1. 参数解决

在上个博客中，咱们能够看到UserMapper.java和UserMapper.xml文件中有这相应的对应，在这里我先将这两个文件的代码展现进去。

1.1 文件展现

UserMapper.java

package com.jt;

import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.Map;

public interface  UserMapper {
   public User selectUser(int id);//单个参数传递
   public User  selectUserByIdAndName(@Param("id") Integer id,@Param("username") String username);// 多个参数传递
   public User  selectUserByIdAndNameUseMap(Map map);//多个参数传递

   public Integer insertUser(User user);
   public boolean updateUser(User user);
   public Integer deleteUserById(int id);
}

UserMapper.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">
<mapper namespace="com.jt.UserMapper">
    <select id="selectUser" resultType="com.jt.User">
        select * from test01 where id = #{id}
    </select>
    <select id="selectUserByIdAndName" resultType="com.jt.User">
        select * from test01 where id = #{id} and username=#{username}
    </select>
    <select id="selectUserByIdAndNameUseMap" resultType="com.jt.User">
        select * from test01 where id = #{id} and username=#{username}
    </select>
    <insert id="insertUser" useGeneratedKeys="true" keyProperty="id">
        insert into test01 (username,password) values(#{username},#{password})
    </insert>
    <update id="updateUser" parameterType="com.jt.User">
        update test01 set username=#{username} where id=#{id}
    </update>
    <delete id="deleteUserById">
        delete from test01 where id=#{id}
    </delete>
</mapper>

1.2 文件剖析

在UserMapper.java接口文件中，传递的参数有，单个参数，多个参数的状况。

1.2.1 单个参数

间接应用#{}或者${}去接管参数即可

public User selectUser(int id);//单个参数传递

<select id="selectUser" resultType="com.jt.User">
     select * from test01 where id = #{id}
</select>

1.2.2 多个参数参数

总结 #{}或者${}这种形式取值，实质是在一个Map对象中依据key值去获取参数值。
（1）应用@Param定义在xml文件中获取参数的key值

   public User  selectUserByIdAndName(@Param("id") Integer id,@Param("username") String username);// 多个参数传递
    <select id="selectUserByIdAndName" resultType="com.jt.User">
        select * from test01 where id = #{id} and username=#{username}
    </select>

（2）或者不必@Param,在xml文件中应用#{param1}这种模式来获取相应参数的值

   public User  selectUserByIdAndName(Integer id,String username);// 多个参数传递
    <select id="selectUserByIdAndName" resultType="com.jt.User">
        select * from test01 where id = #{param1} and username=#{param2}
    </select>

（3）应用pojo类来传递参数

  public Integer insertUser(User user);
    <insert id="insertUser" useGeneratedKeys="true" keyProperty="id">
        insert into test01 (username,password) values(#{username},#{password})
    </insert>

(4)应用map来传递参数

   public User  selectUserByIdAndNameUseMap(Map map);//多个参数传递
    <select id="selectUserByIdAndNameUseMap" resultType="com.jt.User">
        select * from test01 where id = #{id} and username=#{username}
    </select>

1.2.3 #{}和${}的区别

{} 应用了预编译

${}没有应用预编译，安全性绝对比拟低。
下图能够清晰的解释两者的区别。