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java.lang.Objectcom.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.QSignalEmitter
com.trolltech.qt.QtJambiObject
com.trolltech.qt.xml.QXmlStreamReader
public class QXmlStreamReader
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.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 |
---|
public QXmlStreamReader()
setDevice()
, and addData()
.
public QXmlStreamReader(QIODevice device)
setDevice()
, and clear()
.
public QXmlStreamReader(QByteArray data)
addData()
, clear()
, and setDevice()
.
public QXmlStreamReader(java.lang.String data)
addData()
, clear()
, and setDevice()
.
Method Detail |
---|
public final void addData(QByteArray data)
device()
. readNext()
, and clear()
.
public final void addData(java.lang.String data)
device()
. readNext()
, and clear()
.
public final void addExtraNamespaceDeclaration(QXmlStreamNamespaceDeclaration extraNamespaceDeclaraction)
namespaceDeclarations()
, addExtraNamespaceDeclarations()
, and setNamespaceProcessing()
.
public final void addExtraNamespaceDeclarations(java.util.List extraNamespaceDeclaractions)
public final boolean atEnd()
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.
hasError()
, error()
, device()
, and QIODevice::atEnd()
.
public final QXmlStreamAttributes attributes()
StartElement
.
public final long characterOffset()
lineNumber()
, and columnNumber()
.
public final void clear()
device()
or data from the reader and resets its internal state to the initial state. addData()
.
public final long columnNumber()
lineNumber()
, and characterOffset()
.
public final QIODevice device()
setDevice()
.
public final java.lang.String documentEncoding()
StartDocument
, this function returns the encoding string as specified in the XML declaration. Otherwise an empty string is returned.
public final java.lang.String documentVersion()
StartDocument
, this function returns the version string as specified in the XML declaration. Otherwise an empty string is returned.
public final java.lang.String dtdName()
DTD
, this function returns the DTD's name. Otherwise an empty string is returned.
public final java.lang.String dtdPublicId()
DTD
, this function returns the DTD's public identifier. Otherwise an empty string is returned.
public final java.lang.String dtdSystemId()
DTD
, this function returns the DTD's system identifier. Otherwise an empty string is returned.
public final java.util.List entityDeclarations()
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
.
public final QXmlStreamEntityResolver entityResolver()
setEntityResolver()
.
public final QXmlStreamReader.Error error()
NoError
if no error occurred. errorString()
, and raiseError()
.
public final java.lang.String errorString()
raiseError()
. error()
, lineNumber()
, columnNumber()
, and characterOffset()
.
public final boolean hasError()
errorString()
, and error()
.
public final boolean isCDATA()
isCharacters()
, and text()
.
public final boolean isCharacters()
tokenType()
equals Characters
; otherwise returns false. isWhitespace()
, and isCDATA()
.
public final boolean isComment()
tokenType()
equals Comment
; otherwise returns false.
public final boolean isDTD()
tokenType()
equals DTD
; otherwise returns false.
public final boolean isEndDocument()
tokenType()
equals EndDocument
; otherwise returns false.
public final boolean isEndElement()
tokenType()
equals EndElement
; otherwise returns false.
public final boolean isEntityReference()
tokenType()
equals EntityReference
; otherwise returns false.
public final boolean isProcessingInstruction()
tokenType()
equals ProcessingInstruction
; otherwise returns false.
public final boolean isStandaloneDocument()
If no XML declaration has been parsed, this function returns false.
public final boolean isStartDocument()
tokenType()
equals StartDocument
; otherwise returns false.
public final boolean isStartElement()
tokenType()
equals StartElement
; otherwise returns false.
public final boolean isWhitespace()
isCharacters()
, and text()
.
public final long lineNumber()
columnNumber()
, and characterOffset()
.
public final java.lang.String name()
StartElement
, EndElement
, or an EntityReference
. namespaceUri()
, and qualifiedName()
.
public final java.util.List namespaceDeclarations()
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
.
addExtraNamespaceDeclaration()
, and addExtraNamespaceDeclarations()
.
public final boolean namespaceProcessing()
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.
public final java.lang.String namespaceUri()
StartElement
or EndElement
. name()
, and qualifiedName()
.
public final java.util.List notationDeclarations()
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
.
public final java.lang.String prefix()
StartElement
or EndElement
. name()
, and qualifiedName()
.
public final java.lang.String processingInstructionData()
ProcessingInstruction
.
public final java.lang.String processingInstructionTarget()
ProcessingInstruction
.
public final java.lang.String qualifiedName()
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()
.
name()
, prefix()
, and namespaceUri()
.
public final void raiseError()
error()
, and errorString()
.
public final void raiseError(java.lang.String message)
error()
, and errorString()
.
public final java.lang.String readElementText()
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.
public final QXmlStreamReader.TokenType readNext()
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()
.
tokenType()
, and tokenString()
.
public final void setDevice(QIODevice device)
device()
, and clear()
.
public final void setEntityResolver(QXmlStreamEntityResolver resolver)
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.
entityResolver()
.
public final void setNamespaceProcessing(boolean arg__1)
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.
public final java.lang.String text()
Characters
, Comment
, DTD
, or EntityReference
.
public final java.lang.String tokenString()
tokenType()
.
public final QXmlStreamReader.TokenType tokenType()
The current token can also be queried with the convenience functions isStartDocument()
, isEndDocument()
, isStartElement()
, isEndElement()
, isCharacters()
, isComment()
, isDTD()
, isEntityReference()
, and isProcessingInstruction()
.
tokenString()
.
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