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。