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 {@link 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 {@link 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 {@link java.lang.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.

Since: 1.4

UNKNOWN: updated to 1.5