The Java Tutorials have been written for JDK 8.Java教程是为JDK 8编写的。Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.本页中描述的示例和实践没有利用后续版本中引入的改进，并且可能使用不再可用的技术。See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.有关Java SE 9及其后续版本中更新的语言特性的摘要，请参阅Java语言更改。
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.有关所有JDK版本的新功能、增强功能以及已删除或不推荐的选项的信息，请参阅JDK发行说明。
Since the properties are new to the current release, it is recommended that applications catch exceptions proper to the interface, for example, SAXException in the following example. Catching the applications may work properly on older releases, for example the sample code contains the following method that detects if the sample is run with a version of the JDK or a JAXP implementation that supports the new property:
public boolean isNewPropertySupported() {
try {
SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser parser = spf.newSAXParser();
parser.setProperty("http://javax.xml.XMLConstants/property/accessExternalDTD", "file");
} catch (ParserConfigurationException ex) {
fail(ex.getMessage());
} catch (SAXException ex) {
String err = ex.getMessage();
if (err.indexOf("Property 'http://javax.xml.XMLConstants/property/accessExternalDTD' is not recognized.") > -1)
{
//expected, jaxp 1.5 not supported
return false;
}
}
return true;
}If access to external resources is denied due to the restrictions set by the new properties, an exception will be thrown with an error in the following format:
[type of construct]: Failed to read [type of construct] "[name of the external resource]", because "[type of restriction]" access is not allowed due to restriction set by the [property name] property.
For example, if fetching an external DTD is denied by restriction to http protocol such as the following: parser.setProperty("http://javax.xml.XMLConstants/property/accessExternalDTD", "file"); and if the parser parses an XML file that contains external reference to "http://java.sun.com/dtd/properties.dtd", the error message would look like the following:
External DTD: Failed to read external DTD ''http://java.sun.com/dtd/properties.dtd'', because ''http'' access is not allowed due to restriction set by the accessExternalDTD property.