As with the SAX and DOM factory classes, one exception handles requested — but unsupported — features, and another exception handles instantiation errors.

对于SAX和DOM工厂类，一个异常处理已请求的但不受支持的特性，另一个异常处理实例化错误。

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For transparent switch over, applications can be coded to catch the StaleConnection exception and retry a specified number of times to obtain new connection handles.

为了能够透明地切换，可以将应用程序编码为捕获StaleConnection异常，并重试指定的连接次数来获取新的连接句柄。

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This code is included in the code which handles the click event for the Invoke Service button and its purpose is to avoid a null pointer exception when the web service is invoked with an empty string.

它的目的是避免使用空子符串调用 Web 服务而出现空指针异常。

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