• Is an API for the Java programming language that defines how a client may access a database.

• It provides methods for querying and updating data in a database.

• JDBC is oriented towards relational databases.

• The Java Platform, Standard Edition includes the JDBC API together with an ODBC implementation of the API enabling connections to any relational database that supports ODBC. This driver is native code and not Java, and is closed source.

• JDBC has been part of the Java Standard Edition since the release of JDK 1.1. The JDBC classes are contained in the Java package java.sql. Starting with version 3.0, JDBC has been developed under the Java Community Process. JSR 54 specifies JDBC 3.0 (included in J2SE 1.3), JSR 114 specifies the JDBC Rowset additions, and JSR 221 is the specification of JDBC 4.0 (included in Java SE 6).

• JDBC allows multiple implementations to exist and be used by the same application.

• The API provides a mechanism for dynamically loading the correct Java packages and registering them with the JDBC Driver Manager.

• The Driver Manager is used as a connection factory for creating JDBC connections.

• JDBC connections support creating and executing statements. These statements may be update statements such as SQL INSERT, UPDATE and DELETE or they may be query statements using the SELECT statement. Additionally, stored procedures may be invoked through a statement. Statements are one of the following types:

Statement	the statement is sent to the database server each time. (The object used for executing a static SQL statement and returning the results it produces )
PreparedStatement	the statement is cached and then the execution path is pre determined on the database server allowing it to be executed multiple times in an efficient manner. An object that represents a precompiled SQL statement.
CallableStatement	used for executing stored procedures on the database.

• Update statements such as INSERT, UPDATE and DELETE return an update count that indicates how many rows were affected in the database. These statements do not return any other information.

• Query statements return a JDBC row result set. The row result set is used to walk over the result set. Individual columns in a row are retrieved either by name or by column number. There may be any number of rows in the result set. The row result set has metadata that describes the names of the columns and their types.

• There is an extension to the basic JDBC API in the javax.sql package that allows for scrollable result sets and cursor support among other things.

• The URL used is dependent upon the particular JDBC driver. It will always begin with the "jdbc:" protocol, but the rest is up to the particular vendor. Once a connection is established, a statement must be created.

Statement stmt = conn.createStatement(); stmt.executeUpdate( "INSERT INTO MyTable( name ) VALUES ( 'my name' ) " );

 

 

Data is retrieved from the database using a database query mechanism. The example below shows creating a statement and executing a query.

 

Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery( "SELECT * FROM MyTable" ); while ( rs.next() ) { int numColumns = rs.getMetaData().getColumnCount(); for ( int i = 1 ; i <= numColumns ; i++ ) { //Column numbers start at 1. //Also there are many methods on the result set to return // the column as a particular type. Refer to the Sun documentation // for the list of valid conversions. System.out.println( "COLUMN " + i + " = " + rs.getObject(i) ); } } rs.close(); stmt.close();

 

Typically, however, it would be rare for a seasoned Java programmer to code in such a fashion. The usual practice would be to abstract the database logic into an entirely different class and to pass preprocessed strings (perhaps derived themselves from a further abstracted class) containing SQL statements and the connection to the required methods. Abstracting the data model from the application code makes it more likely that changes to the application and data model can be made independently.

An example of a PreparedStatement query. Using conn and class from first example.

 

PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement( "SELECT i.*, j.* FROM Omega i, Zappa j" + "WHERE i = ? AND j = ?" ); // In the prepared statement ps, the question mark denotes variable input, // which can be passed through a parameter list, for example. // The following replaces the question marks, // with the string or int, before sending it to SQL. // The first parameter corresponds to the nth occurrence of the ?, // the second parameter tells Java to replace it with // the second item. ps.setString(1, "Poor Yorick"); ps.setInt(2, 8008); // The ResultSet rs, receives the SQL Query response. rs = ps.executeQuery(); while ( rs.next() ) { int numColumns = rs.getMetaData().getColumnCount(); for ( int i = 1 ; i <= numColumns ; i++ ) { //Column numbers start at 1. //Also there are many methods on the result set to return // the column as a particular type. Refer to the Sun documentation // for the list of valid conversions. System.out.println( "COLUMN " + i + " = " + rs.getObject(i) ); } } } catch (SQLException e) { // typical exception handling here } finally { // note that these resources need to be closed in the finally clause to avoid try { // a resource leak since it should always be called rs.close(); ps.close(); } catch( SQLException e){} // handle errors here or ignore them }

 

For an example of a CallableStatement (to call stored procedures in the database), see the JDBC API Guide.