File path/name from InputStream

Question

How to obtain File Path/Name from an InputStream in Java ?

Answer 1

It's not possible. (not from the FileInputStream in the Java API). The FileInputStream constructor does not store this information in any field:

public FileInputStream(File file) throws FileNotFoundException {
    String name = (file != null ? file.getPath() : null);
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
        security.checkRead(name);
    }
        if (name == null) {
            throw new NullPointerException();
        }
    fd = new FileDescriptor();
    open(name);
    }

Answer 2

You can't because the InputStream might not have been a file or path. You can implement your own InputStream that generates data on the fly

Answer 3

Two important Object Oriented Design principles prevent you from doing what you're asking: abstraction and encapsulation.

• Abstraction is the process of defining a general concept that has only the details necessary for its use in a particular context (more details here). In this situation, the abstraction is InputStream, which is a general interface that can provide bytes, regardless of the source of those bytes. The abstraction of an InputStream has no concept of a file path; that's only relevant to particular implementations of InputStream.
• Encapsulation is the process of hiding implementation details of a class from consumers/users of that class. In this particular situation, FileInputStream encapsulates the details of the file it is reading from, because as an InputStream that information is not relevant to the usage. The path instance field is encapsulated and as such unavailable to users of the class.

Having said that, it is possible to access the path variable if you are willing to accept some important limitations. Basically, the gist is that you can check if the InputStream is, in fact, an instance of FileInputStream and, if so, use reflection to read the path instance field. I'll leave out the details of doing that access since it's easily discoverablein the java.lang.Class Java docs and online, and not really a generally good thing to do in most contexts. Since the question doesn't provide a context about why, it's hard to offer any more reasonable approaches.