com.trolltech.qt.xml
Class QXmlStreamReader

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.xml.QXmlStreamReader
All Implemented Interfaces:
QtJambiInterface

public class QXmlStreamReader
extends QtJambiObject

The QXmlStreamReader class provides a fast parser for reading well-formed XML via a simple streaming API. QXmlStreamReader is a faster and more convenient replacement for Qt's own SAX parser (see QXmlSimpleReader). In some cases it might also be a faster and more convenient alternative for use in applications that would otherwise use a DOM tree (see QDomDocument). QXmlStreamReader reads data either from a QIODevice (see setDevice()), or from a raw QByteArray (see addData()).

Qt provides QXmlStreamWriter for writing XML.

The basic concept of a stream reader is to report an XML document as a stream of tokens, similar to SAX. The main difference between QXmlStreamReader and SAX is how these XML tokens are reported. With SAX, the application must provide handlers (callback functions) that receive so-called XML events from the parser at the parser's convenience. With QXmlStreamReader, the application code itself drives the loop and pulls tokens from the reader, one after another, as it needs them. This is done by calling readNext(), where the reader reads from the input stream until it completes the next token, at which point it returns the tokenType(). A set of convenient functions including isStartElement() and text() can then be used to examine the token to obtain information about what has been read. The big advantage of this pulling approach is the possibility to build recursive descent parsers with it, meaning you can split your XML parsing code easily into different methods or classes. This makes it easy to keep track of the application's own state when parsing XML.

A typical loop with QXmlStreamReader looks like this:

        QXmlStreamReader xml = new QXmlStreamReader();
        //...
        while (!xml.atEnd()) {
            xml.readNext();
            // do processing ...
        }
        if (xml.hasError()) {
            // do error handling ...
        }
QXmlStreamReader is a well-formed XML 1.0 parser that does not include external parsed entities. As long as no error occurs, the application code can thus be assured that the data provided by the stream reader satisfies the W3C's criteria for well-formed XML. For example, you can be certain that all tags are indeed nested and closed properly, that references to internal entities have been replaced with the correct replacement text, and that attributes have been normalized or added according to the internal subset of the DTD.

If an error occurs while parsing, atEnd() and hasError() return true, and error() returns the error that occurred. The functions errorString(), lineNumber(), columnNumber(), and characterOffset() are for constructing an appropriate error or warning message. To simplify application code, QXmlStreamReader contains a raiseError() mechanism that lets you raise custom errors that trigger the same error handling described.

The QXmlStream Bookmarks Example illustrates how to use the recursive descent technique with a subclassed stream reader to read an XML bookmark file (XBEL).

Namespaces

QXmlStream understands and resolves XML namespaces. E.g. in case of a StartElement , namespaceUri() returns the namespace the element is in, and name() returns the element's local name. The combination of namespaceUri and name uniquely identifies an element. If a namespace prefix was not declared in the XML entities parsed by the reader, the namespaceUri is empty.

If you parse XML data that does not utilize namespaces according to the XML specification or doesn't use namespaces at all, you can use the element's qualifiedName() instead. A qualified name is the element's prefix() followed by colon followed by the element's local name() - exactly like the element appears in the raw XML data. Since the mapping namespaceUri to prefix is neither unique nor universal, qualifiedName() should be avoided for namespace-compliant XML data.

In order to parse standalone documents that do use undeclared namespace prefixes, you can turn off namespace processing completely with the namespaceProcessing property.

Incremental parsing

QXmlStreamReader is an incremental parser. It can handle the case where the document can't be parsed all at once because it arrives in chunks (e.g. from multiple files, or over a network connection). When the reader runs out of data before the complete document has been parsed, it reports a PrematureEndOfDocumentError . When more data arrives, either because of a call to addData() or because more data is available through the network device(), the reader recovers from the PrematureEndOfDocumentError error and continues parsing the new data with the next call to readNext().

For example, if you read data from the network using QHttp, you would connect its readyRead() signal to a custom slot. In this slot, you read all available data with readAll() and pass it to the XML stream reader using addData(). Then you call your custom parsing function that reads the XML events from the reader.

Performance and memory consumption

QXmlStreamReader is memory-conservative by design, since it doesn't store the entire XML document tree in memory, but only the current token at the time it is reported. In addition, QXmlStreamReader avoids the many small string allocations that it normally takes to map an XML document to a convenient and Qt-ish API. It does this by reporting all string data as QStringRef rather than real QString objects. QStringRef is a thin wrapper around QString substrings that provides a subset of the QString API without the memory allocation and reference-counting overhead. Calling toString() on any of those objects returns an equivalent real QString object.


Nested Class Summary
static class QXmlStreamReader.Error
          This enum specifies different error cases
static class QXmlStreamReader.TokenType
          This enum specifies the type of token the reader just read.
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QXmlStreamReader()
          Constructs a stream reader.
QXmlStreamReader(QByteArray data)
          Creates a new stream reader that reads from data.
QXmlStreamReader(QIODevice device)
          Creates a new stream reader that reads from device.
QXmlStreamReader(java.lang.String data)
          Creates a new stream reader that reads from data.
 
Method Summary
 void addData(QByteArray data)
          Adds more data for the reader to read.
 void addData(java.lang.String data)
          Adds more data for the reader to read.
 void addExtraNamespaceDeclaration(QXmlStreamNamespaceDeclaration extraNamespaceDeclaraction)
          Adds an extraNamespaceDeclaration.
 void addExtraNamespaceDeclarations(java.util.List extraNamespaceDeclaractions)
           
 boolean atEnd()
          Returns true if the reader has read until the end of the XML document, or if an error() has occurred and reading has been aborted.
 QXmlStreamAttributes attributes()
          Returns the attributes of a StartElement .
 long characterOffset()
          Returns the current character offset, starting with 0.
 void clear()
          Removes any device() or data from the reader and resets its internal state to the initial state.
 long columnNumber()
          Returns the current column number, starting with 0.
 QIODevice device()
          Returns the current device associated with the QXmlStreamReader, or 0 if no device has been assigned.
 java.lang.String documentEncoding()
          If the state() is StartDocument , this function returns the encoding string as specified in the XML declaration.
 java.lang.String documentVersion()
          If the state() is StartDocument , this function returns the version string as specified in the XML declaration.
 java.lang.String dtdName()
          If the state() is DTD , this function returns the DTD's name.
 java.lang.String dtdPublicId()
          If the state() is DTD , this function returns the DTD's public identifier.
 java.lang.String dtdSystemId()
          If the state() is DTD , this function returns the DTD's system identifier.
 java.util.List entityDeclarations()
          If the state() is DTD , this function returns the DTD's unparsed (external) entity declarations.
 QXmlStreamEntityResolver entityResolver()
          Returns the entity resolver, or 0 if there is no entity resolver.
 QXmlStreamReader.Error error()
          Returns the type of the current error, or NoError if no error occurred.
 java.lang.String errorString()
          Returns the error message that was set with raiseError().
 boolean hasError()
          Returns true if an error has occurred, otherwise false.
 boolean isCDATA()
          Returns true if the reader reports characters that stem from a CDATA section; otherwise returns false.
 boolean isCharacters()
          Returns true if tokenType() equals Characters ; otherwise returns false.
 boolean isComment()
          Returns true if tokenType() equals Comment ; otherwise returns false.
 boolean isDTD()
          Returns true if tokenType() equals DTD ; otherwise returns false.
 boolean isEndDocument()
          Returns true if tokenType() equals EndDocument ; otherwise returns false.
 boolean isEndElement()
          Returns true if tokenType() equals EndElement ; otherwise returns false.
 boolean isEntityReference()
          Returns true if tokenType() equals EntityReference ; otherwise returns false.
 boolean isProcessingInstruction()
          Returns true if tokenType() equals ProcessingInstruction ; otherwise returns false.
 boolean isStandaloneDocument()
          Returns true if this document has been declared standalone in the XML declaration; otherwise returns false.
 boolean isStartDocument()
          Returns true if tokenType() equals StartDocument ; otherwise returns false.
 boolean isStartElement()
          Returns true if tokenType() equals StartElement ; otherwise returns false.
 boolean isWhitespace()
          Returns true if the reader reports characters that only consist of white-space; otherwise returns false.
 long lineNumber()
          Returns the current line number, starting with 1.
 java.lang.String name()
          Returns the local name of a StartElement , EndElement , or an EntityReference .
 java.util.List namespaceDeclarations()
          If the state() is StartElement , this function returns the element's namespace declarations.
 boolean namespaceProcessing()
          the namespace-processing flag of the stream reader
 java.lang.String namespaceUri()
          Returns the namespaceUri of a StartElement or EndElement .
 java.util.List notationDeclarations()
          If the state() is DTD , this function returns the DTD's notation declarations.
 java.lang.String prefix()
          Returns the prefix of a StartElement or EndElement .
 java.lang.String processingInstructionData()
          Returns the data of a ProcessingInstruction .
 java.lang.String processingInstructionTarget()
          Returns the target of a ProcessingInstruction .
 java.lang.String qualifiedName()
          Returns the qualified name of a StartElement or EndElement ;
 void raiseError()
          Raises a custom error with an optional error message.
 void raiseError(java.lang.String message)
          Raises a custom error with an optional error message.
 java.lang.String readElementText()
          Convenience function to be called in case a StartElement was read.
 QXmlStreamReader.TokenType readNext()
          Reads the next token and returns its type.
 void setDevice(QIODevice device)
          Sets the current device to device.
 void setEntityResolver(QXmlStreamEntityResolver resolver)
          Makes resolver the new entityResolver().
 void setNamespaceProcessing(boolean arg__1)
          the namespace-processing flag of the stream reader
 java.lang.String text()
          Returns the text of Characters , Comment , DTD , or EntityReference .
 java.lang.String tokenString()
          Returns the reader's current token as string.
 QXmlStreamReader.TokenType tokenType()
          Returns the type of the current token.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QXmlStreamReader

public QXmlStreamReader()
Constructs a stream reader.

See also:
setDevice(), and addData().


QXmlStreamReader

public QXmlStreamReader(QIODevice device)
Creates a new stream reader that reads from device.

See also:
setDevice(), and clear().


QXmlStreamReader

public QXmlStreamReader(QByteArray data)
Creates a new stream reader that reads from data.

See also:
addData(), clear(), and setDevice().


QXmlStreamReader

public QXmlStreamReader(java.lang.String data)
Creates a new stream reader that reads from data.

See also:
addData(), clear(), and setDevice().

Method Detail

addData

public final void addData(QByteArray data)
Adds more data for the reader to read. This function does nothing if the reader has a device().

See also:
readNext(), and clear().


addData

public final void addData(java.lang.String data)
Adds more data for the reader to read. This function does nothing if the reader has a device().

See also:
readNext(), and clear().


addExtraNamespaceDeclaration

public final void addExtraNamespaceDeclaration(QXmlStreamNamespaceDeclaration extraNamespaceDeclaraction)
Adds an extraNamespaceDeclaration. The declaration will be valid for children of the current element, or - should the function be called before any elements are read - for the entire XML document.

See also:
namespaceDeclarations(), addExtraNamespaceDeclarations(), and setNamespaceProcessing().


addExtraNamespaceDeclarations

public final void addExtraNamespaceDeclarations(java.util.List extraNamespaceDeclaractions)

atEnd

public final boolean atEnd()
Returns true if the reader has read until the end of the XML document, or if an error() has occurred and reading has been aborted. Otherwise, it returns false.

When atEnd() and hasError() return true and error() returns PrematureEndOfDocumentError , it means the XML has been well-formed so far, but a complete XML document has not been parsed. The next chunk of XML can be added with addData(), if the XML is being read from a QByteArray, or by waiting for more data to arrive if the XML is being read from a QIODevice. Either way, atEnd() will return false once more adata is available.

See also:
hasError(), error(), device(), and QIODevice::atEnd().


attributes

public final QXmlStreamAttributes attributes()
Returns the attributes of a StartElement .


characterOffset

public final long characterOffset()
Returns the current character offset, starting with 0.

See also:
lineNumber(), and columnNumber().


clear

public final void clear()
Removes any device() or data from the reader and resets its internal state to the initial state.

See also:
addData().


columnNumber

public final long columnNumber()
Returns the current column number, starting with 0.

See also:
lineNumber(), and characterOffset().


device

public final QIODevice device()
Returns the current device associated with the QXmlStreamReader, or 0 if no device has been assigned.

See also:
setDevice().


documentEncoding

public final java.lang.String documentEncoding()
If the state() is StartDocument , this function returns the encoding string as specified in the XML declaration. Otherwise an empty string is returned.


documentVersion

public final java.lang.String documentVersion()
If the state() is StartDocument , this function returns the version string as specified in the XML declaration. Otherwise an empty string is returned.


dtdName

public final java.lang.String dtdName()
If the state() is DTD , this function returns the DTD's name. Otherwise an empty string is returned.


dtdPublicId

public final java.lang.String dtdPublicId()
If the state() is DTD , this function returns the DTD's public identifier. Otherwise an empty string is returned.


dtdSystemId

public final java.lang.String dtdSystemId()
If the state() is DTD , this function returns the DTD's system identifier. Otherwise an empty string is returned.


entityDeclarations

public final java.util.List entityDeclarations()
If the state() is DTD , this function returns the DTD's unparsed (external) entity declarations. Otherwise an empty vector is returned.

The QXmlStreamEntityDeclarations class is defined to be a QVector of QXmlStreamEntityDeclaration.


entityResolver

public final QXmlStreamEntityResolver entityResolver()
Returns the entity resolver, or 0 if there is no entity resolver.

See also:
setEntityResolver().


error

public final QXmlStreamReader.Error error()
Returns the type of the current error, or NoError if no error occurred.

See also:
errorString(), and raiseError().


errorString

public final java.lang.String errorString()
Returns the error message that was set with raiseError().

See also:
error(), lineNumber(), columnNumber(), and characterOffset().


hasError

public final boolean hasError()
Returns true if an error has occurred, otherwise false.

See also:
errorString(), and error().


isCDATA

public final boolean isCDATA()
Returns true if the reader reports characters that stem from a CDATA section; otherwise returns false.

See also:
isCharacters(), and text().


isCharacters

public final boolean isCharacters()
Returns true if tokenType() equals Characters ; otherwise returns false.

See also:
isWhitespace(), and isCDATA().


isComment

public final boolean isComment()
Returns true if tokenType() equals Comment ; otherwise returns false.


isDTD

public final boolean isDTD()
Returns true if tokenType() equals DTD ; otherwise returns false.


isEndDocument

public final boolean isEndDocument()
Returns true if tokenType() equals EndDocument ; otherwise returns false.


isEndElement

public final boolean isEndElement()
Returns true if tokenType() equals EndElement ; otherwise returns false.


isEntityReference

public final boolean isEntityReference()
Returns true if tokenType() equals EntityReference ; otherwise returns false.


isProcessingInstruction

public final boolean isProcessingInstruction()
Returns true if tokenType() equals ProcessingInstruction ; otherwise returns false.


isStandaloneDocument

public final boolean isStandaloneDocument()
Returns true if this document has been declared standalone in the XML declaration; otherwise returns false.

If no XML declaration has been parsed, this function returns false.


isStartDocument

public final boolean isStartDocument()
Returns true if tokenType() equals StartDocument ; otherwise returns false.


isStartElement

public final boolean isStartElement()
Returns true if tokenType() equals StartElement ; otherwise returns false.


isWhitespace

public final boolean isWhitespace()
Returns true if the reader reports characters that only consist of white-space; otherwise returns false.

See also:
isCharacters(), and text().


lineNumber

public final long lineNumber()
Returns the current line number, starting with 1.

See also:
columnNumber(), and characterOffset().


name

public final java.lang.String name()
Returns the local name of a StartElement , EndElement , or an EntityReference .

See also:
namespaceUri(), and qualifiedName().


namespaceDeclarations

public final java.util.List namespaceDeclarations()
If the state() is StartElement , this function returns the element's namespace declarations. Otherwise an empty vector is returned.

The QXmlStreamNamespaceDeclaration class is defined to be a QVector of QXmlStreamNamespaceDeclaration.

See also:
addExtraNamespaceDeclaration(), and addExtraNamespaceDeclarations().


namespaceProcessing

public final boolean namespaceProcessing()
the namespace-processing flag of the stream reader

This property controls whether or not the stream reader processes namespaces. If enabled, the reader processes namespaces, otherwise it does not.

By default, namespace-processing is enabled.


namespaceUri

public final java.lang.String namespaceUri()
Returns the namespaceUri of a StartElement or EndElement .

See also:
name(), and qualifiedName().


notationDeclarations

public final java.util.List notationDeclarations()
If the state() is DTD , this function returns the DTD's notation declarations. Otherwise an empty vector is returned.

The QXmlStreamNotationDeclarations class is defined to be a QVector of QXmlStreamNotationDeclaration.


prefix

public final java.lang.String prefix()
Returns the prefix of a StartElement or EndElement .

See also:
name(), and qualifiedName().


processingInstructionData

public final java.lang.String processingInstructionData()
Returns the data of a ProcessingInstruction .


processingInstructionTarget

public final java.lang.String processingInstructionTarget()
Returns the target of a ProcessingInstruction .


qualifiedName

public final java.lang.String qualifiedName()
Returns the qualified name of a StartElement or EndElement ;

A qualified name is the raw name of an element in the XML data. It consists of the namespace prefix, followed by colon, followed by the element's local name. Since the namespace prefix is not unique (the same prefix can point to different namespaces and different prefixes can point to the same namespace), you shouldn't use qualifiedName(), but the resolved namespaceUri() and the attribute's local name().

See also:
name(), prefix(), and namespaceUri().


raiseError

public final void raiseError()
Raises a custom error with an optional error message.

See also:
error(), and errorString().


raiseError

public final void raiseError(java.lang.String message)
Raises a custom error with an optional error message.

See also:
error(), and errorString().


readElementText

public final java.lang.String readElementText()
Convenience function to be called in case a StartElement was read. Reads until the corresponding EndElement and returns all text in-between. In case of no error, the current token (see tokenType()) after having called this function is EndElement .

The function concatenates text() when it reads either Characters or EntityReference tokens, but skips ProcessingInstruction and Comment . In case anything else is read before reaching EndElement , the function returns what it read so far and raises an UnexpectedElementError . If the current token is not StartElement , an empty string is returned.


readNext

public final QXmlStreamReader.TokenType readNext()
Reads the next token and returns its type.

With one exception, once an error() is reported by readNext(), further reading of the XML stream is not possible. Then atEnd() returns true, hasError() returns true, and this function returns QXmlStreamReader::Invalid .

The exception is when error() return PrematureEndOfDocumentError . This error is reported when the end of an otherwise well-formed chunk of XML is reached, but the chunk doesn't represent a complete XML document. In that case, parsing can be resumed by calling addData() to add the next chunk of XML, when the stream is being read from a QByteArray, or by waiting for more data to arrive when the stream is being read from a device().

See also:
tokenType(), and tokenString().


setDevice

public final void setDevice(QIODevice device)
Sets the current device to device. Setting the device resets the stream to its initial state.

See also:
device(), and clear().


setEntityResolver

public final void setEntityResolver(QXmlStreamEntityResolver resolver)
Makes resolver the new entityResolver().

The stream reader does not take ownership of the resolver. It's the callers responsibility to ensure that the resolver is valid during the entire life-time of the stream reader object, or until another resolver or 0 is set.

See also:
entityResolver().


setNamespaceProcessing

public final void setNamespaceProcessing(boolean arg__1)
the namespace-processing flag of the stream reader

This property controls whether or not the stream reader processes namespaces. If enabled, the reader processes namespaces, otherwise it does not.

By default, namespace-processing is enabled.


text

public final java.lang.String text()
Returns the text of Characters , Comment , DTD , or EntityReference .


tokenString

public final java.lang.String tokenString()
Returns the reader's current token as string.

See also:
tokenType().


tokenType

public final QXmlStreamReader.TokenType tokenType()
Returns the type of the current token.

The current token can also be queried with the convenience functions isStartDocument(), isEndDocument(), isStartElement(), isEndElement(), isCharacters(), isComment(), isDTD(), isEntityReference(), and isProcessingInstruction().

See also:
tokenString().