Package java.beans
PropertyChangeEvent
). However, most of the classes in this
package are meant to be used by a bean editor (that is, a development
environment for customizing and putting together beans to create an
application). In particular, these classes help the bean editor create a user
interface that the user can use to customize the bean. For example, a bean
may contain a property of a special type that a bean editor may not know how
to handle. By using the PropertyEditor
interface, a bean developer
can provide an editor for this special type.
To minimize the resources used by a bean, the classes used by bean editors
are loaded only when the bean is being edited. They are not needed while the
bean is running in an application and therefore not loaded. This information
is kept in what's called a bean-info (see BeanInfo
).
Unless explicitly stated, null values or empty Strings are not valid parameters for the methods in this package. You may expect to see exceptions if these parameters are used.
Long-Term Persistence
As of v1.4, thejava.beans
package provides support for long-term
persistence -- reading and writing a bean as a textual representation of
its property values. The property values are treated as beans, and are
recursively read or written to capture their publicly available state. This
approach is suitable for long-term storage because it relies only on public
API, rather than the likely-to-change private implementation.
Note: The persistence scheme cannot automatically instantiate custom inner classes, such as you might use for event handlers. By using theEventHandler
class instead of inner classes for custom event handlers, you can avoid this problem.
You read and write beans in XML format using the
XMLDecoder
and XMLEncoder
classes,
respectively. One notable feature of the persistence scheme is that reading
in a bean requires no special knowledge of the bean.
Writing out a bean, on the other hand, sometimes requires special knowledge
of the bean's type. If the bean's state can be expressed using only the
no-argument constructor and public getter and setter methods for properties,
no special knowledge is required. Otherwise, the bean requires a custom
persistence delegate -- an object that is in charge of writing out
beans of a particular type. All classes provided in the JDK that descend from
java.awt.Component
, as well as all their properties, automatically
have persistence delegates.
If you need (or choose) to provide a persistence delegate for a bean, you can
do so either by using a DefaultPersistenceDelegate
instance or by creating your own subclass of PersistenceDelegate
. If
the only reason a bean needs a persistence delegate is because you want to
invoke the bean's constructor with property values as arguments, you can
create the bean's persistence delegate with the one-argument
DefaultPersistenceDelegate
constructor. Otherwise, you need to
implement your own persistence delegate, for which you're likely to need the
following classes:
PersistenceDelegate
- The abstract class from which all persistence delegates descend. Your
subclass should use its knowledge of the bean's type to provide whatever
Statement
s andExpression
s are necessary to create the bean and restore its state. Statement
- Represents the invocation of a single method on an object. Includes a set of arguments to the method.
Expression
- A subclass of
Statement
used for methods that return a value.
Once you create a persistence delegate, you register it using the
setPersistenceDelegate
method of XMLEncoder
.
Related Documentation
For overview, architecture, and tutorial documentation, please see:- JavaBeans, a trail in The Java Tutorial.
- Long-Term Persistence, an article in The Swing Connection.
-
ClassDescriptionDeprecated, for removal: This API element is subject to removal in a future version.The Applet API is deprecated.A BeanDescriptor provides global information about a "bean", including its Java class, its displayName, etc.Use the
BeanInfo
interface to create aBeanInfo
class and provide explicit information about the methods, properties, events, and other features of your beans.An annotation used to specify some property-related information for the automatically generatedBeanInfo
classes.This class provides some general purpose beans control methods.An annotation on a constructor that shows how the parameters of that constructor correspond to the constructed object's getter methods.A customizer class provides a complete custom GUI for customizing a target Java Bean.TheDefaultPersistenceDelegate
is a concrete implementation of the abstractPersistenceDelegate
class and is the delegate used by default for classes about which no information is available.This interface is intended to be implemented by, or delegated from, instances of java.beans.beancontext.BeanContext, in order to propagate to its nested hierarchy of java.beans.beancontext.BeanContextChild instances, the current "designTime" property.AnEncoder
is a class which can be used to create files or streams that encode the state of a collection of JavaBeans in terms of their public APIs.TheEventHandler
class provides support for dynamically generating event listeners whose methods execute a simple statement involving an incoming event object and a target object.An EventSetDescriptor describes a group of events that a given Java bean fires.An ExceptionListener is notified of internal exceptions.AnExpression
object represents a primitive expression in which a single method is applied to a target and a set of arguments to return a result - as in"a.getFoo()"
.The FeatureDescriptor class is the common baseclass for PropertyDescriptor, EventSetDescriptor, and MethodDescriptor, etc.An "IndexedPropertyChange" event gets delivered whenever a component that conforms to the JavaBeans specification (a "bean") changes a bound indexed property.An IndexedPropertyDescriptor describes a property that acts like an array and has an indexed read and/or indexed write method to access specific elements of the array.Thrown when an exception happens during Introspection.The Introspector class provides a standard way for tools to learn about the properties, events, and methods supported by a target Java Bean.An annotation used to specify some class-related information for the automatically generatedBeanInfo
classes.A MethodDescriptor describes a particular method that a Java Bean supports for external access from other components.The ParameterDescriptor class allows bean implementors to provide additional information on each of their parameters, beyond the low level type information provided by the java.lang.reflect.Method class.The PersistenceDelegate class takes the responsibility for expressing the state of an instance of a given class in terms of the methods in the class's public API.A "PropertyChange" event gets delivered whenever a bean changes a "bound" or "constrained" property.A "PropertyChange" event gets fired whenever a bean changes a "bound" property.A class which extends theEventListenerProxy
specifically for adding aPropertyChangeListener
with a "bound" property.This is a utility class that can be used by beans that support bound properties.A PropertyDescriptor describes one property that a Java Bean exports via a pair of accessor methods.A PropertyEditor class provides support for GUIs that want to allow users to edit a property value of a given type.The PropertyEditorManager can be used to locate a property editor for any given type name.This is a support class to help build property editors.A PropertyVetoException is thrown when a proposed change to a property represents an unacceptable value.This is a support class to make it easier for people to provide BeanInfo classes.AStatement
object represents a primitive statement in which a single method is applied to a target and a set of arguments - as in"a.setFoo(b)"
.Indicates that an attribute called "transient" should be declared with the givenvalue
when theIntrospector
constructs aPropertyDescriptor
orEventSetDescriptor
classes associated with the annotated code element.A VetoableChange event gets fired whenever a bean changes a "constrained" property.A class which extends theEventListenerProxy
specifically for adding aVetoableChangeListener
with a "constrained" property.This is a utility class that can be used by beans that support constrained properties.Under some circumstances a bean may be run on servers where a GUI is not available.TheXMLDecoder
class is used to read XML documents created using theXMLEncoder
and is used just like theObjectInputStream
.TheXMLEncoder
class is a complementary alternative to theObjectOutputStream
and can used to generate a textual representation of a JavaBean in the same way that theObjectOutputStream
can be used to create binary representation ofSerializable
objects.