Mybatis入门级教程（一）

一、Mybatis介绍

MyBatis是支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis消除了几乎所有的JDBC代码和参数的手工设置以及对结果集的检索封装。MyBatis可以使用简单的XML或注解用于配置和原始映射，将接口和Java的POJO（Plain Old Java Objects，普通的Java对象）映射成数据库中的记录.

JDBC-dbutils(自动封装)-MyBatis-Hibernate

http://blog.csdn.net/softwave/article/details/18604565

为什么要学Mybatis
4000
?而不使用传统的jdbc?

Mybatis是一个持久层框架，使用Mybatis代替传统的jdbc，代替vo+dao持久层。持久化：把内存中的数据保存到可掉电的存储设备中（硬盘、u盘）。

传统的jdbc存在缺点，操作起来相当繁琐，过多的set和get也相当繁琐。因此使用Mybatis简化操作。

二、如何使用Mybatis?

从一个简单的用户管理例子学起，使用步骤：

建库+表（使用mysql需要建库，oracle不用）

定义表所对应的实体类PO

添加jar包

添加Mybatis的配置文件conf.xml

定义操作user表的sql映射文件userMapper.xml

在conf.xml文件中注册userMapper.xml文件

编写测试代码，执行定义的select语句

1.建库和表
create database mybatis;
use mybatis;
CREATE TABLE user(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
INSERT INTO user(NAME, age) VALUES('小明', 22);
INSERT INTO user(NAME, age) VALUES('小红', 23);

2.定义表所对应的实体类 PO持久化对象
public class User {
private int id;
private String name;
private int age;
//get,set方法 和toString()
}

3.添加jar包
【mybatis】
mybatis-3.1.1.jar
【MYSQL驱动包】
mysql-connector-java-5.1.7-bin.jar

4.添加Mybatis的配置文件conf.xml
放到src文件夹下
<?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>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
</configuration>
environments  表示程序的运行模式 有两个选项
development:开发模式
work:工作模式 发布以后写成它 效率高

environments下environment可以写多个,但一般写一个就可以
id中"development" 要和 default的development保持一致

<dataSource type="POOLED">
数据源类型:
POOLED:使用连接池的数据源
UNPOOLED:不使用连接池的数据源
JDNI：使用JNDI实现的数据源

5.定义操作user表的sql映射文件userMapper.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sql文件的唯一标示  通过namespace这个标示 找到这个xml文件 -->
<mapper namespace="com.vo.userMapper">
<select id="getUser" parameterType="int"
resultType="com.vo.User">
select * from users where id=#{id}
</select>
</mapper>

6.在conf.xml中注册userMapper.xml文件
在environments 下面加入以下代码
<mappers>
<mapper resource="com/vo/userMapper.xml"/>
</mappers>

7.编写测试代码：执行定义的select语句
public class Test {
public static void main(String[] args) throws IOException {
String resource = "conf.xml";
//加载mybatis的配置文件（它也加载关联的映射文件）
Reader reader = Resources.getResourceAsReader(resource);
//构建sqlSession的工厂
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//创建能执行映射文件中sql的sqlSession
SqlSession session = sessionFactory.openSession();
//映射sql的标识字符串
String statement = "com.vo.userMapper"+".getUser";
//执行查询返回一个唯一user对象的sql
User user = session.selectOne(statement, 1);
System.out.println(user);
}
}

或者用类加载器也可以

演示代码如下:
package com.vo;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Test {
public static void main(String[] args) {
String resource = "conf.xml";
InputStream is = Test.class.getClassLoader().getResourceAsStream(resource);
SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(is);
SqlSession session = sf.openSession();

User user =  session.selectOne("com.vo.userMapper.getUser",1);
System.out.println(user);
if(session!=null){
session.close();
}
}
}

三、操作user表的CRUD

一）

XML的实现
1).创建SqlSessionFactory的工具类

package com.util;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class SessionFactoryUtil {
private static SqlSessionFactory factory;
static {
String resource = "conf.xml";
InputStream is = SessionFactoryUtil.class.getClassLoader().getResourceAsStream(resource);
factory = new SqlSessionFactoryBuilder().build(is);
}
public static SqlSessionFactory getFactory(){
return factory;
}
public static SqlSession getSqlSession(){
SqlSession session = null;
//默认是false 事务手工提交 即开启事务,true 事务是自动提交,即关闭事务
session = factory.openSession(true);
return session;
}
public static void closeSqlSession(SqlSession session){
if(session!=null){
session.close();
}
}
public static void main(String[] args) {
System.out.println(SessionFactoryUtil.getSqlSession());
}
}

2). 定义sql映射xml文件：

<?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sql文件的唯一标示  通过namespace这个标示 找到这个xml文件 -->
<mapper namespace="com.vo.userMapper">

<!-- 演示CRUD -->
<!-- 1.增加 -->
<insert id="addUser" parameterType="com.vo.User">
insert into user values(null,#{name},#{age})
</insert>

<!-- 2.删除 -->
<delete id="deleteUser" parameterType="com.vo.User">
delete from user where id=#{id}
</delete>

<!-- 3.修改 -->
<update id="updateUser" parameterType="com.vo.User">
update user set name=#{name},age=#{age} where id=#{id}
</update>

<!-- 4.查1 -->
<select id="getUserById" parameterType="java.lang.Integer" resultType="com.vo.User">
select * from user where id=#{id}
</select>

<!-- 5.按sql查询 -->
<select id="getPageByQuery" parameterType="String" resultType="com.vo.User">
${value}
</select>

<!-- 6.按总共有多少条记录 -->
<select id="getTotalRecordSum" parameterType="String" resultType="int">
${value}
</select>
</mapper>

2). 在conf.xml中注册这个映射文件
<mappers>
<mapper resource="com/vo/userMapper.xml" />
</mappers>
3). 在dao中调用：
接口
package com.dao.inter;

import java.util.List;
import com.vo.User;

public interface UserDao {
//一.增加
public void addUser(User user);
//二.删除
public void deleteUser(User user);
//三.修改
public void updateUser(User user);

//四.查1
public User getUserById(Integer id);

//五.按SQL语句查
public List<User> getPageByQuery(String sql);

//六.查询总共有多少条记录
public int getTotalRecordSum(String sql);

}

实现类
package com.dao.impl;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.dao.inter.UserDao;
import com.po.User;
import com.util.SessionFactoryUtil;

public class UserDaoImpl implements UserDao{

private SqlSession session;

public UserDaoImpl(){
session = SessionFactoryUtil.getSqlSession();
}

@Override
public int addUser(User user){
int count;
String statement = "com.po.userMapper.addUser";
try{
count = session.insert(statement, user);
}finally{
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

@Override
public int deleteUser(User user) {
int count;
String statement
1431b
= "com.po.userMapper.deleteUser";
try{
count = session.delete(statement, user);
}finally{
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

@Override
public int updateUser(User user){
int count;
String statement = "com.po.userMapper.updateUser";
try{
count = session.update(statement, user);
}finally{
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

@Override
public User getUserById(Integer userid){
User user = null;

String statement = "com.po.userMapper.getUser";
try {
user = session.selectOne(statement, userid);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}
return user;
}

@Override
public List<User> getPageByQuery(String sql){
List<User> list = null;

String statement = "com.po.userMapper.getPageByQuery";
try{
list = session.selectList(statement, sql);
}finally {
SessionFactoryUtil.closeSqlSession(session);
}

return list;
}

@Override
public int getTotalRecordSum(String sql){
int count = 0;
String statement = "com.po.userMapper.getTotalRecordSum";
try{
count = session.selectOne(statement, sql);
}finally{
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

}

二）. 注解的实现
1). 定义sql映射的接口
package com.dao.inter;

import java.util.List;
import org.apache.ibatis.annotations.*;
import com.po.User;

public interface UserMapper {
//一.增加
@Insert("insert into user values(null,#{name},#{age})")
public int addUser(User user);
//二.删除
@Delete("delete from user where id=#{id}")
public int deleteUser(User user);
//三.修改
@Update("update user set name=#{name},age=#{age} where id=#{id}")
public int updateUser(User user);
//四.查1
@Select("select * from user where id=#{id}")
public User getUserById(Integer userid);
//五.按sql查询
@Select("${value}")
public List<User> getPageByQuery(String sql);
//六.查询总共有多少条记录
@Select("${value}")
public int getTotalRecordSum(String sql);

}

2). 在conf.xml中注册这个映射接口
<mappers>
<mapper class="com.dao.inter.UserMapper"/>
</mappers>

3). 在dao类中调用
package com.dao.impl;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import com.dao.inter.UserMapper;
import com.po.User;
import com.util.SessionFactoryUtil;

public class UserMapperImpl implements UserMapper {

private SqlSession session;

public UserMapperImpl() {
session = SessionFactoryUtil.getSqlSession();
}

@Override
public int addUser(User user) {
int count;

try {
UserMapper userMapper = session.getMapper(UserMapper.class);

count = userMapper.addUser(user);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

@Override
public int deleteUser(User user) {
int count;
try {
UserMapper userMapper = session.getMapper(UserMapper.class);

count = userMapper.deleteUser(user);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

@Override
public int updateUser(User user) {
int count;
try {
UserMapper userMapper = session.getMapper(UserMapper.class);

count = userMapper.updateUser(user);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

@Override
public User getUserById(Integer userid) {
User user = null;

try {
UserMapper userMapper = session.getMapper(UserMapper.class);

user = userMapper.getUserById(userid);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}
return user;
}

@Override
public List<User> getPageByQuery(String sql) {
List<User> list = null;

try {
UserMapper userMapper = session.getMapper(UserMapper.class);

list = userMapper.getPageByQuery(sql);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}
return list;
}

@Override
public int getTotalRecordSum(String sql) {
int count = 0;

try {
UserMapper userMapper = session.getMapper(UserMapper.class);

count = userMapper.getTotalRecordSum(sql);
} finally {
SessionFactoryUtil.closeSqlSession(session);
}

return count;
}

public static void main(String[] args) {
UserMapperImpl dao = new UserMapperImpl();

User user = new User();
user.setName("小刚");
user.setAge(21);
int count = dao.addUser(user);
System.out.println(count);
}

}

强烈推荐使用XML配置方式，原因如下:

1.Java注解是受限的,功能较少，而MyBatis的Mapper内容相当多,相当复杂,功能强大, 使用XML文件方式可以带来更为灵活的空间，显示出MyBatis功能的强大和灵活

2.如果你的SQL很复杂,条件很多,尤其是存在动态SQL的时候,写在Java文件里面可读性较差,增加了维护成本.
总结:
SqlSessionFactoryBuilder
SqlSessionFactory
SqlSession
Mapper 实例

四、几个可以优化的地方

4.1. 连接数据库的配置单独放在一个properties文件中db.properties
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis
username=root
password=root
修改conf.xml
<?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>
<properties resource="db.properties"/>

<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 resource="com/vo/userMapper.xml" />

</mappers>

</configuration>

4.2. 为实体类定义别名,简化sql映射xml文件中的引用
在conf.xml中,environments节点前,加入如下代码即可
<typeAliases>
<typeAlias type="com.vo.User" alias="_User"/>
</typeAliases>

注意:conf.xml配置文件中的节点位置有一定的顺序,如果位置颠倒,会报错

Caused by: org.xml.sax.SAXParseException; lineNumber: 30; columnNumber: 17; 元素类型为 "configuration" 的内容必须匹配 "(properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,plugins?,environments?,databaseIdProvider?,mappers?)"。

或者直接写上
<typeAliases>
<package name="com.vo"/>
</typeAliases>
在userMapper.xml中就可以不需要写类全名com.vo.User了,只需要写简单类名User即可

4.3. 可以在src下加入log4j的配置文件,打印日志信息
1. 添加jar:
log4j-1.2.16.jar

2.1. log4j.properties(方式一)

log4j.properties，
log4j.rootLogger=DEBUG, Console
#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=INFO
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

2.2. log4j.xml(方式二)

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) \n" />
</layout>
</appender>
<logger name="java.sql">
<level value="debug" />
</logger>
<logger name="org.apache.ibatis">
<level value="debug" />
</logger>
<root>
<level value="debug" />
<appender-ref ref="STDOUT" />
</root>
</log4j:configuration>

五、解决字段名和实体类属性名不同的冲突

5. 解决字段名与实体类属性名不相同的冲突
5.1. 准备表和数据：
CREATE TABLE orders(
order_id INT PRIMARY KEY AUTO_INCREMENT,
order_no VARCHAR(20),
order_price FLOAT
);
INSERT INTO orders(order_no, order_price) VALUES('aaaa', 23);
INSERT INTO orders(order_no, order_price) VALUES('bbbb', 33);
INSERT INTO orders(order_no, order_price) VALUES('cccc', 22);
5.2. 定义实体类：
public class Orders {
private int orderId;
private String orderNo;
private float orderPrice;
}
5.3. 实现getOrderById(id)的查询：
方式一: 通过在sql语句中定义别名
<select id="selectOrder" parameterType="int" resultType="_Order">
select order_id orderId, order_no orderNo,order_price orderPrice from orders where order_id=#{id}
</select>

方式二: 通过<resultMap>
<select id="selectOrderResultMap" parameterType="int" resultMap="orderResultMap">
select * from orders where order_id=#{id}
</select>

<resultMap type="Order"  id="orderResultMap">
<id property="orderId" column="order_id"/>
<result property="orderNo" column="order_no"/>
<result property="orderPrice" column="order_price"/>
</resultMap>

方式三:  mybatis开启数据库字段自动映射驼峰命名规则java属性
在conf.xml中 <typeAliases> 节点前加入setting节点
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>

六、实现关联表查询和懒加载

6.1. 一对一关联
1). 提出需求
根据班级id查询班级信息(带老师的信息)
2). 创建表和数据
CREATE TABLE teacher(
t_id INT PRIMARY KEY AUTO_INCREMENT,
t_name VARCHAR(20)
);
CREATE TABLE class(
c_id INT PRIMARY KEY AUTO_INCREMENT,
c_name VARCHAR(20),
teacher_id INT UNIQUE
);
ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);

INSERT INTO teacher(t_name) VALUES('zhangzy');
INSERT INTO teacher(t_name) VALUES('liusp');

INSERT INTO class(c_name, teacher_id) VALUES('基地0620班', 1);
INSERT INTO class(c_name, teacher_id) VALUES('基地16班', 2);
3). 定义实体类：
public class Teacher {
private int id;
private String name;
}
public class Classes {
private int id;
private String name;
private Teacher teacher;
}

4). 定义sql映射文件ClassMapper.xml
<!--
方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集
封装联表查询的数据(去除重复的数据)
-->
<select id="getClass" parameterType="int" resultMap="ClassResultMap">
select * from teacher t inner join class c on(t.t_id=c.teacher_id)
where c_id=#{c_id}
</select>
<resultMap type="Classes" id="ClassResultMap">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
</resultMap>

<!--
方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型
SELECT * FROM class WHERE c_id=1;
SELECT * FROM teacher WHERE t_id=1   //1 是上一个查询得到的teacher_id的值
-->

<select id="getClass2" parameterType="int" resultMap="ClassResultMap2">
select * from class where c_id=#{id}
</select>
<resultMap type="Classes" id="ClassResultMap2">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" column="teacher_id" select="getTeacher">
</association>
</resultMap>

<select id="getTeacher" parameterType="int" resultType="Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>

5). 测试
public Classes getClassesById(Integer id) {
Classes classes = null;
String statement = "com.vo.classMapper.getClass";
classes = session.selectOne(statement, id);
}finally{
session.close();
}
return classes;
}

public Classes getClassesById2(Integer id) {
Classes classes = null;
String statement = "com.vo.classMapper.getClass2";

try{
classes = session.selectOne(statement, id);

}finally{
session.close();
}
return classes;
}

6.2.延迟加载(懒加载)
依赖两个jar包  cglib.jar、asm.jar,Cglib依赖于asm.jar
<settings>
<!--打开延迟加载的开关  -->
<setting name="lazyLoadingEnabled" value="true"/>
<!--将积极加载改为消极加载及按需加载  -->
<setting name="aggressiveLazyLoading" value="false"/>
</settings>

6.3. 一对多关联
1). 提出需求
根据班级id查询对应的班级信息,包括学生,老师
2). 创建表和数据：
CREATE TABLE student(
s_id INT PRIMARY KEY AUTO_INCREMENT,
s_name VARCHAR(20),
class_id INT
);
ALTER TABLE student ADD CONSTRAINT fk_class_id FOREIGN KEY (class_id) REFERENCES class(c_id);

INSERT INTO student(s_name, class_id) VALUES('赵英龙', 1);
INSERT INTO student(s_name, class_id) VALUES('杨帆', 1);
INSERT INTO student(s_name, class_id) VALUES('王爽', 1);
INSERT INTO student(s_name, class_id) VALUES(‘吴亚明’', 2);
INSERT INTO student(s_name, class_id) VALUES('赵文宇', 2);

3). 定义实体类：
public class Student {
private int id;
private String name;
}

public class Classes {
private int id;
private String name;
private Teacher teacher;
private List<Student> students;
}
4). 定义sql映射文件ClassMapper.xml
<!--
方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集
SELECT * FROM class c, teacher t,student s WHERE c.teacher_id=t.t_id AND c.C_id=s.class_id AND  c.c_id=1
-->
<select id="getClass3" parameterType="int" resultMap="ClassResultMap3">
select * from teacher t inner join class c  on(t.t_id=c.teacher_id)
inner join student s on(c.c_id=s.class_id) where c.c_id=1
</select>
<resultMap type="Classes" id="ClassResultMap3">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher"  javaType="Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<!-- ofType指定students集合中的对象类型 -->
<collection property="students" ofType="Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>

<!--
方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型
SELECT * FROM class WHERE c_id=1;
SELECT * FROM teacher WHERE t_id=1   //1 是上一个查询得到的teacher_id的值
SELECT * FROM student WHERE class_id=1  //1是第一个查询得到的c_id字段的值
-->
<select id="getClass4" parameterType="int" resultMap="ClassResultMap4">
select * from class where c_id=#{id}
</select>
<resultMap type="Classes" id="ClassResultMap4">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" column="teacher_id" javaType="Teacher" select="getTeacher2"></association>
<collection property="students" ofType="Student" column="c_id" select="getStudents"></collection>
</resultMap>

<select id="getTeacher2" parameterType="int" resultType="Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>

<select id="getStudents" parameterType="int" resultType="Student">
SELECT s_id id, s_name name FROM student WHERE class_id=#{id}
</select>

5). 测试：
public Classes getClassesById3(Integer id) {
Classes classes = null;
String statement = "com.vo.classMapper.getClass3";
try{
classes = session.selectOne(statement, id);

}finally{
session.close();
}
return classes;
}

public Classes getClassesById4(Integer id) {
Classes classes = null;
String statement = "com.vo.classMapper.getClass4";
try{
classes = session.selectOne(statement, id);
}finally{
session.close();
}
return classes;
}

七、动态SQL与模糊查询

7.1. 提出需求:
实现多条件查询用户(姓名模糊匹配, 年龄在指定的最小值到最大值之间)
7.2. 准备数据表和数据:
create table d_user(
id int primary key auto_increment,
name varchar(10),
age int(3)
);

insert into d_user(name,age) values('小明1',20);
insert into d_user(name,age) values('小明2',21);
insert into d_user(name,age) values('小明3',22);
insert into d_user(name,age) values('小明4',28);

insert into d_user(name,age) values('小红',23);
insert into d_user(name,age) values('小红',18);
7.3. User(表实体类)
private int id;
private String name;
private int age;
7.4. ConditionUser(查询条件实体类)
private String name;
private int minAge;
private int maxAge;

7.5. userMapper.xml(映射文件)
<?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.po.userMapper">
<select id="getUsers" parameterType="com.vo.ConditionUser"
resultType="User">
select * from d_user where 1=1

<if test='name!=null and name!=""'> and name like CONCAT('%','${name}','%')</if>

<if test='minAge!=null'> and age>=#{minAge}</if>

<if test='maxAge!=null'> and age<=#{maxAge}</if>
</select>
</mapper>

7.6. UserTest(测试)
public List<User> getUsers(ConditionUser conditionUser) {
List<User> list;

try {
String statement = "com.po.userMapper.getUsers";

list = sqlSession.selectList(statement, conditionUser);

} finally {
SessionFactoryUtil.closeSqlSession(sqlSession);
}

return list;
}

public static void main(String[] args) {
UserDaoImpl dao = new UserDaoImpl();
ConditionUser conditionUser = new ConditionUser();
conditionUser.setName("小明");
conditionUser.setMinAge(21);
conditionUser.setMaxAge(28);
List<User> users = dao.getUsers(conditionUser);
System.out.println(users);
}
}