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Java™ Platform Standard Ed. 6 |
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java.lang.Object java.beans.PersistenceDelegate java.beans.DefaultPersistenceDelegate
public class DefaultPersistenceDelegate
The DefaultPersistenceDelegate
is a concrete implementation of
the abstract PersistenceDelegate
class and
is the delegate used by default for classes about
which no information is available. The DefaultPersistenceDelegate
provides, version resilient, public API-based persistence for
classes that follow the JavaBeans conventions without any class specific
configuration.
The key assumptions are that the class has a nullary constructor
and that its state is accurately represented by matching pairs
of "setter" and "getter" methods in the order they are returned
by the Introspector.
In addition to providing code-free persistence for JavaBeans,
the DefaultPersistenceDelegate
provides a convenient means
to effect persistent storage for classes that have a constructor
that, while not nullary, simply requires some property values
as arguments.
DefaultPersistenceDelegate(String[])
,
Introspector
Constructor Summary | |
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DefaultPersistenceDelegate()
Creates a persistence delegate for a class with a nullary constructor. |
|
DefaultPersistenceDelegate(String[] constructorPropertyNames)
Creates a default persistence delegate for a class with a constructor whose arguments are the values of the property names as specified by constructorPropertyNames . |
Method Summary | |
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protected void |
initialize(Class<?> type,
Object oldInstance,
Object newInstance,
Encoder out)
This default implementation of the initialize method assumes
all state held in objects of this type is exposed via the
matching pairs of "setter" and "getter" methods in the order
they are returned by the Introspector. |
protected Expression |
instantiate(Object oldInstance,
Encoder out)
This default implementation of the instantiate method returns
an expression containing the predefined method name "new" which denotes a
call to a constructor with the arguments as specified in
the DefaultPersistenceDelegate 's constructor. |
protected boolean |
mutatesTo(Object oldInstance,
Object newInstance)
If the number of arguments in the specified constructor is non-zero and the class of oldInstance explicitly declares an "equals" method
this method returns the value of oldInstance.equals(newInstance) . |
Methods inherited from class java.beans.PersistenceDelegate |
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writeObject |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public DefaultPersistenceDelegate()
DefaultPersistenceDelegate(java.lang.String[])
public DefaultPersistenceDelegate(String[] constructorPropertyNames)
constructorPropertyNames
.
The constructor arguments are created by
evaluating the property names in the order they are supplied.
To use this class to specify a single preferred constructor for use
in the serialization of a particular type, we state the
names of the properties that make up the constructor's
arguments. For example, the Font
class which
does not define a nullary constructor can be handled
with the following persistence delegate:
new DefaultPersistenceDelegate(new String[]{"name", "style", "size"});
constructorPropertyNames
- The property names for the arguments of this constructor.instantiate(java.lang.Object, java.beans.Encoder)
Method Detail |
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protected boolean mutatesTo(Object oldInstance, Object newInstance)
oldInstance
explicitly declares an "equals" method
this method returns the value of oldInstance.equals(newInstance)
.
Otherwise, this method uses the superclass's definition which returns true if the
classes of the two instances are equal.
mutatesTo
in class PersistenceDelegate
oldInstance
- The instance to be copied.newInstance
- The instance that is to be modified.
newInstance
may be
created by applying a series of mutations to oldInstance
.DefaultPersistenceDelegate(String[])
protected Expression instantiate(Object oldInstance, Encoder out)
instantiate
method returns
an expression containing the predefined method name "new" which denotes a
call to a constructor with the arguments as specified in
the DefaultPersistenceDelegate
's constructor.
instantiate
in class PersistenceDelegate
oldInstance
- The instance to be instantiated.out
- The code output stream.
oldInstance
.DefaultPersistenceDelegate(String[])
protected void initialize(Class<?> type, Object oldInstance, Object newInstance, Encoder out)
initialize
method assumes
all state held in objects of this type is exposed via the
matching pairs of "setter" and "getter" methods in the order
they are returned by the Introspector. If a property descriptor
defines a "transient" attribute with a value equal to
Boolean.TRUE
the property is ignored by this
default implementation. Note that this use of the word
"transient" is quite independent of the field modifier
that is used by the ObjectOutputStream
.
For each non-transient property, an expression is created
in which the nullary "getter" method is applied
to the oldInstance
. The value of this
expression is the value of the property in the instance that is
being serialized. If the value of this expression
in the cloned environment mutatesTo
the
target value, the new value is initialized to make it
equivalent to the old value. In this case, because
the property value has not changed there is no need to
call the corresponding "setter" method and no statement
is emitted. If not however, the expression for this value
is replaced with another expression (normally a constructor)
and the corresponding "setter" method is called to install
the new property value in the object. This scheme removes
default information from the output produced by streams
using this delegate.
In passing these statements to the output stream, where they
will be executed, side effects are made to the newInstance
.
In most cases this allows the problem of properties
whose values depend on each other to actually help the
serialization process by making the number of statements
that need to be written to the output smaller. In general,
the problem of handling interdependent properties is reduced to
that of finding an order for the properties in
a class such that no property value depends on the value of
a subsequent property.
initialize
in class PersistenceDelegate
oldInstance
- The instance to be copied.newInstance
- The instance that is to be modified.out
- The stream to which any initialization statements should be written.Introspector.getBeanInfo(java.lang.Class>)
,
PropertyDescriptor
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Java™ Platform Standard Ed. 6 |
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