A stored procedure is a group of SQL statements that form a logical unit and perform a particular task, and they are used to encapsulate a set of operations or queries to execute on a database server. For example, operations on an employee database (hire, fire, promote, lookup) could be coded as stored procedures executed by application code. Stored procedures can be compiled and executed with different parameters and results, and they may have any combination of input, output, and input/output parameters.

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Note:   Stored procedures are supported by most DBMSs, but there is a fair amount of variation in their syntax and capabilities. For this reason, this simple example of what a stored procedure looks like and how it is invoked from JDBC is not intended to be run.

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This simple stored procedure has no parameters. Even though most stored procedures do something more complex than this example, it serves to illustrate some basic points about them. As previously stated, the syntax for defining a stored procedure is different for each DBMS. For example, some use   begin . . . end ,  or other keywords to indicate the beginning and ending of the procedure definition. In some DBMSs, the following SQL statement creates a stored procedure:

create procedure SHOW_SUPPLIERS
as
select SUPPLIERS.SUP_NAME, COFFEES.COF_NAME
from SUPPLIERS, COFFEES
where SUPPLIERS.SUP_ID = COFFEES.SUP_ID
order by SUP_NAME

The following code puts the SQL statement into a string and assigns it to the variable createProcedure, which we will use later:

String createProcedure = "create procedure SHOW_SUPPLIERS " +
			 "as " +
			 "select SUPPLIERS.SUP_NAME, COFFEES.COF_NAME " +
			 "from SUPPLIERS, COFFEES " +
			 "where SUPPLIERS.SUP_ID = COFFEES.SUP_ID " +
			 "order by SUP_NAME";

The following code fragment uses the Connection object con to create a Statement object, which is used to send the SQL statement creating the stored procedure to the database:

Statement stmt = con.createStatement();
stmt.executeUpdate(createProcedure);

The procedure SHOW_SUPPLIERS is compiled and stored in the database as a database object that can be called, similar to the way you would call a method.

Calling a Stored Procedure from JDBC

JDBC allows you to call a database stored procedure from an application written in the Java programming language. The first step is to create a CallableStatement object. As with Statement and PreparedStatement objects, this is done with an open Connection object. A callableStatement object contains a call to a stored procedure; it does not contain the stored procedure itself. The first line of code below creates a call to the stored procedure SHOW_SUPPLIERS using the connection con. The part that is enclosed in curly braces is the escape syntax for stored procedures. When the driver encounters "{call SHOW_SUPPLIERS}", it will translate this escape syntax into the native SQL used by the database to call the stored procedure named SHOW_SUPPLIERS.

CallableStatement cs = con.prepareCall("{call SHOW_SUPPLIERS}");
ResultSet rs = cs.executeQuery();

The ResultSet rs will be similar to the following:

SUP_NAME			COF_NAME
----------------		-----------------------
Acme, Inc.			Colombian
Acme, Inc.			Colombian_Decaf
Superior Coffee			French_Roast
Superior Coffee			French_Roast_Decaf
The High Ground			Espresso

Note that the method used to execute cs is executeQuery because cs calls a stored procedure that contains one query and thus produces one result set. If the procedure had contained one update or one DDL statement, the method executeUpdate would have been the one to use. It is sometimes the case, however, that a stored procedure contains more than one SQL statement, in which case it will produce more than one result set, more than one update count, or some combination of result sets and update counts. In this case, where there are multiple results, the method execute should be used to execute the CallableStatement .

The class CallableStatement is a subclass of PreparedStatement, so a CallableStatement object can take input parameters just as a PreparedStatement object can. In addition, a CallableStatement object can take output parameters, or parameters that are for both input and output. INOUT parameters and the method execute are used rarely.