一、问题
在启动springboot项目中遇到如下问题：
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).
这个问题其实是url和数据源配置错误问题，果断查看配置文件和依赖。
另外，本项目用的是mybatisPlus+MySQL，使用默认连接池hakis
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二、原代码展示
1、配置文件
server: port: 9999spring: redis: host: 127.0.0.1 port: 6379 datasource: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://localhost:3306/lkd_user?characterEncoding=utf-8&serverTimezone=UTC username: root password: root经过校对，没有问题2、依赖
<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> <packaging>pom</packaging> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.6.RELEASE</version> </parent> <groupId>com.zb</groupId> <artifactId>mysec</artifactId> <version>1.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.10</version> <scope>provided</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-security</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.33</version> </dependency> <dependency> <groupId>io.jsonwebtoken</groupId> <artifactId>jjwt</artifactId> <version>0.9.0</version> </dependency> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.4.3</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency> </dependencies></project>经过校对，暂时没有发现错误———————————————————————————————
三、发现
发现没有存在明显的配置文件和依赖的问题，于是又看了下控制台打印日志，真正错误其实在上面，日志级别为warn。
2022-08-21 19:10:31.248 WARN 39656 — [ main] ConfigServletWebServerApplicationContext :
Exception encountered during context initialization – cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘userDetailServiceImpl’: Unsatisfied dependency expressed through field ‘tbUserMapper’; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘tbUserMapper’ defined in file [D:\maven\spring\springcloud\mysec\target\classes\com\zb\mapper\TbUserMapper.class]: Unsatisfied dependency expressed through bean property ‘sqlSessionFactory’; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘sqlSessionFactory’ defined in class path resource [com/baomidou/mybatisplus/autoconfigure/MybatisPlusAutoConfiguration.class]: Unsatisfied dependency expressed through method ‘sqlSessionFactory’ 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 H i k a r i . c l a s s ] : B e a n i n s t a n t i a t i o n v i a f a c t o r y m e t h o d f a i l e d ; n e s t e d e x c e p t i o n i s o r g . s p r i n g f r a m e w o r k . b e a n s . B e a n I n s t a n t i a t i o n E x c e p t i o n : F a i l e d t o i n s t a n t i a t e [ c o m . z a x x e r . h i k a r i . H i k a r i D a t a S o u r c e ] : F a c t o r y m e t h o d ′ d a t a S o u r c e ′ t h r e w e x c e p t i o n ; n e s t e d e x c e p t i o n i s o r g . s p r i n g f r a m e w o r k . b o o t . a u t o c o n f i g u r e . j d b c . D a t a S o u r c e P r o p e r t i e s 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 Hikari.class]:Beaninstantiationviafactorymethodfailed;nestedexceptionisorg.springframework.beans.BeanInstantiationException:Failedtoinstantiate[com.zaxxer.hikari.HikariDataSource]:Factorymethod′dataSource′threwexception;nestedexceptionisorg.springframework.boot.autoconfigure.jdbc.DataSourcePropertiesDataSourceBeanCreationException: Failed to determine a suitable driver class
这里打印了bean的依赖问题，如下：
userDetailServiceImpl——依赖——》tbUserMapperl——依赖——》 sqlSessionFactory——依赖——》MybatisPlusAutoConfiguration ——依赖——》dataSource——依赖——》jdbc.DataSourceProperties
这里最终原因是：Failed to determine a suitable driver class，翻译下就是：无法确定合适的驱动程序类。错误主要跟DataSource有关。
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四、找原因
1、查看DataSourceConfiguration类，看看导入的实际DataSource配置。
abstract class DataSourceConfiguration {//创建DataBase@SuppressWarnings("unchecked")protected static <T> T createDataSource(DataSourceProperties properties, Class<? extends DataSource> type) {return (T) properties.initializeDataSourceBuilder().type(type).build();}/** * Hikari DataSource configuration. */@Configuration@ConditionalOnClass(HikariDataSource.class)@ConditionalOnMissingBean(DataSource.class)@ConditionalOnProperty(name = "spring.datasource.type", havingValue = "com.zaxxer.hikari.HikariDataSource",matchIfMissing = true)static class Hikari {@Bean@ConfigurationProperties(prefix = "spring.datasource.hikari")public HikariDataSource dataSource(DataSourceProperties properties) {HikariDataSource dataSource = createDataSource(properties, HikariDataSource.class);if (StringUtils.hasText(properties.getName())) {dataSource.setPoolName(properties.getName());}return dataSource;}//省略其他Database配置（tomcat 、dbcp2、generic）}}这里断点，走的是HikariDataSource的dataSource()工厂方法，然后调用createDataSource()。
评估表达式(ALT+F8)计算createDataSource()，正好是导致异常的最终原因：
org.springframework.boot.autoconfigure.jdbc.DataSourceProperties$DataSourceBeanCreationException: Failed to determine a suitable driver class
（断点的时候已经发现jdbc爆红，没有成功导入）
继续往下走，进入到DataSourceProperties类initializeDataSourceBuilder()
public DataSourceBuilder<?> initializeDataSourceBuilder() {return DataSourceBuilder.create(getClassLoader()).type(getType()).driverClassName(determineDriverClassName()).url(determineUrl()).username(determineUsername()).password(determinePassword());}这里采用建造者模式链式调用，方法依次为创建——》类型——》驱动类名——》URL——》用户名——》密码。
评估表达式(ALT+F8)递进式计算：链式调用的返回结果。发现链式调用到driverClassName(determineDriverClassName())报错，并且后面也的determine()全部报错。
（这里已经发现问题，猜测配置文件声明的DriverClassName、url、username、password没有被识别到）
继续往下走，进入到determineDriverClassName()方法
public String determineDriverClassName() {if (StringUtils.hasText(this.driverClassName)) {Assert.state(driverClassIsLoadable(), () -> "Cannot load driver class: " + this.driverClassName);return this.driverClassName;}String driverClassName = null;if (StringUtils.hasText(this.url)) {driverClassName = DatabaseDriver.fromJdbcUrl(this.url).getDriverClassName();}if (!StringUtils.hasText(driverClassName)) {driverClassName = this.embeddedDatabaseConnection.getDriverClassName();}if (!StringUtils.hasText(driverClassName)) {//这里正好是控制台日志warn信息的最后一行提示throw new DataSourceBeanCreationException("Failed to determine a suitable driver class", this,this.embeddedDatabaseConnection);}return driverClassName;}运行到这已经结束，错误信息中嵌套的最后异常就是出自这里
DataSourceBeanCreationException: Failed to determine a suitable driver class
断点中发现，该方法的类DataSourceProperties中的字段driverClassName、url、username、password全部为NULL。
于是又打开了其他运行正常的项目，断点上述各个位置，重新debug
首先进入到DataSourceConfiguration类的dataSource方法
可以看到，这个时候已经完成配置项的读取，往下走到DataSourceProperties类的initializeDataSourceBuilder()方法
这里并没有引发异常，同时发现determineXXX()方法都能得到对应的值。
到这，可以确定是配置信息没有成功被读取到，也就是YAML配置失效。
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五、解决方案
１、检查YAML文件位置、是否存在语法错误（四个配置项都没有成功读取，可以排除）
２、查看POM文件是否存在配置错误
最后发现问题是POM打包方式错误，多写了一行
<modelVersion>4.0.0</modelVersion><!-- pom--> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.6.RELEASE</version> </parent>———————————————————————————————
六、建议
1、不用看mybatis的mapper接口和映射文件、实体类。
项目启动时没有查数据库，也就没有调用mapper层，自然不会引发这个错误。就算报错上提示信息也很明确，网上很多说要检查这个，感觉没有必要。2、看yml/properties配置文件中跟url相关的，是否存在错误。
配置写多了，基本不会出现语法或声明错误，而且有代码提示