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();
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).
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:
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).
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.
org.xml.sax.XMLFilter , org.xml.sax.ContentHandler
| Modifier and Type | Field and Description |
|---|---|
| private int | |
| private final Attributes | |
| private String | |
| private final CharacterEscapeHandler | |
| private String | header
This string will be written right after the xml declaration without any escaping. |
| private final HashMap | |
| private Writer | |
| private boolean | |
| private boolean |
| Access | Constructor and Description |
|---|---|
| public | XMLWriter(Writer
The output destination, or null to use standard output. writer, String If non-null string is specified, it is written as a part
of the XML declaration. encoding, CharacterEscapeHandler _escapeHandler)Create a new XML writer. |
| public |
| Modifier and Type | Method and Description |
|---|---|
| public void | characters(char[]
The array of characters to write. ch, int The starting position in the array. start, int The number of characters to write. len)Overrides org. Implements org. Write character data. |
| public void | |
| public void | dataElement(String
The element's Namespace URI. uri, String The element's local name. localName, String The element's default qualified name. qName, Attributes The element's attributes. atts, String The character data content. content)Write an element with character data content. |
| public void | dataElement(String
The element's Namespace URI. uri, String The element's local name. localName, String The character data content. content)Write an element with character data content but no attributes. |
| public void | dataElement(String
The element's local name. localName, String The character data content. content)Write an element with character data content but no attributes or Namespace URI. |
| public void | endDocument()
Overrides org. Implements org. Write a newline at the end of the document. |
| public void | endElement(String
The Namespace URI, or the empty string if none
is available. uri, String The element's local (unprefixed) name (required). localName, String 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. qName)Overrides org. Implements org. Write an end tag. |
| public void | endElement(String
The element's Namespace URI. uri, String The element's local name. localName)End an element without a qname. |
| public void | endElement(String
The element's local name. localName)End an element without a Namespace URI or qname. |
| public void | |
| public void | ignorableWhitespace(char[]
The array of characters to write. ch, int The starting position in the array. start, int The number of characters to write. length)Overrides org. Implements org. Write ignorable whitespace. |
| private void | |
| public void | processingInstruction(String
The PI target. target, String The PI data. data)Overrides org. Implements org. Write a processing instruction. |
| public void | |
| public void | |
| public void | |
| public void | setXmlDecl(boolean _writeXmlDecl)
Set whether the writer should print out the XML declaration
( |
| public void | startDocument()
Overrides org. Implements org. Write the XML declaration at the beginning of the document. |
| public void | startElement(String
The Namespace URI, or the empty string if none
is available. uri, String The element's local (unprefixed) name (required). localName, String 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. qName, Attributes The element's attribute list (must not be null). atts)Overrides org. Implements org. Write a start tag. |
| public void | startElement(String
The element's Namespace URI. uri, String The element's local name. localName)Start a new element without a qname or attributes. |
| public void | startElement(String
The element's local name. localName)Start a new element without a qname, attributes or a Namespace URI. |
| public void | startPrefixMapping(String prefix, String uri)
Overrides org. Implements org. Filter a start Namespace prefix mapping event. |
| protected final void | |
| protected final void | |
| private void | writeAttributes(Attributes
The attribute list to write. atts)Write out an attribute list, escaping values. |
| private void | writeEsc(char[]
The array of characters. ch, int The starting position. start, int The number of characters to use. length, boolean true if this is an attribute value literal. isAttVal)Write an array of data characters with escaping. |
| protected void |
| elementLevel | back to summary |
|---|---|
| private int elementLevel | |
| EMPTY_ATTS | back to summary |
|---|---|
| private final Attributes EMPTY_ATTS | |
| encoding | back to summary |
|---|---|
| private String encoding | |
| escapeHandler | back to summary |
|---|---|
| private final CharacterEscapeHandler escapeHandler | |
| header | back to summary |
|---|---|
| private String header This string will be written right after the xml declaration without any escaping. Useful for generating a boiler-plate DOCTYPE decl , PIs, and comments. | |
| locallyDeclaredPrefix | back to summary |
|---|---|
| private final HashMap<String, String> locallyDeclaredPrefix | |
| output | back to summary |
|---|---|
| private Writer output | |
| startTagIsClosed | back to summary |
|---|---|
| private boolean startTagIsClosed | |
| writeXmlDecl | back to summary |
|---|---|
| private boolean writeXmlDecl | |
| XMLWriter | back to summary |
|---|---|
| public XMLWriter(Writer writer, String encoding, CharacterEscapeHandler _escapeHandler) Create a new XML writer. Write to the writer provided. | |
| XMLWriter | back to summary |
|---|---|
| public XMLWriter(Writer writer, String encoding) | |
| characters | back to summary |
|---|---|
| public void characters(char[] ch, int start, int len) throws SAXException Overrides org. Implements org. Write character data. Pass the event on down the filter chain for further processing.
| |
| characters | back to summary |
|---|---|
| public void characters(String data) throws 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
| |
| dataElement | back to summary |
|---|---|
| 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
| |
| dataElement | back to summary |
|---|---|
| public void dataElement(String uri, String localName, String content) throws SAXException 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
| |
| dataElement | back to summary |
|---|---|
| public void dataElement(String localName, String content) throws SAXException 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
| |
| endDocument | back to summary |
|---|---|
| public void endDocument() throws SAXException Overrides org. Implements org. Write a newline at the end of the document. Pass the event on down the filter chain for further processing.
| |
| endElement | back to summary |
|---|---|
| public void endElement(String uri, String localName, String qName) throws SAXException Overrides org. Implements org. Write an end tag. Pass the event on down the filter chain for further processing.
| |
| endElement | back to summary |
|---|---|
| public void endElement(String uri, String localName) throws SAXException End an element without a qname. This method will supply an empty string for the qName.
It invokes
| |
| endElement | back to summary |
|---|---|
| public void endElement(String localName) throws 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
| |
| flush | back to summary |
|---|---|
| public void flush() throws 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
| |
| ignorableWhitespace | back to summary |
|---|---|
| public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException Overrides org. Implements org. Write ignorable whitespace. Pass the event on down the filter chain for further processing.
| |
| init | back to summary |
|---|---|
| private void init(Writer writer, String encoding) Internal initialization method. All of the public constructors invoke this method.
| |
| processingInstruction | back to summary |
|---|---|
| public void processingInstruction(String target, String data) throws SAXException Overrides org. Implements org. Write a processing instruction. Pass the event on down the filter chain for further processing.
| |
| reset | back to summary |
|---|---|
| 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 This method is invoked automatically by the
Note this method will not clear the prefix or URI information in the writer or the selected output writer.
| |
| setHeader | back to summary |
|---|---|
| public void setHeader(String _header) 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.
| |
| setOutput | back to summary |
|---|---|
| public void setOutput(Writer writer, String _encoding) Set a new output destination for the document. | |
| setXmlDecl | back to summary |
|---|---|
| public void setXmlDecl(boolean _writeXmlDecl) Set whether the writer should print out the XML declaration
( This option is set to true by default. | |
| startDocument | back to summary |
|---|---|
| public void startDocument() throws SAXException Overrides org. Implements org. Write the XML declaration at the beginning of the document. Pass the event on down the filter chain for further processing.
| |
| startElement | back to summary |
|---|---|
| public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException Overrides org. Implements org. Write a start tag. Pass the event on down the filter chain for further processing.
| |
| startElement | back to summary |
|---|---|
| public void startElement(String uri, String localName) throws 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 | back to summary |
|---|---|
| public void startElement(String localName) throws 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.
| |
| startPrefixMapping | back to summary |
|---|---|
| public void startPrefixMapping(String prefix, String uri) throws SAXException Overrides org. Implements org. Doc from org. Filter a start Namespace prefix mapping event.
| |
| write | back to summary |
|---|---|
| protected final void write(char c) throws IOException Write a raw character.
| |
| write | back to summary |
|---|---|
| protected final void write(String s) throws IOException Write a raw string. | |
| writeAttributes | back to summary |
|---|---|
| private void writeAttributes(Attributes atts) throws IOException Write out an attribute list, escaping values. The names will have prefixes added to them.
| |
| writeEsc | back to summary |
|---|---|
| private void writeEsc(char[] ch, int start, int length, boolean isAttVal) throws IOException Write an array of data characters with escaping.
| |
| writeXmlDecl | back to summary |
|---|---|
| protected void writeXmlDecl(String decl) throws IOException | |