Spring PlaceholderResolver

类全路径: org.springframework.util.PropertyPlaceholderHelper.PlaceholderResolver
类作用将占位符中的内容替换成属性值.
- 假设现有属性表: user.dir = c:\home 传入参数 user.dir 会获得 c:\home

	@FunctionalInterface
	public interface PlaceholderResolver {

		/**
		 * Resolve the supplied placeholder name to the replacement value.
		 * @param placeholderName the name of the placeholder to resolve
		 * @return the replacement value, or {@code null} if no replacement is to be made
		 */
		@Nullable
		String resolvePlaceholder(String placeholderName);
	}

类图如下