| A
org.xml.sax.ContentHandler for the Java Object Configuration Language.
JOCL provides an XML syntax for constructing arbitrary Java
java.lang.Object instances. It does not define a full
XML document type (there's no root element), but rather an
XML fragment describing the
java.lang.Object Objects to be
constructed.
In a JOCL fragment, one may define a series of objects using
the object element. A trivial example is:
<object class="java.util.Date"/>
which constructs an instance of java.util.Date
using the no-argument constructor.
After a "root-level" <object> element has been processed
(that is, once
JOCLContentHandler.endElement(java.lang.String,java.lang.String,java.lang.String) has been invoked by the
XMLReader ), it will be appended to a list of Objects
maintained by the JOCLContentHandler.
(See
JOCLContentHandler.size ,
JOCLContentHandler.clear ,
JOCLContentHandler.clear(int) ,
JOCLContentHandler.getType(int) ,
JOCLContentHandler.getValue(int) ,
JOCLContentHandler.getTypeArray ,
and
JOCLContentHandler.getValueArray .)
You can list multiple object elements in a fragment. For example,
after processing the JOCL fragment:
<object class="java.util.Date"/>
<object class="java.util.Date"/>
The
JOCLContentHandler.getTypeArray method
will return an composed
of two instances of java.util.Date. The sequence of
java.lang.Object Objects in the array
will correspond to the sequence of <object> elements in the JOCL fragment.
As we've seen, when used with no child-elements, the <object>
tag will cause the no-argument constructor of the specified class to be invoked.
It is also possible to nest <object> tags to provide arguments
for the constructor.
For example, the fragment:
<object class="mypackage.Foo">
<object class="mypackage.Bar"/>
</object>
will add an instance of mypackage.Foo to the object list, constructed via
new mypackage.Foo(new mypackage.Bar()).
There is a special syntax available creating primative values and arguments,
as well as for constructing
java.lang.String String s. Some examples:
<byte value="3"/>
<boolean value="false"/>
<char value="c"/>
<double value="3.14159"/>
<float value="3.14"/>
<int value="17"/>
<long value="1700000"/>
<short value="1"/>
<string value="The quick brown fox..."/>
When invoked at the "root" level (that is, with no <object> parent),
this will cause the corresponding "object wrapper" to be added to the list of
java.lang.Object Object s. The
JOCLContentHandler.getType type for these
objects will reflect the proper primative type, however. When invoked with an
<object> parent, these will be treated as primitive arguments to the
specified
java.lang.Object Object 's constructor. For example, while:
<int value="5"/>
<int value="26"/>
<int value="100"/>
results in three
java.lang.Integer instances being added to the
list of values, with types corresponding to
java.lang.Integer , the fragment:
<int value="5"/>
<int value="26"/>
<int value="100"/>
results in three
java.lang.Integer instances being added to the
list of values, with types corresponding to
java.lang.Integer.TYPE .
Hence if you want to invoke the mypackage.Foo(java.lang.Integer,java.lang.Integer,java.lang.Integer)
constructor, use:
<object class="mypackage.Foo"/>
<object class="java.lang.Integer"><int value="5"/></object>
<object class="java.lang.Integer"><int value="26"/></object>
<object class="java.lang.Integer"><int value="100"/></object>
</object>
If you want to invoke the mypackage.Foo(int,int,int)
constructor, use:
<object class="mypackage.Foo"/>
<int value="5"/>
<int value="26"/>
<int value="100"/>
</object>
If you'd like to creat a null object, use:
<object class="mypackage.Bar" null="true"/>
Here's a simple but complete example:
<?xml version="1.0"?>
<arbitrary-root xmlns="http://apache.org/xml/xmlns/jakarta/commons/jocl">
<string value="Hello World!"/>
<string/>
<boolean/>
<boolean value="true"/>
<byte value="1"/>
<short value="1"/>
<int value="1"/>
<long value="1"/>
<float value="1.0"/>
<double value="1.0"/>
<object class="java.util.Date"/>
<object class="java.util.Date">
<int value="1"/>
<int value="1"/>
<int value="1"/>
</object>
</arbitrary-root>
Formally, a DTD for the JOCL grammar is as follows:
<!ELEMENT object (object|byte|boolean|char|double|float|int|long|short|string)*>
<!ATTLIST object
class CDATA #REQUIRED
null (true|false) "false">
<!ELEMENT byte EMPTY>
<!ATTLIST byte value CDATA #REQUIRED>
<!ELEMENT boolean EMPTY>
<!ATTLIST boolean value (true|false) #REQUIRED>
<!ELEMENT char EMPTY>
<!ATTLIST char value CDATA #REQUIRED>
<!ELEMENT double EMPTY>
<!ATTLIST double value CDATA #REQUIRED>
<!ELEMENT float EMPTY>
<!ATTLIST float value CDATA #REQUIRED>
<!ELEMENT int EMPTY>
<!ATTLIST int value CDATA #REQUIRED>
<!ELEMENT long EMPTY>
<!ATTLIST long value CDATA #REQUIRED>
<!ELEMENT short EMPTY>
<!ATTLIST short value CDATA #REQUIRED>
<!ELEMENT string EMPTY>
<!ATTLIST string value CDATA #REQUIRED>
This class can also be used as a base class for
org.xml.sax.ContentHandler s
that include JOCL as part of their grammar. Simply extend this class, and override the
JOCLContentHandler.startElement ,
JOCLContentHandler.characters ,
and
JOCLContentHandler.endElement methods to handle
your tags, and invoke the method of the parent class (i.e., super.XXX for
elements and data that you don't handle.
A number of static methods are available for simply reading a list of objects from
a
InputStream ,
Reader or
InputSource .
Note that this class is not synchronized.
author:
Rodney Waldhoff
version:
$Revision: 491655 $ $Date: 2007-01-01 15:05:30 -0700 (Mon, 01 Jan 2007) $ | 