gnu.xml.util

Class XMLWriter

Implemented Interfaces:
ContentHandler, DeclHandler, DTDHandler, LexicalHandler
Known Direct Subclasses:
TextConsumer, XHTMLWriter

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.

See Also:
TextConsumer

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

void
attributeDecl(String eName, String aName, String type, String mode, String value)
SAX2: called on attribute declarations
void
characters(ch[] , int start, int length)
SAX1: reports content characters
void
comment(ch[] , int start, int length)
SAX2: called when comments are parsed.
void
elementDecl(String name, String model)
SAX2: called on element declarations
void
endCDATA()
SAX2: called after parsing CDATA characters
void
endDTD()
SAX2: called after the doctype is parsed
void
endDocument()
SAX1: indicates the completion of a parse.
void
endElement(String uri, String localName, String qName)
SAX2: indicates the end of an element
void
endEntity(String name)
SAX2: called after parsing a general entity in content
void
endPrefixMapping(String prefix)
SAX2: ignored.
void
externalEntityDecl(String name, String publicId, String systemId)
SAX2: called on external entity declarations
protected void
fatal(String message, Exception e)
Used internally and by subclasses, this encapsulates the logic involved in reporting fatal errors.
void
flush()
Flushes the output stream.
void
ignorableWhitespace(ch[] , int start, int length)
SAX1: reports ignorable whitespace
void
internalEntityDecl(String name, String value)
SAX2: called on internal entity declarations
boolean
isCanonical()
Returns value of flag controlling canonical output.
boolean
isExpandingEntities()
Returns true if the output will have no entity references; returns false (the default) otherwise.
boolean
isPrettyPrinting()
Returns value of flag controlling pretty printing.
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.
void
notationDecl(String name, String publicId, String systemId)
SAX1: called on notation declarations
void
processingInstruction(String target, String data)
SAX1: reports a PI.
void
setCanonical(boolean value)
Sets the output style to be canonicalized.
void
setDocumentLocator(Locator l)
SAX1: provides parser status information
void
setEOL(String eolString)
Assigns the line ending style to be used on output.
void
setErrorHandler(ErrorHandler handler)
Assigns the error handler to be used to present most fatal errors.
void
setExpandingEntities(boolean value)
Controls whether the output text contains references to entities (the default), or instead contains the expanded values of those entities.
void
setPrettyPrinting(boolean value)
Controls pretty-printing, which by default is not enabled (and currently is most useful for XHTML output).
void
setWriter(Writer writer, String encoding)
Resets the handler to write a new text document.
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.
void
skippedEntity(String name)
SAX1: indicates a non-expanded entity reference
void
startCDATA()
SAX2: called before parsing CDATA characters
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.
void
startDocument()
SAX1: indicates the beginning of a document parse.
void
startElement(String uri, String localName, String qName, Attributes atts)
SAX2: indicates the start of an element.
void
startEntity(String name)
SAX2: called before parsing a general entity in content
void
startPrefixMapping(String prefix, String uri)
SAX2: ignored.
void
unparsedEntityDecl(String name, String publicId, String systemId, String notationName)
SAX1: called on unparsed entity declarations
void
write(String data)
Writes the string as if characters() had been called on the contents of the string.
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.
void
writeElement(String uri, String localName, String qName, Attributes atts, String content)
Writes an element that has content consisting of a single string.
void
writeEmptyElement(String uri, String localName, String qName, Attributes atts)
Writes an empty element.

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

XMLWriter

public XMLWriter()
            throws IOException
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)
            throws IOException
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 Details

attributeDecl

public final void attributeDecl(String eName,
                                String aName,
                                String type,
                                String mode,
                                String value)
            throws SAXException
SAX2: called on attribute declarations
Specified by:
attributeDecl in interface DeclHandler

characters

public final void characters(ch[] ,
                             int start,
                             int length)
            throws SAXException
SAX1: reports content characters
Specified by:
characters in interface ContentHandler

comment

public final void comment(ch[] ,
                          int start,
                          int length)
            throws SAXException
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
Specified by:
comment in interface LexicalHandler

elementDecl

public final void elementDecl(String name,
                              String model)
            throws SAXException
SAX2: called on element declarations
Specified by:
elementDecl in interface DeclHandler

endCDATA

public final void endCDATA()
            throws SAXException
SAX2: called after parsing CDATA characters
Specified by:
endCDATA in interface LexicalHandler

endDTD

public final void endDTD()
            throws SAXException
SAX2: called after the doctype is parsed
Specified by:
endDTD in interface LexicalHandler

endDocument

public void endDocument()
            throws SAXException
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.
Specified by:
endDocument in interface ContentHandler

endElement

public final void endElement(String uri,
                             String localName,
                             String qName)
            throws SAXException
SAX2: indicates the end of an element
Specified by:
endElement in interface ContentHandler

endEntity

public final void endEntity(String name)
            throws SAXException
SAX2: called after parsing a general entity in content
Specified by:
endEntity in interface LexicalHandler

endPrefixMapping

public final void endPrefixMapping(String prefix)
SAX2: ignored.
Specified by:
endPrefixMapping in interface ContentHandler

externalEntityDecl

public final void externalEntityDecl(String name,
                                     String publicId,
                                     String systemId)
            throws SAXException
SAX2: called on external entity declarations
Specified by:
externalEntityDecl in interface DeclHandler

fatal

protected void fatal(String message,
                     Exception e)
            throws SAXException
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()
            throws IOException
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(ch[] ,
                                      int start,
                                      int length)
            throws SAXException
SAX1: reports ignorable whitespace
Specified by:
ignorableWhitespace in interface ContentHandler

internalEntityDecl

public final void internalEntityDecl(String name,
                                     String value)
            throws SAXException
SAX2: called on internal entity declarations
Specified by:
internalEntityDecl in interface DeclHandler

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)
            throws SAXException
SAX1: called on notation declarations
Specified by:
notationDecl in interface DTDHandler

processingInstruction

public final void processingInstruction(String target,
                                        String data)
            throws SAXException
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.
Specified by:
processingInstruction in interface ContentHandler

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:
  • Namespace prefixes must not have been changed from those in the original document. (This may only be ensured by setting the SAX2 XMLReader namespace-prefixes feature flag; by default, it is cleared.)
  • Redundant namespace declaration attributes have been removed. (If an ancestor element defines a namespace prefix and that declaration hasn't been overriden, an element must not redeclare it.)
  • If comments are not to be included in the canonical output, they must first be removed from the input event stream; this Canonical XML with comments by default.
  • If the input character encoding was not UCS-based, the character data must have been normalized using Unicode Normalization Form C. (UTF-8 and UTF-16 are UCS-based.)
  • Attribute values must have been normalized, as is done by any conformant XML processor which processes all external parameter entities.
  • Similarly, attribute value defaulting has been performed.

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
Specified by:
setDocumentLocator in interface ContentHandler

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 endDocument())

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:

  • Element and attribute names must be in lower case, both in the document and in any CSS style sheet.
  • All XML constructs must be valid as defined by the XHTML "transitional" DTD (including all familiar constructs, even deprecated ones).
  • The root element must be "html".
  • Elements that must be empty (such as <br> must have no content.
  • Use both lang and xml:lang attributes when specifying language.
  • Similarly, use both id and name attributes when defining elements that may be referred to through URI fragment identifiers ... and make sure that the value is a legal NMTOKEN, since not all such HTML 4.0 identifiers are valid in XML.
  • Be careful with character encodings; make sure you provide a <meta http-equiv="Content-type" content="text/xml;charset=..." /> element in the HTML "head" element, naming the same encoding used to create this handler. Also, if that encoding is anything other than US-ASCII, make sure that if the document is given a MIME content type, it has a charset=... attribute with that encoding.

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

  • Processing instructions may be rendered, so avoid them. (Similarly for an XML declaration.)
  • Embedded style sheets and scripts should not contain XML markup delimiters: &, <, and ]]> are trouble.
  • Attribute values should not have line breaks or multiple consecutive white space characters.
  • Use no more than one of the deprecated (transitional) <isindex> elements.
  • Some boolean attributes (such as compact, checked, disabled, readonly, selected, and more) confuse some browsers, since they only understand minimized versions which are illegal in XML.

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)
            throws SAXException
SAX1: indicates a non-expanded entity reference
Specified by:
skippedEntity in interface ContentHandler

startCDATA

public final void startCDATA()
            throws SAXException
SAX2: called before parsing CDATA characters
Specified by:
startCDATA in interface LexicalHandler

startDTD

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

startDocument

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

startElement

public final void startElement(String uri,
                               String localName,
                               String qName,
                               Attributes atts)
            throws SAXException
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.
Specified by:
startElement in interface ContentHandler

startEntity

public final void startEntity(String name)
            throws SAXException
SAX2: called before parsing a general entity in content
Specified by:
startEntity in interface LexicalHandler

startPrefixMapping

public final void startPrefixMapping(String prefix,
                                     String uri)
SAX2: ignored.
Specified by:
startPrefixMapping in interface ContentHandler

unparsedEntityDecl

public final void unparsedEntityDecl(String name,
                                     String publicId,
                                     String systemId,
                                     String notationName)
            throws SAXException
SAX1: called on unparsed entity declarations
Specified by:
unparsedEntityDecl in interface DTDHandler

write

public final void write(String data)
            throws SAXException
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,
                         int content)
            throws SAXException
Writes an element that has content consisting of a single integer, encoded as a decimal string.

writeElement

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

writeEmptyElement

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

XMLWriter.java -- Copyright (C) 1999,2000,2001 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.