title: how to use the InputSupplier or OutputSupplier api of Guava?
body: <p>I am new to the guava library, and I am quite confused with the InputSupplier and OutputSupplier. According to the javadoc, they are just factories for InputStream and OutputStream respectively. However, I don't see anything quite useful of these two interface, could anyone show me a example why I should use these two APIs besides for higher abstraction?</p>