三层架构 + MVC
框架：
    Spring IOC AOP
    SpringBoot，新一代的JavaEE开发标准，自动装配
    模块化~  all in one，代码没变化~
微服务架构四个核心问题？
    1.服务很多，客户端该怎么访问
    2.这么多服务？服务之间如何通信？
    3.这么多服务？如何治理？
    4.服务挂了怎么办？
解决方案：
    SpringCloud 生态！ SpringBoot
    1.SpringCloud NetFlix 一站式解决方案！
      api网关，zuul组件
      Feign --- HttpClient --- Http通信方式，同步，阻塞
      服务注册发现：Eureka
      熔断机制：Hystrix
      。。。。。。
    2.Apache Dubbo Zookeeper 半自动，需要整合别人的！
      API：没有，找第三方组件，或者自己实现
      Dubbo
      Zookeeper
      没有：借助Hystrix
      Dubbo这个方案并不完善~
    3.SpringCloud Alibaba 一站式解决方案！更简单
    新概念：服务网格~Server Mesh
      istio
    万变不离其宗
      1.API
      2.HTTP,RPC
      3.注册与发现
      4.熔断机制

IDEA 工具里面使用Maven开发的一个个独立的小Module，它具体是使用SpringBoot开发的一个小模块，专业的事情交给专业的模块来做，一个模块就做这一件事情
强调的是一个个的个体，每个个体完成一个具体的任务或者功能！

Spring Cloud是一个由众多子项目组成的大型综合项目，每个子项目有不同的发行节奏，都维护着自己的发布版本号。Spring Cloud通过一个资源清单BOM（Bill of Materials）来管理每个版本的子项目清单。为避免与子项目的发布号混淆，所有没有采用版本号的方式，而是通过命名的方式。
这些版本名称的命名方式采用了伦敦地铁站的名称，同时根据字母表的顺序来对应版本时间顺序，比如：最早的Release版本：Angel，第二个Release版本：Brixton，然后是Camden、Dalston、Edgware，目前是按时间来对应版本。

一个简单的Maven模块结构是这样的：
--- app-parent：一个父项目（app-parent）聚合很多子项目（app-util，app-dao，app-web...）
    |-- pom.xml
    |
    |-- app-core
    ||----pom.xml
    |
    |-- app-web
    ||----pom.xml
    ......

<?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>com.kuang</groupId>
    <artifactId>springcloud</artifactId>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>springcloud-api</module>
        <module>springcloud-provider-dept-8001</module>
    </modules>
    <!--打包方式 pom-->
    <packaging>pom</packaging>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <junit.version>4.13.2</junit.version>
        <lombok.version>1.18.22</lombok.version>
    </properties>
    <dependencyManagement>
        <dependencies>
            <!--SpringCloud的依赖-->
            <!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-dependencies -->
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>2021.0.2</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <!--SpringBoot-->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.6.7</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <!--数据库-->
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.28</version>
            </dependency>
            <!--数据源-->
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid</artifactId>
                <version>1.2.9</version>
            </dependency>
            <!--SpringBoot启动器-->
            <!--mybatis启动器-->
            <dependency>
                <groupId>org.mybatis.spring.boot</groupId>
                <artifactId>mybatis-spring-boot-starter</artifactId>
                <version>2.2.2</version>
            </dependency>
            <!--日志和测试-->
            <dependency>
                <groupId>ch.qos.logback</groupId>
                <artifactId>logback-core</artifactId>
                <version>1.2.11</version>
            </dependency>
            <!--junit-->
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>${junit.version}</version>
            </dependency>
            <!--lombok-->
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <version>${lombok.version}</version>
            </dependency>
            <!--Log4j-->
            <dependency>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
                <version>1.2.17</version>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

<?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">
    <parent>
        <artifactId>springcloud</artifactId>
        <groupId>com.kuang</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>springcloud-api</artifactId>
    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <!--当前的Module自己需要的依赖，如果父依赖中已经配置了版本，这里就不用写了-->
    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies>
</project>

@Data
@NoArgsConstructor
@Accessors(chain = true) //链式写法
public class Dept implements Serializable { //Dept 实体类， orm mysql--dept 类表关系映射
    private Long deptno; //主键
    private String dname;
    //这个数据是存在哪个数据库的字段~ 微服务，一个服务对应一个数据库，同一个信息可能存在不同的数据库
    private String db_source;
    public Dept(String dname){ //构造器
        this.dname = dname;
    }
    /*
    链式写法：
        Dept dept = new Dept();
        dept.setDeptNo(11).setDname('ssss').setDb_source('001');
     */
}

<?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">
    <parent>
        <artifactId>springcloud</artifactId>
        <groupId>com.kuang</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>springcloud-provider-dept-8001</artifactId>
    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <dependencies>
        <!--我们需要拿到实体类，所以要配置api module-->
        <dependency>
            <groupId>com.kuang</groupId>
            <artifactId>springcloud-api</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
        </dependency>
        <!--test-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-test</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!--jetty-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jetty</artifactId>
        </dependency>
        <!--热部署工具-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>
    </dependencies>
</project>

server:
  port: 8001
#mybatis配置
mybatis:
  type-aliases-package: com.kuang.springcloud.pojo
  config-location: classpath:mybatis/mybatis-config.xml
  mapper-locations: classpath:mybatis/mapper/*.xml
#spring的配置
spring:
  application:
    name: springcloud-provider-dept
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/db01?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT
    username: root
    password: 123456

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <!--开启二级缓存-->
        <setting name="cacheEnabled" value="true"/>
    </settings>
</configuration>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.kuang.springcloud.dao.DeptDao">
    <insert id="addDept" parameterType="Dept">
        insert into db01.dept (dname, db_source)
        values (#{dname},DATABASE());
    </insert>
    <select id="queryDeptById" resultType="Dept" parameterType="Long">
        select * from db01.dept where deptno = #{deptno};
    </select>
    <select id="queryAll" resultType="Dept">
        select * from db01.dept;
    </select>
</mapper>

@Mapper
@Repository
public interface DeptDao {
    public boolean addDept(Dept dept);
    public Dept queryDeptById(Long id);
    public List<Dept> queryAll();
}

public interface DeptService {
    public boolean addDept(Dept dept);
    public Dept queryDeptById(Long id);
    public List<Dept> queryAll();
}

@Service
public class DeptServiceImpl implements DeptService{
    @Autowired
    private DeptDao deptDao;
    @Override
    public boolean addDept(Dept dept) {
        return deptDao.addDept(dept);
    }
    @Override
    public Dept queryDeptById(Long id) {
        return deptDao.queryDeptById(id);
    }
    @Override
    public List<Dept> queryAll() {
        return deptDao.queryAll();
    }
}

//提供Restful服务！
@RestController
public class DeptController {
    @Autowired
    private DeptService deptService;
    @PostMapping("/dept/add")
    public boolean addDept(Dept dept){
        return deptService.addDept(dept);
    }
    @GetMapping("/dept/get/{id}")
    public Dept get(@PathVariable("id") Long id){
        return deptService.queryDeptById(id);
    }
    @GetMapping("/dept/list")
    public List<Dept> queryAll(){
        return deptService.queryAll();
    }
}

//启动类
@SpringBootApplication
public class DeptProvider_8001 {
    public static void main(String[] args) {
        SpringApplication.run(DeptProvider_8001.class,args);
    }
}

<?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">
    <parent>
        <artifactId>springcloud</artifactId>
        <groupId>com.kuang</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>springcloud-consumer-dept-80</artifactId>
    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <!--实体类+web-->
    <dependencies>
        <dependency>
            <groupId>com.kuang</groupId>
            <artifactId>springcloud-api</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!--热部署工具-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>
    </dependencies>
</project>

server:
  port: 80

@Configuration
public class ConfigBean { //@Configuration -- spring applicationContext.xml
    @Bean
    public RestTemplate getRestTemplate(){
        return new RestTemplate();
    }
}

@RestController
public class DeptConsumerController {
    //理解：消费者，不应该有service层~
    //RestFul RestTemplate... 供我们直接调用就可以了！注册到Spring中
    //(url, 实体: Map, Class<T> responseType)
    @Autowired
    private RestTemplate restTemplate;//提供多种便捷访问远程http服务的方法，简单的restful服务模板~
    private static final String REST_URL_PREFIX = "http://localhost:8001";
    @RequestMapping("/consumer/dept/add")
    public boolean add(Dept dept){
        return restTemplate.postForObject(REST_URL_PREFIX+"/dept/add",dept,Boolean.class);
    }
    @RequestMapping("/consumer/dept/get/{id}")
    public Dept get(@PathVariable("id") Long id){
        return restTemplate.getForObject(REST_URL_PREFIX+"/dept/get/"+id,Dept.class);
    }
    @RequestMapping("/consumer/dept/list")
    public List<Dept> list(){
        return restTemplate.getForObject(REST_URL_PREFIX+"/dept/list",List.class);
    }
}

@SpringBootApplication
public class DeptConsumer_80 {
    public static void main(String[] args) {
        SpringApplication.run(DeptConsumer_80.class,args);
    }
}

1、导入依赖
2、编写配置文件
3、开启这个功能 @Enable...
4、配置类