Package org.ccil.cowan.tagsoup

Class XMLWriter

  • All Implemented Interfaces:
    org.xml.sax.ContentHandler, org.xml.sax.DTDHandler, org.xml.sax.EntityResolver, org.xml.sax.ErrorHandler, org.xml.sax.ext.LexicalHandler, org.xml.sax.XMLFilter, org.xml.sax.XMLReader
    public class XMLWriter
extends org.xml.sax.helpers.XMLFilterImpl
implements org.xml.sax.ext.LexicalHandler
    Filter to write an XML document from a SAX event stream.

    This class can be used by itself or as part of a SAX event stream: it takes as input a series of SAX2 ContentHandler events and uses the information in those events to write an XML document. Since this class is a filter, it can also pass the events on down a filter chain for further processing (you can use the XMLWriter to take a snapshot of the current state at any point in a filter chain), and it can be used directly as a ContentHandler for a SAX2 XMLReader.

    The client creates a document by invoking the methods for standard SAX2 events, always beginning with the startDocument method and ending with the endDocument method. There are convenience methods provided so that clients to not have to create empty attribute lists or provide empty strings as parameters; for example, the method invocation

     w.startElement("foo");

    is equivalent to the regular SAX2 ContentHandler method

     w.startElement("", "foo", "", new AttributesImpl());

    Except that it is more efficient because it does not allocate a new empty attribute list each time. The following code will send a simple XML document to standard output:

     XMLWriter w = new XMLWriter();

 w.startDocument();
 w.startElement("greeting");
 w.characters("Hello, world!");
 w.endElement("greeting");
 w.endDocument();

    The resulting document will look like this:

     <?xml version="1.0" standalone="yes"?>

 <greeting>Hello, world!</greeting>

    In fact, there is an even simpler convenience method, dataElement, designed for writing elements that contain only character data, so the code to generate the document could be shortened to

     XMLWriter w = new XMLWriter();

 w.startDocument();
 w.dataElement("greeting", "Hello, world!");
 w.endDocument();

    Whitespace

    According to the XML Recommendation, all whitespace in an XML document is potentially significant to an application, so this class never adds newlines or indentation. If you insert three elements in a row, as in

     w.dataElement("item", "1");
 w.dataElement("item", "2");
 w.dataElement("item", "3");

    you will end up with

     <item>1</item><item>3</item><item>3</item>

    You need to invoke one of the characters methods explicitly to add newlines or indentation. Alternatively, you can use DataWriter, which is derived from this class -- it is optimized for writing purely data-oriented (or field-oriented) XML, and does automatic linebreaks and indentation (but does not support mixed content properly).

    Namespace Support

    The writer contains extensive support for XML Namespaces, so that a client application does not have to keep track of prefixes and supply xmlns attributes. By default, the XML writer will generate Namespace declarations in the form _NS1, _NS2, etc., wherever they are needed, as in the following example:

     w.startDocument();
 w.emptyElement("http://www.foo.com/ns/", "foo");
 w.endDocument();

    The resulting document will look like this:

     <?xml version="1.0" standalone="yes"?>

 <_NS1:foo xmlns:_NS1="http://www.foo.com/ns/"/>

    In many cases, document authors will prefer to choose their own prefixes rather than using the (ugly) default names. The XML writer allows two methods for selecting prefixes:

    1. the qualified name
    2. the setPrefix method.

    Whenever the XML writer finds a new Namespace URI, it checks to see if a qualified (prefixed) name is also available; if so it attempts to use the name's prefix (as long as the prefix is not already in use for another Namespace URI).

    Before writing a document, the client can also pre-map a prefix to a Namespace URI with the setPrefix method:

     w.setPrefix("http://www.foo.com/ns/", "foo");
 w.startDocument();
 w.emptyElement("http://www.foo.com/ns/", "foo");
 w.endDocument();

    The resulting document will look like this:

     <?xml version="1.0" standalone="yes"?>

 <foo:foo xmlns:foo="http://www.foo.com/ns/"/>

    The default Namespace simply uses an empty string as the prefix:

     w.setPrefix("http://www.foo.com/ns/", "");
 w.startDocument();
 w.emptyElement("http://www.foo.com/ns/", "foo");
 w.endDocument();

    The resulting document will look like this:

     <?xml version="1.0" standalone="yes"?>

 <foo xmlns="http://www.foo.com/ns/"/>

    By default, the XML writer will not declare a Namespace until it is actually used. Sometimes, this approach will create a large number of Namespace declarations, as in the following example:

     <xml version="1.0" standalone="yes"?>

 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description about="http://www.foo.com/ids/books/12345">
   <dc:title xmlns:dc="http://www.purl.org/dc/">A Dark Night</dc:title>
   <dc:creator xmlns:dc="http://www.purl.org/dc/">Jane Smith</dc:title>
   <dc:date xmlns:dc="http://www.purl.org/dc/">2000-09-09</dc:title>
  </rdf:Description>
 </rdf:RDF>

    The "rdf" prefix is declared only once, because the RDF Namespace is used by the root element and can be inherited by all of its descendants; the "dc" prefix, on the other hand, is declared three times, because no higher element uses the Namespace. To solve this problem, you can instruct the XML writer to predeclare Namespaces on the root element even if they are not used there:

     w.forceNSDecl("http://www.purl.org/dc/");

    Now, the "dc" prefix will be declared on the root element even though it's not needed there, and can be inherited by its descendants:

     <xml version="1.0" standalone="yes"?>

 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
             xmlns:dc="http://www.purl.org/dc/">
  <rdf:Description about="http://www.foo.com/ids/books/12345">
   <dc:title>A Dark Night</dc:title>
   <dc:creator>Jane Smith</dc:title>
   <dc:date>2000-09-09</dc:title>
  </rdf:Description>
 </rdf:RDF>

    This approach is also useful for declaring Namespace prefixes that be used by qualified names appearing in attribute values or character data.

    See Also:
    XMLFilter, ContentHandler

    • Constructor Summary

      Constructors 
      Constructor Description
      XMLWriter()
      Create a new XML writer.
      XMLWriter​(java.io.Writer writer)
      Create a new XML writer.
      XMLWriter​(org.xml.sax.XMLReader xmlreader)
      Create a new XML writer.
      XMLWriter​(org.xml.sax.XMLReader xmlreader, java.io.Writer writer)
      Create a new XML writer.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void characters​(char[] ch, int start, int len)
      Write character data.
      void characters​(java.lang.String data)
      Write a string of character data, with XML escaping.
      void comment​(char[] ch, int start, int length)  
      void dataElement​(java.lang.String localName, java.lang.String content)
      Write an element with character data content but no attributes or Namespace URI.
      void dataElement​(java.lang.String uri, java.lang.String localName, java.lang.String content)
      Write an element with character data content but no attributes.
      void dataElement​(java.lang.String uri, java.lang.String localName, java.lang.String qName, org.xml.sax.Attributes atts, java.lang.String content)
      Write an element with character data content.
      void emptyElement​(java.lang.String localName)
      Add an empty element without a Namespace URI, qname or attributes.
      void emptyElement​(java.lang.String uri, java.lang.String localName)
      Add an empty element without a qname or attributes.
      void emptyElement​(java.lang.String uri, java.lang.String localName, java.lang.String qName, org.xml.sax.Attributes atts)
      Write an empty element.
      void endCDATA()  
      void endDocument()
      Write a newline at the end of the document.
      void endDTD()  
      void endElement​(java.lang.String localName)
      End an element without a Namespace URI or qname.
      void endElement​(java.lang.String uri, java.lang.String localName)
      End an element without a qname.
      void endElement​(java.lang.String uri, java.lang.String localName, java.lang.String qName)
      Write an end tag.
      void endEntity​(java.lang.String name)  
      void flush()
      Flush the output.
      void forceNSDecl​(java.lang.String uri)
      Force a Namespace to be declared on the root element.
      void forceNSDecl​(java.lang.String uri, java.lang.String prefix)
      Force a Namespace declaration with a preferred prefix.
      java.lang.String getOutputProperty​(java.lang.String key)  
      java.lang.String getPrefix​(java.lang.String uri)
      Get the current or preferred prefix for a Namespace URI.
      void ignorableWhitespace​(char[] ch, int start, int length)
      Write ignorable whitespace.
      void processingInstruction​(java.lang.String target, java.lang.String data)
      Write a processing instruction.
      void reset()
      Reset the writer.
      void setOutput​(java.io.Writer writer)
      Set a new output destination for the document.
      void setOutputProperty​(java.lang.String key, java.lang.String value)  
      void setPrefix​(java.lang.String uri, java.lang.String prefix)
      Specify a preferred prefix for a Namespace URI.
      void startCDATA()  
      void startDocument()
      Write the XML declaration at the beginning of the document.
      void startDTD​(java.lang.String name, java.lang.String publicid, java.lang.String systemid)  
      void startElement​(java.lang.String localName)
      Start a new element without a qname, attributes or a Namespace URI.
      void startElement​(java.lang.String uri, java.lang.String localName)
      Start a new element without a qname or attributes.
      void startElement​(java.lang.String uri, java.lang.String localName, java.lang.String qName, org.xml.sax.Attributes atts)
      Write a start tag.
      void startEntity​(java.lang.String name)  

      • Methods inherited from class org.xml.sax.helpers.XMLFilterImpl

        endPrefixMapping, error, fatalError, getContentHandler, getDTDHandler, getEntityResolver, getErrorHandler, getFeature, getParent, getProperty, notationDecl, parse, parse, resolveEntity, setContentHandler, setDocumentLocator, setDTDHandler, setEntityResolver, setErrorHandler, setFeature, setParent, setProperty, skippedEntity, startPrefixMapping, unparsedEntityDecl, warning

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • XMLWriter

        public XMLWriter()
        Create a new XML writer.

        Write to standard output.

      • XMLWriter

        public XMLWriter​(java.io.Writer writer)
        Create a new XML writer.

        Write to the writer provided.

        Parameters:
        writer - The output destination, or null to use standard output.

      • XMLWriter

        public XMLWriter​(org.xml.sax.XMLReader xmlreader)
        Create a new XML writer.

        Use the specified XML reader as the parent.

        Parameters:
        xmlreader - The parent in the filter chain, or null for no parent.

      • XMLWriter

        public XMLWriter​(org.xml.sax.XMLReader xmlreader,
                 java.io.Writer writer)
        Create a new XML writer.

        Use the specified XML reader as the parent, and write to the specified writer.

        Parameters:
        xmlreader - The parent in the filter chain, or null for no parent.
        writer - The output destination, or null to use standard output.

    • Method Detail

      • reset

        public void reset()
        Reset the writer.

        This method is especially useful if the writer throws an exception before it is finished, and you want to reuse the writer for a new document. It is usually a good idea to invoke flush before resetting the writer, to make sure that no output is lost.

        This method is invoked automatically by the startDocument method before writing a new document.

        Note: this method will not clear the prefix or URI information in the writer or the selected output writer.

        See Also:
        flush()

      • flush

        public void flush()
           throws java.io.IOException
        Flush the output.

        This method flushes the output stream. It is especially useful when you need to make certain that the entire document has been written to output but do not want to close the output stream.

        This method is invoked automatically by the endDocument method after writing a document.

        Throws:
        java.io.IOException
        See Also:
        reset()

      • setOutput

        public void setOutput​(java.io.Writer writer)
        Set a new output destination for the document.
        Parameters:
        writer - The output destination, or null to use standard output.
        See Also:
        flush()

      • getPrefix

        public java.lang.String getPrefix​(java.lang.String uri)
        Get the current or preferred prefix for a Namespace URI.
        Parameters:
        uri - The Namespace URI.
        Returns:
        The preferred prefix, or "" for the default Namespace.
        See Also:
        setPrefix(java.lang.String, java.lang.String)

      • forceNSDecl

        public void forceNSDecl​(java.lang.String uri)
        Force a Namespace to be declared on the root element.

        By default, the XMLWriter will declare only the Namespaces needed for an element; as a result, a Namespace may be declared many places in a document if it is not used on the root element.

        This method forces a Namespace to be declared on the root element even if it is not used there, and reduces the number of xmlns attributes in the document.

        Parameters:
        uri - The Namespace URI to declare.
        See Also:
        forceNSDecl(java.lang.String,java.lang.String), setPrefix(java.lang.String, java.lang.String)

      • startDocument

        public void startDocument()
                   throws org.xml.sax.SAXException
        Write the XML declaration at the beginning of the document. Pass the event on down the filter chain for further processing.
        Specified by:
        startDocument in interface org.xml.sax.ContentHandler
        Overrides:
        startDocument in class org.xml.sax.helpers.XMLFilterImpl
        Throws:
        org.xml.sax.SAXException - If there is an error writing the XML declaration, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.startDocument()

      • endDocument

        public void endDocument()
                 throws org.xml.sax.SAXException
        Write a newline at the end of the document. Pass the event on down the filter chain for further processing.
        Specified by:
        endDocument in interface org.xml.sax.ContentHandler
        Overrides:
        endDocument in class org.xml.sax.helpers.XMLFilterImpl
        Throws:
        org.xml.sax.SAXException - If there is an error writing the newline, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.endDocument()

      • startElement

        public void startElement​(java.lang.String uri,
                         java.lang.String localName,
                         java.lang.String qName,
                         org.xml.sax.Attributes atts)
                  throws org.xml.sax.SAXException
        Write a start tag. Pass the event on down the filter chain for further processing.
        Specified by:
        startElement in interface org.xml.sax.ContentHandler
        Overrides:
        startElement in class org.xml.sax.helpers.XMLFilterImpl
        Parameters:
        uri - The Namespace URI, or the empty string if none is available.
        localName - The element's local (unprefixed) name (required).
        qName - The element's qualified (prefixed) name, or the empty string is none is available. This method will use the qName as a template for generating a prefix if necessary, but it is not guaranteed to use the same qName.
        atts - The element's attribute list (must not be null).
        Throws:
        org.xml.sax.SAXException - If there is an error writing the start tag, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.startElement(java.lang.String, java.lang.String, java.lang.String, org.xml.sax.Attributes)

      • endElement

        public void endElement​(java.lang.String uri,
                       java.lang.String localName,
                       java.lang.String qName)
                throws org.xml.sax.SAXException
        Write an end tag. Pass the event on down the filter chain for further processing.
        Specified by:
        endElement in interface org.xml.sax.ContentHandler
        Overrides:
        endElement in class org.xml.sax.helpers.XMLFilterImpl
        Parameters:
        uri - The Namespace URI, or the empty string if none is available.
        localName - The element's local (unprefixed) name (required).
        qName - The element's qualified (prefixed) name, or the empty string is none is available. This method will use the qName as a template for generating a prefix if necessary, but it is not guaranteed to use the same qName.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the end tag, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.endElement(java.lang.String, java.lang.String, java.lang.String)

      • characters

        public void characters​(char[] ch,
                       int start,
                       int len)
                throws org.xml.sax.SAXException
        Write character data. Pass the event on down the filter chain for further processing.
        Specified by:
        characters in interface org.xml.sax.ContentHandler
        Overrides:
        characters in class org.xml.sax.helpers.XMLFilterImpl
        Parameters:
        ch - The array of characters to write.
        start - The starting position in the array.
        length - The number of characters to write.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the characters, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.characters(char[], int, int)

      • ignorableWhitespace

        public void ignorableWhitespace​(char[] ch,
                                int start,
                                int length)
                         throws org.xml.sax.SAXException
        Write ignorable whitespace. Pass the event on down the filter chain for further processing.
        Specified by:
        ignorableWhitespace in interface org.xml.sax.ContentHandler
        Overrides:
        ignorableWhitespace in class org.xml.sax.helpers.XMLFilterImpl
        Parameters:
        ch - The array of characters to write.
        start - The starting position in the array.
        length - The number of characters to write.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the whitespace, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.ignorableWhitespace(char[], int, int)

      • processingInstruction

        public void processingInstruction​(java.lang.String target,
                                  java.lang.String data)
                           throws org.xml.sax.SAXException
        Write a processing instruction. Pass the event on down the filter chain for further processing.
        Specified by:
        processingInstruction in interface org.xml.sax.ContentHandler
        Overrides:
        processingInstruction in class org.xml.sax.helpers.XMLFilterImpl
        Parameters:
        target - The PI target.
        data - The PI data.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the PI, or if a handler further down the filter chain raises an exception.
        See Also:
        ContentHandler.processingInstruction(java.lang.String, java.lang.String)

      • emptyElement

        public void emptyElement​(java.lang.String uri,
                         java.lang.String localName,
                         java.lang.String qName,
                         org.xml.sax.Attributes atts)
                  throws org.xml.sax.SAXException
        Write an empty element. This method writes an empty element tag rather than a start tag followed by an end tag. Both a startElement and an endElement event will be passed on down the filter chain.
        Parameters:
        uri - The element's Namespace URI, or the empty string if the element has no Namespace or if Namespace processing is not being performed.
        localName - The element's local name (without prefix). This parameter must be provided.
        qName - The element's qualified name (with prefix), or the empty string if none is available. This parameter is strictly advisory: the writer may or may not use the prefix attached.
        atts - The element's attribute list.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the empty tag, or if a handler further down the filter chain raises an exception.
        See Also:
        startElement(java.lang.String, java.lang.String, java.lang.String, org.xml.sax.Attributes), endElement(java.lang.String, java.lang.String, java.lang.String)

      • startElement

        public void startElement​(java.lang.String uri,
                         java.lang.String localName)
                  throws org.xml.sax.SAXException
        Start a new element without a qname or attributes.

        This method will provide a default empty attribute list and an empty string for the qualified name. It invokes startElement(String, String, String, Attributes) directly.

        Parameters:
        uri - The element's Namespace URI.
        localName - The element's local name.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the start tag, or if a handler further down the filter chain raises an exception.
        See Also:
        startElement(String, String, String, Attributes)

      • startElement

        public void startElement​(java.lang.String localName)
                  throws org.xml.sax.SAXException
        Start a new element without a qname, attributes or a Namespace URI.

        This method will provide an empty string for the Namespace URI, and empty string for the qualified name, and a default empty attribute list. It invokes #startElement(String, String, String, Attributes)} directly.

        Parameters:
        localName - The element's local name.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the start tag, or if a handler further down the filter chain raises an exception.
        See Also:
        startElement(String, String, String, Attributes)

      • endElement

        public void endElement​(java.lang.String uri,
                       java.lang.String localName)
                throws org.xml.sax.SAXException
        End an element without a qname.

        This method will supply an empty string for the qName. It invokes endElement(String, String, String) directly.

        Parameters:
        uri - The element's Namespace URI.
        localName - The element's local name.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the end tag, or if a handler further down the filter chain raises an exception.
        See Also:
        endElement(String, String, String)

      • endElement

        public void endElement​(java.lang.String localName)
                throws org.xml.sax.SAXException
        End an element without a Namespace URI or qname.

        This method will supply an empty string for the qName and an empty string for the Namespace URI. It invokes endElement(String, String, String) directly.

        Parameters:
        localName - The element's local name.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the end tag, or if a handler further down the filter chain raises an exception.
        See Also:
        endElement(String, String, String)

      • emptyElement

        public void emptyElement​(java.lang.String uri,
                         java.lang.String localName)
                  throws org.xml.sax.SAXException
        Add an empty element without a qname or attributes.

        This method will supply an empty string for the qname and an empty attribute list. It invokes emptyElement(String, String, String, Attributes) directly.

        Parameters:
        uri - The element's Namespace URI.
        localName - The element's local name.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the empty tag, or if a handler further down the filter chain raises an exception.
        See Also:
        emptyElement(String, String, String, Attributes)

      • emptyElement

        public void emptyElement​(java.lang.String localName)
                  throws org.xml.sax.SAXException
        Add an empty element without a Namespace URI, qname or attributes.

        This method will supply an empty string for the qname, and empty string for the Namespace URI, and an empty attribute list. It invokes emptyElement(String, String, String, Attributes) directly.

        Parameters:
        localName - The element's local name.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the empty tag, or if a handler further down the filter chain raises an exception.
        See Also:
        emptyElement(String, String, String, Attributes)

      • characters

        public void characters​(java.lang.String data)
                throws org.xml.sax.SAXException
        Write a string of character data, with XML escaping.

        This is a convenience method that takes an XML String, converts it to a character array, then invokes characters(char[], int, int).

        Parameters:
        data - The character data.
        Throws:
        org.xml.sax.SAXException - If there is an error writing the string, or if a handler further down the filter chain raises an exception.
        See Also:
        characters(char[], int, int)

      • comment

        public void comment​(char[] ch,
                    int start,
                    int length)
             throws org.xml.sax.SAXException
        Specified by:
        comment in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • endCDATA

        public void endCDATA()
              throws org.xml.sax.SAXException
        Specified by:
        endCDATA in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • endDTD

        public void endDTD()
            throws org.xml.sax.SAXException
        Specified by:
        endDTD in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • endEntity

        public void endEntity​(java.lang.String name)
               throws org.xml.sax.SAXException
        Specified by:
        endEntity in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • startCDATA

        public void startCDATA()
                throws org.xml.sax.SAXException
        Specified by:
        startCDATA in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • startDTD

        public void startDTD​(java.lang.String name,
                     java.lang.String publicid,
                     java.lang.String systemid)
              throws org.xml.sax.SAXException
        Specified by:
        startDTD in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • startEntity

        public void startEntity​(java.lang.String name)
                 throws org.xml.sax.SAXException
        Specified by:
        startEntity in interface org.xml.sax.ext.LexicalHandler
        Throws:
        org.xml.sax.SAXException

      • getOutputProperty

        public java.lang.String getOutputProperty​(java.lang.String key)

      • setOutputProperty

        public void setOutputProperty​(java.lang.String key,
                              java.lang.String value)