Java Database Connectivity

JDBC is a Java-based data access technology (Java Standard Edition platform) from Sun Microsystems, Inc.. It is an acronym as it is unofficially referred to as Java Database Connectivity, with DB being universally recognized as the abbreviation for database. This technology 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. A JDBC-to-ODBC bridge enables connections to any ODBC-accessible data source in the JVM host environment.

Functionality

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 may be update statements such as SQL's CREATE, INSERT, UPDATE and DELETE, or they may be query statements such as SELECT. Additionally, stored procedures may be invoked through a JDBC connection. JDBC represents statements using one of the following classes:

• Statement – the statement is sent to the database server each and every time.
• 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.
• 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.

JDBC connections are often managed via a connection pool rather than obtained directly from the driver. Examples of connection pools include BoneCP, C3P0 and DBCP

JDBC drivers

JDBC drivers are client-side adapters (installed on the client machine, not on the server) that convert requests from Java programs to a protocol that the DBMS can understand.

Types

There are commercial and free drivers available for most relational database servers. These drivers fall into one of the following types:

• Type 1 that calls native code of the locally available ODBC driver.
• Type 2 that calls database vendor native library on a client side. This code then talks to database over network.
• Type 3, the pure-java driver that talks with the server-side middleware that then talks to database.
• Type 4, the pure-java driver that uses database native protocol.

There is also a type called internal JDBC driver, driver embedded with JRE in Java-enabled SQL databases. It's used for Java stored procedures. This does not belong to the above classification, although it would likely be either a type 2 or type 4 driver (depending on whether the database itself is implemented in Java or not). An example of this is the KPRB driver supplied with Oracle RDBMS. "jdbc:default:connection" is a relatively standard way of referring making such a connection (at least Oracle and Apache Derby support it). The distinction here is that the JDBC client is actually running as part of the database being accessed, so access can be made directly rather than through network protocols.