一般寫JDBC程式碼的時候都會有這麼一句程式碼：

1 Class.forName("com.mysql.jdbc.Driver");

這是載入資料庫的註冊驅動。但是從JDBC4.0後，就不用顯式載入了，也就是人家DriverManager類自動幫你載入了，這句程式碼你不用寫了，直接獲取資料庫連線就行。

可以看下：java.sql.DriverManager 類中的註釋：

*<P> The <code>DriverManager</code> methods <code>getConnection</code> and
 * <code>getDrivers</code> have been enhanced to support the Java Standard Edition
 
 
* <a href="../../../technotes/guides/jar/jar.html#Service%20Provider">Service Provider</a> mechanism. JDBC 4.0 Drivers must
 * include the file <code>META-INF/services/java.sql.Driver</code>. This file contains the name of the JDBC drivers
 * implementation of <code>java.sql.Driver</code>.  For example, to load the <code>my.sql.Driver</code> class,
 * the <code>META-INF/services/java.sql.Driver</code> file would contain the entry:
 
 
* <pre>
 * <code>my.sql.Driver</code>
 * </pre>
 *
 * <P>Applications no longer need to explicitly load JDBC drivers using <code>Class.forName()</code>. Existing programs
 * which currently load JDBC drivers using <code>Class.forName()</code> will continue
 
 to work without
 * modification.

<P>When the method <code>getConnection</code> is called,
 * the <code>DriverManager</code> will attempt to
 * locate a suitable driver from amongst those loaded at
 * initialization and those loaded explicitly using the same classloader
 * as the current applet or application.

著重看這一句話：

1 * <P>Applications no longer need to explicitly load JDBC drivers using <code>Class.forName()</code>. Existing programs
2  * which currently load JDBC drivers using <code>Class.forName()</code> will continue to work without
3  * modification.

上面的註釋的意思就是說，JDBC4.0後必須包含：the file <code>META-INF/services/java.sql.Driver</code>這個檔案，並且檔案中必須有如下程式碼：

<code>my.sql.Driver</code>

我看了下我資料庫jar包下對應的目錄，確實有這個檔案，而這個檔案的內容確實有這段程式碼：

在獲取連線的時候，會自動的查詢合適的驅動類，並初始化當前使用相同驅動的類。

所以啊，就不勞我們費心自己手動載入註冊驅動了：Class.forName("com.mysql.jdbc.Driver);不寫也罷，當然，你想寫也可以加上。