@EnableConfigurationProperties 跟 @ConfigurationProperties 的使用

@ConfigurationProperties 可以 将application.properties 以指定前缀的属性应用到指定的类。

@EnableConfigurationProperties 导入启用的属性类

以mybatis的自动导入的源代码为例：

// 相当于<beans>
@org.springframework.context.annotation.Configuration
// 相当于 Class.forName("org.apache.ibatis.session.SqlSessionFactory") 有异常说明不存在
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
// 相当于 beanFactory.getBeanByType(javax.sql.DataSource.class)
@ConditionalOnBean(DataSource.class)
// 启用配置属性
@EnableConfigurationProperties(MybatisProperties.class)
// 顺序在DataSourceAutoConfiguration.class之后
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration {

  private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class);

  private final MybatisProperties properties;

  private final Interceptor[] interceptors;

  private final ResourceLoader resourceLoader;

  private final DatabaseIdProvider databaseIdProvider;

  private final List<ConfigurationCustomizer> configurationCustomizers;

  public MybatisAutoConfiguration(MybatisProperties properties,
                                  ObjectProvider<Interceptor[]> interceptorsProvider,
                                  ResourceLoader resourceLoader,
                                  ObjectProvider<DatabaseIdProvider> databaseIdProvider,
                                  ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) {
    this.properties = properties;
    this.interceptors = interceptorsProvider.getIfAvailable();
    this.resourceLoader = resourceLoader;
    this.databaseIdProvider = databaseIdProvider.getIfAvailable();
    this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable();
  }


}

@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX)
public class MybatisProperties {

  public static final String MYBATIS_PREFIX = "mybatis";

  /**
   * Location of MyBatis xml config file.
   */
  private String configLocation;

  /**
   * Locations of MyBatis mapper files.
   */
  private String[] mapperLocations;

  /**
   * Packages to search type aliases. (Package delimiters are ",; \t\n")
   */
  private String typeAliasesPackage;

  /**
   * Packages to search for type handlers. (Package delimiters are ",; \t\n")
   */
  private String typeHandlersPackage;

  /**
   * Indicates whether perform presence check of the MyBatis xml config file.
   */
  private boolean checkConfigLocation = false;

  /**
   * Execution mode for {@link org.mybatis.spring.SqlSessionTemplate}.
   */
  private ExecutorType executorType;

  /**
   * Externalized properties for MyBatis configuration.
   */
  private Properties configurationProperties;

  /**
   * A Configuration object for customize default settings. If {@link #configLocation}
   * is specified, this property is not used.
   */
  @NestedConfigurationProperty
  private Configuration configuration;

}

mybatis.configLocation

mybatis.mapperLocations

mybatis.typeAliasesPackage

mybatis.configuration

如果嵌套属性  要加 @NestedConfigurationProperty