I've seen some Spring code that read config files and other resources directly off the runtime classpath using the classpath:/some/path/to/resource URL protocol.
Is this a Spring construct or a Java construct?
I can't find any documentation besides this question - URL to load resources from the classpath in Java, which doesn't indicate either way.
If it's a Java construct, can anyone point me to its official documentation?
Well you can always register URL handlers. Java also has a file:/// and jar: handler. Also class.getResource will by default read from the classpath.
http://code.google.com/p/madura-classpath-protocol-handler/
apparently it is a spring feature.
"You can see these standard handlers, and associated implementation classes,in the JDK's RT.JAR file. Look for classes whose fully-qualified name starts with sun.net.www.protocol.For example,the class sun.net.www.protocol.http.Handler defines the HTTP protocol handler. Class sun.net.www.protocol.ftp.Handler defines the FTP protocol handler class."
http://java.sun.com/developer/onlineTraining/protocolhandlers/
"Exception in thread "main" java.net.MalformedURLException: unknown protocol: classpath" (says java 1.6)
类路径：特定于spring。Spring 的资源解析机制（即PathMatchingResourcePatternResolver或其他实现）知道"classpath:"和“classpath*:”前缀。
它接受并解析为ClassPathResource对象，这些对象恰好实现了 springsResource接口。
Resource接口，除其他外，有一个方法getInputStream()可以用来获取内容，而不必知道它是什么类型的资源。
这与任何 URL 协议处理完全分开，因此您不一定能够直接将其添加为协议处理程序。
但是，您可以将ClassPathResource类本身用作协议处理程序的一部分。