Mybatis-02(log4j,注解实现增删改查, #{}和${}的区别是什么？，lombok)

Log4j

①先导包

<dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>

②配置log4j.properites

#将等级为DEBUG的日志信息输出到console和file这两个目的地，console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file

#控制台输出的相关设置
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%c]-%m%n

#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/kuang.log
log4j.appender.file.MaxFileSize=10mb
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n

#日志输出级别
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

③mybatis-config中添加setting

<settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

 注解实现增删改查：

①编写mybatis-config

<?xml version="1.0" encoding="UTF8" ?>
<!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?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="admin"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="dao.UserMapper"/>
    </mappers>
</configuration>

②编写工具类MybatisUtils

package utils;

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

//SqlSessionFacory
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession(){
        return  sqlSessionFactory.openSession(true);//这里有一个参数true，表示自动提交事务
    }


}

③编写实体类User

package pojo;

public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return pwd;
    }

    public void setPassword(String password) {
        this.pwd = password;
    }

    @Override
    public String toString() {
        return "pojo.User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

④编写接口UserMapper

package dao;

import org.apache.ibatis.annotations.Select;
import pojo.User;

import java.util.List;
import java.util.Map;

public interface UserMapper {
    @Select("select * from user")
    List<User> getUserList();
    @Select("select * from user where id=#{id}")
    User getUserById(int id)；

　　@Insert("insert into user(id,name,pwd) values (#{id},#{name},#{pwd})")
　　int addUser(User user);
　　@Delete("delete from user where id = #{id}")
　　int deleteUser(User user);
　　@Update("update user set name=#{name},pwd=#{pwd} where id=#{id}")
　　int updateUser(User user);

}

注解实现只需将方法上添加注解，如上代码，然后需要在Mybatis-congfig中添加mapper映射（已在①中代码添加 ）

如果参数有很多个，可以用以下代码：

    @Select("select * from user where id=#{id}")
    User getUserById(@Param("id")int id);

在参数前面加上@Param

⑤编写测试代码

import dao.UserMapper;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import pojo.User;
import utils.MybatisUtils;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MyTest {
    @Test
    public void test(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        for (User user:
             userList) {
            System.out.println(user.toString());

        }
        User user=mapper.getUserById(1);
        System.out.println(user.toString());
    }
}

一个面试题：

#{}和${}的区别是什么？

a、#{}是预编译处理，${}是字符串替换。

b、Mybatis 在处理#{}时，会将 sql 中的#{}替换为?号，调用 PreparedStatement 的 set 方法来赋值；
c、Mybatis 在处理${}时，就是把${}替换成变量的值。
d、使用#{}可以有效的防止 SQL 注入，提高系统安全性。

#将传入的数据都当成一个字符串，会对自动传入的数据加一个双引号。如：order by #{user_id}，如果传入的值是111,那么解析成sql时的值为order by “111”, 如果传入的值是id，则解析成的sql为order by “id”. 

Lombok的使用:

①下载插件

②导入jar包

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
            <scope>provided</scope>
        </dependency>

③在实体类上添加注解：

@Data
@AllArgsConstructor
@NoArgsConstructor

@Data：无参构造，get、set、tostring、hashcode，equals

@AllArgsConstructor有参构造

@NoArgsConstructor无参构造

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