Spring Boot将yaml映射为Java对象始终为null问题求助

1. AppProperties配置错误修复 #

1.1 YAML结构层级错误 #

你的application.yaml中将oauth2节点错误放到了app.auth层级下，但AppProperties类中auth和oauth2是平级属性，同属于app的直接子节点，同时authorizedRedirectUris的缩进层级也不正确，修改后的对应配置如下：

app:
  auth:
    tokenSecret: 04ca023b39512e46d0c2cf4b48d5aac61d34302994c87ed4eff225dcf3b0a218739f3897051a057f9b846a69ea2927a587044164b7bae5e1306219d50b588cb1
    tokenExpirationMsec: 864000000
  oauth2:
    # After successfully authenticating with the OAuth2 Provider,
    # we'll be generating an auth token for the user and sending the token to the
    # redirectUri mentioned by the client in the /oauth2/authorize request.
    # We're not using cookies because they won't work well in mobile clients.
    authorizedRedirectUris:
      - http://localhost:8080/oauth2/redirect

提示：YAML语法严格要求缩进必须使用空格，不能用Tab键，同级节点缩进保持一致，否则会解析失败。

1.2 配置类构造与字段错误 #

@ConfigurationProperties绑定要求配置类必须有可用的无参构造函数，同时绑定的字段不能用final修饰（final字段无法调用setter赋值）：

@ConfigurationProperties(prefix = "app")
@Data
@NoArgsConstructor // 新增无参构造
public class AppProperties {
    // 去掉字段的final修饰符
    private Auth auth = new Auth();
    private OAuth2 oauth2 = new OAuth2();
    
    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public static class Auth {
        private String tokenSecret;
        private long tokenExpirationMsec;
    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public static final class OAuth2 {
        private List<String> authorizedRedirectUris = new ArrayList<>();
    }
}

2. ClientConfig配置错误修复 #

2.1 支持YAML格式的PropertySource #

Spring默认的@PropertySource仅支持加载.properties格式文件，要加载YAML需要自定义解析工厂：
第一步：新建YAML解析工厂类

public class YamlPropertySourceFactory implements PropertySourceFactory {
    @Override
    public PropertySource<?> createPropertySource(String name, EncodedResource resource) throws IOException {
        YamlPropertiesFactoryBean factory = new YamlPropertiesFactoryBean();
        factory.setResources(resource.getResource());
        Properties properties = factory.getObject();
        return new PropertiesPropertySource(resource.getResource().getFilename(), properties);
    }
}

第二步：修改ClientConfig注解，指定自定义工厂，同时确保路径正确：

@ConfigurationProperties
@PropertySource(value = "classpath:clientConfig.yaml", factory = YamlPropertySourceFactory.class)
@Data
public class ClientConfig {
    private Urls urls;

    @Data
    public static class Urls {
        private String user;
    }
}

2.2 配置文件路径校验 #

确保clientConfig.yaml放在项目src/main/resources根目录下，和注解中配置的classpath:clientConfig.yaml路径匹配。 #

3. 注入方式校验 #

配置类必须从Spring容器中获取，不能手动new实例，正确的注入方式如下：

@Service // 或其他被Spring管理的组件类
public class YourBusinessService {
    @Autowired
    private AppProperties appProperties;
    @Autowired
    private ClientConfig clientConfig;

    public void testConfig() {
        // 此处读取的配置就不会为null
        System.out.println(appProperties.getAuth().getTokenSecret());
        System.out.println(clientConfig.getUrls().getUser());
    }
}

内容的提问来源于stack exchange，提问作者roberto