#5 Apache HttpClient 4.1, MS SQL Server JDBC driver, database shutdown handling, connection pool work

[Mark Pollard]

1. Changes to support the following environment: Hibernate 4.2.6 (with schema validation enabled [database metadata]), Microsoft SQL Server, Microsoft SQL Server JDBC driver (sqljdbc4.jar)
   a. ConnectionPrepareStatementCommand: ObjectOutput.writeUTF() is limited to 65,535 bytes, so output raw bytes
   b. RowPacket: SQL Server JDBC driver small int handling
   c. StreamingResultSet: SQL Server JDBC driver clob and timestamp handling
2. Convert VJDBC to use Apache HttpClient 4.1
3. Use KeepAliveTimerTask across all connections
4. Generally named all threads and set to daemon
5. Closed ResultSet in TableCache
6. Eliminated several finalize() statements
7. Converted isValid() from sleep-based approach to wait
8. Improved handling of unexpected database shutdown (see usage of ConnectionClosedException, UnknownConnectionException)
9. Similar to RequestEnhancer pattern, introduced ResponseHandler to allow inspection of response headers
10. Allow HTTP SSL hostname and certificate verification to be disabled
11. Support public key pinning for HTTP SSL host verification (see https://www.owasp.org/index.php/Certificate_and_Public_Key_Pinning)
12. Ensure only a single DBCP connection pool is instantiated

Changes since original submission on 2015-10-27, after load and stress testing of product using VJDBC:

1. Counteract Java [de]serialization code that shifts Timestamps; this contradicts our desire to universally maintain timestamps as UTC even when VJDBC clients and server are in different time-zones -- see TimestampParameter, RowPacket, StreamingResultSet and TimeUtil
2. Update VJDBC to use the Apache Commons dbcp 2.1.1 and pool 2.4.2
3. Added server-side "lack of use" connection closing (PingCommand does not count towards "use")
4. Added ability for HTTP sink to seamlessly reconnect on UnknownConnectionException (in certain conditions), thereby allowing server to be restarted and clients to generally not notice the interruption -- see DecoratedCommandSink
5. Configure HTTP connections to close after 30 seconds lifespan, ahead of the Tomcat 1 minute connection idle timeout [need to make this configurable]

[Mark Pollard]

This was based on revision 72