Develop Reference

TransformerFactory - Using multiple stylesheets

I have multiple XSL's or style sheets for schematron validation of an XML (where one is the root and others being imported to the root). The below code is for one stylesheet.
public XMLSaxonTransformer(InputStream styleSheet) {
final TransformerFactory transformerFactory = TransformerFactory.newInstance("net.sf.saxon.TransformerFactoryImpl", null);
try {
styleSheetTemplate = transformerFactory.newTemplates(new StreamSource(styleSheet), new StreamSource(styleSheet));
} catch (TransformerConfigurationException e) {
throw new Exception("Exception caught while parsing StyleSheet", e);
}
}
The above works for single stylesheet. but, my requirement is for multiple stylesheets with one root and others being included in the root.
My code should look something like below.
public XMLSaxonTransformer(List<InputStream> styleSheetList) {
final TransformerFactory transformerFactory = TransformerFactory.newInstance("net.sf.saxon.TransformerFactoryImpl", null);
try {
// do something to add the XSL's list to the transformer
} catch (TransformerConfigurationException e) {
throw new Exception("Exception caught while parsing StyleSheet", e);
}}

You should only specify the top-level stylesheet to the TransformerFactory.newTemplates() method. The top-level stylesheet will pull in other stylesheet modules using xsl:include or xsl:import. If those stylesheet modules exist only in memory, you will need to nominate a URIResolver to the TransformerFactory. Your URIResolver will be called when an xsl:include or xsl:import declaration is encountered, and it should return a Source object (for example a StreamSource) to deliver the contents of the stylesheet module.

fop render to pdf one page out of many

I have a code which runs apache fop against xml content and xsl markup and gives me the apache Intermediate Format output:
StreamSource contentSource = new StreamSource(xmlContentStream);
StreamSource transformSource = new StreamSource(xslMarkupStream);
ByteArrayOutputStream outStream = new ByteArrayOutputStream();
Transformer xslfoTransformer = getTransformer(transformSource);
FOUserAgent foUserAgent = fopFactory.newFOUserAgent();
IFDocumentHandler targetHandler = foUserAgent.getRendererFactory().createDocumentHandler(
foUserAgent, MimeConstants.MIME_PDF);
FPSIFSerializer fpsSerializer = new FPSIFSerializer();
fpsSerializer.setContext(new IFContext(foUserAgent));
fpsSerializer.mimicDocumentHandler(targetHandler);
foUserAgent.setDocumentHandlerOverride(fpsSerializer);
Fop fop = fopFactory.newFop("application/X-fop-intermediate-format", foUserAgent, outStream);
DefaultHandler defaultHandler = fop.getDefaultHandler();
Result res = new SAXResult(defaultHandler);
xslfoTransformer.transform(contentSource, res);
Then I use that Intermediate Format file to render pdf and png files out of it.
I'm able to set up my own serilaizer here (FPSIFSerializer()).
I have several pages reports, but I don't need to process all of them. Is there any way to skip some pages or extract them from IntermediateFormat so I will be able e.g. to render only 1st page as png and then 2nd to pdf, etc ?
There
http://svn.apache.org/viewvc/xmlgraphics/fop/branches/archive/fop-1_1/examples/embedding/java/embedding/intermediate/ExampleConcat.java?view=markup
is an example of how to concatenate files via IFConcatenator, so I wonder about the best way to split the multipage file?
Thank_you!

The way I've done it is using custom document handler.
/**
* Custom Apache FOP Intermediate Format document handler which allows page skipping.
* Not thread safe.
*/
public class IFPageFilter extends IFDocumentHandlerProxy {
private static final Logger LOGGER = LoggerFactory.getLogger(IFPageFilter.class);
private int currentPage;
private final int desiredPage;
/**
* #param delegate The real document handler
* #param desiredPage the page you want to render (1-based). Other pages will be skipped.
*/
public IFPageFilter(final IFDocumentHandler delegate, final int desiredPage) {
super(delegate);
this.desiredPage = desiredPage;
}
#Override
public void startPage(final int index, final String name, final String pageMasterName, final Dimension size) throws IFException {
currentPage = index + 1;
if (currentPage == desiredPage) {
super.startPage(index, name, pageMasterName, size);
} else {
// do nothing
LOGGER.debug("Page skipped");
}
}
#Override
public IFPainter startPageContent() throws IFException {
if (currentPage == desiredPage) {
return super.startPageContent();
} else {
return EmptyPainter.getInstance();
}
}
#Override
public void endPageContent() throws IFException {
if (currentPage == desiredPage) {
super.endPageContent();
}
}
}
Then you can attach your handler like that:
final IFDocumentHandler targetHandler = FOP_FACTORY.getRendererFactory().createDocumentHandler(userAgent, mime);
final IFPageFilter documentHandler = new IFPageFilter(targetHandler, page);
final ByteArrayOutputStream mimeOut = new ByteArrayOutputStream(XSL_STREAM_BUFFER_SIZE);
IFUtil.setupFonts(documentHandler);
// Tell the target handler where to write the PDF to
targetHandler.setResult(new StreamResult(mimeOut));
try (final InputStream is = ifStream.toInputStream()) {
final Source src = new StreamSource(is);
new IFParser().parse(src, documentHandler, userAgent);
}
return mimeOut;
and you will get the only page you need in the output stream.
Class EmptyPainter is a dirty hack. It is empty implementation of apache IFPainter, it used here to skip page content and avoid NPE. I'm not happy about it, but that is the only way I was able to make it work.
Please note that I use FOP 1.1, and if you faced with such problems it worth to look at trunk - some of them already solved there. I guess dirty hack with EmptyPainter will not be necessary in trunk.
Please give tips if something could be done better here.
Thanks

How to extract useful information from TransformerException

I am using javax.xml.transform.* to do XSLT transformation. Since the xslt file to be used comes from the outside world there could be errors in that file, and I am going to give back some meaningful response to the user.
Although I can easily catch the TransformationExceptions, I found no way to obtain enough information from it. For example, if there is a tag to be terminated by an end-tag, printStackTrace() gives scarring message
javax.xml.transform.TransformerConfigurationException: Could not compile stylesheet
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTemplates(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTransformer(Unknown Source)
... (100 lines)
and getMessage() gives only
Could not compile stylesheet
None of them gives the real reason of the error.
I noticed that in Eclipse test console I can see the following
[Fatal Error] :259:155: The element type "sometag" must be terminated by the matching end-tag "</sometag>".
ERROR: 'The element type "sometag" must be terminated by the matching end-tag "</sometag>".'
FATAL ERROR: 'Could not compile stylesheet'
This is exactly what I want. Unfortunately, since this is a web application, the user cannot see this.
How can I display the correct error message to the user?

Put your own ErrorListener on your Transformer instance using Transformer.setErrorListener, like so:
final List<TransformationException> errors = new ArrayList<TransformationException>();
Transformer transformer = ... ;
transformer.setErrorListener(new ErrorListener() {
#Override
public void error(TransformerException exception) {
errors.add(exception);
}
#Override
public void fatalError(TransformerException exception) {
errors.add(exception);
}
#Override
public void warning(TransformerException exception) {
// handle warnings as well if you want them
}
});
// Any other transformer setup
Source xmlSource = ... ;
Result outputTarget = ... ;
try {
transformer.transform(xmlSource, outputTarget);
} catch (TransformerException e) {
errors.add(e); // Just in case one is thrown that isn't handled
}
if (!errors.isEmpty()) {
// Handle errors
} else {
// Handle output since there were no errors
}
This will log all the errors that occur into the errors list, then you can use the messages off those errors to get what you want. This has the added benefit that it will try to resume the transformation after the errors occur. If this causes any problems, just rethrow the exception by doing:
#Override
public void error(TransformerException exception) throws TransformationException {
errors.add(exception);
throw exception;
}
#Override
public void fatalError(TransformerException exception) throws TransformationException {
errors.add(exception);
throw exception;
}

Firstly, it's likely that any solution will dependent on your choice of XSLT processor. Different implementations of the JAXP interface might well provide different information in the exceptions they generate.
It's possible that the error from the XML parser is available in a wrapped exception. For historic reasons, TransformerConfigurationException offers both getException() and getCause() to access wrapped exceptions, and it may be worth checking them both.
Alternatively it's possible that the information was supplied in a separate call to the ErrorListener.
Finally, this particular error is detected by the XML parser (not the XSLT processor) so in the first instance it will be handled by the parser. It may well be worth setting the parser's ErrorHandler and catching parsing errors at that level. If you want explicit control over the XML parser used by the transformation, use a SAXSource whose XMLReader is suitably initialized.

You can configure System.out to write in your own OutputStream.
Use of ErrorListener don't catch all output.
If you work with threads you can look here (http://maiaco.com/articles/java/threadOut.php) to avoid change of System.out for other threads.
example
public final class XslUtilities {
private XslUtilities() {
// only static methods
}
public static class ConvertWithXslException extends Exception {
public ConvertWithXslException(String message, Throwable cause) {
super(message, cause);
}
}
public static String convertWithXsl(String input, String xsl) throws ConvertWithXslException {
ByteArrayOutputStream systemOutByteArrayOutputStream = new ByteArrayOutputStream();
PrintStream oldSystemOutPrintStream = System.out;
System.setOut(new PrintStream(systemOutByteArrayOutputStream));
ByteArrayOutputStream systemErrByteArrayOutputStream = new ByteArrayOutputStream();
PrintStream oldSystemErrPrintStream = System.err;
System.setErr(new PrintStream(systemErrByteArrayOutputStream));
String resultXml;
try {
System.setProperty("javax.xml.transform.TransformerFactory", "net.sf.saxon.TransformerFactoryImpl");
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer(new StreamSource(new StringReader(xsl)));
StringWriter stringWriter = new StringWriter();
transformer.transform(new StreamSource(new StringReader(input)), new StreamResult(stringWriter));
resultXml = stringWriter.toString();
} catch (TransformerException e) {
System.out.flush();
final String systemOut = systemOutByteArrayOutputStream.toString();
System.err.flush();
final String systemErr = systemErrByteArrayOutputStream.toString();
throw new ConvertWithXslException("TransformerException - " + e.getMessageAndLocation()
+ (systemOut.length() > 0 ? ("\nSystem.out:" + systemOut) : "")
+ (systemErr.length() > 0 ? ("\nSystem.err:" + systemErr) : ""), e);
} finally {
System.setOut(oldSystemOutPrintStream);
System.setErr(oldSystemErrPrintStream);
}
return resultXml;
}
}

Is it possible to create an URL pointing to an in-memory object?

I'm trying to extend my library for integrating Swing and JPA by making JPA config as automatic (and portable) as can be done, and it means programmatically adding <class> elements. (I know it can be done via Hibernate's AnnotationConfiguration or EclipseLInk's ServerSession, but - portability). I'd also like to avoid using Spring just for this single purpose.
I can create a persistence.xml on the fly, and fill it with <class> elements from specified packages (via the Reflections library). The problem starts when I try to feed this persistence.xml to a JPA provider. The only way I can think of is setting up a URLClassLoader, but I can't think of a way what wouldn't make me write the file to the disk somewhere first, for sole ability to obtain a valid URL. Setting up a socket for serving the file via an URL(localhost:xxxx) seems... I don't know, evil?
Does anyone have an idea how I could solve this problem? I know it sounds like a lot of work to avoid using one library, but I'd just like to know if it can be done.
EDIT (a try at being more clear):
Dynamically generated XML is kept in a String object. I don't know how to make it available to a persistence provider. Also, I want to avoid writing the file to disk.
For purpose of my problem, a persistence provider is just a class which scans the classpath for META-INF/persistence.xml. Some implementations can be made to accept dynamic creation of XML, but there is no common interface (especially for a crucial part of the file, the <class> tags).
My idea is to set up a custom ClassLoader - if you have any other I'd be grateful, I'm not set on this one.
The only easily extendable/configurable one I could find was a URLClassLoader. It works on URL objects, and I don't know if I can create one without actually writing XML to disk first.
That's how I'm setting things up, but it's working by writing the persistenceXmlFile = new File("META-INF/persistence.xml") to disk:
Thread.currentThread().setContextClassLoader(
new URLResourceClassLoader(
new URL[] { persistenceXmlFile.toURI().toURL() },
Thread.currentThread().getContextClassLoader()
)
);
URLResourceClassLoader is URLCLassLoader's subclass, which allows for looking up resources as well as classes, by overriding public Enumeration<URL> findResources(String name).

Maybe a bit late (after 4 years), but for others that are looking for a similar solution, you may be able to use the URL factory I created:
public class InMemoryURLFactory {
public static void main(String... args) throws Exception {
URL url = InMemoryURLFactory.getInstance().build("/this/is/a/test.txt", "This is a test!");
byte[] data = IOUtils.toByteArray(url.openConnection().getInputStream());
// Prints out: This is a test!
System.out.println(new String(data));
}
private final Map<URL, byte[]> contents = new WeakHashMap<>();
private final URLStreamHandler handler = new InMemoryStreamHandler();
private static InMemoryURLFactory instance = null;
public static synchronized InMemoryURLFactory getInstance() {
if(instance == null)
instance = new InMemoryURLFactory();
return instance;
}
private InMemoryURLFactory() {
}
public URL build(String path, String data) {
try {
return build(path, data.getBytes("UTF-8"));
} catch (UnsupportedEncodingException ex) {
throw new RuntimeException(ex);
}
}
public URL build(String path, byte[] data) {
try {
URL url = new URL("memory", "", -1, path, handler);
contents.put(url, data);
return url;
} catch (MalformedURLException ex) {
throw new RuntimeException(ex);
}
}
private class InMemoryStreamHandler extends URLStreamHandler {
#Override
protected URLConnection openConnection(URL u) throws IOException {
if(!u.getProtocol().equals("memory")) {
throw new IOException("Cannot handle protocol: " + u.getProtocol());
}
return new URLConnection(u) {
private byte[] data = null;
#Override
public void connect() throws IOException {
initDataIfNeeded();
checkDataAvailability();
// Protected field from superclass
connected = true;
}
#Override
public long getContentLengthLong() {
initDataIfNeeded();
if(data == null)
return 0;
return data.length;
}
#Override
public InputStream getInputStream() throws IOException {
initDataIfNeeded();
checkDataAvailability();
return new ByteArrayInputStream(data);
}
private void initDataIfNeeded() {
if(data == null)
data = contents.get(u);
}
private void checkDataAvailability() throws IOException {
if(data == null)
throw new IOException("In-memory data cannot be found for: " + u.getPath());
}
};
}
}
}

We can use the Jimfs google library for that.
First, we need to add the maven dependency to our project:
<dependency>
<groupId>com.google.jimfs</groupId>
<artifactId>jimfs</artifactId>
<version>1.2</version>
</dependency>
After that, we need to configure our filesystem behavior, and write our String content to the in-memory file, like this:
public static final String INPUT =
"\n"
+ "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
+ "<note>\n"
+ " <to>Tove</to>\n"
+ " <from>Jani</from>\n"
+ " <heading>Reminder</heading>\n"
+ " <body>Don't forget me this weekend!</body>\n"
+ "</note>";
#Test
void usingJIMFS() throws IOException {
try (var fs = Jimfs.newFileSystem(Configuration.unix())) {
var path = fs.getPath(UUID.randomUUID().toString());
Files.writeString(path, INPUT);
var url = path.toUri().toURL();
assertThat(url.getProtocol()).isEqualTo("jimfs");
assertThat(Resources.asCharSource(url, UTF_8).read()).isEqualTo(INPUT);
}
}
We can find more examples in the official repository.
If we look inside the jimfs source code we will find the implementation is similar to #NSV answer.

Why am I getting "MalformedURLException: no protocol" when using SAXParser?

I'm copying code from one part of our application (an applet) to inside the app. I'm parsing XML as a String. It's been awhile since I parsed XML, but from the error that's thrown it looks like it might have to do with not finding the .dtd. The stack trace makes it difficult to find the exact cause of the error, but here's the message:
java.net.MalformedURLException: no protocol: http://www.mycomp.com/MyComp.dtd
and the XML has this as the first couple lines:
<?xml version='1.0'?>
<!DOCTYPE MYTHING SYSTEM 'http://www.mycomp.com/MyComp.dtd'>
and here's the relevant code snippets
class XMLImportParser extends DefaultHandler {
private SAXParser m_SaxParser = null;
private String is_InputString = "";
XMLImportParser(String xmlStr) throws SAXException, IOException {
super();
is_InputString = xmlStr;
createParser();
try {
preparseString();
parseString(is_InputString);
} catch (Exception e) {
throw new SAXException(e); //"Import Error : "+e.getMessage());
}
}
void createParser() throws SAXException {
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(true);
try {
factory.setFeature("http://xml.org/sax/features/namespaces", true);
factory.setFeature("http://xml.org/sax/features/namespace-prefixes", true);
m_SaxParser = factory.newSAXParser();
m_SaxParser.getXMLReader().setFeature("http://xml.org/sax/features/namespaces", true);
m_SaxParser.getXMLReader().setFeature("http://xml.org/sax/features/namespace-prefixes", true);
} catch (SAXNotRecognizedException snre){
throw new SAXException("Failed to create XML parser");
} catch (SAXNotSupportedException snse) {
throw new SAXException("Failed to create XML parser");
} catch (Exception ex) {
throw new SAXException(ex);
}
}
void preparseString() throws SAXException {
try {
InputSource lSource = new InputSource(new StringReader(is_InputString));
lSource.setEncoding("UTF-8");
m_SaxParser.parse(lSource, this);
} catch (Exception ex) {
throw new SAXException(ex);
}
}
}
It looks like the error is happening in the preparseString() method, on the line that actually does the parsing, the m_SaxParser.parse(lSource, this); line.
FYI, the 'MyComp.dtd' file does exist at that location and is accessible via http. The XML file comes from a different service on the server, so I can't change it to a file:// format and put the .dtd file on the classpath.

I think you have some extra code in the XML declaration. Try this:
<?xml version='1.0'?>
<!DOCTYPE MYTHING SYSTEM "http://www.mycomp.com/MyComp.dtd">
The above was captured from the W3C Recommendations: http://www.w3.org/QA/2002/04/valid-dtd-list.html
You can use the http link to set the Schema on the SAXParserFactory before creating your parser.
void createParser() throws SAXException {
Schema schema = SchemaFactory.newSchema(new URL("http://www.mycomp.com/MyComp.dtd"));
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(true);
factory.setSchema(schema);

The problem is that this:
http://www.mycomp.com/MyComp.dtd
is an HTML hyperlink, not a URL. Replace it with this:
http://www.mycomp.com/MyComp.dtd

Since this XML comes from an external source, the first thing to do would be to complain to them that they are sending invalid XML.
As a workaround, you can set an EntityResolver on your parser that compares the SystemId to this invalid url and returns a correct http url:
m_SaxParser.getXMLReader().setEntityResolver(
new EntityResolver() {
public InputSource resolveEntity(final String publicId, final String systemId) throws SAXException {
if ("http://www.mycomp.com/MyComp.dtd".equals(systemId)) {
return new InputSource("http://www.mycomp.com/MyComp.dtd");
} else {
return null;
}
}
}
);