Spring Boot启动失败：缺少org.modelmapper.ModelMapper类型Bean

Spring Boot启动失败是因为ProgrammingLanguageManager的构造函数需要org.modelmapper.ModelMapper类型的Bean，但Spring容器中没有定义该Bean，导致依赖注入无法完成。

需要完成两个步骤：确保引入ModelMapper依赖，然后在Spring配置中注册ModelMapper Bean。

1. 确认ModelMapper依赖已引入 #

Maven项目（修改pom.xml） #

<dependency>
    <groupId>org.modelmapper</groupId>
    <artifactId>modelmapper</artifactId>
    <version>3.1.1</version> <!-- 可替换为最新稳定版本 -->
</dependency>

Gradle项目（修改build.gradle） #

implementation 'org.modelmapper:modelmapper:3.1.1'

2. 注册ModelMapper Bean #

有两种简单的方式可以实现：

方式一：创建独立配置类 #

新建一个配置类，专门负责ModelMapper的Bean注册：

import org.modelmapper.ModelMapper;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ModelMapperConfig {
    
    @Bean
    public ModelMapper modelMapper() {
        ModelMapper modelMapper = new ModelMapper();
        // 可选：添加自定义配置，比如严格匹配策略
        // modelMapper.getConfiguration().setMatchingStrategy(MatchingStrategies.STRICT);
        return modelMapper;
    }
}

方式二：在启动类中直接注册 #

如果不想新建配置类，也可以直接在Spring Boot启动类中添加Bean定义：

import org.modelmapper.ModelMapper;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class YourApplication {

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

    @Bean
    public ModelMapper modelMapper() {
        return new ModelMapper();
    }
}

额外优化建议 #

Spring 4.3+版本支持构造函数自动注入，你可以省略@Autowired注解，让代码更简洁：

@Service
public class ProgrammingLanguageManager implements ProgrammingLanguageService {

    private final ProgrammingLanguageRepository programmingLanguageRepository;
    private final ModelMapper modelMapper;

    // 无需@Autowired，Spring会自动注入构造函数参数
    public ProgrammingLanguageManager(ProgrammingLanguageRepository programmingLanguageRepository,
            ModelMapper modelMapper) {
        this.programmingLanguageRepository = programmingLanguageRepository;
        this.modelMapper = modelMapper;
    }

    // 其他业务方法...
}

内容的提问来源于stack exchange，提问作者Fatih Selvi