Accessing Relational Data with JDBC

The JDBC API is a Java API for accessing relational (tabular) data, especially those stores in a relational database. JDBC has been an integral part of Sun's Java Development Kit since 1.1, and is supported by virtually all relational database vendors.
 

Pieces of the puzzle

1. The Java Development Kit. The JDK contains the JDBC API interfaces as well as the JDBC driver manager. The JDBC API interfaces allows Java applications to access data with a uniform vendor independent fashion. The JDBC driver manager is responsible for finding and loading the correct JDBC driver based on the connection string.
2. The JDBC driver for a particular brand of relational database. The JDBC driver contain classes that implement the standard JDBC interfaces. The JDBC driver is responsible for actually communicating with the database and carry out SQL commands and queries. JDBC drivers can be implemented in four typical ways:
1. JDBC-ODBC bridge plus ODBC driver: The JDK contains a JDBC-ODBC bridge which takes JDBC calls from a Java application and turns them into ODBC calls, utilizing the ODBC driver that are installed on the same machine.
2. Native-API partly-Java driver: This kind of drivers take JDBC calls from a Java application and turns them into calls to the database vendor's native client access software that are installed on the same machine.
3. JDBC-Net pure Java driver: This kind of drivers take JDBC calls from a Java application and turns them into a vendor independent net protocol. At the other end of the network, the protocol is translated by a middleware server into vendor specific protocol.
4. Native-protocol pure Java driver: This kind of drivers takes called from Java applications and turns them into vendor specific protocols.

The JDBC API is easy to write to

import java.sql.*;

public class employee {
  public static void main(String[] args) {
    try {
      // Load the driver class
      Class.forName("postgresql.Driver");

      // Make a connection
      Connection conn = DriverManager.getConnection
        ("jdbc:postgresql://myhost/mydatabase", "myuserid", "mypassword");

      // Create a SQL statement
      Statement stmt = conn.createStatement();

      // Execute a query
      ResultSet rs = stmt.executeQuery
        ("select first_name, hobby from employee");

      // Fetch the data from the query result set
      while (rs.next()) {
        System.out.println("first_name: " + rs.getString(1));
        System.out.println("hobby: " + rs.getString(2));
      }
    } catch (Exception e) {
      System.out.println("Exception: " + e.getMessage());
    }
  }
}

Benefits of JDBC

1. Wide availability. Since JDBC is included with the Java Platform, it is available everywhere Java is available. This makes the Java application that uses the JDBC API portable to a lot of platforms.
2. Vendor independence. Since Java applications that uses the JDBC API uses only interfaces from the JDBC packages, the code has a high likelihood of being portable from one vendors database to another's.
3. Multi-tiered applications. The JDBC API encourages Java applications to be designed into multiple tiers, separating business logic from presentation logic. This will aid the scalability, reliability and maintainability of the application tremendously.
4. Robustness, security, automatically downloadable code, and other Java pluses. By virtual of being written in Java, the JDBC application automatically enjoys these benefits that Java offers.

JDBC is the basis for other technologies

JDBC 2.0

The JDBC API 2.0 standard extension (javax.sql.*) offers JNDI support, connection pooling, and distributed transactions.

More information

http://java.sun.com/products/jdbc/: The official Sun Java JDBC site.