Spring Framework 为 SQL 数据库提供了广泛的支持。从直接使用 JdbcTemplate 进行 JDBC 访问到完全的对象关系映射（object relational mapping）技术，比如 Hibernate。Spring Data 提供了更多级别的功能，直接从接口创建的 Repository 实现，并使用了约定从方法名生成查询。

1、JDBC

1、创建项目，导入需要的依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

2、配置数据源

spring:
  datasource:
    username: college_dev
    password: college_dev
    url: jdbc:mysql://10.155.10.123:4502/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8
    driver-class-name: com.mysql.jdbc.Driver

3、测试类代码

package com.lyx.springboot.data.springbootdata;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

@SpringBootTest
class DataApplicationTests {

    @Autowired
    DataSource dataSource;

    @Test
    void contextLoads() throws SQLException {
        System.out.println(">>>>>dataSource:" + dataSource.getClass());
        Connection connection = dataSource.getConnection();
        System.out.println(">>>>>connection"+connection);
        connection.close();
    }

}
//可以看到默认配置的数据源为class com.zaxxer.hikari.HikariDataSource，我们没有经过任何配置，说明springboot默认情况下支持的就是这种数据源，可以在DataSourceProperties.java文件中查看具体的属性配置

4、crud操作

    1、有了数据源(com.zaxxer.hikari.HikariDataSource)，然后可以拿到数据库连接(java.sql.Connection)，有了连接，就可以使用连接和原生的 JDBC 语句来操作数据库

    2、即使不使用第三方第数据库操作框架，如 MyBatis等，Spring 本身也对原生的JDBC 做了轻量级的封装，即 org.springframework.jdbc.core.JdbcTemplate。

    3、数据库操作的所有 CRUD 方法都在 JdbcTemplate 中。

    4、Spring Boot 不仅提供了默认的数据源，同时默认已经配置好了 JdbcTemplate 放在了容器中，只需自己注入即可使用

    5、JdbcTemplate 的自动配置原理是依赖 org.springframework.boot.autoconfigure.jdbc 包下的 org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration 类

package com.lyx.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

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

@RestController
public class JDBCController {

    @Autowired
    JdbcTemplate jdbcTemplate;

    @GetMapping("/emp-list")
    public List<Map<String, Object>> empList() {
        String sql = "select * from emp";
        List<Map<String, Object>> maps = jdbcTemplate.queryForList(sql);
        return maps;
    }

    @GetMapping("/add-emp")
    public String addUser(@RequestParam("id") Integer id, @RequestParam("name") String name) {
        String sql = "insert into emp(id, name) values(?, ?)";
        jdbcTemplate.update(sql, id, name);
        return "success";
    }

    @GetMapping("/update-emp")
    public String updateEmp(@RequestParam("id") Integer id, @RequestParam("name") String name) {
        String sql = "update emp set name = ? where id = " + id;
        jdbcTemplate.update(sql, name);
        return "update success";
    }

    @GetMapping("/delete-emp/{id}")
    public String deleteEmp(@PathVariable("id") Integer id) {
        String sql = "delete from emp where id = ?";
        jdbcTemplate.update(sql, id);
        return "delete success";
    }
}

2、自定义数据源DruidDataSource

通过源码查看DataSourceAutoConfiguration.java

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({ DataSourcePoolMetadataProvidersConfiguration.class, DataSourceInitializationConfiguration.class })
public class DataSourceAutoConfiguration {

    @Configuration(proxyBeanMethods = false)
    @Conditional(EmbeddedDatabaseCondition.class)
    @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
    @Import(EmbeddedDataSourceConfiguration.class)
    protected static class EmbeddedDatabaseConfiguration {

    }

    @Configuration(proxyBeanMethods = false)
    @Conditional(PooledDataSourceCondition.class)
    @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
    @Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class,
            DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class,
            DataSourceJmxConfiguration.class })
    protected static class PooledDataSourceConfiguration {

    }

    /**
     * {@link AnyNestedCondition} that checks that either {@code spring.datasource.type}
     * is set or {@link PooledDataSourceAvailableCondition} applies.
     */
    static class PooledDataSourceCondition extends AnyNestedCondition {

        PooledDataSourceCondition() {
            super(ConfigurationPhase.PARSE_CONFIGURATION);
        }

        @ConditionalOnProperty(prefix = "spring.datasource", name = "type")
        static class ExplicitType {

        }

        @Conditional(PooledDataSourceAvailableCondition.class)
        static class PooledDataSourceAvailable {

        }

    }

1、添加druid的maven配置

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.12</version>
</dependency>

2、添加数据源的配置

spring:
  datasource:
    username: college_dev
    password: college_dev
    url: jdbc:mysql://10.155.10.123:4502/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8
    driver-class-name: com.mysql.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource

3、测试发现数据源已经更改

4、druid是数据库连接池，可以添加druid的独有配置

spring:
  datasource:
    username: college_dev
    password: college_dev
    url: jdbc:mysql://10.155.10.123:4502/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8
    driver-class-name: com.mysql.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource
    #Spring Boot 默认是不注入这些属性值的，需要自己绑定
    #druid 数据源专有配置
    initialSize: 5
    minIdle: 5
    maxActive: 20
    maxWait: 60000
    timeBetweenEvictionRunsMillis: 60000
    minEvictableIdleTimeMillis: 300000
    validationQuery: SELECT 1 FROM DUAL
    testWhileIdle: true
    testOnBorrow: false
    testOnReturn: false
    poolPreparedStatements: true

    #配置监控统计拦截的filters，stat:监控统计、log4j：日志记录、wall：防御sql注入
    #如果允许时报错  java.lang.ClassNotFoundException: org.apache.log4j.Priority
    #则导入 log4j 依赖即可，Maven 地址： https://mvnrepository.com/artifact/log4j/log4j
    filters: stat,wall,log4j
    maxPoolPreparedStatementPerConnectionSize: 20
    useGlobalDataSourceStat: true
    connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=500

测试类，发现配置的参数没有生效

package com.lyx.springboot.data.springbootdata;

import com.alibaba.druid.pool.DruidDataSource;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

@SpringBootTest
class DataApplicationTests {

    @Autowired
    DataSource dataSource;

    @Test
    void contextLoads() throws SQLException {
        System.out.println(dataSource.getClass());
        Connection connection = dataSource.getConnection();
        System.out.println(connection);

        DruidDataSource druidDataSource = (DruidDataSource)dataSource;
        System.out.println(druidDataSource.getMaxActive());
        System.out.println(druidDataSource.getInitialSize());
        connection.close();
    }

}

需要定义druidDatasource的配置类，绑定参数

package com.lyx.springboot.data.springbootdata.config;

import com.alibaba.druid.pool.DruidDataSource;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;

@Configuration
public class DruidConfig {
    @ConfigurationProperties(prefix = "spring.datasource")
    @Bean
    public DataSource druidDataSource(){
        return new DruidDataSource();
    }
}

Druid数据源还具有监控的功能，并提供了一个web界面方便用户进行查看。

加入log4j的日志依赖

        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>

向DruidConfig中添加代码，配置druid监控管理台的servlet

package com.lyx.config;

import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.support.http.StatViewServlet;
import com.alibaba.druid.support.http.WebStatFilter;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.servlet.Servlet;
import javax.sql.DataSource;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

@Configuration
public class DruidConfig {

    @ConfigurationProperties(prefix = "spring.datasource")
    @Bean
    public DataSource druidDataSource() {
        return new DruidDataSource();
    }

    @Bean
    public ServletRegistrationBean druidServletRegistrationBean() {
        ServletRegistrationBean<Servlet> servletRegistrationBean = new ServletRegistrationBean<Servlet>(new StatViewServlet(), "/druid/*");
        Map<String, String> initParams = new HashMap<String, String>();
        initParams.put("loginUsername", "admin");
        initParams.put("loginPassword", "123456");
        //后台允许谁可以访问
        //initParams.put("allow", "localhost")：表示只有本机可以访问
        //initParams.put("allow", "")：为空或者为null时，表示允许所有访问
        initParams.put("allow", "");
        //deny：Druid 后台拒绝谁访问
        //initParams.put("msb", "192.168.1.20");表示禁止此ip访问

        servletRegistrationBean.setInitParameters(initParams);
        return servletRegistrationBean;
    }

    //配置 Druid 监控 之  web 监控的 filter
    //WebStatFilter：用于配置Web和Druid数据源之间的管理关联监控统计
    @Bean
    public FilterRegistrationBean webStatFilter() {
        FilterRegistrationBean bean = new FilterRegistrationBean();
        bean.setFilter(new WebStatFilter());

        //exclusions：设置哪些请求进行过滤排除掉，从而不进行统计
        Map<String, String> initParams = new HashMap<String, String>();
        initParams.put("exclusions", "*.js,*.css,/druid/*");
        bean.setInitParameters(initParams);

        //"/*" 表示过滤所有请求
        bean.setUrlPatterns(Arrays.asList("/*"));
        return bean;
    }
}

3、springboot配置多数据源并动态切换

    DataSource是和线程绑定的，动态数据源的配置主要是通过继承AbstractRoutingDataSource类实现的，实现在AbstractRoutingDataSource类中的 protected Object determineCurrentLookupKey()方法来获取数据源，所以我们需要先创建一个多线程线程数据隔离的类来存放DataSource，然后在determineCurrentLookupKey()方法中通过这个类获取当前线程的DataSource，在AbstractRoutingDataSource类中，DataSource是通过Key-value的方式保存的，我们可以通过ThreadLocal来保存Key，从而实现数据源的动态切换。

1、修改配置文件类

spring:
  datasource:
    local:
      username: ceshi
      password: CeShi*0409.
      driver-class-name: com.mysql.jdbc.Driver
      jdbc-url: jdbc:mysql://10.155.10.123:4501/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8
    remote:
      username: college_dev
      password: college_dev
      driver-class-name: com.mysql.jdbc.Driver
      jdbc-url: jdbc:mysql://10.155.10.123:4502/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8

2、创建数据源枚举类

package com.lyx.springboot.data.springbootdata.mult;

public enum DataSourceType {
    REMOTE,
    LOCAL
}

3、数据源切换处理

    创建一个数据源切换处理类，有对数据源变量的获取、设置和情况的方法，其中threadlocal用于保存某个线程共享变量。

package com.lyx.mult;

public class DynamicDataSourceContextHolder {

    /**
     * 使用ThreadLocal维护变量，ThreadLocal为每个使用该变量的线程提供独立的变量副本，
     *  所以每一个线程都可以独立地改变自己的副本，而不会影响其它线程所对应的副本。
     */
    private static final ThreadLocal<String> CONTEXT_HOLDER = new ThreadLocal<String>();

    /**
     * 设置数据源变量
     * @param dataSourceType
     */
    public static void setDataSourceType(String dataSourceType){
        System.out.printf("切换到{%s}数据源", dataSourceType);
        CONTEXT_HOLDER.set(dataSourceType);
    }

    /**
     * 获取数据源变量
     * @return
     */
    public static String getDataSourceType(){
        return CONTEXT_HOLDER.get();
    }

    /**
     * 清空数据源变量
     */
    public static void clearDataSourceType(){
        CONTEXT_HOLDER.remove();
    }
}

4、继承AbstractRoutingDataSource

    动态切换数据源主要依靠AbstractRoutingDataSource。创建一个AbstractRoutingDataSource的子类，重写determineCurrentLookupKey方法，用于决定使用哪一个数据源。这里主要用到AbstractRoutingDataSource的两个属性defaultTargetDataSource和targetDataSources。defaultTargetDataSource默认目标数据源，targetDataSources（map类型）存放用来切换的数据源。

package com.lyx.springboot.data.springbootdata.mult;

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

import javax.sql.DataSource;
import java.util.Map;

public class DynamicDataSource extends AbstractRoutingDataSource {

    public DynamicDataSource(DataSource defaultTargetDataSource, Map<Object, Object> targetDataSources) {
        super.setDefaultTargetDataSource(defaultTargetDataSource);
        super.setTargetDataSources(targetDataSources);
        // afterPropertiesSet()方法调用时用来将targetDataSources的属性写入resolvedDataSources中的
        super.afterPropertiesSet();
    }

    /**
     * 根据Key获取数据源的信息
     *
     * @return
     */
    @Override
    protected Object determineCurrentLookupKey() {
        return DynamicDataSourceContextHolder.getDataSourceType();
    }
}

5、注入数据源

package com.lyx.mult;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;

import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

@Configuration
public class DataSourceConfig {
    @Bean
    @ConfigurationProperties("spring.datasource.remote")
    public DataSource remoteDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean
    @ConfigurationProperties("spring.datasource.local")
    public DataSource localDataSource() {
        return DataSourceBuilder.create().build();
    }
    
    @Bean(name = "dynamicDataSource")
    @Primary
    public DynamicDataSource dataSource(DataSource remoteDataSource, DataSource localDataSource) {
        Map<Object, Object> targetDataSources = new HashMap<Object, Object>();
        targetDataSources.put(DataSourceType.REMOTE.name(), remoteDataSource);
        targetDataSources.put(DataSourceType.LOCAL.name(), localDataSource);
        return new DynamicDataSource(remoteDataSource, targetDataSources);
    }
}

6、自定义多数据源切换注解

    设置拦截数据源的注解，可以设置在具体的类上，或者在具体的方法上

package com.lyx.springboot.data.springbootdata.mult;

import java.lang.annotation.*;

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DataSource {
    /**
     * 切换数据源名称
     */
    DataSourceType value() default DataSourceType.REMOTE;
}

7、AOP拦截类的实现

    通过拦截上面的注解，在其执行之前处理设置当前执行SQL的数据源的信息，CONTEXT_HOLDER.set(dataSourceType)这里的数据源信息从我们设置的注解上面获取信息，如果没有设置就是用默认的数据源的信息。

package com.lyx.mult;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;

@Aspect
@Order(1)
@Component
public class DataSourceAspect {

    @Pointcut("@annotation(com.lyx.mult.DataSource)")
    public void dsPointCut() {

    }

    @Around("dsPointCut()")
    public Object around(ProceedingJoinPoint point) throws Throwable {
        MethodSignature signature = (MethodSignature) point.getSignature();
        Method method = signature.getMethod();
        DataSource dataSource = method.getAnnotation(DataSource.class);
        if (dataSource != null) {
            DynamicDataSourceContextHolder.setDataSourceType(dataSource.value().name());
        }
        try {
            return point.proceed();
        } finally {
            // 销毁数据源 在执行方法之后
            DynamicDataSourceContextHolder.clearDataSourceType();
        }
    }
}

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-aop</artifactId>
</dependency>
<dependency>
  <groupId>org.aspectj</groupId>
  <artifactId>aspectjweaver</artifactId>
</dependency>

8、使用切换数据源注解

package com.lyx.controller;

import com.lyx.mult.DataSource;
import com.lyx.mult.DataSourceType;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

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


@RestController
public class EmpController {

    @Autowired
    JdbcTemplate jdbcTemplate;

    @GetMapping("/local")
    @DataSource(value = DataSourceType.LOCAL)
    public List<Map<String, Object>> local(){
        List<Map<String, Object>> maps = jdbcTemplate.queryForList("select * from emp");
        return maps;
    }
    @GetMapping("/remote")
    @DataSource(value = DataSourceType.REMOTE)
    public List<Map<String, Object>> remote(){
        List<Map<String, Object>> maps = jdbcTemplate.queryForList("select * from emp");
        return maps;
    }
}

9、在启动项目的过程中会发生循环依赖的问题，直接修改启动类即可

package com.lyx.springboot.data.springbootdata;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;

@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)
public class SpringbootDataApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringbootDataApplication.class, args);
    }
}

4、springboot整合mybatis

1、导入mybatis的依赖

<!-- https://mvnrepository.com/artifact/org.mybatis.spring.boot/mybatis-spring-boot-starter -->
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.1</version>
</dependency>

2、配置数据源

spring:
  datasource:
    username: college_dev
    password: college_dev
    url: jdbc:mysql://10.155.10.123:4502/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8
    driver-class-name: com.mysql.jdbc.Driver

3、测试类

package com.lyx.springboot.data.springbootdata;

import com.alibaba.druid.pool.DruidDataSource;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

@SpringBootTest
class DataApplicationTests {

    @Autowired
    DataSource dataSource;

    @Test
    void contextLoads() throws SQLException {
        System.out.println(dataSource.getClass());
        Connection connection = dataSource.getConnection();
        System.out.println(connection);
        System.out.println(connection.getMetaData().getURL());

        connection.close();
    }
}

4、创建实体类

package com.lyx.entity;

public class Emp {
    private Integer id;
    private String name;

    public Emp() {
    }

    public Emp(Integer id, String name) {
        this.id = id;
        this.name = name;
    }

    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;
    }

    @Override
    public String toString() {
        return "Emp{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

5、配置Mapper接口类

package com.lyx.mapper;

import com.lyx.entity.Emp;
import org.apache.ibatis.annotations.Mapper;
import org.springframework.stereotype.Repository;

import java.util.List;

@Mapper
@Repository
public interface EmpMapper {

    List<Emp> selectEmp();

    Emp selectEmpById(Integer id);

    Integer addEmp(Emp emp);

    Integer updateEmp(Emp emp);

    Integer deleteEmp(Integer id);
}

6、在resources下创建EmpMapper.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.lyx.mapper.EmpMapper">

    <select id="selectEmp" resultType="com.lyx.entity.Emp">
    select * from emp
  </select>

    <select id="selectEmpById" resultType="com.lyx.entity.Emp">
    select * from emp where id = #{id}
    </select>

    <insert id="addEmp" parameterType="com.lyx.entity.Emp">
    insert into emp (id, name) values (#{id}, #{name})
    </insert>

    <update id="updateEmp" parameterType="com.lyx.entity.Emp">
    update emp set ename = #{name} where id = #{id}
    </update>

    <delete id="deleteEmp" parameterType="int">
    delete from emp where id = #{id}
</delete>
</mapper>

7、添加配置文件

spring:
  datasource:
    username: college_dev
    password: college_dev
    url: jdbc:mysql://10.155.10.123:4502/db_sharks?serverTimezone=UTC&useUnicode=true@characterEncoding=utf-8
    driver-class-name: com.mysql.jdbc.Driver
mybatis:
  mapper-locations: classpath:mapper/*.xml
  type-aliases-package: com.lyx.entity

8、编写controller

package com.lyx.controller;

import com.lyx.entity.Emp;
import com.lyx.mapper.EmpMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
public class EmpController {
    @Autowired
    private EmpMapper empMapper;

    //选择全部用户
    @GetMapping("/selectEmp")
    public String selectEmp(){
        List<Emp> emps = empMapper.selectEmp();
        for (Emp Emp : emps) {
            System.out.println(Emp);
        }
        return "ok";
    }
    //根据id选择用户
    @GetMapping("/selectEmpById")
    public String selectEmpById(){
        Emp emp = empMapper.selectEmpById(1);
        System.out.println(emp);
        return "ok";
    }
    //添加一个用户
    @GetMapping("/addEmp")
    public String addEmp(){
        empMapper.addEmp(new Emp(3333,"heheda"));
        return "ok";
    }
    //修改一个用户
    @GetMapping("/updateEmp")
    public String updateEmp(){
        empMapper.updateEmp(new Emp(1111,"heihei"));
        return "ok";
    }
    //根据id删除用户
    @GetMapping("/deleteEmp")
    public String deleteEmp(){
        empMapper.deleteEmp(3333);
        return "ok";
    }
}

9、测试即可