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com.trolltech.qt.xml
Class QXmlStreamReader

java.lang.Object
  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 well-formed XML parser with a simple streaming API.

QXmlStreamReader is a faster and more convenient replacement for Qt's own SAX parser (see QXmlSimpleReader), and in some cases also for applications that would previously use a DOM tree (see QDomDocument). QXmlStreamReader reads data either from a QIODevice (see setDevice), or from a raw QByteArray (see addData). With QXmlStreamWriter, Qt provides a related class 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 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, which makes the reader read from the input stream until it has completed a new token, and then returns its tokenType. A set of convenient functions like isStartElement or text then allows to examine this token, and to obtain information about what has been read. The big advantage of the pulling approach is the possibility to build recursive descent parsers, 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;
    ...
    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 does occur while parsing, atEnd returns true and error returns the kind of error that occurred. hasError can also be used to check whether an error has occurred. The functions errorString, lineNumber, columnNumber, and characterOffset make it possible to generate a verbose human-understandable error or warning message. In order to simplify application code, QXmlStreamReader contains a raiseError mechanism that makes it possible to raise custom errors that then trigger the same error handling code path.

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. If you can't parse the entire input in one go (for example, it is huge, or is being delivered over a network connection), data can be fed to the parser in pieces. If the reader runs out of data before the document has been parsed completely, it reports a PrematureEndOfDocumentError. Once more data has arrived, either through the device or because it has been added with addData, it recovers from that error and continues parsing on the next call to read().

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.Signal0, QSignalEmitter.Signal1<A>, QSignalEmitter.Signal2<A,B>, QSignalEmitter.Signal3<A,B,C>, QSignalEmitter.Signal4<A,B,C,D>, QSignalEmitter.Signal5<A,B,C,D,E>, QSignalEmitter.Signal6<A,B,C,D,E,F>, QSignalEmitter.Signal7<A,B,C,D,E,F,G>, QSignalEmitter.Signal8<A,B,C,D,E,F,G,H>, QSignalEmitter.Signal9<A,B,C,D,E,F,G,H,I>
 
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.
 boolean atEnd()
          Returns true if the reader has read until the end of the XML document, or an error has occurred and reading has been aborted; otherwise returns false.
 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 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.util.List<QXmlStreamEntityDeclaration> entityDeclarations()
          If the state() is DTD, this function returns the DTD's unparsed (external) entity declarations.
 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.
static QXmlStreamReader fromNativePointer(QNativePointer nativePointer)
          This function returns the QXmlStreamReader instance pointed to by nativePointer
 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<QXmlStreamNamespaceDeclaration> 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<QXmlStreamNotationDeclaration> notationDeclarations()
          If the state() is DTD, this function returns the DTD's notation declarations.
 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()
          Equivalent to raiseError(QString()).
 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 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, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class java.lang.Object
clone, equals, 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(QByteArray data)

Creates a new stream reader that reads from data.

See Also:
addData, clear, setDevice

QXmlStreamReader

public QXmlStreamReader(java.lang.String data)

Creates a new stream reader that reads from data.

See Also:
addData, clear, setDevice

QXmlStreamReader

public QXmlStreamReader()

Constructs a stream reader.

See Also:
setDevice, addData

QXmlStreamReader

public QXmlStreamReader(QIODevice device)

Creates a new stream reader that reads from device.

See Also:
setDevice, clear
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:
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:
clear

atEnd

public final boolean atEnd()

Returns true if the reader has read until the end of the XML document, or an error has occurred and reading has been aborted; otherwise returns false.

Has reading been aborted with a PrematureEndOfDocumentError because the device no longer delivered data, atEnd will return true once more data has arrived.

See Also:
device, 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, columnNumber

clear

public final void clear()

Removes any device or data from the reader, and resets its state to the initial state.

See Also:
addData

columnNumber

public final long columnNumber()

Returns the current column number, starting with 0.

See Also:
lineNumber, 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

entityDeclarations

public final java.util.List<QXmlStreamEntityDeclaration> 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.


error

public final QXmlStreamReader.Error error()

Returns the type of the current error, or NoError if no error occurred.

See Also:
errorString, raiseError

errorString

public final java.lang.String errorString()

Returns the error message that was set with raiseError.

See Also:
error, lineNumber, columnNumber, characterOffset

hasError

public final boolean hasError()

Returns true if an error has occurred, otherwise false.

See Also:
errorString, 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, text

isCharacters

public final boolean isCharacters()

Returns true if tokenType equals Characters; otherwise returns false.

See Also:
isWhitespace, 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, text

lineNumber

public final long lineNumber()

Returns the current line number, starting with 1.

See Also:
columnNumber, characterOffset

name

public final java.lang.String name()

Returns the local name of a StartElement, EndElement, or an EntityReference.

See Also:
namespaceUri, qualifiedName

namespaceDeclarations

public final java.util.List<QXmlStreamNamespaceDeclaration> 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.


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.

See Also:
setNamespaceProcessing

namespaceUri

public final java.lang.String namespaceUri()

Returns the namespaceUri of a StartElement or EndElement.

See Also:
name, qualifiedName

notationDeclarations

public final java.util.List<QXmlStreamNotationDeclaration> 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.


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, namespaceUri

raiseError

public final void raiseError()

Equivalent to raiseError(QString()).


raiseError

public final void raiseError(java.lang.String message)

Raises a custom error with an optional error message.

See Also:
error, 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 token 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.

If an error has been reported, reading is no longer possible. In this case, atEnd always returns true, and this function will do nothing but return Invalid.

The one exception to this rule are errors of type PrematureEndOfDocumentError. Subsequent calls to atEnd and readNext will resume this error type and try to read from the device again. This iterative parsing approach makes sense if you can't or don't want to read the entire data in one go, for example, if it is huge, or it is being delivered over a network connection

See Also:
tokenType, 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, clear

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.

See Also:
namespaceProcessing

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

fromNativePointer

public static QXmlStreamReader fromNativePointer(QNativePointer nativePointer)
This function returns the QXmlStreamReader instance pointed to by nativePointer

Parameters:
nativePointer - the QNativePointer of which object should be returned.

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