package com.gong.mybatis.mapper;

import java.util.List;
 java.util.Map;

 org.apache.ibatis.annotations.MapKey;

 com.gong.mybatis.bean.Employee;

public interface EmployeeMapperDynamicsql {
    public List<Employee> getEmpByConditionIf(Employee employee);
}

<?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.gong.mybatis.mapper.EmployeeMapperDynamicsql">
    <!-- 查询，要查那个就带上那个条件 -->
    select id="getEmpByConditionIf" resultType="com.gong.mybatis.bean.Employee">
        select * from tbl_employee 
        where>
            choose>
                when test="id!=null"
                    id=#{id}
                </when="lastName!=null"
                    last_name like #{lastName}
                ="email!=null"
                    email=#{email}
                otherwise>
        select>
mapper>

 com.gong.mybatis.test;

 java.io.IOException;
 java.io.InputStream;
 org.apache.ibatis.io.Resources;
 org.apache.ibatis.session.sqlSession;
 org.apache.ibatis.session.sqlSessionFactory;
 org.apache.ibatis.session.sqlSessionFactoryBuilder;
 org.junit.Test;

 com.gong.mybatis.bean.Employee;
 com.gong.mybatis.mapper.EmployeeMapperDynamicsql;

class TestMybatis3 {
    
    public sqlSessionFactory getsqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        return new sqlSessionFactoryBuilder().build(is);
    }

    @Test
    void test()  IOException {
        sqlSessionFactory sqlSessionFactory = getsqlSessionFactory();
        sqlSession openSession = sqlSessionFactory.openSession();
        try {
            EmployeeMapperDynamicsql mapper = openSession.getMapper(EmployeeMapperDynamicsql.);
            Employee employee =  Employee();
//            employee.setId(3);
            employee.setLastName("%小%");
            employee.setEmail("xiaoming@qq.com");
            List<Employee> es = mapper.getEmpByConditionIf(employee);
            for(Employee e:es) {
                System.err.println(e);
            }
            openSession.commit();
        } finally {
            openSession.close();
        }
        
    }
    
}

DEBUG 01-21 13:45:17,288 ==>  Preparing: select * from tbl_employee WHERE id=?   (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:45:17,339 ==> Parameters: 3(Integer)  (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:45:17,410 ==      Total: 1  (BaseJdbcLogger.java:145) 
Employee [id=3,lastName=小红,1)">gender=0,1)">email=xiaohong@qq.com,1)">dept=null]

DEBUG 01-21 13:46:04,385 ==>  Preparing: select * from tbl_employee WHERE last_name like ?   (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:46:04,417 ==> Parameters: %小%(String)  (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:46:04,502 2  (BaseJdbcLogger.java:145) 
Employee [id=null]
Employee [id=4,1)">=小明,1)">=xiaoming@qq.com,1)">=null]

DEBUG 01-21 13:46:43,284 ==>  Preparing: select * from tbl_employee WHERE email=?   (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:46:43,347 ==> Parameters: xiximayou@qq.com(String)  (BaseJdbcLogger.java:145) 
Employee [id=1,lastName=xiximayou,gender=1,email=xiximayou@qq.com,dept=null]
DEBUG 01-21 13:46:43,394 1  (BaseJdbcLogger.java:145) 

DEBUG 01-21 13:47:30,447 ==>  Preparing: select * from tbl_employee WHERE id=?   (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:47:30,522 ==> Parameters: 3(Integer)  (BaseJdbcLogger.java:145) 
DEBUG 01-21 13:47:30,553 =null]

DEBUG 01-21 14:18:25,159 ==>  Preparing: select * from tbl_employee   (BaseJdbcLogger.java:145) 
DEBUG 01-21 14:18:25,243 ==> Parameters:   (BaseJdbcLogger.java:145) 
DEBUG 01-21 14:18:25,274 4  (BaseJdbcLogger.java:145) 
Employee [id=1,1)">=xiximayou,1)">=xiximayou@qq.com,1)">=2,1)">=jack,1)">=675544321@qq.com,1)">=null]