一个简单的mybatis入门demo-蒲公英云

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

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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>
  <!-- 设置源代码编码格式为utf-8 -->
  <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  <!-- 设置依赖 -->
  <dependencies>
      <!-- mybatis依赖 -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.4.6</version>
    </dependency>
    <!-- mysql依赖 -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.46</version>
    </dependency>
    <!-- slf4j依赖 -->
    <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.7.25</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.7.25</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/log4j/log4j -->
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
    <!-- junit依赖 -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
  </dependencies>
  <!-- 设置JDK的版本 -->
  <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>
    <!-- 引入外部资源文件，默认同resources目录下 -->
    <properties resource="jdbc.properties"></properties>
    <settings>
        <!-- 设置驼峰匹配 -->
        <setting name="mapUnderscoreToCamelCase" value="true" />
        <!-- 配置指定使用log4j输出日志 -->
        <setting name="logImpl" value="LOG4J" />
    </settings>
    <!-- 设置包扫描(别名) -->
    <typeAliases>
        <package name="cn.mybatis.mapper.model" />
    </typeAliases>
    <!-- 配置环境：可以配置多个环境，default：配置某一个环境的唯一标识，表示默认使用哪个环境 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <!-- 配置连接信息 -->
                <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>
    <!-- 配置映射文件：用来配置sql语句和结果集类型等，路径与resources下面路径相同 -->
    <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">
<!-- 定义当前XML的命名空间 -->
<mapper namespace="cn.mybatis.mapper.model.CountryMapper">
    <!-- ID属性，定义当前select查询的唯一ID；resultType，定义当前查询的返回值类型，如果没有设置别名，则需要写成cn.mybatis.model.Country -->
    <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