spring-boot-autoconfigure误引入spring-boot-starter-data-jpa而导致数据源初始化异常

一、现状描述

某个Grade类引入了jpa的注解：

import javax.persistence.Column;
import javax.persistence.Embeddable;

/**
 * 年级
 */
@Embeddable
public class Grade {
    @Column(name = "code")
    private int code;
}

并且pom.xml中引入该jar包：spring-boot-starter-data-jpa

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

不出意外，在启动的时候会报错如下：

2024-01-02 14:35:23.242  WARN [xxx-service,,,] 2778322 --- [           main] o.s.boot.actuate.endpoint.EndpointId     : Endpoint ID 'hystrix.stream' contains invalid characters, please migrate to a valid format.
2024-01-02 14:35:24.919  WARN [xxx-service,,,] 2778322 --- [           main] c.n.c.sources.URLConfigurationSource     : No URLs will be polled as dynamic configuration sources.

2024-01-02 14:35:25.564 ERROR [xxx-service,,,] 2778322 --- [           main] o.s.b.web.embedded.tomcat.TomcatStarter  : Error starting Tomcat context. Exception: org.springframework.beans.factory.BeanCreationException. Message: 
Error creating bean with name 'servletEndpointRegistrar' defined in class path resource [org/springframework/boot/actuate/autoconfigure/endpoint/web/ServletEndpointManagementContextConfiguration$WebMvcServletEndpointManagementContextConfiguration.class]: 
Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.boot.actuate.endpoint.web.ServletEndpointRegistrar]: 
Factory method 'servletEndpointRegistrar' threw exception; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'healthEndpoint' defined in class path resource [org/springframework/boot/actuate/autoconfigure/health/HealthEndpointConfiguration.class]: 
Unsatisfied dependency expressed through method 'healthEndpoint' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'healthContributorRegistry' defined in class path resource [org/springframework/boot/actuate/autoconfigure/health/HealthEndpointConfiguration.class]: 
Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: 
Failed to instantiate [org.springframework.boot.actuate.health.HealthContributorRegistry]: Factory method 'healthContributorRegistry' threw exception; 
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.boot.actuate.autoconfigure.jdbc.DataSourceHealthContributorAutoConfiguration': Unsatisfied dependency expressed through constructor parameter 0; 
nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class]: 
Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: 
Failed to instantiate [com.zaxxer.hikari.HikariDataSource]: Factory method 'dataSource' threw exception; nested exception is org.springframework.boot.autoconfigure.jdbc.DataSourceProperties$DataSourceBeanCreationException: Failed to determine a suitable driver class

2024-01-02 14:35:25.595  WARN [xxx-service,,,] 2778322 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
Disconnected from the target VM, address: '127.0.0.1:35843', transport: 'socket'

2024-01-02 14:35:25.625 ERROR [xxx-service,,,] 2778322 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

***************************
APPLICATION FAILED TO START
***************************

Description:

Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured.

Reason: Failed to determine a suitable driver class


Action:

Consider the following:
	If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.
	If you have database settings to be loaded from a particular profile you may need to activate it (the profiles dev are currently active).

错误在于你没有配置rdb的数据源，默认是com.zaxxer.hikari.HikariDataSource。

可是我整个项目都只依赖Mongodb和redis数据库，并无需使用mysql等关系型数据库。

二、解决办法

1、方法一，忽略数据源的自动加载

在application.java启动类上作处理：

@EnableAutoConfiguration(exclude = {DataSourceAutoConfiguration.class})
public class XxxApplication {

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

2、方法二，去除数据源jdbc的依赖

		<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
            <exclusions>
                <exclusion>
                    <artifactId>spring-boot-starter-jdbc</artifactId>
                    <groupId>org.springframework.boot</groupId>
                </exclusion>
            </exclusions>
        </dependency>

3、方法三，去掉jpa（建议方法）

既然没有使用到关系型数据库，就没必要jpa包了。

这里需要说明的是，文章开头说的Grade类，是不必要那些字段的注解。

估计是从其他项目中将代码copy过来的时候，偷懒做法，没有去掉注解。

三、总结

1、查找mvn依赖关系，定位到Hikari包是被谁引入的。

通过问题的报错，反过去推导。

2、不要引入不必要的jar包，方法一和二虽然解决了问题，但多少有点画蛇添足的嫌疑。

当然，还有人会说，没配置rdb的数据源就配置啊。

这就非常提倡，为了一双玉的筷子，反过来去买一个金碗，再进而去买银碗篮。。。