接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Employee;

import java.util.List;

public interface EmployeeMapper {

    //携带了哪个字段查询条件就带上这个字段的值

    public List<Employee> getEmpsByConditionIf(Employee employee);

    public List<Employee> getEmpsByConditionIfWhere(Employee employee);

}

mapper定义：

<?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.mybatis.dao.EmployeeMapper">

    <!-- 查询员工，要求，携带了哪个字段查询条件就带上这个字段的值 -->

    <!-- public List<Employee> getEmpsByConditionIf(Employee employee); -->

    <select id="getEmpsByConditionIf" resultType="com.mybatis.bean.Employee">

        select * from tbl_employee

        where 1=1

        <if test="id!=null">

            and id=#{id}

        </if>

        <if test="lastName!=null && lastName!=''">

            and last_name like #{lastName}

        </if>

        <if test="email!=null and email.trim()!=""">

            and email=#{email}

        </if>

        <!-- ognl会进行字符串与数字的转换判断  "0"==0 -->

        <if test="gender==0 or gender==1">

            and gender=#{gender}

        </if>

    </select>

    <!--public List<Employee> getEmpsByConditionIfWhere(Employee employee);-->

    <select id="getEmpsByConditionIfWhere" resultType="com.mybatis.bean.Employee">

        select * from tbl_employee

        <where>

            <if test="id!=null">

                id=#{id}

            </if>

            <if test="lastName!=null && lastName!=''">

                and last_name like #{lastName}

            </if>

            <if test="email!=null and email.trim()!=""">

                and email=#{email}

            </if>

            <!-- ognl会进行字符串与数字的转换判断  "0"==0 -->

            <if test="gender==0 or gender==1">

                and gender=#{gender}

            </if>

        </where>

    </select>

</mapper>

测试代码：

package com.mybatis.demo;

import com.mybatis.bean.Employee;

import com.mybatis.dao.EmployeeMapper;

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.Test;

import java.io.IOException;

import java.io.InputStream;

import java.util.List;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void test() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

            //查询的时候如果某些条件没带可能sql拼装会有问题

            //1、给where后面加上1=1，以后的条件都and xxx.

            //2、mybatis使用where标签来将所有的查询条件包括在内。mybatis就会将where标签中拼装的sql，多出来的and或者or去掉

            //where只会去掉第一个多出来的and或者or。

            List<Employee> emps = mapper.getEmpsByConditionIf(new Employee(null, "jetty", "jetty@126.com", 1));

            for (Employee emp : emps) {

                System.out.println(emp);

            }

            System.out.println("-------------------");

            List<Employee> employees = mapper.getEmpsByConditionIfWhere(new Employee(null, "jetty", "jetty@126.com", 1));

            for (Employee emp : employees) {

                System.out.println(emp);

            }

        } finally {

            openSession.close();

        }

    }

}