Class DefaultPersistenceDelegate

public DefaultPersistenceDelegate()

Creates a persistence delegate for a class with a nullary constructor.

public 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. 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"});
 

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). Otherwise, this method uses the superclass's definition which returns true if the classes of the two instances are equal.

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 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. 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.