JDBC is an API specification developed by Sun Microsystems that defines a uniform interface for accessing various relational databases. JDBC is a core part of the Java platform and is included in the standard JDK distribution.
The primary function of the JDBC API is to provide a means for the developer to issue SQL statements and process the results in a consistent, database-independent manner. JDBC provides rich, object-oriented access to databases by defining classes and interfaces that represent objects such as:
Database connections SQL statements Result Set Database metadata Prepared statements Binary Large Objects (BLOBs) Character Large Objects (CLOBs) Callable statements Database drivers Driver manager The JDBC API uses a Driver Manager and database-specific drivers to provide transparent connectivity to heterogeneous databases. The JDBC driver manager ensures that the correct driver is used to access each data source. The Driver Manager is capable of supporting multiple concurrent drivers connected to multiple heterogeneous databases. The location of the driver manager with respect to the JDBC drivers and the servlet is shown in Figure 1.
Layers of the JDBC Architecture
A JDBC driver translates standard JDBC calls into a network or database protocol or into a database library API call that facilitates communication with the database. This translation layer provides JDBC applications with database independence. If the back-end database changes, only the JDBC driver need be replaced with few code modifications required. There are four distinct types of JDBC drivers.
Type 1 JDBC-ODBC Bridge. Type 1 drivers act as a "bridge" between JDBC and another database connectivity mechanism such as ODBC. The JDBC- ODBC bridge provides JDBC access using most standard ODBC drivers. This driver is included in the Java 2 SDK within the sun.jdbc.odbc package. In this driver the java statements are converted to a jdbc statements. JDBC statements calls the ODBC by using the JDBC-ODBC Bridge. And finally the query is executed by the database. This driver has serious limitation for many applications. (See Figure 2.)
Type 1 JDBC Architecture
Type 2 Java to Native API. Type 2 drivers use the Java Native Interface (JNI) to make calls to a local database library API. This driver converts the JDBC calls into a database specific call for databases such as SQL, ORACLE etc. This driver communicates directly with the database server. It requires some native code to connect to the database. Type 2 drivers are usually faster than Type 1 drivers. Like Type 1 drivers, Type 2 drivers require native database client libraries to be installed and configured on the client machine. (See Figure 3.)