你好老师。我按照你得代码来进行操作，却出现这种异常，为啥？
java.io.UnsupportedEncodingException: UIF-8
at sun.nio.cs.StreamDecoder.forInputStreamReader(Unknown Source)
at java.io.InputStreamReader.<init>(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.createReader(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.setEncoding(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanXMLDeclOrTextDecl(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$XMLDeclDriver.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
at javax.xml.parsers.DocumentBuilder.parse(Unknown Source)
at javadashen.DOMTest.main(DOMTest.java:26)
