com.trolltech.qt.xml
Class QXmlSimpleReader

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.QXmlReader
                  extended by com.trolltech.qt.xml.QXmlSimpleReader
All Implemented Interfaces:
QtJambiInterface

public class QXmlSimpleReader
extends QXmlReader

The QXmlSimpleReader class provides an implementation of a simple XML parser. This XML reader is suitable for a wide range of applications. It is able to parse well-formed XML and can report the namespaces of elements to a content handler; however, it does not parse any external entities. For historical reasons, Attribute Value Normalization and End-of-Line Handling as described in the XML 1.0 specification is not performed.

The easiest pattern of use for this class is to create a reader instance, define an input source, specify the handlers to be used by the reader, and parse the data.

For example, we could use a QFile to supply the input. Here, we create a reader, and define an input source to be used by the reader:

        QXmlSimpleReader xmlReader = new QXmlSimpleReader();
        QXmlInputSource source = new QXmlInputSource(file);
    
A handler lets us perform actions when the reader encounters certain types of content, or if errors in the input are found. The reader must be told which handler to use for each type of event. For many common applications, we can create a custom handler by subclassing QXmlDefaultHandler, and use this to handle both error and content events:
        Handler handler = new Handler();
        xmlReader.setContentHandler(handler);
        xmlReader.setErrorHandler(handler);
    
If you don't set at least the content and error handlers, the parser will fall back on its default behavior---and will do nothing.

The most convenient way to handle the input is to read it in a single pass using the parse() function with an argument that specifies the input source:

        boolean ok = xmlReader.parse(source);

        if (!ok)
            System.err.println("Parsing failed.");
    
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. This is achieved by telling parse() to work incrementally, and making subsequent calls to the parseContinue() function, until all the data has been processed.

A common way to perform incremental parsing is to connect the readyRead() signal of the input source to a slot, and handle the incoming data there. For example, the following code shows how a parser for RSS feeds can be used to incrementally parse data that it receives from a QHttp object:

void readData(QHttpResponseHeader resp)
{
    boolean sok;

    if (resp.statusCode() != 200)
        http.abort();
    else {
        xmlInput.setData(http.readAll());

        if (newInformation) {
            ok = xmlReader.parse(xmlInput, true);
            newInformation = false;
        }
        else
            ok = xmlReader.parseContinue();

        if (!ok)
            http.abort();
    }
}
Aspects of the parsing behavior can be adapted using setFeature() and setProperty(). For example, the following code could be used to enable reporting of namespace prefixes to the content handler:

QXmlSimpleReader is not reentrant. If you want to use the class in threaded code, lock the code using QXmlSimpleReader with a locking mechanism, such as a QMutex.

        xmlReader.setFeature("http://xml.org/sax/features/namespace-prefixes", true);


Nested Class Summary
 
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
QXmlSimpleReader()
           Constructs a simple XML reader.
 
Method Summary
 boolean parse(QXmlInputSource input, boolean incremental)
          Reads an XML document from input and parses it.
 boolean parseContinue()
          Continues incremental parsing, taking input from the QXmlInputSource that was specified with the most recent call to parse().
 
Methods inherited from class com.trolltech.qt.xml.QXmlReader
contentHandler, declHandler, DTDHandler, entityResolver, errorHandler, feature, hasFeature, hasProperty, lexicalHandler, parse, setContentHandler, setDeclHandler, setDTDHandler, setEntityResolver, setErrorHandler, setFeature, setLexicalHandler
 
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

QXmlSimpleReader

public QXmlSimpleReader()
Constructs a simple XML reader.

Method Detail

parse

public boolean parse(QXmlInputSource input,
                     boolean incremental)
Reads an XML document from input and parses it. Returns true if the parsing is completed successfully; otherwise returns false, indicating that an error occurred.

If incremental is false, this function will return false if the XML file is not read completely. The parsing cannot be continued in this case.

If incremental is true, the parser does not return false if it reaches the end of the input before reaching the end of the XML file. Instead, it stores the state of the parser so that parsing can be continued later when more data is available. In such a case, you can use the function parseContinue() to continue with parsing. This class stores a pointer to the input source input and the parseContinue() function tries to read from that input source. Therefore, you should not delete the input source input until you no longer need to call parseContinue().

If this function is called with incremental set to true while an incremental parse is in progress, a new parsing session will be started, and the previous session will be lost.

See also:
parseContinue(), and QTcpSocket.


parseContinue

public boolean parseContinue()
Continues incremental parsing, taking input from the QXmlInputSource that was specified with the most recent call to parse(). To use this function, you must have called parse() with the incremental argument set to true.

Returns false if a parsing error occurs; otherwise returns true, even if the end of the XML file has not been reached. You can continue parsing at a later stage by calling this function again when there is more data available to parse.

Calling this function when there is no data available in the input source indicates to the reader that the end of the XML file has been reached. If the input supplied up to this point was not well-formed then a parsing error occurs, and false is returned. If the input supplied was well-formed, true is returned. It is important to end the input in this way because it allows you to reuse the reader to parse other XML files.

Calling this function after the end of file has been reached, but without available data will cause false to be returned whether the previous input was well-formed or not.

See also:
parse(), QXmlInputSource::data(), and QXmlInputSource::next().