Question

I understand that you cannot access java.io.File from a GAE app (its restricted). However, I remember reading somewhere that it’s possible to have access to anything in your WAR (perhaps anything under WEB-INF/?).

So I ask: is there a way to access a file inside your WAR from a GAE app? In other words, if I deploy a WAR with the following structure:

MyApp/
    WEB-INF/
        web.xml
        appengine-web.xml
        ...etc.

        my-special-config.xml

Is there any way for me to read my-special-config.xml from inside my GAE app? If so, how and with what classes? I see in the GAE SDK that there is an AppEngineFile, and wondering if I can use this. Thanks in advance.

Answer 1

Check out the dev guide here:

The Filesystem

A Java application cannot use any classes used to write to the filesystem, such as java.io.FileWriter. An application can read its own files from the filesystem using classes such as java.io.FileReader. An application can also access its own files as "resources", such as with Class.getResource() or ServletContext.getResource().

Only files that are considered "resource files" are accessible to the application via the filesystem. By default, all files in the WAR are "resource files." You can exclude files from this set using the appengine-web.xml file.

Sample code to read resource file under classpath in POJO class:

String file = "/WEB-INF/my-special-config.xml";
InputStream in = getClass().getResourceAsStream(file);

Sample code to read resource file under classpath in Servlet class:

String file = "/WEB-INF/my-special-config.xml";
InputStream in = getServletContext().getResourceAsStream(file);