The singleton pattern ensures that only a single instance of a class is normally used by an application, but still allows alternate instances to be created as required.
单元素模式可以确保应用程序通常只使用类的单个实例，但是仍然允许根据需要创建备用实例。
Over the years, dissatisfied hackers have created alternate ways to bridge this gap between Web servers and application code.
这些年来，不满的黑客已经创造了多种替代方式来在Web服务器和应用程序代码之间架起桥梁。
When you use the alternate method and specify a userid and password, this sensitive information is stored in plain text in the application code (that is, in the import or export file).
当您使用替代方法并指定用户 ID 和密码时，该敏感信息以纯文本形式存储在应用程序代码中（也就是在导入或导出文件中）。
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