After the SpringBoot / SpringCloud project is deployed, if you use a hard-coded method to define the data source, then if you need to replace the database, you can only reach your source by changing the source code and restarting.
And SpringCloud ecology has a configuration center, we can write data source connection properties in the configuration center, you need to modify the connection attribute to modify and release from the configuration center, so you can heat-modify the data source location without restart service

Then, the following actual meant explains how to configure data sources using NACOS configuration / registration centers (please note the comments I wrote to avoid pits)

First explain the version

1. SpringBoot 2.2.0.RELEASE
2. Druid 1.1.22 (when rewritten, the class will vary from the version)
3. MySQL 8.0.18
4. NACOS 1.3.1 (NACOS version is not very likely to step on the pit)
5. IDEA 2020.3.2
6. Mybatis 2.1.4 (useless, but if used does not conflict)

The article is longer, but most are copy paste operations, first explain the steps of the entire configuration.

1. Create a SpringBoot project and introduce dependence (direct copy paste)
2. Create a bootstrap.yml file (directly copy paste)
3. Create a configuration class (directly copy paste)
4. Rewrive the Druid DruidabStractDataSource class (this needs to be modified according to the version)
5. New configuration in the NACOS Configuration Center

Complete the configuration project directory

Please note: I will use Idea to create a SpringBoot project using IDEA, and you can install NACOS yourself.

1.maven dependence

 	<properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <maven-jar-plugin.version>3.1.1</maven-jar-plugin.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>2.1.1.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.4</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.22</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
            <scope>provided</scope>
            <version>1.18.12</version>
        </dependency>
    </dependencies>

2.bootstrap.yml (this priority is higher than the Properties file for configuring NACOS)

If you need to distinguish the production environment or take NACOS to Mysql, please learn from the NACOS official document.

spring:
  application:
  	#       name with the lowermost file-extension:  Properties
  	   #   QuestionBank.Properties name is the name of the NACOS profile
    name: questionBank
  cloud:
    nacos:
             # Register Center
      discovery:
                 # Whether to enable 
        enabled: true
                 # NACOS service address
        server-addr: 127.0.0.1:8848
                 # Service Name 
        #service: ${spring.application.name}
                 # group name 
        group: DEFAULT
                 # Weights 
        weight: 2
                 #    
        metadata:
          auth: sty
          version: 1.0
                 #    
        log-name: ${spring.application.name}
                 # Whether to open Watch
        watch: true
                 # How long is pulled from the server?
        watch-delay: 30000
                 #   name
        cluster-name: DEFAULT
                 # Whether to open a registration, iffalseWill not register itself
        register-enabled: true
        # https
        secure: false
             # Configuration Center
      config:
        server-addr: 127.0.0.1:8848
                 #                                
        file-extension: properties
server:
  port: 8080

3. Configuration class: druidconfiguration (called )

import com.alibaba.druid.pool.DruidDataSource;
import lombok.Data;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
/**
 * @Author：STY
   * @Description: Data Source Get Configuration (Configuration Center)
 * @Date：2021/3/17
 */
@Configuration
@RefreshScope
@Data
public class DruidConfiguration {

    @Value("${spring.datasource.druid.url}")
    private String url;

    @Value("${spring.datasource.druid.username}")
    private String username;

    @Value("${spring.datasource.druid.password}")
    private String password;

    @Value("${spring.datasource.druid.url.driverClassName}")
    private String driverClassName;

    @Bean(name="datasource")
    @RefreshScope
    public DruidDataSource dataSource()
    {
        DruidDataSource datasource = new DruidDataSource();
        System.out.println(url);
        datasource.setUrl(this.url);
        datasource.setUsername(username);
        datasource.setPassword(password);
        datasource.setDriverClassName(driverClassName);
        return datasource;
    }
}

Attention please:@Refreshscope must be added! ! ! ! ! ! ! Otherwise, you will not be able to automatically refresh the new data released from the NACOS, because Lombok is more useful, @Data directly uses him.

4. Then is the most important step (this is modified as the Druid version)

Reiterate the Druid version I used to 1.1.22

Rewrite com.alibaba.druid.pool.druidabstractdataSource Class
Due to DruidOnly allow initialization onceSo you can only modify his source, and the version can cause this class and must be particularly payable when modifying the source code! ! ! ! ! !

Create alibaba.druid.pool under the COM package (the path is wrong)

DruidabStractDataSource class directly copies

Then find the following two methods in the copy of the copy.
Note out of the painting position

At this point, the local item has been configured, and the last step is left, create a configuration file on NACOS.

This DATA ID corresponds to the name of the name in the second step in the second step (notes the comment)
Configuring the format to check Properties

Click to release, get it!