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java.lang.Objectjava.beans.XMLDecoder
public class XMLDecoder
The XMLDecoder reads XML data that is structured according to
this DTD
and creates objects according to the content. Usually such data is generated using the
XMLEncoder class.
An example XML document might look like this:
<java>
<string>Hello World</string>
<int>200</int>
</java>
To read the String and the Integer instance the following can be used (assume
the XML data can be obtained from the InputStream):
XMLDecoder decoder = new XMLDecoder(inputStreamContainingXMLData);
String message = (String) decoder.readObject();
Integer number = (Integer) decoder.readObject();
Besides this basic functionality the XMLDecoder has some more features that might come
handy in certain situations:
An owner object can be set using the setOwner method which can then be accessed when
decoding. This feature is only useful if the XML data is aware of the owner object. Such data may
look like this (assume that the owner object is a JFrame instance):
<java>
<void method="getOwner">
<void method="setVisible">
<boolean>true<boolean>
</void>
</void>
</java>
This accesses the JFrame and makes it visible using the setVisible method.
Please note that changing the owner after the having read the first object has no effect, because all object have been decoded then.
If the XMLDecoder is created with no ExceptionListener instance a default one
is used that prints an error message to System.err whenever a recoverable exception
is thrown. Recovarable exceptions occur when the XML data cannot be interpreted correctly (e.g
unknown classes or methods, invocation on null, ...). In general be very careful when the
XMLDecoder provoked such exceptions because the resulting object(s) may be in an
undesirable state.
Note that changing the ExceptionListener instance after readObject has been called
once has no effect because the decoding is completed then.
At last one can provide a specific ClassLoader which is then used when Class
objects are accessed. See Class.forName(String, boolean, ClassLoader) for details
on this.
Note: If the InputStream instance given to any of the constructors is null
the resulting XMLDecoder will be silently (without any exception) useless. Each call
to readObject will return null and never throws an
ArrayIndexOutOfBoundsException.
| Constructor Summary | |
|---|---|
XMLDecoder(InputStream in)
Creates a XMLDecoder instance that parses the XML data of the given input stream. |
|
XMLDecoder(InputStream in,
Object owner)
Creates a XMLDecoder instance that parses the XML data of the given input stream. |
|
XMLDecoder(InputStream in,
Object owner,
ExceptionListener exceptionListener)
Creates a XMLDecoder instance that parses the XML data of the given input stream. |
|
XMLDecoder(InputStream in,
Object owner,
ExceptionListener listener,
ClassLoader cl)
Creates a XMLDecoder instance that parses the XML data of the given input stream. |
|
| Method Summary | |
|---|---|
void |
close()
Closes the stream associated with this decoder. |
ExceptionListener |
getExceptionListener()
Returns the ExceptionListener instance associated with this decoder. |
Object |
getOwner()
Returns the owner object of the decoder. |
Object |
readObject()
Returns the next available decoded object. |
void |
setExceptionListener(ExceptionListener listener)
Sets the ExceptionListener instance to which notifications of exceptions are send while parsing the XML data. |
void |
setOwner(Object newOwner)
Sets the owner object which can be accessed from the parsed XML data. |
| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
|---|
public XMLDecoder(InputStream in)
in - InputStream to read XML data from.
public XMLDecoder(InputStream in,
Object owner)
in - InputStream to read XML data from.owner - Owner object which can be accessed and modified while parsing.
public XMLDecoder(InputStream in,
Object owner,
ExceptionListener exceptionListener)
in - InputStream to read XML data from.owner - Owner object which can be accessed and modified while parsing.exceptionListener - ExceptionListener instance to which exception notifications are send.
public XMLDecoder(InputStream in,
Object owner,
ExceptionListener listener,
ClassLoader cl)
in - InputStream to read XML data from.owner - Owner object which can be accessed and modified while parsing.listener - ExceptionListener instance to which exception notifications are send.cl - ClassLoader instance that is used for calls to Class.forName(String, boolean, ClassLoader)| Method Detail |
|---|
public void close()
See the description of the readObject() for the effect caused by close.
public ExceptionListener getExceptionListener()
See the description of XMLDecoder class for more information on the ExceptionListener.
public Object getOwner()
See the description of XMLDecoder class for more information on the owner object.
public Object readObject()
throws ArrayIndexOutOfBoundsException
Note that the actual decoding takes place when the method is called for the first time.
If the close method was already called a NoSuchElementException
is thrown.
If the InputStream instance used in the constructors was null this method
will always return null itself.
ArrayIndexOutOfBoundsException - When no more objects are available.public void setExceptionListener(ExceptionListener listener)
See the description of XMLDecoder class for more information on the ExceptionListener.
listener - public void setOwner(Object newOwner)
See the description of XMLDecoder class for more information on the owner object.
newOwner -
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