Java：MyBatis动态SQL实践（1）

$ tree
.
├── README.md
├── pom.xml
└── src
    ├── main
    │   ├── java
    │   │   └── com
    │   │       └── mouday
    │   │           ├── mapper
    │   │           │   ├── PersonMapper.java
    │   │           │   └── PersonMapper.xml
    │   │           ├── pojo
    │   │           │   └── Person.java
    │   │           └── util
    │   │               └── MyBatisUtil.java
    │   └── resources
    │       ├── db.properties
    │       ├── mybatis-config.xml
    │       └── sql
    │           └── person.sql
    └── test
        └── java
            └── com
                └── mouday
                    └── PersonTest.java

<?xml version="1.0" encoding="UTF-8"?>
<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>com.mouday</groupId>
    <artifactId>mybatis-demo</artifactId>
    <version>1.0-SNAPSHOT</version>
    <build>
        <resources>
            <!--编译src/main/java目录下的xml文件-->
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.20</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

<?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>
    <!-- 加载数据库配置 -->
    <properties resource="db.properties" />
    <!-- 打印sql日志 -->
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <!-- 指定整个包下的类都是别名 -->
    <typeAliases>
        <package name="com.mouday.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 class="com.mouday.mapper.PersonMapper"/>
    </mappers>
</configuration>

-- 建表
create table person(
    id int not null primary key auto_increment,
    name varchar(20),
    age int
);
-- 插入数据
insert into person(name, age) values('刘备', 25);
insert into person(name, age) values('关羽', 24);
insert into person(name, age) values('张飞', 23);
insert into person(name, age) values('曹操', 25);
insert into person(name, age) values('许褚', 24);
insert into person(name, age) values('孙权', 25);
insert into person(name, age) values('周瑜', 24);

package com.mouday.util;
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 java.io.IOException;
import java.io.InputStream;
public class MyBatisUtil {
    private static SqlSessionFactory factory = null;
    // 使用static静态代码块，随着类的加载而加载，只执行一次
    static {
        try {
            String resource = "mybatis-config.xml";
            // 加载MyBatis的主配置文件
            InputStream inputStream = Resources.getResourceAsStream(resource);
            // 通过构建器（SqlSessionFactoryBuilder）构建一个SqlSessionFactory工厂对象
            factory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession() throws IOException {
        return factory.openSession();
    }
}