DOCSP-26393: FAQ entry for NoClassDefFoundError (#425)

* DOCSP-26393: FAQ entry for NoClasDefFoundError

Author: Chris Cho

source/api-documentation.txt

@@ -1,3 +1,5 @@
+.. _java-api-landing:
+
 =================
 API Documentation
 =================

source/faq.txt

@@ -146,6 +146,30 @@ When ``MongoClient.close()`` is called by any thread, the driver
 closes all idle sockets and closes all sockets that are in
 use as they are returned to the pool.
 
+How do I prevent the "java.lang.NoClassDefFoundError: com/mongodb/MongoClient" error?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You may encounter a ``java.lang.NoClassDefFoundError`` exception when your
+Java runtime environment cannot locate a class file at runtime. When you
+attempt to run application code that uses the {+driver-long+}, you must include
+the appropriate driver JAR files on the classpath.
+
+If you receive this error after adding the {+driver-short+} JAR files to
+your classpath, check the following items in your environment:
+
+- The JAR files exist in the locations specified by the classpath.
+- The classpath syntax is correct.
+- If you define the classpath in an environment variable, the Java runtime
+  environment uses that variable.
+- If you use a dependency manager, it does not report any unresolvable conflicts.
+
+.. tip::
+
+   This error contains the package and class name, which can help you identify
+   which driver JAR may be missing from your classpath. To locate the
+   driver JAR that the error refers to, check each of the entries in the
+   :ref:`API documentation <java-api-landing>`.
+
 
 How do I prevent the "IllegalArgumentException: Invalid BSON field name" error?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~