While using com.sun.org.apache.xerces parser, if XML has reference to external DTDs, it will be tried to load.
Exception will be thrown either network is not available or SocketPermission is not there.
Generally, this issue seen in JAVA Applet.
network: Cache entry not found [url: http://www.w3.org/TR/html4/strict.dtd, version: null]
network: Connecting http://www.w3.org/TR/html4/strict.dtd with proxy=HTTP
network: Cache entry not found [url: http://www.w3.org:80/crossdomain.xml, version: null]
network: Connecting http://www.w3.org:80/crossdomain.xml with proxy=HTTP
java.security.AccessControlException: access denied ("java.net.SocketPermission" "www.w3.org:80" "connect,resolve")
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkConnect(Unknown Source)
at sun.plugin2.applet.SecurityManagerHelper.checkConnectHelper(Unknown Source)
at sun.plugin2.applet.AWTAppletSecurityManager.checkConnect(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.http.HttpClient.(Unknown Source)
at sun.net.www.http.HttpClient.New(Unknown Source)
at sun.net.www.http.HttpClient.New(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startEntity(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startDTDEntity(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.setInputSource(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.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
To overcome, set load-external-dtd feature to false.
DocumentBuilderFactory localDocumentBuilderFactory = DocumentBuilderFactory.newInstance();
localDocumentBuilderFactory.setNamespaceAware(true);
localDocumentBuilderFactory.setValidating(false);
localDocumentBuilderFactory.setFeature(
"http://apache.org/xml/features/nonvalidating/load-external-dtd", false);