MC365 JDBC and Server-Side Programming: Updating a database via JDBC & Connection Pooling

Today We Will Cover: Prepared Statements Performing Updates and Inserts in JDBC Connection Pooling Stored Procedures

Prepared Statements –A PreparedStatement is a subinterface of Statement that offers several benefits:PreparedStatement The contained SQL is sent to the database and compiled or prepared beforehand. From this point on, the prepared SQL is sent and this step is bypassed. The more dynamic Statement requires this step on every execution. Depending on the DB engine, the SQL may be cached and reused even for a different PreparedStatement and most of the work is done by the DB engine rather than the driver. –A PreparedStatement can take IN parameters, which act much like arguments to a method, for column values. –PreparedStatements deal with data conversions that can be error prone in straight ahead, built on the fly SQL; handling quotes and dates in a manner transparent to the developer, for example.

JDBC Updates and Inserts Must use executeUpdate method instead of executeQuery for inserts, updates and deletes –executeUpdate() returns an int containing the affected row count for INSERT, UPDATE, or DELETE statements, or zero for SQL statements that do not return anything. Example of a JDBC Update Notes/JDBCUpdate.java Notes/JDBCUpdate.java Example of a JDBC Insert Notes/JDBCInsert.java Notes/JDBCInsert.java Checking for nulls from a Select –To do this simply check the ResultSet for null after performing a Select statement.

Connection Pooling What is connection pooling? –Connection pooling is a technique used for managing server resources. The program does this by making a limited set of connections to the database. –Clients or servlets go through this connection pool to get a connection to the database. –The connection pool class manages connections that are in use and ones that are available. Why do we use it? –Connecting to a database is one of the most resource-intensive processes. It can take a long time and really slow down your server if a large number of connections are made. In fact, it can even stall your server. –The biggest benefit of connection pooling is that it creates the connections in advance. –When a servlet needs a connection, it is already available. This is much more efficient than having each servlet make its own connection. –In addition, it limits the number of connections made to the db. Many servlets can share a small set of connections because once they use the connection, they can release it fairly quickly.

Connection Pooling Some app servers have built-in connection pooling. You can also write your own or find shareware code online. Here is an example of a class that manages connection pooling that you can use: Notes/ConnectionPool.java Notes/ConnectionPool.java Here is an example of a servlet using this ConnectionPool class: Notes/ConnectionPoolServlet.java Notes/ConnectionPoolServlet.java

Stored Procedures What are they? –These are basically SQL statements, or a set of SQL statements, that are stored directly on the database. Why do we use them? –Offers a lot more flexibility. –Leaves the SQL coding the DBA. This is a true separation of the data layer. –Even more efficient. Examples Notes/SQLExamples.doc Notes/SQLExamples.doc