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Provides support for the encoding of objects, and the objects reachable from them,
into XML; and the complementary reconstruction of the
object graph from XML.
Key Advantages:
- Real-time characteristics with no adverse effect on memory footprint or
garbage collection (e.g. it can be used for time critical communications).
{@link javolution.xml.XMLFormat XMLFormat} is basically a "smart"
wrapper around our real-time StAX-like
{@link javolution.xml.stream.XMLStreamReader XMLStreamReader} and
{@link javolution.xml.stream.XMLStreamWriter XMLStreamWriter}.
- Works directly with your existing Java classes, no need to create new classes
or customize your implementation in any way.
- The XML representation can be high level and impervious to obfuscation
or changes to your implementation.
- Performance on a par or better than default JavaTM Serialization/Deserialization
(See bindmark for performance comparison).
- Runs on any platform including J2ME CLDC 1.0 It does not require reflection or
or any interface (e.g.
Serializable) to be implemented.
- The XML mapping can be defined for a top class (or interface) and is automatically
inherited by all sub-classes (or all implementing classes).
- Supports object references (to avoid expanding objects already formatted).
The default XML mapping for a class and its sub-classes is typically defined using
a static final {@link javolution.xml.XMLFormat XMLFormat} instance.
For example:[code]
public abstract class Graphic implements XMLSerializable {
private boolean _isVisible;
private Paint _paint; // null if none.
private Stroke _stroke; // null if none.
private Transform _transform; // null if none.
// Default XML format with name associations (members identified by an unique name).
// See XMLFormat for examples of positional associations.
protected static final XMLFormat XML = new XMLFormat(Graphic.class) {
public void write(Graphic g, OutputElement xml) throws XMLStreamException {
xml.setAttribute("isVisible", g._isVisible);
xml.add(g._paint, "Paint");
xml.add(g._stroke, "Stroke");
xml.add(g._transform, "Transform");
}
public void read(InputElement xml, Graphic g) throws XMLStreamException {
g._isVisible = xml.getAttribute("isVisible", true);
g._paint = xml.get("Paint");
g._stroke = xml.get("Stroke");
g._transform = xml.get("Transform");
}
};
}[/code]
Sub-classes may override the inherited XML format:[code]
public class Area extends Graphic {
private Shape _geometry;
// Adds geometry to format.
protected static final XMLFormat XML = new XMLFormat(Area.class) {
public void write(Area area, OutputElement xml) throws XMLStreamException {
Graphic.XML.write(area, xml); // Calls parent write.
xml.add(area._geometry, "Geometry");
}
public void read(InputElement xml, Area area) throws XMLStreamException {
Graphic.XML.read(xml, area); // Calls parent read.
area._geometry = xml.get("Geometry");
}
};
}[/code]
The following writes a graphic area to a file, then reads it:[code]
// Creates some useful aliases for class names.
XMLBinding binding = new XMLBinding();
binding.setAlias(Color.class, "Color");
binding.setAlias(Polygon.class, "Polygon");
binding.setClassAttribute("type"); // Use "type" instead of "class" for class attribute.
// Writes the area to a file.
XMLObjectWriter writer = XMLObjectWriter.newInstance(new FileOutputStream("C:/area.xml"));
writer.setBinding(binding); // Optional.
writer.setIndentation("\t"); // Optional (use tabulation for indentation).
writer.write(area, "Area", Area.class);
writer.close();
// Reads the area back
XMLObjectReader reader = XMLObjectReader.newInstance(new FileInputStream("C:/area.xml"));
reader.setBinding(binding);
Area a = reader.read("Area", Area.class);
reader.close();
[/code]
Here is an example of valid XML representation for an area:[code]
[/code]
The following table illustrates the variety of XML representations supported
(Foo class with a single String member named text):
| XML FORMAT |
XML DATA |
| [code]XMLFormat XML = new XMLFormat(Foo.class) {
public void write(Foo foo, OutputElement xml) throws XMLStreamException {
xml.setAttribute("text", foo.text);
}
public void read(InputElement xml, Foo foo) throws XMLStreamException {
foo.text = xml.getAttribute("text", "");
}
};[/code] |
<!-- Member as attribute -->
<Foo text="This is a text"/>
|
| [code]XMLFormat XML = new XMLFormat(Foo.class) {
public void write(Foo foo, OutputElement xml) throws XMLStreamException {
xml.add(foo.text);
}
public void read(InputElement xml, Foo foo) throws XMLStreamException {
foo.text = xml.getNext();
}
};[/code] |
<!-- Member as anonymous nested element -->
<Foo>
<java.lang.String value="This is a text"/>
</Foo>
|
| [code]XMLFormat XML = new XMLFormat(Foo.class) {
public void write(Foo foo, OutputElement xml) throws XMLStreamException {
xml.addText(foo.text);
// or xml.getStreamWriter().writeCDATA(foo.text) to use CDATA block.
}
public void read(InputElement xml, Foo foo) throws XMLStreamException {
foo.text = xml.getText().toString(); // Content of a text-only element.
}
};[/code] |
<!-- Member as Character Data -->
<Foo>This is a text</Foo>
|
| [code]XMLFormat XML = new XMLFormat(Foo.class) {
public void write(Foo foo, OutputElement xml) throws XMLStreamException {
xml.add(foo.text, "Text");
}
public void read(InputElement xml, Foo foo) throws XMLStreamException {
foo.text = xml.get("Text");
}
};[/code] |
<!-- Member as named element of unknown type -->
<Foo>
<Text class="java.lang.String" value="This is a text"/>
</Foo>
|
| [code]XMLFormat XML = new XMLFormat(Foo.class) {
public void write(Foo foo, OutputElement xml) throws XMLStreamException {
xml.add(foo.text, "Text", String.class);
}
public void read(InputElement xml, Foo foo) throws XMLStreamException {
foo.text = xml.get("Text", String.class);
}
};[/code] |
<!-- Member as named element of actual type known -->
<Foo>
<Text value="This is a text"/>
</Foo>
|
The {@link javolution.xml.XMLFormat XMLFormat} does not have to use the class
public no-arg constructor, instances can be created using factory methods,
private constructors (with constructor parameters set from the XML element) or even retrieved from a collection
(if the object is shared or unique). For example:[code]
public final class Point implements XMLSerializable {
// Default XMLFormat can be private as the class cannot be extended.
static final XMLFormat XML = new XMLFormat(Point.class) {
public boolean isReferencable() {
return false; // Always manipulates by value.
}
public Point newInstance(Class cls, InputElement xml) throws XMLStreamException {
return Point.valueOf(xml.getAttribute("x", 0), xml.getAttribute("y", 0));
}
public void write(Point point, OutputElement xml) throws XMLStreamException {
xml.setAttribute("x", point._x);
xml.setAttribute("y", point._y);
}
public void read(InputElement xml, Point point) throws XMLStreamException {
// Do nothing immutable.
}
};
private int _x;
private int _y;
private Point() {}; // No-arg constructor not visible.
public static Point valueOf(int x, int y) { ... }
}[/code]
Document cross-references are supported, including circular references.
Let's take for example:[code]
public class Polygon implements Shape, XMLSerializable {
private Point[] _vertices;
static final XMLFormat XML = new XMLFormat(Polygon.class) {
public void write(Polygon polygon, OutputElement xml) throws XMLStreamException {
xml.setAttibutes("count", _vertices.length);
for (int i=0; i < _vertices.length; i++) {
xml.add(_vertices[i], "Vertex", Point.class);
}
}
public void read(InputElement xml, Polygon polygon) throws XMLStreamException {
int count = xml.getAttributes("count", 0);
polygon._vertices = new Point[count];
for (int i=0; i < count; i++) {
_vertices[i] = xml.get("Vertex", Point.class);
}
}
};
}
Polygon[] polygons = new Polygon[] {p1, p2, p1};
...
TextBuilder xml = TextBuilder.newInstance();
AppendableWriter out = new AppendableWriter().setOutput(xml)
XMLObjectWriter writer = XMLObjectWriter.newInstance(out);
writer.setXMLReferenceResolver(new XMLReferenceResolver()); // Enables cross-references.
writer.write(polygons, "Polygons", Polygon[].class);
writer.close();
System.out.println(xml);
[/code]
Prints the following (noticed that the first polygon and last one are being shared).[code]
[/code]
ALGORITHMS:
Our {@link javolution.xml.XMLObjectReader XMLObjectReader}/{@link javolution.xml.XMLObjectWriter XMLObjectWriter}
are in fact simple wrappers around our Javolution high-performance StAX-like
{@link javolution.xml.stream.XMLStreamReader XMLStreamReader} and
{@link javolution.xml.stream.XMLStreamWriter XMLStreamWriter} classes.
The logic of these wrappers is described below:
Marshalling:
Input: object, referenceResolver, binding
Output: outputElement
1. class = object.getClass()
2. outputElement.getStreamWriter().writeStartElement(name/uri)
The new element name/uri is:
a - Specified by caller, e.g. add(object, name, uri, class)
If the class is not specified e.g. add(object, name, uri) a class attribute is written.
b - binding.getLocalName(class)/binding.getURI(class), e.g add(object)
3. isReference = referenceResolver.writeReference(object, outputElement)
4. if (!isReference) binding.getFormat(class).write(object, outputElement)
5. outputElement.getStreamWriter().writeEndElement()
6. end
Unmarshalling:
Input: inputElement, referenceResolver, binding
Output: object
1. object = referenceResolver.readReference(inputElement)
2. if (object != null) Goto 8 // Found reference
3. class is either:
a - Specified by caller, e.g. get("name", class)
b - binding.getClass(class attribute value)
c - binding.getClass(element name, element uri)
4. format = binding.getFormat(class)
5. object = format.newInstance(class, inputElement)
6. referenceResolver.createReference(object, inputElement) // Done before parsing to support circular references.
7. format.read(inputElement, object)
8. inputElement.getStreamReader().nextTag()
9. end
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