# 2.1. 介绍

不幸的是，Java 的标准 `java.net.URL` 类和各种 `URL` 前缀的标准处理程序不足以满足对低级资源的所有访问。例如，没有可用于访问需要从类路径或相对于 `ServletContext` 获取的资源的标准化`URL`实现。虽然可以为专门的 URL 前缀注册新的处理程序（类似于`http:`等前缀的现有处理程序），但这通常相当复杂，并且 URL 接口仍然缺乏一些理想的功能，例如检查是否存在的方法所指向的资源的名称。


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