gnu.xml.util

Class XMLWriter

public class XMLWriter extends Object implements ContentHandler, LexicalHandler, DTDHandler, DeclHandler

This class is a SAX handler which writes all its input as a well formed XML or XHTML document. If driven using SAX2 events, this output may include a recreated document type declaration, subject to limitations of SAX (no internal subset exposed) or DOM (the important declarations, with their documentation, are discarded).

By default, text is generated "as-is", but some optional modes are supported. Pretty-printing is supported, to make life easier for people reading the output. XHTML (1.0) output has can be made particularly pretty; all the built-in character entities are known. Canonical XML can also be generated, assuming the input is properly formed.


Some of the methods on this class are intended for applications to use directly, rather than as pure SAX2 event callbacks. Some of those methods access the JavaBeans properties (used to tweak output formats, for example canonicalization and pretty printing). Subclasses are expected to add new behaviors, not to modify current behavior, so many such methods are final.

The write*() methods may be slightly simpler for some applications to use than direct callbacks. For example, they support a simple policy for encoding data items as the content of a single element.

To reuse an XMLWriter you must provide it with a new Writer, since this handler closes the writer it was given as part of its endDocument() handling. (XML documents have an end of input, and the way to encode that on a stream is to close it.)


Note that any relative URIs in the source document, as found in entity and notation declarations, ought to have been fully resolved by the parser providing events to this handler. This means that the output text should only have fully resolved URIs, which may not be the desired behavior in cases where later binding is desired.

Note that due to SAX2 defaults, you may need to manually ensure that the input events are XML-conformant with respect to namespace prefixes and declarations. NSFilter is one solution to this problem, in the context of processing pipelines. Something as simple as connecting this handler to a parser might not generate the correct output. Another workaround is to ensure that the namespace-prefixes feature is always set to true, if you're hooking this directly up to some XMLReader implementation.

Version: $Date: 2001/11/20 01:15:45 $

Author: David Brownell

See Also:

Constructor Summary
XMLWriter()
Constructs this handler with System.out used to write SAX events using the UTF-8 encoding.
XMLWriter(OutputStream out)
Constructs a handler which writes all input to the output stream in the UTF-8 encoding, and closes it when endDocument is called.
XMLWriter(Writer writer)
Constructs a handler which writes all input to the writer, and then closes the writer when the document ends.
XMLWriter(Writer writer, String encoding)
Constructs a handler which writes all input to the writer, and then closes the writer when the document ends.
Method Summary
voidattributeDecl(String eName, String aName, String type, String mode, String value)
SAX2: called on attribute declarations
voidcharacters(char[] ch, int start, int length)
SAX1: reports content characters
voidcomment(char[] ch, int start, int length)
SAX2: called when comments are parsed.
voidelementDecl(String name, String model)
SAX2: called on element declarations
voidendCDATA()
SAX2: called after parsing CDATA characters
voidendDocument()
SAX1: indicates the completion of a parse.
voidendDTD()
SAX2: called after the doctype is parsed
voidendElement(String uri, String localName, String qName)
SAX2: indicates the end of an element
voidendEntity(String name)
SAX2: called after parsing a general entity in content
voidendPrefixMapping(String prefix)
SAX2: ignored.
voidexternalEntityDecl(String name, String publicId, String systemId)
SAX2: called on external entity declarations
protected voidfatal(String message, Exception e)
Used internally and by subclasses, this encapsulates the logic involved in reporting fatal errors.
voidflush()
Flushes the output stream.
voidignorableWhitespace(char[] ch, int start, int length)
SAX1: reports ignorable whitespace
voidinternalEntityDecl(String name, String value)
SAX2: called on internal entity declarations
booleanisCanonical()
Returns value of flag controlling canonical output.
booleanisExpandingEntities()
Returns true if the output will have no entity references; returns false (the default) otherwise.
booleanisPrettyPrinting()
Returns value of flag controlling pretty printing.
booleanisXhtml()
Returns true if the output attempts to echo the input following "transitional" XHTML rules and matching the "HTML Compatibility Guidelines" so that an HTML version 3 browser can read the output as HTML; returns false (the default) othewise.
voidnotationDecl(String name, String publicId, String systemId)
SAX1: called on notation declarations
voidprocessingInstruction(String target, String data)
SAX1: reports a PI.
voidsetCanonical(boolean value)
Sets the output style to be canonicalized.
voidsetDocumentLocator(Locator l)
SAX1: provides parser status information
voidsetEOL(String eolString)
Assigns the line ending style to be used on output.
voidsetErrorHandler(ErrorHandler handler)
Assigns the error handler to be used to present most fatal errors.
voidsetExpandingEntities(boolean value)
Controls whether the output text contains references to entities (the default), or instead contains the expanded values of those entities.
voidsetPrettyPrinting(boolean value)
Controls pretty-printing, which by default is not enabled (and currently is most useful for XHTML output).
voidsetWriter(Writer writer, String encoding)
Resets the handler to write a new text document.
voidsetXhtml(boolean value)
Controls whether the output should attempt to follow the "transitional" XHTML rules so that it meets the "HTML Compatibility Guidelines" appendix in the XHTML specification.
voidskippedEntity(String name)
SAX1: indicates a non-expanded entity reference
voidstartCDATA()
SAX2: called before parsing CDATA characters
voidstartDocument()
SAX1: indicates the beginning of a document parse.
voidstartDTD(String name, String publicId, String systemId)
SAX2: called when the doctype is partially parsed Note that this, like other doctype related calls, is ignored when XHTML is in use.
voidstartElement(String uri, String localName, String qName, Attributes atts)
SAX2: indicates the start of an element.
voidstartEntity(String name)
SAX2: called before parsing a general entity in content
voidstartPrefixMapping(String prefix, String uri)
SAX2: ignored.
voidunparsedEntityDecl(String name, String publicId, String systemId, String notationName)
SAX1: called on unparsed entity declarations
voidwrite(String data)
Writes the string as if characters() had been called on the contents of the string.
voidwriteElement(String uri, String localName, String qName, Attributes atts, String content)
Writes an element that has content consisting of a single string.
voidwriteElement(String uri, String localName, String qName, Attributes atts, int content)
Writes an element that has content consisting of a single integer, encoded as a decimal string.
voidwriteEmptyElement(String uri, String localName, String qName, Attributes atts)
Writes an empty element.

Constructor Detail

XMLWriter

public XMLWriter()
Constructs this handler with System.out used to write SAX events using the UTF-8 encoding. Avoid using this except when you know it's safe to close System.out at the end of the document.

XMLWriter

public XMLWriter(OutputStream out)
Constructs a handler which writes all input to the output stream in the UTF-8 encoding, and closes it when endDocument is called. (Yes it's annoying that this throws an exception -- but there's really no way around it, since it's barely possible a JDK may exist somewhere that doesn't know how to emit UTF-8.)

XMLWriter

public XMLWriter(Writer writer)
Constructs a handler which writes all input to the writer, and then closes the writer when the document ends. If an XML declaration is written onto the output, and this class can determine the name of the character encoding for this writer, that encoding name will be included in the XML declaration.

See the description of the constructor which takes an encoding name for imporant information about selection of encodings.

Parameters: writer XML text is written to this writer.

XMLWriter

public XMLWriter(Writer writer, String encoding)
Constructs a handler which writes all input to the writer, and then closes the writer when the document ends. If an XML declaration is written onto the output, this class will use the specified encoding name in that declaration. If no encoding name is specified, no encoding name will be declared unless this class can otherwise determine the name of the character encoding for this writer.

At this time, only the UTF-8 ("UTF8") and UTF-16 ("Unicode") output encodings are fully lossless with respect to XML data. If you use any other encoding you risk having your data be silently mangled on output, as the standard Java character encoding subsystem silently maps non-encodable characters to a question mark ("?") and will not report such errors to applications.

For a few other encodings the risk can be reduced. If the writer is a java.io.OutputStreamWriter, and uses either the ISO-8859-1 ("8859_1", "ISO8859_1", etc) or US-ASCII ("ASCII") encodings, content which can't be encoded in those encodings will be written safely. Where relevant, the XHTML entity names will be used; otherwise, numeric character references will be emitted.

However, there remain a number of cases where substituting such entity or character references is not an option. Such references are not usable within a DTD, comment, PI, or CDATA section. Neither may they be used when element, attribute, entity, or notation names have the problematic characters.

Parameters: writer XML text is written to this writer. encoding if non-null, and an XML declaration is written, this is the name that will be used for the character encoding.

Method Detail

attributeDecl

public final void attributeDecl(String eName, String aName, String type, String mode, String value)
SAX2: called on attribute declarations

characters

public final void characters(char[] ch, int start, int length)
SAX1: reports content characters

comment

public final void comment(char[] ch, int start, int length)
SAX2: called when comments are parsed. When XHTML is used, the old HTML tradition of using comments to for inline CSS, or for JavaScript code is discouraged. This is because XML processors are encouraged to discard, on the grounds that comments are for users (and perhaps text editors) not programs. Instead, use external scripts

elementDecl

public final void elementDecl(String name, String model)
SAX2: called on element declarations

endCDATA

public final void endCDATA()
SAX2: called after parsing CDATA characters

endDocument

public void endDocument()
SAX1: indicates the completion of a parse. Note that all complete SAX event streams make this call, even if an error is reported during a parse.

endDTD

public final void endDTD()
SAX2: called after the doctype is parsed

endElement

public final void endElement(String uri, String localName, String qName)
SAX2: indicates the end of an element

endEntity

public final void endEntity(String name)
SAX2: called after parsing a general entity in content

endPrefixMapping

public final void endPrefixMapping(String prefix)
SAX2: ignored.

externalEntityDecl

public final void externalEntityDecl(String name, String publicId, String systemId)
SAX2: called on external entity declarations

fatal

protected void fatal(String message, Exception e)
Used internally and by subclasses, this encapsulates the logic involved in reporting fatal errors. It uses locator information for good diagnostics, if available, and gives the application's ErrorHandler the opportunity to handle the error before throwing an exception.

flush

public final void flush()
Flushes the output stream. When this handler is used in long lived pipelines, it can be important to flush buffered state, for example so that it can reach the disk as part of a state checkpoint.

ignorableWhitespace

public final void ignorableWhitespace(char[] ch, int start, int length)
SAX1: reports ignorable whitespace

internalEntityDecl

public final void internalEntityDecl(String name, String value)
SAX2: called on internal entity declarations

isCanonical

public final boolean isCanonical()
Returns value of flag controlling canonical output.

isExpandingEntities

public final boolean isExpandingEntities()
Returns true if the output will have no entity references; returns false (the default) otherwise.

isPrettyPrinting

public final boolean isPrettyPrinting()
Returns value of flag controlling pretty printing.

isXhtml

public final boolean isXhtml()
Returns true if the output attempts to echo the input following "transitional" XHTML rules and matching the "HTML Compatibility Guidelines" so that an HTML version 3 browser can read the output as HTML; returns false (the default) othewise.

notationDecl

public final void notationDecl(String name, String publicId, String systemId)
SAX1: called on notation declarations

processingInstruction

public final void processingInstruction(String target, String data)
SAX1: reports a PI. This doesn't check for illegal target names, such as "xml" or "XML", or namespace-incompatible ones like "big:dog"; the caller is responsible for ensuring those names are legal.

setCanonical

public final void setCanonical(boolean value)
Sets the output style to be canonicalized. Input events must meet requirements that are slightly more stringent than the basic well-formedness ones, and include:

Note that fragments of XML documents, as specified by an XPath node set, may be canonicalized. In such cases, elements may need some fixup (for xml:* attributes and application-specific context).

Throws: IllegalArgumentException if the output encoding is anything other than UTF-8.

setDocumentLocator

public final void setDocumentLocator(Locator l)
SAX1: provides parser status information

setEOL

public final void setEOL(String eolString)
Assigns the line ending style to be used on output.

Parameters: eolString null to use the system default; else "\n", "\r", or "\r\n".

setErrorHandler

public void setErrorHandler(ErrorHandler handler)
Assigns the error handler to be used to present most fatal errors.

setExpandingEntities

public final void setExpandingEntities(boolean value)
Controls whether the output text contains references to entities (the default), or instead contains the expanded values of those entities.

setPrettyPrinting

public final void setPrettyPrinting(boolean value)
Controls pretty-printing, which by default is not enabled (and currently is most useful for XHTML output). Pretty printing enables structural indentation, sorting of attributes by name, line wrapping, and potentially other mechanisms for making output more or less readable.

At this writing, structural indentation and line wrapping are enabled when pretty printing is enabled and the xml:space attribute has the value default (its other legal value is preserve, as defined in the XML specification). The three XHTML element types which use another value are recognized by their names (namespaces are ignored).

Also, for the record, the "pretty" aspect of printing here is more to provide basic structure on outputs that would otherwise risk being a single long line of text. For now, expect the structure to be ragged ... unless you'd like to submit a patch to make this be more strictly formatted!

Throws: IllegalStateException thrown if this method is invoked after output has begun.

setWriter

public final void setWriter(Writer writer, String encoding)
Resets the handler to write a new text document.

Parameters: writer XML text is written to this writer. encoding if non-null, and an XML declaration is written, this is the name that will be used for the character encoding.

Throws: IllegalStateException if the current document hasn't yet ended (with XMLWriter)

setXhtml

public final void setXhtml(boolean value)
Controls whether the output should attempt to follow the "transitional" XHTML rules so that it meets the "HTML Compatibility Guidelines" appendix in the XHTML specification. A "transitional" Document Type Declaration (DTD) is placed near the beginning of the output document, instead of whatever DTD would otherwise have been placed there, and XHTML empty elements are printed specially. When writing text in US-ASCII or ISO-8859-1 encodings, the predefined XHTML internal entity names are used (in preference to character references) when writing content characters which can't be expressed in those encodings.

When this option is enabled, it is the caller's responsibility to ensure that the input is otherwise valid as XHTML. Things to be careful of in all cases, as described in the appendix referenced above, include:

Additionally, some of the oldest browsers have additional quirks, to address with guidelines such as:

Also, some characteristics of the resulting output may be a function of whether the document is later given a MIME content type of text/html rather than one indicating XML (application/xml or text/xml). Worse, some browsers ignore MIME content types and prefer to rely URI name suffixes -- so an "index.xml" could always be XML, never XHTML, no matter its MIME type.

skippedEntity

public void skippedEntity(String name)
SAX1: indicates a non-expanded entity reference

startCDATA

public final void startCDATA()
SAX2: called before parsing CDATA characters

startDocument

public void startDocument()
SAX1: indicates the beginning of a document parse. If you're writing (well formed) fragments of XML, neither this nor endDocument should be called.

startDTD

public final void startDTD(String name, String publicId, String systemId)
SAX2: called when the doctype is partially parsed Note that this, like other doctype related calls, is ignored when XHTML is in use.

startElement

public final void startElement(String uri, String localName, String qName, Attributes atts)
SAX2: indicates the start of an element. When XHTML is in use, avoid attribute values with line breaks or multiple whitespace characters, since not all user agents handle them correctly.

startEntity

public final void startEntity(String name)
SAX2: called before parsing a general entity in content

startPrefixMapping

public final void startPrefixMapping(String prefix, String uri)
SAX2: ignored.

unparsedEntityDecl

public final void unparsedEntityDecl(String name, String publicId, String systemId, String notationName)
SAX1: called on unparsed entity declarations

write

public final void write(String data)
Writes the string as if characters() had been called on the contents of the string. This is particularly useful when applications act as producers and write data directly to event consumers.

writeElement

public void writeElement(String uri, String localName, String qName, Attributes atts, String content)
Writes an element that has content consisting of a single string.

See Also: XMLWriter XMLWriter

writeElement

public void writeElement(String uri, String localName, String qName, Attributes atts, int content)
Writes an element that has content consisting of a single integer, encoded as a decimal string.

See Also: XMLWriter XMLWriter

writeEmptyElement

public void writeEmptyElement(String uri, String localName, String qName, Attributes atts)
Writes an empty element.

See Also: XMLWriter

Source code is under GPL (with library exception) in the JAXP project at http://www.gnu.org/software/classpathx/jaxp
This documentation was derived from that source code on 2011-08-26.