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2.2. JDBC Basics

Before we discuss all of the individual components of JDBC, let's look at a simple example that incorporates most of the major pieces of JDBC functionality. Example 2-1 loads a driver, connects to the database, executes some SQL, and retrieves the results. It also keeps an eye out for any database-related errors.

Example 2-1. A Simple JDBC Example

import java.sql.*;

public class JDBCSample {

  public static void main(java.lang.String[] args) {
    try {
      // This is where we load the driver
      Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
    } 
    catch (ClassNotFoundException e) {
      System.out.println("Unable to load Driver Class");
      return;
    }
  
    try {
      // All database access is within a try/catch block. Connect to database,
      // specifying particular database, username, and password
      Connection con = DriverManager.getConnection("jdbc:odbc:companydb",
                       "", "");
   
      // Create and execute an SQL Statement
      Statement stmt = con.createStatement();
      ResultSet rs = stmt.executeQuery("SELECT FIRST_NAME FROM EMPLOYEES");

      // Display the SQL Results
      while(rs.next()) {
        System.out.println(rs.getString("FIRST_NAME"));
      }

      // Make sure our database resources are released
      rs.close();
      stmt.close();
      con.close();

    } 
    catch (SQLException se) {
      // Inform user of any SQL errors
      System.out.println("SQL Exception: " + se.getMessage());
      se.printStackTrace(System.out);
    } 
  } 
}

Example 2-1 starts out by loading a JDBC driver class (in this case, Sun's JDBC-ODBC Bridge). Then it creates a database connection, represented by a Connection object, using that driver. With the database connection, we can create a Statement object to represent an SQL statement. Executing an SQL statement produces a ResultSet that contains the results of a query. The program displays the results and then cleans up the resources it has used. If an error occurs, a SQLException is thrown, so our program traps that exception and displays some of the information it encapsulates.

Clearly, there is a lot going on in this simple program. Every Java application that uses JDBC follows these basic steps, so the following sections discuss each step in much more detail.



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