Mybatis的底层是JDBC，关于JDBC的操作，我们都知道有PreparedStatement (预处理)和Statement这两个，PreparedStatement可以防止SQL注入的危险，而在Mybatis中，传入参数的两种方式#{参数}、KaTeX parse error: Expected 'EOF', got '#' at position 6: {参数}。#̲对应的是采用PreparedS…{参数}对应的是Statement的方式。推荐使用#的方式。
相关用法：

使用#{}传入多个参数

如果Mapper接口中有多个参数，无论参数名是什么，在Mapper.xml文件中，参数都是arg0、arg1…或者param1、param2…
如果非要使用自己的参数名，可以通过@Param注解自定义
EmpMapper接口

public Integer addEmp1(String ename,String job) throws IOException;
	public Integer addEmp2(String ename,String job) throws IOException;

采用#传入多个参数,在接口中对应的方法内有多个参数，无论参数名是什么，在Mapper.xml文件中，参数都是arg0、arg1…或者param1、param2…

<insert id="addEmp1">
		insert into emp(ename,job)values(#{arg0},#{arg1})
	</insert>
	
	<insert id="addEmp2">
		insert into emp(ename,job)values(#{param1},#{param2})
	</insert>

如果非要使用自己的参数名，可以通过@Param注解自定义

public Integer addEmp4(@Param("ename")String ename,@Param("job")String job) throws IOException;

<insert id="addEmp4">
		insert into emp(ename,job)values(#{ename},#{job})
	</insert>

这边要说明一下，如何接口中对应的方法传入的参数是pojo对象，而映射文件里的是该对象的属性，则可以直接使用属性名

public Integer addEmp(Emp emp) throws IOException;

<insert id="addEmp" parameterType="emp">
		insert into emp(ename,job)values(#{ename},#{job})
	</insert>

##使用${}传入多个参数 如果使用$传入多个参数如果使用，需要在Mapper种指定参数名字，如果没有指定@Param注解就会报错

public Emp getEmpById(@Param("empno")Integer empno) throws IOException;

<select id="getEmpById" resultType="emp"> 
		select * from emp where empno=${empno}   
	</select>

这里如果使用$，只是单纯的指定@Param注解，进行新增和修改等DML操作，还是会报错

##包装类
pojo

public class UserWrapper {

	private User user;

	public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}
}

映射文件

<!-- 从包装对象中获取信息 包装对象的别名. 取信息 -->
<insert id="addUser4" parameterType="UserWrapper">
	insert into t_user(name,age,favorites)values(#{user.name},#{user.age}
	,#{user.favorites})
</insert>

不建议使用Map做参数。

##返回数据

###resultType
 对于简单数据类型，例如查询总记录数、查询某一个用户名这一类返回值是一个基本数据类型的，直接写Java中的基本数据类型即可。
  如果返回的是一个对象或者集合，并且对象中的属性和查询的字段名是一一对应的，那么resultType也可以直接写一个对象。

接口：

public Emp getEmpById(@Param("empno")Integer empno) throws IOException;

public List<Emp> selEmp() throws IOException;

映射文件：

<select id="getEmpById" resultType="emp"> 
		select * from emp where empno=${empno}   
	</select>

<select id="selEmp" resultType="emp" resultMap="baseMap"> 
		select * from emp   
	</select>

###resultMap
resultMap主要用来解决属性名和字段名不一致以及一对多、一对一查询等问题 字段名不一致时，首先可以通过取别名解决.

pojo

package com.zsl.pojo;

import java.util.List;

public class Emp {
	private Integer empno;
	private String ename;
	private String job;
	private Integer mgrA;//这里与数据库字段名称不同，数据库字段为mgr
	public Integer getEmpno() {
		return empno;
	}
	public void setEmpno(Integer empno) {
		this.empno = empno;
	}
	public String getEname() {
		return ename;
	}
	public void setEname(String ename) {
		this.ename = ename;
	}
	public String getJob() {
		return job;
	}
	public void setJob(String job) {
		this.job = job;
	}

	public Emp() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Integer getMgrA() {
		return mgrA;
	}
	public void setMgrA(Integer mgrA) {
		this.mgrA = mgrA;
	}
	public Emp(Integer empno, String ename, String job, Integer mgrA) {
		super();
		this.empno = empno;
		this.ename = ename;
		this.job = job;
//		this.mgrA = mgrA;
	}
	@Override
	public String toString() {
		return "Emp [empno=" + empno + ", ename=" + ename + ", job=" + job  + "]";
		//+ ", mgrA=" + mgrA
	}
}

Pojo属性名mgrA在数据表中字段名为mgr，
可以发现pojo与数据表出现属性名和字段名不一致的问题

解决办法一：查询时，可以给查询结果取别名
这种方式，可以解决问题，但是有缺陷，最大缺陷是不能复用（可以sql片段解决，但是不完美）。

<select id="selEmp3" resultType="emp"> 
		select empno empno,ename ename,job job,mgr mgrA from emp   
	</select>

解决办法二：最佳解决方案就是使用resultMap
在映射文件中进行配置：
resultMap

<resultMap type="emp" id="baseMap">
		<id column="empno" property="empno" />
		<result property="ename" column="ename" />
		<result property="job" column="job" />
	    <result property="mgrA" column="mgr" /> 
	</resultMap>

可以类似这么去使用：

<select id="selEmp" resultType="emp" resultMap="baseMap"> 
		select * from emp   
	</select>

<select id="getEmpById" parameterType="int" resultType="emp"> 
		select empno,ename,job,pwd from emp where empno=#{empno}   
	</select>

resultType：返回值类型
parameterType：参数类型
这里使用了别名，取别名可以在全局配置文件中自定义别名

<!-- 自定义别名 -->
    <typeAliases>
        <typeAlias type="com.zsl.pojo.Emp" alias="emp"/>
    </typeAliases>

##主键回写

一般情况下，主键有两种生成方式：
1.主键自增长
2.自定义主键（一般可以使用UUID）
  如果是第二种，主键一般是在Java代码中生成，然后传入数据库执行，如果是第一个主键自增长，此时，Java可能需要知道数据添加成功后的主键。 在MyBatis中，可以通过主键回填来解决这个问题（推荐）。

方法一：
该方法不适用于Oracle数据库，只适用于MySQL，因为Oracle数据库不会默认主键自增长，而是使用的是序列，而MySQL默认支持主键自增长

<!-- useGeneratedKeys:使用生成的主键 keyProperty="id"：将生成的主键的值保存到对象的id属性中 -->
 	<insert id="addEmp" parameterType="emp" useGeneratedKeys="true"
		keyProperty="empno">
		insert into emp(ename,job)values(#{ename},#{job})
	</insert>

方法二：可以利用MySQL自带的==last_insert_id()==函数查询刚刚插入的id

<insert id="addEmp6" parameterType="emp">
		<selectKey keyProperty="empno" resultType="int">
			select
			LAST_INSERT_ID()
		</selectKey>
		insert into emp(ename,job)values(#{ename},#{job})
	</insert>

全部代码：
EmpMapper接口

package com.zsl.dao;

import java.io.IOException;
import java.util.List;

import org.apache.ibatis.annotations.Param;

import com.zsl.pojo.Emp;

public interface EmpMapper {
	public Integer addEmp(Emp emp) throws IOException;
	
	public Integer deleteEmpById(Integer empno) throws IOException;
	public Integer updateEmprById(Emp emp) throws IOException;
	
	public Emp getEmpById(@Param("empno")Integer empno) throws IOException;
	
	public Integer addEmp1(String ename,String job) throws IOException;
	public Integer addEmp2(String ename,String job) throws IOException;
	
	public Integer addEmp3(@Param("ename")String ename,@Param("job")String job) throws IOException;
	
	public Integer addEmp4(@Param("ename")String ename,@Param("job")String job) throws IOException;
	
	public List<Emp> selEmp() throws IOException;
	
	public Emp getEmpById2(@Param("empno")Integer empno) throws IOException;
	
	public Emp getEmpById3(Emp emp) throws IOException;
	public Integer updateEmprById2(Emp emp) throws IOException;
	public Emp getEmpById4(Emp emp) throws IOException;
	public Integer updateEmprById3(Emp emp) throws IOException;
	// 如果不指定@Param 默认是array
	public List<Emp> getEmpById5(@Param("empnos")List<Integer> empno);
	public int addEmp6(@Param("emps")List<Emp> emps);
	public List<Emp> selEmp1() throws IOException;
	public Emp getEmpById6()throws IOException;
}

EmpMapper.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.zsl.dao.EmpMapper">
	<!-- <insert id="addEmp" parameterType="emp">
		insert into emp(ename,job)values(#{ename},#{job})
	</insert> -->
	<delete id="deleteEmpById" parameterType="int"> 
		delete from emp where empno=#{empno}    
	</delete>
	<update id="updateEmprById" parameterType="emp"> 
		update emp set name = #{ename} where empno=#{empno}    
	</update>
	
	<select id="getEmpById" resultType="emp"> 
		select * from emp where empno=${empno}   
	</select>
	
	<insert id="addEmp1">
		insert into emp(ename,job)values(#{arg0},#{arg1})
	</insert>
	
	<insert id="addEmp2">
		insert into emp(ename,job)values(#{param1},#{param2})
	</insert>
	
	<insert id="addEmp3">
		insert into emp(ename,job)values(${ename},${job})
	</insert>
	
	<insert id="addEmp4">
		insert into emp(ename,job)values(#{ename},#{job})
	</insert>
	
    <select id="selEmp3" resultType="emp"> 
		select empno empno,ename ename,job job,mgr mgrA from emp   
	</select> 

 	<resultMap type="emp" id="baseMap">
		<id column="empno" property="empno" />
		<result property="ename" column="ename" />
		<result property="job" column="job" />
	    <result property="mgrA" column="mgr" /> 
	</resultMap> 

	
	<select id="selEmp" resultType="emp" resultMap="baseMap"> 
		select * from emp   
	</select>

	<!-- useGeneratedKeys:使用生成的主键 keyProperty="id"：将生成的主键的值保存到对象的id属性中 -->
 	<insert id="addEmp" parameterType="emp" useGeneratedKeys="true"
		keyProperty="empno">
		insert into emp(ename,job)values(#{ename},#{job})
	</insert> 
	
	<insert id="addEmp6" parameterType="emp">
		<selectKey keyProperty="empno" resultType="int">
			select
			LAST_INSERT_ID()
		</selectKey>
		insert into emp(ename,job)values(#{ename},#{job})
	</insert>

	<select id="getEmpById2" resultType="emp"> 
		SELECT * FROM emp WHERE 1=1
		<if test="empno != null">
			AND empno = #{empno}
		</if>   
	</select>

	<select id="getEmpById3" resultType="emp" parameterType="emp">
		SELECT * FROM EMP 
		<where>
			<choose>
				<when test="empno != null">
					AND empno like #{empno}
				</when>
				<when test="ename != null">
					AND ename like #{ename}
				</when>
				<otherwise>
					AND  job = "zz"
				</otherwise>
			</choose>
		</where>
	</select>


	<update id="updateEmprById2" parameterType="emp">
		UPDATE emp
		<set>
			<if test="ename!=null"> ename=#{ename},</if>
			<if test="job!=null"> job=#{job},</if>
		</set>
		<where>
			<if test="empno!=null">
				empno=#{empno};
			</if>
		</where>
	</update>
	
	<!-- 代替where -->
	<select id="getEmpById4" resultType="emp" parameterType="emp">
		SELECT * FROM emp
		<!-- <where> <if test="username!=null"> and name = #{username} </if> </where> -->
		<trim prefix="where" prefixOverrides="AND |OR ">
			<if test="empno != null">
				and empno = #{empno}
			</if>
			<if test="ename!=null">
				AND ename = #{ename}
			</if>
		</trim>
	</select>

<!-- 代替set -->
	<update id="updateEmprById3" parameterType="emp">
		update emp
		<trim prefix="set" suffixOverrides=",">
			<if test="ename!=null">
				ename = #{ename},
			</if>
			<if test="job != null">
				job = #{job}
			</if>
		</trim>
		<trim prefix="where" prefixOverrides="AND |OR ">
			<if test="empno != null">
				and empno = #{empno}
			</if>
		</trim>
	</update>

	<select id="getEmpById5" resultType="emp">
		select * from emp where empno in
		<foreach collection="empnos" open="(" close=")" separator=","
			item="empno">
			#{empno}
		</foreach>
	</select>

	<insert id="addEmp6">
		insert into emp(ename,job)values
		<foreach collection="emps" item="emp" separator=",">
			(#{emp.ename},#{emp.job})
		</foreach>
	</insert>
	
	<sql id="baseSql">
		empno,ename,job
	</sql>
	
	<select id="selEmp1" resultType="emp">
		select 
		<include refid="baseSql"/>
		 from emp 
	</select>


	<select id="getEmpById6" resultType="emp">
		<!-- 声明了一个参数empno 在后面就可以使用了 -->
		<bind name="empno" value="7975" />
		select * from emp where empno=${empno}
	</select>
	
	
</mapper>

全局配置文件
mybatis-cfg.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>
 <!-- 导入外部资源 -->
 <properties resource="db.properties"/> 
 
  <!-- 自定义别名 -->
    <typeAliases>
        <typeAlias type="com.zsl.pojo.Emp" alias="emp"/>
    </typeAliases>
    
    
 <!-- 环境 -->
  <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>
  
  <!-- 注册映射文件 -->
  <mappers>
  	<mapper resource="EmpMapper.xml"/>
  </mappers>
  
</configuration>
  

DBUtils工具类

package com.zsl.utils;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class DbUtils {
	public static SqlSession getSession() throws IOException {
		// TODO Auto-generated method stub
		// 1.通过Resources对象加载配置文件
		InputStream inputStream = Resources.getResourceAsStream("mybatis-cfg.xml");
		// 2.获取SqlSessionFactory对象
		SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
		// 3.通过SqlSessionFactory对象获取SQLSession对象
		SqlSession session = factory.openSession();
		return session;
	}
	
	public static void commit(SqlSession session) {
		// TODO Auto-generated method stub
		session.commit();
	}
	
	public static void close(SqlSession session) {
		// TODO Auto-generated method stub
		session.close();
	}
}

测试类Test

package com.zsl.test;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

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 com.zsl.dao.EmpMapper;
import com.zsl.pojo.Emp;
import com.zsl.utils.DbUtils;


public class Test {
	public static void main(String[] args) throws IOException {

		Test test = new Test();
		System.out.println(test.addUser3());
	}

	public Integer addUser1() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Integer integer = mapper.addEmp1("zsladd1", "程序员1");
		session.commit();
		session.close();
		return integer;
	}

	public Integer addUser2() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Integer integer = mapper.addEmp2("zsladd2", "程序员2");
		session.commit();
		session.close();
		return integer;
	}

	public Integer addUser3() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Integer integer = mapper.addEmp3("zsladd3", "程序员3");
		session.commit();
		session.close();
		return integer;
	}

	public Integer addUser4() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Integer integer = mapper.addEmp4("zsladd4", "程序员4");
		session.commit();
		session.close();
		return integer;
	}

	public Emp getEmpById() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp = mapper.getEmpById(7902);
		session.close();
		return emp;
	}

	public List<Emp> selEmp() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		List<Emp> list = mapper.selEmp();
		return list;
	}

	public Integer addUser() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp = new Emp();
		emp.setEname("zsl00");
		emp.setJob("程序员00");
		Integer integer = mapper.addEmp(emp);
		System.out.println("该条记录主键：" + emp.getEmpno());
		session.commit();
		session.close();
		return integer;
	}

	public Emp getEmpById2() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp = mapper.getEmpById2(7900);
		session.close();
		return emp;
	}
	
	public Emp getEmpById3() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp2 = new Emp();
		emp2.setEname("JAMES");
		Emp emp = mapper.getEmpById3(emp2);
		return emp;
	}

	public Integer updateEmprById2() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp = new Emp();
		emp.setEmpno(7941);
		emp.setEname("zsl55");
		emp.setJob("程序员55");
		Integer integer = mapper.updateEmprById2(emp);
		session.commit();
		session.close();
		return integer;
	}
	
	public Integer updateEmprById3() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp = new Emp();
		emp.setEmpno(7941);
		emp.setEname("zsl77");
		emp.setJob("程序员77");
		Integer integer = mapper.updateEmprById2(emp);
		session.commit();
		session.close();
		return integer;
	}
	
	public Emp getEmpById4() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp2 = new Emp();
		emp2.setEname("JAMES");
		Emp emp = mapper.getEmpById3(emp2);
		session.close();
		return emp;
	}
	
	public List<Emp> getEmpById5() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		List<Integer> list = new ArrayList<>();
		list.add(7969);
		list.add(7970);
		list.add(7971);
		List<Emp> empList = mapper.getEmpById5(list);
		session.close();
		return empList;
	}
	
	public Integer addEmp6() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		List<Emp> emps = new ArrayList<>();
		Emp emp = new Emp();
		emp.setEname("zsl88");
		emp.setJob("程序员88");
		emps.add(emp);
		Emp empA = new Emp();
		empA.setEname("zsl99");
		empA.setJob("程序员99");
		emps.add(empA);
		int addEmp6 = mapper.addEmp6(emps);
		session.commit();
		session.close();
		return addEmp6;
	}
	
	public List<Emp> selEmp1() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		List<Emp> list = mapper.selEmp1();
		session.close();
		return list;
	}
	
	public Emp getEmpById6() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		Emp emp = mapper.getEmpById6();
		session.close();
		return emp;

	}
}