DriverManager - Loading JDBC Driver

JDBC for SQL Server - Herong's Tutorial Examples

∟JDBC (Java Database Connectivity) Introduction

∟DriverManager - Loading JDBC Driver

This section describes how to load a JDBC driver and register it with DriverManager.

If you want to use DriverManager class to create a connection to a database server, you need to load a JDBC driver that knows how to create a connection to that database server. The loaded JDBC driver class will be automatically registered to DriverManager.

There are two ways to load a JDBC driver:

Using the Class.forName() method - Loading the specified driver class when you need it.
Using the java.lang.System property jdbc.drivers setting - Loading the specified driver classes when the first call to a DriverManager method is made.

I wrote the following program to test both ways of loading JDBC drivers. To test this program, you need to download Microsoft JDBC Driver as described in another tutorial in this book.

/* LoadJdbcDriver.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.sql.*;
import java.util.*;
public class LoadJdbcDriver {
  public static void main(String [] args) {
    Connection con = null;
    try {
      System.out.println("Before loading SQLServerDriver:");
      listDrivers();

// Load Microsoft JDBC Driver
      Class.forName(
        "com.microsoft.sqlserver.jdbc.SQLServerDriver");

      System.out.println("After loading SQLServerDriver:");
      listDrivers();
    } catch (Exception e) {
      System.err.println("Exception: "+e.getMessage());
    }
  }
  private static void listDrivers() {
    Enumeration driverList = DriverManager.getDrivers();
    while (driverList.hasMoreElements()) {
      Driver driverClass = (Driver) driverList.nextElement();
      System.out.println("   "+driverClass.getClass().getName());
    }
  }
}

Test 1 - Load Microsoft JDBC Driver with Class.forName() with newer versions of JDK by follow the commands below:

herong> java -version

java version "17.0.1" 2021-10-19 LTS

herong> java -cp mssql-jdbc.jar LoadJdbcDriver.java

Before loading SQLServerDriver:
   com.microsoft.sqlserver.jdbc.SQLServerDriver
After loading SQLServerDriver:
   com.microsoft.sqlserver.jdbc.SQLServerDriver

Test 2 - Load Microsoft JDBC Driver with jdbc.drivers property with JDK by follow the commands below. The backslash at the end of line indicates that the command continues on the next line.

herong> java -cp mssql-jdbc.jar \
   -Djdbc.drivers="com.microsoft.sqlserver.jdbc.SQLServerDriver" \
   LoadJdbcDriver.java

Before loading SQLServerDriver:
   com.microsoft.sqlserver.jdbc.SQLServerDriver
After loading SQLServerDriver:
   com.microsoft.sqlserver.jdbc.SQLServerDriver

What I learned from the outputs of the two tests:

JDK automatically loads JDBC drivers specified in the classpath, even before the call of the forName().
There is no difference in behavior by adding the "-Djdbc.drivers=*" option

If we compare the output of the same tests with JDK 1.6 as presented below, you will see that newer versions of JDK have changed on how JDBC drivers are loaded.

Test 3 - Load Microsoft JDBC Driver with Class.forName() with JDK 1.6 by follow the commands below:

herong> java -version
java version "1.6.0_02"
Java(TM) SE Runtime Environment (build 1.6.0_02-b06)
Java HotSpot(TM) Client VM (build 1.6.0_02-b06, mixed mode, sharing)

herong> javac LoadJdbcDriver.java

herong> java -cp sqljdbc.jar LoadJdbcDriver

Before loading SQLServerDriver:
   sun.jdbc.odbc.JdbcOdbcDriver
After loading SQLServerDriver:
   sun.jdbc.odbc.JdbcOdbcDriver
   com.microsoft.sqlserver.jdbc.SQLServerDriver

Test 4 - Load Microsoft JDBC Driver with jdbc.drivers property with JDK 1.6 by follow the commands below:

herong> java -cp sqljdbc.jar \
   -Djdbc.drivers="com.microsoft.sqlserver.jdbc.SQLServerDriver" \
   LoadJdbcDriver

Before loading SQLServerDriver:
   sun.jdbc.odbc.JdbcOdbcDriver
   com.microsoft.sqlserver.jdbc.SQLServerDriver
After loading SQLServerDriver:
   sun.jdbc.odbc.JdbcOdbcDriver
   com.microsoft.sqlserver.jdbc.SQLServerDriver

What I learned from the outputs of the two tests with JDK 1.6:

sun.jdbc.odbc.JdbcOdbcDriver, the JDBC-ODBC Bridge driver is loaded automatically by the JVM, because it showed up in the driver list automatically.
The loaded driver class is automatically registered to the DriverManager class, because I didn't call any DriverManager method to register any class.
The "-Djdbc.drivers=*" option worked correctly to bring driver classes to the DriverManager class, because the Microsoft class specified in the option showed in the driver list before the call of the forName() method.