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body bgcolor="white">
0N/AContains classes related to developing
0N/A<
em>beans</
em> -- components
3731N/Abased on the JavaBeans™ architecture.
0N/Aclasses are used by beans while they run in an application.
0N/AFor example, the event classes are
0N/Aused by beans that fire property and vetoable change
0N/Apackage are meant to be used by a bean editor (that is, a development environment
0N/Afor customizing and putting together beans to create an application). In
0N/Aparticular, these classes help the bean editor create a user
0N/Ainterface that the user can use to customize the bean. For example, a bean may
0N/Acontain a property of a special type that a bean editor may not know how to handle.
0N/ABy using the <
code>PropertyEditor</
code> interface, a bean developer can
0N/Aprovide an editor for this special type.
0N/ATo minimize the resources used by a bean, the classes used by bean editors are loaded only
0N/Awhen the bean is being edited. They are not needed while the bean is running in an application
0N/Aand therefore not loaded. This information is kept in what's called a bean-info (see {@link
java.
beans.
BeanInfo}).
0N/AUnless explicitly stated, null values or empty Strings are not valid
0N/Aparameters for the methods in this package. You may expect to see
0N/Aexceptions if these parameters are used.
0N/A<
h2>Long-Term Persistence</
h2>
0N/A<
em>long-term persistence</
em> -- reading and
0N/Awriting a bean as a textual representation of its property values.
0N/AThe property values are treated as beans,
0N/Aand are recursively read or written to capture
0N/Atheir publicly available state.
0N/AThis approach is suitable for long-term storage
0N/Abecause it relies only on public API,
0N/Arather than the likely-to-change private implementation.
0N/AThe persistence scheme cannot automatically instantiate
0N/Acustom inner classes, such as you might use for event handlers.
0N/Ainstead of inner classes for custom event handlers,
0N/Ayou can avoid this problem.
0N/AYou read and write beans in XML format using the
0N/Aclasses, respectively.
0N/AOne notable feature of the persistence scheme is that
0N/Areading in a bean requires no special knowledge of the bean.
0N/AWriting out a bean, on the other hand,
0N/Asometimes requires special knowledge of the bean's type.
0N/AIf the bean's state can be
0N/Aexpressed using only the no-argument constructor and
0N/Apublic getter and setter methods for properties,
0N/Ano special knowledge is required.
0N/AOtherwise, the bean requires a custom <
em>persistence delegate</
em> --
0N/Aan object that is in charge of writing out beans of a particular type.
0N/AAll classes provided in the JDK that descend
0N/Aas well as all their properties,
0N/Aautomatically have persistence delegates.
0N/AIf you need (or choose) to provide a persistence delegate for a bean,
0N/Ayou can do so either by using a
0N/Aor by creating your own subclass of <
code>PersistenceDelegate</
code>.
0N/AIf the only reason a bean needs a persistence delegate
0N/Ais because you want to invoke the bean's constructor with
0N/Aproperty values as arguments,
0N/Ayou can create the bean's persistence delegate
0N/Awith the one-argument
0N/A<
code>DefaultPersistenceDelegate</
code>
0N/Ayou need to implement your own persistence delegate,
0N/Afor which you're likely to need the following classes:
0N/A<
dd> The abstract class from which all persistence delegates descend.
0N/A Your subclass should use its knowledge of the bean's type to provide
0N/A whatever <
code>Statement</
code>s and <
code>Expression</
code>s
0N/A are necessary to create the bean
0N/A and restore its state.
0N/A<
dd> Represents the invocation of a single method on an object.
0N/A Includes a set of arguments to the method.
0N/A<
dd> A subclass of <
code>Statement</
code>
0N/A used for methods that return a value.
0N/AOnce you create a persistence delegate,
0N/Ayou register it using the
0N/A<
code>setPersistenceDelegate</
code> method of
0N/A<
code>XMLEncoder</
code>.
0N/A<
h2>Related Documentation</
h2>
0N/AFor overview, architecture, and tutorial documentation, please see: