error：If you want an embedded database (H2, HSQL or Derby)

Posted 2021-06-20 劭兮劭兮

错误代码

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-05-30 15:00:35.740 ERROR 17800 --- [           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 (no profiles are currently active).

错误原因：

触发了数据源的自动化配置，然而当前项目其实并不需要数据源。究其根源是依赖方提供的API依赖中（本项目创建时导入了web，mysql，jpa 等依赖），多余的依赖触发了该自动化配置的加载。

很多人说是数据库连接的问题，但是我的IDEA连接数据库成功，

错误解决办法

//默认程序入口
@SpringBootApplication
public class BlogApplication {

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

}

//修改为，就是在注解后面加上(exclude = DataSourceAutoConfiguration.class)
@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)
public class BlogApplication {

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

}

@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)作用：

排除自动注入数据源的配置（取消数据库配置），即禁止 springboot 自动注入数据源配置；
DataSourceAutoConfiguration.class 会自动查找 application.yml 或者 properties 文件里的 spring.datasource.* 相关属性并自动配置单数据源；而往往在项目中我们需要配置多数据源，也就是需要自己手动配置数据源；关于单数据源和多数据源的区别参考：单数据源与多数据源（本人小白一个，有点不太懂）

错误介绍

用springboot 写项目时，导入依赖如下：

导入依赖后的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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

未导入依赖的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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo3</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo3</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

对比发现：

触发了数据源的自动化配置，然而当前项目其实并不需要数据源。究其根源是依赖方提供的API依赖中（本项目创建时导入了web，mysql，jpa 等依赖），多余的依赖触发了该自动化配置的加载。

小白一个，有不对的地方，还请指教！