如何让 XPathFactory newInstance 在 Java 中失败？

Question

XPathFactory.newInstance（字符串 uri）的文档是 here。

我正试图使它像这样失败：

println(System.getProperty("DEFAULT_PROPERTY_NAME"));
System.setProperty("DEFAULT_PROPERTY_NAME", "dummy");
println(System.getProperty("DEFAULT_PROPERTY_NAME"));
XPathFactory xPathFactory = XPathFactory.newInstance();
println(xPathFactory.getClass());

我得到的输出是：

null
dummy
class org.apache.xpath.jaxp.XPathFactoryImpl

我预计 ClassLoader 会因要点而失败：

If the system property DEFAULT_PROPERTY_NAME + ":uri" is present, where uri is the parameter to this method, then its value is read as a class name. The method will try to create a new instance of this class by using the class loader, and returns it if it is successfully created.

但事实并非如此，我显然遗漏了一些东西。

我做错了什么？

Answer 1

I am expecting that the ClassLoader will fail due to the bullet point:

这个要点指的是方法：

public static final XPathFactory newInstance(String uri)

但是您正在调用：

public static final XPathFactory newInstance()

其中指出：

This method is functionally equivalent to:

newInstance(DEFAULT_OBJECT_MODEL_URI)

Since the implementation for the W3C DOM is always available, this method will never fail.

Answer 2

请更改

System.setProperty("DEFAULT_PROPERTY_NAME", "dummy");

到

System.setProperty(XPathFactory.DEFAULT_OBJECT_MODEL_URI, "dummy");