不再需要Class.forName（JDBC_DRIVER）？ [英] Class.forName(JDBC_DRIVER) no longer needed?

问题描述

我在这里读过，因为java 6你不再需要使用以下命令注册JDBC驱动程序：

  Class。的forName（JDBC_DRIVER）; 
  

因为DriverManager使用系统属性中的路径jdbc.drivers
来检索正确的驱动程序。

但是当我执行以下操作时：

 是System.out.print（System.getProperty（ jdbc.drivers中））; 
  

null 被打印。

你有什么线索为什么我的应用程序正常工作？ ;）

解决方案

这与该系统属性无关。 Java6（和JDBC4）引入了一个名为服务提供商，JVM在启动期间可以检测到已知接口的实现。符合该标准的驱动程序将由DriverManager自动注册。这就是 Class.forName（）不再需要的原因 - 但仅限于驱动程序支持的情况。

服务如果在META-INF目录内的驱动程序的jar文件中有 services 目录，则启动注册。该目录需要包含一个文本文件，其中包含在包含实现类的 java.sql.Driver 的JDBC驱动程序的情况下实现的接口的名称。 / p>

I've read here on SO that since java 6 you no longer need to register JDBC Driver using:

Class.forName(JDBC_DRIVER);

because DriverManager uses the path located in system property "jdbc.drivers" to retrieve the correct driver.

But when I do the followng:

System.out.print(System.getProperty("jdbc.drivers"));

null gets printed.

Do you have any clue why my app works correctly ?? ;)

解决方案

That has nothing to do with that system property. Java6 (and JDBC4) introduced a concept known as "service provider" where implementations of known interface can be detected by the JVM during startup. A driver that is compliant with that will be registered by the DriverManager automatically. That's why Class.forName() is no longer necessary - but only if the driver supports that.

The service registration is initiated if there is a services directory in the driver's jar file inside the META-INF directory. That directory needs to contain a text file with the name of the interface that is implemented in the case of a JDBC driver that is java.sql.Driver containing the implementing class.

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