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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>JDBC 驱动程序 URL</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 3 页（共9 页）</nobr></font></td>
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一旦 JDBC 驱动程序用 <code>DriverManager</code> 注册了，就可以用于建立到数据库的连接。但是很多不同的驱动程序都可能被实际注册过，<code>DriverManager</code> 怎样选择正确的驱动程序呢？（请记住，单个的 JVM 可能支持多个并发应用程序，它们可能用不同的驱动程序连接到不同的数据库。）方法非常简单：每个 JDBC 驱动程序使用一个专门的 JDBC URL（它与 Web 地址有相同的格式）作为自我标识的一种方法。URL 的格式是直观的，看起来还可能很熟悉：<code>jdbc:<i>sub-protocol</i>:<i>database locator</i></code>。<i>子协议（sub-protocol）</i>与 JDBC 驱动程序有关，可以是 <i>odbc</i>、<i>oracle</i>、<i>db2</i> 等等，根据实际的 JDBC 驱动程序厂商而不同。<i>数据库定位器（database locator）</i>是与驱动程序有关的指示器，用于唯一指定应用程序要和哪个数据库进行交互。根据驱动程序的类型，该定位器可能包括主机名、端口和数据库系统名。
</p>
<p>
当提供了具体的 URL 之后，<code>DriverManager</code> 在已注册的驱动程序集合中循环，直到其中一个驱动程序识别出指定的 URL。如果没有发现适合的驱动程序，就抛出一个 <code>SQLException</code>。
下面的清单说明了几个实际 JDBC URL 的具体示例：</p>
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<li>
<code>jdbc:odbc:jdbc</code>
</li>
<li>
<code>jdbc:oracle:thin:@persistentjava.com:1521:jdbc";</code>
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<li>
<code>jdbc:db2:jdbc</code>
</li>
</ul>
<p>很多驱动程序（包括 JDBC-ODBC 桥驱动程序）接受在 URL 末尾的附加参数，如用户名和密码。
</p>
<p>
给定具体的 JDBC URL，获取数据库连接的方法就是在 <code>DriverManager</code> 对象上调用 <code>getConnection()</code>。这种方法有几种形式：</p>
<ul>
<li>
<code>DriverManager.getConnection(url) ; </code>
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<li>
<code>DriverManager.getConnection(url, username, password) ; </code>
</li>
<li>
<code>DriverManager.getConnection(url, dbproperties) ; </code>
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</ul>
<p>在这里，<code>url</code> 是一个 <code>String</code> 对象，也就是 JDBC URL；用户名和密码是 <code>String</code> 对象，它们是 JDBC 应用程序要用来连接到数据源的用户名和密码；而 <code>dbproperties</code> 是一个包括所有参数（可能包括用户名和密码）的 Java <code>properties</code> 对象，JDBC 驱动程序需要这些参数作成功的连接。
</p>
<p>
现在我们掌握了驱动程序的基础知识，就可以更详细地检查个别的驱动程序类型了。
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