mybatis动态标签——choose、when、otherwise

<?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="com.xxx.dynamicSQL.mapper.EmpMapper">

    <!--
        choose、when、otherwise相当于if, else if ，else
        when至少设置一个，匹配上条件后，其他的条件不执行
　　　　 otherwise最多设置一个，when中的条件都不符合时，执行该条件
    -->
    <select id="getEmp" resultType="emp">
        select * from t_emp
        <where>
            <choose>
                <when test="empName != null and empName != ''">
                    emp_name = #{empName}
                </when>
                <when test="age != null and age != ''">
                    age = #{age}
                </when>
                <when test="gender != null and gender != ''">
                    gender = #{gender}
                </when>
                <otherwise>
                    emp_id = 1
                </otherwise>
            </choose>
        </where>
    </select>
</mapper>

测试代码1：

 @Test
    public void test1(){
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
        Emp emp = new Emp(null,"",11,"男");
        List<Emp> list = mapper.getEmp(emp);

        list.forEach(System.out::println);
    }

测试代码2：

@Test
    public void test1(){
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
        Emp emp = new Emp(null,"",null,"");
        List<Emp> list = mapper.getEmp(emp);

        list.forEach(System.out::println);
    }