: /images/20220404/e2c7a60f9f8445e08125fd5aafe4907a.png
[https_download.csdn.net_download_magi1201_10859774]: https://download.csdn.net/download/magi1201/10859774