问题

今天在项目启动类SuperJsonManagerApplication中，加上这行代码@MapperScan("com.**.mapper")后，如下所示：

package com.superjson.superjsonmanager;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author zs
 * @datetime 2022/8/5 15:16
 * @desc superjson框架的启动类
 */
@SpringBootApplication
@MapperScan("com.**.mapper")
public class SuperJsonManagerApplication {

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

启动项目时，报出如下错误：

com.superjson.superjsonmanager.SuperJsonManagerApplication
Connected to the target VM, address: '127.0.0.1:58651', transport: 'socket'

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.7.1)

2022-08-05 16:06:56.891  INFO 138836 --- [           main] c.s.s.SuperJsonManagerApplication        : Starting SuperJsonManagerApplication using Java 1.8.0_102 on DESKTOP-UVTEHFR with PID 138836 (D:\project\1myProject\superjson\superjsonmanager\target\classes started by zby in D:\project\1myProject\superjson\superjsonmanager)
2022-08-05 16:06:56.893  INFO 138836 --- [           main] c.s.s.SuperJsonManagerApplication        : No active profile set, falling back to 1 default profile: "default"
2022-08-05 16:06:57.322  WARN 138836 --- [           main] o.m.s.mapper.ClassPathMapperScanner      : No MyBatis mapper was found in '[com.superjson.superjsonmanager]' package. Please check your configuration.
2022-08-05 16:06:57.561  INFO 138836 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8088 (http)
2022-08-05 16:06:57.566  INFO 138836 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2022-08-05 16:06:57.567  INFO 138836 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.64]
2022-08-05 16:06:57.651  INFO 138836 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2022-08-05 16:06:57.651  INFO 138836 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 725 ms
2022-08-05 16:06:57.885  WARN 138836 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration': Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.boot.context.properties.ConfigurationPropertiesBindException: Error creating bean with name 'mybatis-org.mybatis.spring.boot.autoconfigure.MybatisProperties': Could not bind properties to 'MybatisProperties' : prefix=mybatis, ignoreInvalidFields=false, ignoreUnknownFields=true; nested exception is org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'mybatis.configuration' to org.apache.ibatis.session.Configuration
2022-08-05 16:06:57.887  INFO 138836 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2022-08-05 16:06:57.894  INFO 138836 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2022-08-05 16:06:57.906 ERROR 138836 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

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

Description:

Failed to bind properties under 'mybatis.configuration' to org.apache.ibatis.session.Configuration:

    Reason: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.String] to type [@org.springframework.boot.context.properties.NestedConfigurationProperty org.apache.ibatis.session.Configuration]

Action:

Update your application's configuration

Disconnected from the target VM, address: '127.0.0.1:58651', transport: 'socket'

Process finished with exit code 1

分析问题

定位到上诉问题中的这行语句：

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.String] to type [@org.springframework.boot.context.properties.NestedConfigurationProperty org.apache.ibatis.session.Configuration]

正如我们所知道的那样，spring项目在启动时，会加载及初始化配置文件的数据。

spring拿到这些数据后，然后，实例化对应的实体类。如果数据中没有待实例化的实体类所需要的属性信息，那就回出现转换失败的问题。

基于此，可能是配置文件出现了问题，导致spring无法获取对应属性的值。

我的配置文件如下所示：

server:
  port: 8088

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    password: root
    username: root
    url: jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false
    
mybatis:
  check-config-location: true
  configuration:
  log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  type-aliases-package: com.superjson.superjsonmanager.mapper
  mapper-locations: classpath:mapper/*.xml

发现mybatis下的configuration字段没有初始化值，因而，便出现了上诉错误。

解决问题

删除configuration字段即可，如下所示：

mybatis:
  check-config-location: true
  log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  type-aliases-package: com.superjson.superjsonmanager.mapper
  mapper-locations: classpath:mapper/*.xml

重新启动spring ，发现没有报出错误：