聊聊Spring的环境抽象Environment，以及配置@Profile使用详解（介绍profile的6种激活方式）【享学Spring】(上)

public abstract class AbstractPropertyResolver implements ConfigurablePropertyResolver {
  ...
  private String placeholderPrefix = SystemPropertyUtils.PLACEHOLDER_PREFIX; // ${
  private String placeholderSuffix = SystemPropertyUtils.PLACEHOLDER_SUFFIX; // }
  @Nullable
  private String valueSeparator = SystemPropertyUtils.VALUE_SEPARATOR; // :
  ...
}

public class PropertySourcesPropertyResolver extends AbstractPropertyResolver {
  ...
  @Nullable
  private final PropertySources propertySources; //内部持有一组PropertySource
  // 由此可以看出propertySources的顺序很重要~~~
  // 并且还能处理占位符~~~~~ resolveNestedPlaceholders支持内嵌、嵌套占位符
  @Nullable
  protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
    if (this.propertySources != null) {
      for (PropertySource<?> propertySource : this.propertySources) {
        Object value = propertySource.getProperty(key);
        if (value != null) {
          if (resolveNestedPlaceholders && value instanceof String) {
            value = resolveNestedPlaceholders((String) value);
          }
          logKeyFound(key, propertySource, value);
          return convertValueIfNecessary(value, targetValueType);
        }
      }
    }
    return null;
  }
  ...
}

public class MutablePropertySources implements PropertySources {
  // 内部确实是持有多个PropertySource
  private final List<PropertySource<?>> propertySourceList = new CopyOnWriteArrayList<>();
  public void addFirst(PropertySource<?> propertySource) {
    removeIfPresent(propertySource);
    this.propertySourceList.add(0, propertySource);
  }
  public void addLast(PropertySource<?> propertySource) {
    removeIfPresent(propertySource);
    this.propertySourceList.add(propertySource);
  }
  ... 
}

// @since 3.1
public interface Environment extends PropertyResolver {
  // 返回此环境下激活的配置文件集
  String[] getActiveProfiles();
  // 如果未设置激活配置文件，则返回默认的激活的配置文件集
  String[] getDefaultProfiles();
  // @since 5.1
  @Deprecated
  boolean acceptsProfiles(String... profiles);
  boolean acceptsProfiles(Profiles profiles);
}

public interface ConfigurableEnvironment extends Environment, ConfigurablePropertyResolver {
    // 指定该环境下的 profile 集
    void setActiveProfiles(String... profiles);
    // 增加此环境的 profile
    void addActiveProfile(String profile);
    // 设置默认的 profile
    void setDefaultProfiles(String... profiles);
    // 返回此环境的 PropertySources
    MutablePropertySources getPropertySources();
   // 尝试返回 System.getenv() 的值，若失败则返回通过 System.getenv(string) 的来访问各个键的映射
    Map<String, Object> getSystemEnvironment();
    // 尝试返回 System.getProperties() 的值，若失败则返回通过 System.getProperties(string) 的来访问各个键的映射
    Map<String, Object> getSystemProperties();
    void merge(ConfigurableEnvironment parent);
}

public abstract class AbstractEnvironment implements ConfigurableEnvironment {
  public static final String IGNORE_GETENV_PROPERTY_NAME = "spring.getenv.ignore";
  // 请参考：ConfigurableEnvironment#setActiveProfiles
  public static final String ACTIVE_PROFILES_PROPERTY_NAME = "spring.profiles.active";
  // 请参考：ConfigurableEnvironment#setDefaultProfiles
  public static final String DEFAULT_PROFILES_PROPERTY_NAME = "spring.profiles.default";
  private final Set<String> defaultProfiles = new LinkedHashSet<>(getReservedDefaultProfiles());
  // 默认的profile名称
  protected static final String RESERVED_DEFAULT_PROFILE_NAME = "default";
  ...
  protected Set<String> doGetActiveProfiles() {
    synchronized (this.activeProfiles) {
      if (this.activeProfiles.isEmpty()) {
        String profiles = getProperty(ACTIVE_PROFILES_PROPERTY_NAME);
        if (StringUtils.hasText(profiles)) {
          setActiveProfiles(StringUtils.commaDelimitedListToStringArray(
              StringUtils.trimAllWhitespace(profiles)));
        }
      }
      return this.activeProfiles;
    }
  }
  ...
}

// @since 3.1  能标注在类上、方法上~
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(ProfileCondition.class)
public @interface Profile {
  // 注意此处是个数组，也就是说可以激活多个的
  String[] value();
}

class ProfileCondition implements Condition {
  @Override
  public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
    // 因为value值是个数组，所以此处有多个值 用的MultiValueMap
    MultiValueMap<String, Object> attrs = metadata.getAllAnnotationAttributes(Profile.class.getName());
    if (attrs != null) {
      for (Object value : attrs.get("value")) {
        // 多个值中，但凡只要有一个acceptsProfiles了，那就返回true~
        if (context.getEnvironment().acceptsProfiles(Profiles.of((String[]) value))) {
          return true;
        }
      }
      return false;
    }
    return true;
  }
}