Class AbstractJDBCDatabaseInterface

java.lang.Object
com.mckoi.database.jdbcserver.AbstractJDBCDatabaseInterface
All Implemented Interfaces:
DatabaseInterface
Direct Known Subclasses:
JDBCDatabaseInterface

public abstract class AbstractJDBCDatabaseInterface extends Object implements DatabaseInterface
An abstract implementation of JDBCDatabaseInterface that provides a connection between a single DatabaseConnection and a DatabaseInterface implementation.

This receives database commands from the JDBC layer and dispatches the queries to the database system. It also manages ResultSet maps for query results.

This implementation does not handle authentication (login) / construction of the DatabaseConnection object, or disposing of the connection.

This implementation ignores the AUTO-COMMIT flag when a query is executed. To implement AUTO-COMMIT, you should 'commit' after a command is executed.

SYNCHRONIZATION: This interface is NOT thread-safe. To make a thread-safe implementation use the LockingMechanism.

See JDBCDatabaseInterface for a standard server-side implementation of this class.

Author:
Tobias Downer
  • Constructor Details

    • AbstractJDBCDatabaseInterface

      public AbstractJDBCDatabaseInterface(Database database)
      Sets up the database interface.
  • Method Details

    • init

      protected final void init(User user, DatabaseConnection connection)
      Initializes this database interface with a User and DatabaseConnection object. This would typically be called from inside an authentication method, or from 'login'. This must be set before the object can be used.
    • getDatabase

      protected final Database getDatabase()
      Returns the Database that is the context of this interface.
    • getUser

      protected final User getUser()
      Returns the User object for this connection.
    • Debug

      public final DebugLogger Debug()
      Returns a DebugLogger object that can be used to log debug messages against.
    • getDatabaseConnection

      protected final DatabaseConnection getDatabaseConnection()
      Returns the DatabaseConnection objcet for this connection.
    • clearResultSetMap

      protected final void clearResultSetMap()
      Clears the contents of the result set map. This removes all result_id ResultSetInfo maps.
    • handleExecuteThrowable

      protected final SQLException handleExecuteThrowable(Throwable e, SQLQuery query)
      Wraps a Throwable thrown by the execution of a query in DatabaseConnection with an SQLException and puts the appropriate error messages to the debug log.
    • internalDispose

      protected final void internalDispose()
      Disposes all resources associated with this object. This clears the ResultSet map, and NULLs all references to help the garbage collector. This method would normally be called from implementations of the 'dispose' method.
    • checkNotDisposed

      protected final void checkNotDisposed() throws SQLException
      Checks if the interface is disposed, and if it is generates a friendly SQLException informing the user of this.
      Throws:
      SQLException
    • pushStreamableObjectPart

      public void pushStreamableObjectPart(byte type, long object_id, long object_length, byte[] buf, long offset, int length) throws SQLException
      Description copied from interface: DatabaseInterface
      Pushes a part of a streamable object from the client onto the server. The server stores the large object for use with a future query. For example, a sequence of with a query with large objects may operate as follows;

       1) Push 100 MB object (id = 104)
       2) execQuery with query that contains a streamable object with id 104
       

      Note that the client may push any part of a streamable object onto the server, however the streamable object must have been completely pushed for the query to execute correctly. For example, an 100 MB byte array may be pushed onto the server in blocks of 64K (in 1,600 separate blocks).

      Specified by:
      pushStreamableObjectPart in interface DatabaseInterface
      Parameters:
      type - the StreamableObject type (1 = byte array, 2 = char array)
      object_id - the identifier of the StreamableObject for future queries.
      object_length - the total length of the StreamableObject.
      buf - the byte[] array representing the block of information being sent.
      offset - the offset into of the object of this block.
      length - the length of the block being pushed.
      Throws:
      SQLException
    • execQuery

      public QueryResponse execQuery(SQLQuery query) throws SQLException
      Description copied from interface: DatabaseInterface
      Executes the query and returns a QueryResponse object that describes the result of the query. The QueryResponse object describes the number of rows, describes the columns, etc. This method will block until the query has completed. The QueryResponse can be used to obtain the 'result id' variable that is used in subsequent queries to the engine to retrieve the actual result of the query.
      Specified by:
      execQuery in interface DatabaseInterface
      Throws:
      SQLException
    • getResultPart

      public ResultPart getResultPart(int result_id, int row_number, int row_count) throws SQLException
      Description copied from interface: DatabaseInterface
      Returns a part of a result set. The result set part is referenced via the 'result id' found in the QueryResponse. This is used to read parts of the query once it has been found via 'execQuery'.

      The returned List object contains the result requested.

      If the result contains any StreamableObject objects, then the server allocates a channel to the object via the 'getStreamableObjectPart' and the identifier of the StreamableObject. The channel may only be disposed if the 'disposeStreamableObject' method is called.

      Specified by:
      getResultPart in interface DatabaseInterface
      Throws:
      SQLException
    • disposeResult

      public void disposeResult(int result_id) throws SQLException
      Description copied from interface: DatabaseInterface
      Disposes of a result of a query on the server. This frees up server side resources allocated to a query. This should be called when the ResultSet of a query closes. We should try and use this method as soon as possible because it frees locks on tables and allows deleted rows to be reclaimed.
      Specified by:
      disposeResult in interface DatabaseInterface
      Throws:
      SQLException
    • getStreamableObjectPart

      public StreamableObjectPart getStreamableObjectPart(int result_id, long streamable_object_id, long offset, int len) throws SQLException
      Description copied from interface: DatabaseInterface
      Returns a section of a large binary or character stream in a result set. This is used to stream large values over the connection. For example, if a row contained a multi megabyte object and the client is only interested in the first few characters and the last few characters of the stream. This would require only a few queries to the database and the multi- megabyte object would not need to be downloaded to the client in its entirety.
      Specified by:
      getStreamableObjectPart in interface DatabaseInterface
      Throws:
      SQLException
    • disposeStreamableObject

      public void disposeStreamableObject(int result_id, long streamable_object_id) throws SQLException
      Description copied from interface: DatabaseInterface
      Disposes a streamable object channel with the given identifier. This should be called to free any resources on the server associated with the object. It should be called as soon as possible because it frees locks on the tables and allows deleted rows to be reclaimed.
      Specified by:
      disposeStreamableObject in interface DatabaseInterface
      Throws:
      SQLException
    • finalize

      public void finalize() throws Throwable
      Clean up if this object is GC'd.
      Overrides:
      finalize in class Object
      Throws:
      Throwable