public static Subject getSubject() {
        return (Subject) get(SUBJECT_KEY);
    }
Convenience method that simplifies retrieval of a thread-bound Subject.  If there is no
Subject bound to the thread, this method returns <tt>null</tt>.  It is merely a convenient wrapper
for the following:
<p/>
<code>return (Subject)get( SUBJECT_KEY );</code>
<p/>
This method only returns the bound value if it exists - it does not remove it
from the thread.  To remove it, one must call {@link #unbindSubject() unbindSubject()} instead.

@return the Subject object bound to the thread, or <tt>null</tt> if there isn't one bound.
@since 0.2
core/src/main/java/org/apache/shiro/util/ThreadContext.java