Class XMLWriter
- All Implemented Interfaces:
ContentHandler
,DTDHandler
,EntityResolver
,ErrorHandler
,LexicalHandler
,XMLFilter
,XMLReader
- Direct Known Subclasses:
DataWriter
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:
- the qualified name
- the
startPrefixMapping(String, String)
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.
- Since:
- JAXB 1.0
- Version:
- 0.2
- Author:
- David Megginson, david@megginson.com
- See Also:
-
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
characters
(char[] ch, int start, int len) Write character data.void
characters
(String data) Write a string of character data, with XML escaping.void
comment
(char[] ch, int start, int length) void
dataElement
(String localName, String content) Write an element with character data content but no attributes or Namespace URI.void
dataElement
(String uri, String localName, String content) Write an element with character data content but no attributes.void
dataElement
(String uri, String localName, String qName, Attributes atts, String content) Write an element with character data content.void
endCDATA()
void
Write a newline at the end of the document.void
endDTD()
void
endElement
(String localName) End an element without a Namespace URI or qname.void
endElement
(String uri, String localName) End an element without a qname.void
endElement
(String uri, String localName, String qName) Write an end tag.void
void
flush()
Flush the output.void
ignorableWhitespace
(char[] ch, int start, int length) Write ignorable whitespace.void
processingInstruction
(String target, String data) Write a processing instruction.void
reset()
Reset the writer.void
setEncoding
(String encoding) void
Sets the header string.void
Set a new output destination for the document.void
setXmlDecl
(boolean _writeXmlDecl) Set whether the writer should print out the XML declaration (<?xml version='1.0' ... ?>
).void
void
Write the XML declaration at the beginning of the document.void
void
startElement
(String localName) Start a new element without a qname, attributes or a Namespace URI.void
startElement
(String uri, String localName) Start a new element without a qname or attributes.void
startElement
(String uri, String localName, String qName, Attributes atts) Write a start tag.void
startEntity
(String name) void
startPrefixMapping
(String prefix, String uri) 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, unparsedEntityDecl, warning
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface org.xml.sax.ContentHandler
declaration
-
Constructor Details
-
XMLWriter
Create a new XML writer.Write to the writer provided.
- Parameters:
writer
- The output destination, or null to use standard output.encoding
- If non-null string is specified, it is written as a part of the XML declaration.
-
XMLWriter
-
-
Method Details
-
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 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 _commit the output stream.
This method is invoked automatically by the
endDocument
method after writing a document.- Throws:
IOException
- See Also:
-
setOutput
Set a new output destination for the document.- Parameters:
writer
- The output destination, or null to use standard output.- See Also:
-
setEncoding
-
setXmlDecl
public void setXmlDecl(boolean _writeXmlDecl) Set whether the writer should print out the XML declaration (<?xml version='1.0' ... ?>
).This option is set to true by default.
-
setHeader
Sets the header string. This string will be written right after the xml declaration without any escaping. Useful for generating a boiler-plate DOCTYPE decl, PIs, and comments.- Parameters:
_header
- passing null will work as if the empty string is passed.
-
startPrefixMapping
- Specified by:
startPrefixMapping
in interfaceContentHandler
- Overrides:
startPrefixMapping
in classXMLFilterImpl
- Throws:
SAXException
-
startDocument
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 interfaceContentHandler
- Overrides:
startDocument
in classXMLFilterImpl
- Throws:
SAXException
- If there is an error writing the XML declaration, or if a handler further down the filter chain raises an exception.- See Also:
-
endDocument
Write a newline at the end of the document. Pass the event on down the filter chain for further processing.- Specified by:
endDocument
in interfaceContentHandler
- Overrides:
endDocument
in classXMLFilterImpl
- Throws:
SAXException
- If there is an error writing the newline, or if a handler further down the filter chain raises an exception.- See Also:
-
startElement
public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException Write a start tag. Pass the event on down the filter chain for further processing.- Specified by:
startElement
in interfaceContentHandler
- Overrides:
startElement
in classXMLFilterImpl
- 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:
SAXException
- If there is an error writing the start tag, or if a handler further down the filter chain raises an exception.- See Also:
-
endElement
Write an end tag. Pass the event on down the filter chain for further processing.- Specified by:
endElement
in interfaceContentHandler
- Overrides:
endElement
in classXMLFilterImpl
- 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:
SAXException
- If there is an error writing the end tag, or if a handler further down the filter chain raises an exception.- See Also:
-
characters
Write character data. Pass the event on down the filter chain for further processing.- Specified by:
characters
in interfaceContentHandler
- Overrides:
characters
in classXMLFilterImpl
- Parameters:
ch
- The array of characters to write.start
- The starting position in the array.len
- The number of characters to write.- Throws:
SAXException
- If there is an error writing the characters, or if a handler further down the filter chain raises an exception.- See Also:
-
ignorableWhitespace
Write ignorable whitespace. Pass the event on down the filter chain for further processing.- Specified by:
ignorableWhitespace
in interfaceContentHandler
- Overrides:
ignorableWhitespace
in classXMLFilterImpl
- Parameters:
ch
- The array of characters to write.start
- The starting position in the array.length
- The number of characters to write.- Throws:
SAXException
- If there is an error writing the whitespace, or if a handler further down the filter chain raises an exception.- See Also:
-
processingInstruction
Write a processing instruction. Pass the event on down the filter chain for further processing.- Specified by:
processingInstruction
in interfaceContentHandler
- Overrides:
processingInstruction
in classXMLFilterImpl
- Parameters:
target
- The PI target.data
- The PI data.- Throws:
SAXException
- If there is an error writing the PI, or if a handler further down the filter chain raises an exception.- See Also:
-
startElement
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:
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
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:
SAXException
- If there is an error writing the start tag, or if a handler further down the filter chain raises an exception.- See Also:
-
endElement
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:
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
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:
SAXException
- If there is an error writing the end tag, or if a handler further down the filter chain raises an exception.- See Also:
-
dataElement
public void dataElement(String uri, String localName, String qName, Attributes atts, String content) throws SAXException Write an element with character data content.This is a convenience method to write a complete element with character data content, including the start tag and end tag.
This method invokes
startElement(String, String, String, Attributes)
, followed bycharacters(String)
, followed byendElement(String, String, String)
.- Parameters:
uri
- The element's Namespace URI.localName
- The element's local name.qName
- The element's default qualified name.atts
- The element's attributes.content
- The character data content.- Throws:
SAXException
- If there is an error writing the empty tag, or if a handler further down the filter chain raises an exception.- See Also:
-
dataElement
Write an element with character data content but no attributes.This is a convenience method to write a complete element with character data content, including the start tag and end tag. This method provides an empty string for the qname and an empty attribute list.
This method invokes
startElement(String, String, String, Attributes)
, followed bycharacters(String)
, followed byendElement(String, String, String)
.- Parameters:
uri
- The element's Namespace URI.localName
- The element's local name.content
- The character data content.- Throws:
SAXException
- If there is an error writing the empty tag, or if a handler further down the filter chain raises an exception.- See Also:
-
dataElement
Write an element with character data content but no attributes or Namespace URI.This is a convenience method to write a complete element with character data content, including the start tag and end tag. The method provides an empty string for the Namespace URI, and empty string for the qualified name, and an empty attribute list.
This method invokes
startElement(String, String, String, Attributes)
, followed bycharacters(String)
, followed byendElement(String, String, String)
.- Parameters:
localName
- The element's local name.content
- The character data content.- Throws:
SAXException
- If there is an error writing the empty tag, or if a handler further down the filter chain raises an exception.- See Also:
-
characters
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:
SAXException
- If there is an error writing the string, or if a handler further down the filter chain raises an exception.- See Also:
-
startDTD
- Specified by:
startDTD
in interfaceLexicalHandler
- Throws:
SAXException
-
endDTD
- Specified by:
endDTD
in interfaceLexicalHandler
- Throws:
SAXException
-
startEntity
- Specified by:
startEntity
in interfaceLexicalHandler
- Throws:
SAXException
-
endEntity
- Specified by:
endEntity
in interfaceLexicalHandler
- Throws:
SAXException
-
startCDATA
- Specified by:
startCDATA
in interfaceLexicalHandler
- Throws:
SAXException
-
endCDATA
- Specified by:
endCDATA
in interfaceLexicalHandler
- Throws:
SAXException
-
comment
- Specified by:
comment
in interfaceLexicalHandler
- Throws:
SAXException
-