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MyBatis高级第一章 #{}和${}符号的区别
github源码（day56-mybatis-senior）https://github.com/1196557363/ideaMavenProject
#{}和${}符号的区别
项目准备
- 使用idea创建maven项目（不用web项目）
- pom.xml导包
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>mybatis-senior</groupId><artifactId>day56-mybatis-senior</artifactId><version>1.0-SNAPSHOT</version><dependencies><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency><!-- 添加Mybatis的依赖--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.4.5</version></dependency><!-- MySQL的驱动包 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.6</version></dependency><dependency><groupId>org.apache.logging.log4j</groupId><artifactId>log4j-core</artifactId><version>2.3</version></dependency><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-log4j12</artifactId><version>1.7.25</version></dependency></dependencies>
</project>
- 配置文件
3.1 MyBatis.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><properties resource="jdbc.properties"/><typeAliases><package name="com.wpj.bean"/></typeAliases><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${jdbc.driverClass}"/><property name="url" value="${jdbc.jdbcUrl}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/></dataSource></environment></environments><mappers><mapper resource="mapper/IUserDao2.xml"/></mappers>
</configuration>
3.2 jdbc.properties
jdbc.jdbcUrl=jdbc:mysql://localhost:3306/day56-mybatis-seniorjdbc.driverClass=com.mysql.jdbc.Driverjdbc.username=rootjdbc.password=123456
3.3 log4j.properties
### #配置根Logger ###
log4j.rootLogger = debug,stdout,E,MAIL### 输出到控制台 ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.Encoding=UTF-8
log4j.appender.stdout.layout.ConversionPattern= %d{yyy-MM-dd HH\:mm\:ss} %p %c{0}\:%L - %m%n
- 创建数据库day56-mybatis-senior和表user
create database day56-mybatis-senior;
use day56-mybatis-senior
create table user(id int primary key,name varchar(20),pwd varchar(20),age int
)
1. #和$符号的区别
1.1 定义User
package com.wpj.bean;/*** ClassName: User* Description:* 提供无参全参构造方法，getter和setter方法，toString方法* @author JieKaMi* @version 1.0* @date: 2020\1\7 0007 19:10* @since JDK 1.8*/
public class User {private Integer id;private String name;private String pwd;private Integer age;public User() { }public User(Integer id, String name, String pwd, Integer age) {this.id = id;this.name = name;this.pwd = pwd;this.age = age;}public Integer getId() { return id; }public void setId(Integer id) { this.id = id; }public String getName() { return name; }public void setName(String name) { this.name = name; }public String getPwd() { return pwd; }public void setPwd(String pwd) { this.pwd = pwd; }public Integer getAge() { return age; }public void setAge(Integer age) { this.age = age; }@Overridepublic String toString() {return "User{" +"id=" + id +", name='" + name + '\'' +", pwd='" + pwd + '\'' +", age=" + age +'}';}
}
1.2 定义IUserDao2接口
因为我是一个project多个模块，IUserDao之前定义过了，所以定义IUserDao2。
package com.wpj.dao;import com.wpj.bean.*;/*** ClassName: IUserDao2* Description:** @author JieKaMi* @version 1.0* @date: 2020\1\7 0007 19:02* @since JDK 1.8*/
public interface IUserDao2 {/*** 根据id查询对象，但是对象要显示的属性由用户指定* @param id id* @param column {id,name}* @return*/User getUserById(@Param("id")Integer id, @Param("column")String column);
}
1.3 创建接口对应mapper #{column}
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wpj.dao.IUserDao2"><select id="getUserById" resultType="user">select #{column} from user</select>
</mapper>
1.3 创建接口对应mapper ${column}
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wpj.dao.IUserDao2"><select id="getUserById" resultType="user">select ${column} from user</select>
</mapper>
1.4 Test
import com.wpj.bean.*;
import com.wpj.dao.*;
import org.apache.ibatis.io.*;
import org.apache.ibatis.session.*;
import org.junit.*;import java.io.*;/*** ClassName: MyBatisTest* Description:** @author JieKaMi* @version 1.0* @date: 2020\1\7 0007 19:19* @since JDK 1.8*/
public class MyBatisTest {@Testpublic void testGetUserById(){String config = "MyBatis.xml";InputStream is = null;try {is = Resources.getResourceAsStream(config);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);SqlSession sqlSession = sqlSessionFactory.openSession();IUserDao2 userDao = sqlSession.getMapper(IUserDao2.class);User user = userDao.getUserById(1,"id,name");System.out.println(user);sqlSession.close();} catch (IOException e) {e.printStackTrace();} finally {if(is!=null) {try {is.close();} catch (IOException e) {e.printStackTrace();}}}}
}
1.5 结果
1.5.1 使用#{}
Preparing: select ? from user where id = ?
Parameters: id,name(String), 1(Integer)
Total: 1
null
1.5.2 使用${}
Preparing: select id,name from user where id = ?
Parameters: 1(Integer)
Total: 1
User{id=1, name=‘wpj’, pwd=‘null’, age=null}
1.6 ${} 的应用场景
/*** 根据用户输入的sql查询* @param sql 用户输入的sql语句* @return 查询的结果集*/
List<Map<Object,Object>> findBySql(@Param("sql") String sql);
<select id="findBySql" resultType="map">${sql}
</select>
List<Map<Object,Object>> list =userDao.findBySql("select * from user");
for(Map<Object,Object> map : list){System.out.println(map);
}
1.7 update标签中可以写delete语句
public int deleteUser(Integer id);
<update id="deleteUser">delete from t_user where id = #{id}
</update>
userDaoImpl.deleteUser(5);
因为mybatis底层也是jdbc，而jdbc操作数据库只有select 和 update（update-delete-insert）
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