Develop Reference

Java Stax for Complex / Large XML

I have an XML file that is 4.2 GB! Obviously parsing the entire DOM is not practical. I have been looking at SAX and STAX to accomplish parsing this gigantic XML file. However all the examples I've seen are simple. The XML file I am dealing with has nested on nested on nested. There are areas where it goes 10+ levels.
I found this tutorial but not sure if its a viable solution.
http://www.javacodegeeks.com/2013/05/parsing-xml-using-dom-sax-and-stax-parser-in-java.html (botton example using STAX)
I'm not really sure how to handle nested objects.
I have created Java objects to mimic the structure of the XML. Here are a few, too many to display.
Record.java
public class Record implements Serializable {
String uid;
StaticData staticData;
DynamicData dynamicData;
}
Summary.java
public class Summary {
EWUID ewuid;
PubInfo pubInfo;
Titles titles;
Names names;
DocTypes docTypes;
Publishers publishers;
}
EWUID.java
public class EWUID {
String collId;
String edition;
}
PubInfo.java
public class PubInfo {
String coverDate;
String hasAbstract;
String issue;
String pubMonth;
String pubType;
String pubYear;
String sortDate;
String volume;
}
This is the code I've come up with so far.
public class TRWOSParser {
XMLEventReader eventReader;
XMLInputFactory inputFactory;
InputStream inputStream;
public TRWOSParser(String file) throws FileNotFoundException, XMLStreamException {
inputFactory = XMLInputFactory.newInstance();
inputStream = new FileInputStream(file);
eventReader = inputFactory.createXMLEventReader(inputStream);
}
public void parse() throws XMLStreamException{
while (eventReader.hasNext()) {
XMLEvent event = eventReader.nextEvent();
if (event.isStartElement()) {
StartElement startElement = event.asStartElement();
if (startElement.getName().getLocalPart().equals("record")) {
Record record = new Record();
Iterator<Attribute> attributes = startElement.getAttributes();
while (attributes.hasNext()) {
Attribute attribute = attributes.next();
if (attribute.getName().toString().equals("UID")) {
System.out.println("UID: " + attribute.getValue());
}
}
}
}
}
}
}
Update:
The data in the XML is licensed so I cannot show the full file. This is a very very small segment in which I have scrambled the data.
<?xml version="1.0" encoding="UTF-8"?>
<records>
<REC>
<UID>WOS:000310438600004</UID>
<static_data>
<summary>
<EWUID>
<WUID coll_id="WOS" />
<edition value="WOS.SCI" />
</EWUID>
<pub_info coverdate="NOV 2012" has_abstract="N" issue="5" pubmonth="NOV" pubtype="Journal" pubyear="2012" sortdate="2012-11-01" vol="188">
<page begin="1662" end="1663" page_count="2">1662-1663</page>
</pub_info>
<titles count="6">
<title type="source">JOURNAL OF UROLOGY</title>
<title type="source_abbrev">J UROLOGY</title>
<title type="abbrev_iso">J. Urol.</title>
<title type="abbrev_11">J UROL</title>
<title type="abbrev_29">J UROL</title>
<title type="item">Something something</title>
</titles>
<names count="1">
<name addr_no="1 2 3" reprint="Y" role="author" seq_no="1">
<display_name>John Doe</display_name>
<full_name>John Doe</full_name>
<wos_standard>Doe, John</wos_standard>
<first_name>John</first_name>
<last_name>Doe</last_name>
</name>
</names>
<doctypes count="1">
<doctype>Editorial Material</doctype>
</doctypes>
<publishers>
<publisher>
<address_spec addr_no="1">
<full_address>360 PARK AVE SOUTH, NEW YORK, NY 10010-1710 USA</full_address>
<city>NEW YORK</city>
</address_spec>
<names count="1">
<name addr_no="1" role="publisher" seq_no="1">
<display_name>ELSEVIER SCIENCE INC</display_name>
<full_name>ELSEVIER SCIENCE INC</full_name>
</name>
</names>
</publisher>
</publishers>
</summary>
</static_data>
</REC>
</records>

A similar solution to lscoughlin's answer is to use DOM4J which has mechanims to deal with this scenario: http://dom4j.sourceforge.net/
In my opionin it is more straight forward and easier to follow. It might not support namespaces, though.

I'm making two assumptions 1) that there is an early level of repetition, and 2) that you can do something meaningful with a partial document.
Let's assume you can move some level of nesting in, and then handle the document multiple times, removing the nodes at the working level each time you "handle" the document. This means that only a single working subtree will be in memory at any given time.
Here's a working code snippet:
package bigparse;
import static javax.xml.stream.XMLStreamConstants.CHARACTERS;
import static javax.xml.stream.XMLStreamConstants.END_DOCUMENT;
import static javax.xml.stream.XMLStreamConstants.END_ELEMENT;
import static javax.xml.stream.XMLStreamConstants.START_DOCUMENT;
import static javax.xml.stream.XMLStreamConstants.START_ELEMENT;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.StringWriter;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
public class BigParse {
public static void main(String... args) {
XMLInputFactory factory = XMLInputFactory.newInstance();
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
try {
XMLStreamReader streamReader = factory.createXMLStreamReader(new FileReader("src/main/resources/test.xml"));
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
Document document = documentBuilder.newDocument();
Element rootElement = null;
Element currentElement = null;
int branchLevel = 0;
int maxBranchLevel = 1;
while (streamReader.hasNext()) {
int event = streamReader.next();
switch (event) {
case START_DOCUMENT:
continue;
case START_ELEMENT:
if (branchLevel < maxBranchLevel) {
Element workingElement = readElementOnly(streamReader, document);
if (rootElement == null) {
document.appendChild(workingElement);
rootElement = document.getDocumentElement();
currentElement = rootElement;
} else {
currentElement.appendChild(workingElement);
currentElement = workingElement;
}
branchLevel++;
} else {
workingLoop(streamReader, document, currentElement);
}
continue;
case CHARACTERS:
currentElement.setTextContent(streamReader.getText());
continue;
case END_ELEMENT:
if (currentElement != rootElement) {
currentElement = (Element) currentElement.getParentNode();
branchLevel--;
}
continue;
case END_DOCUMENT:
break;
}
}
} catch (ParserConfigurationException
| FileNotFoundException
| XMLStreamException e) {
throw new RuntimeException(e);
}
}
private static Element readElementOnly(XMLStreamReader streamReader, Document document) {
Element workingElement = document.createElement(streamReader.getLocalName());
for (int attributeIndex = 0; attributeIndex < streamReader.getAttributeCount(); attributeIndex++) {
workingElement.setAttribute(
streamReader.getAttributeLocalName(attributeIndex),
streamReader.getAttributeValue(attributeIndex));
}
return workingElement;
}
private static void workingLoop(final XMLStreamReader streamReader, final Document document, final Element fragmentRoot)
throws XMLStreamException {
Element startElement = readElementOnly(streamReader, document);
fragmentRoot.appendChild(startElement);
Element currentElement = startElement;
while (streamReader.hasNext()) {
int event = streamReader.next();
switch (event) {
case START_DOCUMENT:
continue;
case START_ELEMENT:
Element workingElement = readElementOnly(streamReader, document);
currentElement.appendChild(workingElement);
currentElement = workingElement;
continue;
case CHARACTERS:
currentElement.setTextContent(streamReader.getText());
continue;
case END_ELEMENT:
if (currentElement != startElement) {
currentElement = (Element) currentElement.getParentNode();
continue;
} else {
handleDocument(document, startElement);
fragmentRoot.removeChild(startElement);
startElement = null;
return;
}
}
}
}
// THIS FUNCTION DOES SOMETHING MEANINFUL
private static void handleDocument(Document document, Element startElement) {
System.out.println(stringify(document));
}
private static String stringify(Document document) {
try {
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
StreamResult result = new StreamResult(new StringWriter());
DOMSource source = new DOMSource(document);
transformer.transform(source, result);
String xmlString = result.getWriter().toString();
return xmlString;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
EDIT: I made an incredibly silly mistake. It's fixed now. It's working but imperfect -- should be enough to lead you in a useful direction.

Consider using an XSLT 3.0 streaming transformation of the form:
<xsl:template name="main">
<xsl:stream href="bigInput.xml">
<xsl:for-each select="copy-of(/records/REC)">
<!-- process one record -->
</xsl:for-each>
</xsl:stream>
</xsl:template>
You can process this using Saxon-EE 9.6.
The "process one record" logic could use the Saxon SQL extension, or it could invoke an extension function: the context node will be a REC element with its contained tree, fully navigable within the subtree, but with no ability to navigate outside the REC element currently being processed.

Convert DOC file to DOCX with Java

I need to use DOCX files (actually the XML contained in them) in a Java software I'm currently developing, but some people in my company still use the DOC format.
Do you know if there is a way to convert a DOC file to the DOCX format using Java ? I know it's possible using C#, but that's not an option
I googled it, but nothing came up...
Thanks

You may try Aspose.Words for Java. It allows you to load a DOC file and save it as DOCX format. The code is very simple as shown below:
// Open a document.
Document doc = new Document("input.doc");
// Save document.
doc.save("output.docx");
Please see if this helps in your scenario.
Disclosure: I work as developer evangelist at Aspose.

Check out JODConverter to see if it fits the bill. I haven't personally used it.

Use newer versions of jars jodconverter-core-4.2.2.jar and jodconverter-local-4.2.2.jar
String inputFile = "*.doc";
String outputFile = "*.docx";
LocalOfficeManager localOfficeManager = LocalOfficeManager.builder()
.install()
.officeHome(getDefaultOfficeHome()) //your path to openoffice
.build();
try {
localOfficeManager.start();
final DocumentFormat format
= DocumentFormat.builder()
.from(DefaultDocumentFormatRegistry.DOCX)
.build();
LocalConverter
.make()
.convert(new FileInputStream(new File(inputFile)))
.as(DefaultDocumentFormatRegistry.getFormatByMediaType("application/msword"))
.to(new File(outputFile))
.as(format)
.execute();
} catch (OfficeException ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
} catch (FileNotFoundException ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
} finally {
OfficeUtils.stopQuietly(localOfficeManager);
}

JODConvertor calls OpenOffice/LibreOffice via a network protocol. It can therefore 'do anything you can do in OpenOffice'. This includes converting formats. But it only does as good a job as whatever version of OpenOffice you are running. I have some art in one of my docs, and it doesn't convert them as I hoped.
JODConvertor is no longer supported, according to the google code web site for v3.
To get JOD to do the job you need to do something like
private static void transformBinaryWordDocToDocX(File in, File out)
{
OfficeDocumentConverter converter = new OfficeDocumentConverter(officeManager);
DocumentFormat docx = converter.getFormatRegistry().getFormatByExtension("docx");
docx.setStoreProperties(DocumentFamily.TEXT,
Collections.singletonMap("FilterName", "MS Word 2007 XML"));
converter.convert(in, out, docx);
}
private static void transformBinaryWordDocToW2003Xml(File in, File out)
{
OfficeDocumentConverter converter = new OfficeDocumentConverter(officeManager);;
DocumentFormat w2003xml = new DocumentFormat("Microsoft Word 2003 XML", "xml", "text/xml");
w2003xml.setInputFamily(DocumentFamily.TEXT);
w2003xml.setStoreProperties(DocumentFamily.TEXT, Collections.singletonMap("FilterName", "MS Word 2003 XML"));
converter.convert(in, out, w2003xml);
}
private static OfficeManager officeManager;
#BeforeClass
public static void setupStatic() throws IOException {
/*officeManager = new DefaultOfficeManagerConfiguration()
.setOfficeHome("C:/Program Files/LibreOffice 3.6")
.buildOfficeManager();
*/
officeManager = new ExternalOfficeManagerConfiguration().setConnectOnStart(true).setPortNumber(8100).buildOfficeManager();
officeManager.start();
}
#AfterClass
public static void shutdownStatic() throws IOException {
officeManager.stop();
}
For this to work you need to be running LibreOffice as a networked server ( I could not get the 'run on demand' part of JODConvertor to work under windows with LO 3.6 very well )

To convert DOC file to HTML look at this
(Convert Word doc to HTML programmatically in Java)
Use this: http://poi.apache.org/
Or use this :
XWPFDocument docx = new XWPFDocument(OPCPackage.openOrCreate(new File("hello.docx")));
XWPFWordExtractor wx = new XWPFWordExtractor(docx);
String text = wx.getText();
System.out.println("text = "+text);

I needed the same conversion ,after researching a lot found Jodconvertor can be useful in it , you can download the jar from
https://code.google.com/p/jodconverter/downloads/list
Add jodconverter-core-3.0-beta-4-sources.jar file to your project lib
//1) Create OfficeManger Object
OfficeManager officeManager = new DefaultOfficeManagerConfiguration()
.setOfficeHome(new File("/opt/libreoffice4.4"))
.buildOfficeManager();
officeManager.start();
// 2) Create JODConverter converter
OfficeDocumentConverter converter = new OfficeDocumentConverter(
officeManager);
// 3)Create DocumentFormat for docx
DocumentFormat docx = converter.getFormatRegistry().getFormatByExtension("docx");
docx.setStoreProperties(DocumentFamily.TEXT,
Collections.singletonMap("FilterName", "MS Word 2007 XML"));
//4)Call convert funtion in converter object
converter.convert(new File("doc/AdvancedTable.doc"), new File(
"docx/AdvancedTable.docx"), docx);

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.OutputStream;
import com.lowagie.text.Document;
import com.lowagie.text.DocumentException;
import com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
import org.apache.poi.hwpf.HWPFDocument;
import org.apache.poi.hwpf.extractor.WordExtractor;
import org.apache.poi.hwpf.usermodel.Range;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
public class TestCon {
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
POIFSFileSystem fs = null;
Document document = new Document();
try {
System.out.println("Starting the test");
fs = new POIFSFileSystem(new FileInputStream("C:/Users/312845/Desktop/a.doc"));
HWPFDocument doc = new HWPFDocument(fs);
WordExtractor we = new WordExtractor(doc);
OutputStream file = new FileOutputStream(new File("C:/Users/312845/Desktop/test.docx"));
System.out.println("Document testing completed");
} catch (Exception e) {
System.out.println("Exception during test");
e.printStackTrace();
} finally {
// close the document
document.close();
}
}
}

Find the value of a specific attribute in an XML file in java

I need to just read the value of a single attribute inside an XML file using java. The XML would look something like this:
<behavior name="Fred" version="2.0" ....>
and I just need to read out the version. Can someone point in the direction of a resource that would show me how to do this?

You don't need a fancy library -- plain old JAXP versions of DOM and XPath are pretty easy to read and write for this. Whatever you do, don't use a regular expression.
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
public class GetVersion {
public static void main(String[] args) throws Exception {
XPath xpath = XPathFactory.newInstance().newXPath();
Document doc = DocumentBuilderFactory.newInstance()
.newDocumentBuilder().parse("file:////tmp/whatever.xml");
String version = xpath.evaluate("//behavior/#version", doc);
System.out.println(version);
}
}

JAXB for brevity:
private static String readVersion(File file) {
#XmlRootElement class Behavior {
#XmlAttribute String version;
}
return JAXB.unmarshal(file, Behavior.class).version;
}
StAX for efficiency:
private static String readVersionEfficient(File file)
throws XMLStreamException, IOException {
XMLInputFactory inFactory = XMLInputFactory.newInstance();
XMLStreamReader xmlReader = inFactory
.createXMLStreamReader(new StreamSource(file));
try {
while (xmlReader.hasNext()) {
if (xmlReader.next() == XMLStreamConstants.START_ELEMENT) {
if (xmlReader.getLocalName().equals("behavior")) {
return xmlReader.getAttributeValue(null, "version");
} else {
throw new IOException("Invalid file");
}
}
}
throw new IOException("Invalid file");
} finally {
xmlReader.close();
}
}

Here's one.
import javax.xml.parsers.SAXParser;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.SAXException;
import org.xml.sax.Attributes;
import javax.xml.parsers.SAXParserFactory;
/**
* Here is sample of reading attributes of a given XML element.
*/
public class SampleOfReadingAttributes {
/**
* Application entry point
* #param args command-line arguments
*/
public static void main(String[] args) {
try {
// creates and returns new instance of SAX-implementation:
SAXParserFactory factory = SAXParserFactory.newInstance();
// create SAX-parser...
SAXParser parser = factory.newSAXParser();
// .. define our handler:
SaxHandler handler = new SaxHandler();
// and parse:
parser.parse("sample.xml", handler);
} catch (Exception ex) {
ex.printStackTrace(System.out);
}
}
/**
* Our own implementation of SAX handler reading
* a purchase-order data.
*/
private static final class SaxHandler extends DefaultHandler {
// we enter to element 'qName':
public void startElement(String uri, String localName,
String qName, Attributes attrs) throws SAXException {
if (qName.equals("behavior")) {
// get version
String version = attrs.getValue("version");
System.out.println("Version is " + version );
}
}
}
}

As mentioned you can use the SAXParser.
Digester mentioned using regular expressions, which I won't recommend as it would lead to code that is difficult to maintain: What if you add another version attribute in another tag, or another behaviour tag? You can handle it, but it won't be pretty.
You can also use XPath, which is a language for querying xml. That's what I would recommend.

If all you need is to read the version, then you can use regex. But really, I think you need apache digester

Apache Commons Configuration is nice, too. Commons Digester is based on it.

Can JAXB parse large XML files in chunks

I need to parse potentially large XML files, of which the schema is already provided to me in several XSD files, so XML binding is highly favored. I'd like to know if I can use JAXB to parse the file in chunks and if so, how.

Because code matters, here is a PartialUnmarshaller who reads a big file into chunks. It can be used that way new PartialUnmarshaller<YourClass>(stream, YourClass.class)
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.*;
import java.io.InputStream;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import static javax.xml.stream.XMLStreamConstants.*;
public class PartialUnmarshaller<T> {
XMLStreamReader reader;
Class<T> clazz;
Unmarshaller unmarshaller;
public PartialUnmarshaller(InputStream stream, Class<T> clazz) throws XMLStreamException, FactoryConfigurationError, JAXBException {
this.clazz = clazz;
this.unmarshaller = JAXBContext.newInstance(clazz).createUnmarshaller();
this.reader = XMLInputFactory.newInstance().createXMLStreamReader(stream);
/* ignore headers */
skipElements(START_DOCUMENT, DTD);
/* ignore root element */
reader.nextTag();
/* if there's no tag, ignore root element's end */
skipElements(END_ELEMENT);
}
public T next() throws XMLStreamException, JAXBException {
if (!hasNext())
throw new NoSuchElementException();
T value = unmarshaller.unmarshal(reader, clazz).getValue();
skipElements(CHARACTERS, END_ELEMENT);
return value;
}
public boolean hasNext() throws XMLStreamException {
return reader.hasNext();
}
public void close() throws XMLStreamException {
reader.close();
}
void skipElements(int... elements) throws XMLStreamException {
int eventType = reader.getEventType();
List<Integer> types = asList(elements);
while (types.contains(eventType))
eventType = reader.next();
}
}

This is detailed in the user guide. The JAXB download from http://jaxb.java.net/ includes an example of how to parse one chunk at a time.
When a document is large, it's
usually because there's repetitive
parts in it. Perhaps it's a purchase
order with a large list of line items,
or perhaps it's an XML log file with
large number of log entries.
This kind of XML is suitable for
chunk-processing; the main idea is to
use the StAX API, run a loop, and
unmarshal individual chunks
separately. Your program acts on a
single chunk, and then throws it away.
In this way, you'll be only keeping at
most one chunk in memory, which allows
you to process large documents.
See the streaming-unmarshalling
example and the partial-unmarshalling
example in the JAXB RI distribution
for more about how to do this. The
streaming-unmarshalling example has an
advantage that it can handle chunks at
arbitrary nest level, yet it requires
you to deal with the push model ---
JAXB unmarshaller will "push" new
chunk to you and you'll need to
process them right there.
In contrast, the partial-unmarshalling
example works in a pull model (which
usually makes the processing easier),
but this approach has some limitations
in databinding portions other than the
repeated part.

Yves Amsellem's answer is pretty good, but only works if all elements are of exactly the same type. Otherwise your unmarshall will throw an exception, but the reader will have already consumed the bytes, so you would be unable to recover. Instead, we should follow Skaffman's advice and look at the sample from the JAXB jar.
To explain how it works:
Create a JAXB unmarshaller.
Add a listener to the unmarshaller for intercepting the appropriate elements. This is done by "hacking" the ArrayList to ensure the elements are not stored in memory after being unmarshalled.
Create a SAX parser. This is where the streaming happens.
Use the unmarshaller to generate a handler for the SAX parser.
Stream!
I modified the solution to be generic*. However, it required some reflection. If this is not OK, please look at the code samples in the JAXB jars.
ArrayListAddInterceptor.java
import java.lang.reflect.Field;
import java.util.ArrayList;
public class ArrayListAddInterceptor<T> extends ArrayList<T> {
private static final long serialVersionUID = 1L;
private AddInterceptor<T> interceptor;
public ArrayListAddInterceptor(AddInterceptor<T> interceptor) {
this.interceptor = interceptor;
}
#Override
public boolean add(T t) {
interceptor.intercept(t);
return false;
}
public static interface AddInterceptor<T> {
public void intercept(T t);
}
public static void apply(AddInterceptor<?> interceptor, Object o, String property) {
try {
Field field = o.getClass().getDeclaredField(property);
field.setAccessible(true);
field.set(o, new ArrayListAddInterceptor(interceptor));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
Main.java
public class Main {
public void parsePurchaseOrders(AddInterceptor<PurchaseOrder> interceptor, List<File> files) {
try {
// create JAXBContext for the primer.xsd
JAXBContext context = JAXBContext.newInstance("primer");
Unmarshaller unmarshaller = context.createUnmarshaller();
// install the callback on all PurchaseOrders instances
unmarshaller.setListener(new Unmarshaller.Listener() {
public void beforeUnmarshal(Object target, Object parent) {
if (target instanceof PurchaseOrders) {
ArrayListAddInterceptor.apply(interceptor, target, "purchaseOrder");
}
}
});
// create a new XML parser
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setNamespaceAware(true);
XMLReader reader = factory.newSAXParser().getXMLReader();
reader.setContentHandler(unmarshaller.getUnmarshallerHandler());
for (File file : files) {
reader.parse(new InputSource(new FileInputStream(file)));
}
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
*This code has not been tested and is for illustrative purposes only.

I wrote a small library (available on Maven Central) to help to read big XML files and process them by chunks. Please note it can only be applied for files with a unique container having a list of data (even from different types). In other words, your file has to follow the structure:
<container>
<type1>...</type1>
<type2>...</type2>
<type1>...</type1>
...
</container>
Here is an example where Type1, Type2, ... are the JAXB representation of the repeating data in the file:
try (StreamingUnmarshaller unmarshaller = new StreamingUnmarshaller(Type1.class, Type2.class, ...)) {
unmarshaller.open(new FileInputStream(fileName));
unmarshaller.iterate((type, element) -> doWhatYouWant(element));
}
You can find more information with detailed examples on the GitHub page of the library.

Why am I getting a NullPointerException when trying to read a file?

I use this test to convert txt to pdf :
package convert.pdf;
//getResourceAsStream(String name) : Returns an input stream for reading the specified resource.
//toByteArray : Get the contents of an InputStream as a byte[].
import java.io.FileOutputStream;
import java.io.IOException;
import org.apache.commons.io.IOUtils;
import convert.pdf.txt.TextConversion;
public class TestConversion {
private static byte[] readFilesInBytes(String file) throws IOException {
return IOUtils.toByteArray(TestConversion.class.getResourceAsStream(file));
}
private static void writeFilesInBytes(byte[] file, String name) throws IOException {
IOUtils.write(file, new FileOutputStream(name));
}
//just change the extensions and test conversions
public static void main(String args[]) throws IOException {
ConversionToPDF algorithm = new TextConversion();
byte[] file = readFilesInBytes("/convert/pdf/text.txt");
byte[] pdf = algorithm.convertDocument(file);
writeFilesInBytes(pdf, "text.pdf");
}
}
Problem:
Exception in thread "main" java.lang.NullPointerException
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1025)
at org.apache.commons.io.IOUtils.copy(IOUtils.java:999)
at org.apache.commons.io.IOUtils.toByteArray(IOUtils.java:218)
at convert.pdf.TestConversion.readFilesInBytes(TestConversion.java:17)
at convert.pdf.TestConversion.main(TestConversion.java:28)
I use the debugger, and the problem seems to be located here :
private static byte[] readFilesInBytes(String file) throws IOException {
return IOUtils.toByteArray(TestConversion.class.getResourceAsStream(file));
}
What is my problem?

Sounds like the resource probably doesn't exist with that name.
Are you aware that Class.getResourceAsStream() finds a resource relative to that class's package, whereas ClassLoader.getResourceAsStream() doesn't? You can use a leading forward slash in Class.getResourceAsStream() to mimic this, so
Foo.class.getResourceAsStream("/bar.png")
is roughly equivalent to
Foo.class.getClassLoader().getResourceAsStream("bar.png")
Is this actually a file (i.e. a specific file on the normal file system) that you're trying to load? If so, using FileInputStream would be a better bet. Use Class.getResourceAsStream() if it's a resource bundled in a jar file or in the classpath in some other way; use FileInputStream if it's an arbitrary file which could be anywhere in the file system.
EDIT: Another thing to be careful of, which has caused me problems before now - if this has worked on your dev box which happens to be Windows, and is now failing on a production server which happens to be Unix, check the case of the filename. The fact that different file systems handle case-sensitivity differently can be a pain...

Are you checking to see if the file exists before you pass it to readFilesInBytes()? Note that Class.getResourceAsStream() returns null if the file cannot be found. You probably want to do:
private static byte[] readFilesInBytes(String file) throws IOException {
File testFile = new File(file);
if (!testFile.exists()) {
throw new FileNotFoundException("File " + file + " does not exist");
}
return IOUtils.toByteArray(TestConversion.class.getResourceAsStream(file));
}
or better yet:
private static byte[] readFilesInBytes(String file) throws IOException {
InputStream stream = TestConversion.class.getResourceAsStream(file);
if (stream == null) {
throw new FileNotFoundException("readFilesInBytes: File " + file
+ " does not exist");
}
return IOUtils.toByteArray(stream);
}

This class reads a TXT file in the classpath and uses TextConversion to convert to PDF, then save the pdf in the file system.
Here TextConversion code :
package convert.pdf.txt;
//Conversion to PDF from text using iText.
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import convert.pdf.ConversionToPDF;
import convert.pdf.ConvertDocumentException;
import com.lowagie.text.Document;
import com.lowagie.text.DocumentException;
import com.lowagie.text.Font;
import com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
public class TextConversion implements ConversionToPDF {
public byte[] convertDocument(byte[] documents) throws ConvertDocumentException {
try {
return this.convertInternal(documents);
} catch (DocumentException e) {
throw new ConvertDocumentException(e);
} catch (IOException e) {
throw new ConvertDocumentException(e);
}
}
private byte[] convertInternal(byte[] documents) throws DocumentException, IOException {
Document document = new Document();
ByteArrayOutputStream pdfResultBytes = new ByteArrayOutputStream();
PdfWriter.getInstance(document, pdfResultBytes);
document.open();
BufferedReader reader = new BufferedReader( new InputStreamReader( new ByteArrayInputStream(documents) ) );
String line = "";
while ((line = reader.readLine()) != null) {
if ("".equals(line.trim())) {
line = "\n"; //white line
}
Font fonteDefault = new Font(Font.COURIER, 10);
Paragraph paragraph = new Paragraph(line, fonteDefault);
document.add(paragraph);
}
reader.close();
document.close();
return pdfResultBytes.toByteArray();
}
}
And here the code to ConversionToPDF :
package convert.pdf;
// Interface implemented by the conversion algorithms.
public interface ConversionToPDF {
public byte[] convertDocument(byte[] documentToConvert) throws ConvertDocumentException;
}
I think the problem come from my file system (devbox on windows and server is Unix).
I will try to modify my classpath.

This problem may be caused by calling methods on test.txt, which can be a folder shortcut. In other words, you're calling a method on a file that doesn't exist, resulting in a NullPointerException.