DefaultPersistenceDelegatepublic class DefaultPersistenceDelegate extends PersistenceDelegate 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. |
| Fields Summary |
|---|
| private String[] | constructor | | private Boolean | definesEquals |
| Constructors Summary |
|---|
public DefaultPersistenceDelegate()Creates a persistence delegate for a class with a nullary constructor.
this(new String[0]);
| 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"});
this.constructor = constructorPropertyNames;
|
| Methods Summary |
|---|
| private static boolean | definesEquals(java.lang.Class type)
try {
type.getDeclaredMethod("equals", new Class[]{Object.class});
return true;
}
catch(NoSuchMethodException e) {
return false;
}
| | private boolean | definesEquals(java.lang.Object instance)
if (definesEquals != null) {
return (definesEquals == Boolean.TRUE);
}
else {
boolean result = definesEquals(instance.getClass());
definesEquals = result ? Boolean.TRUE : Boolean.FALSE;
return result;
}
| | private void | doProperty(java.lang.Class type, java.beans.PropertyDescriptor pd, java.lang.Object oldInstance, java.lang.Object newInstance, java.beans.Encoder out)
Method getter = pd.getReadMethod();
Method setter = pd.getWriteMethod();
if (getter != null && setter != null && !isTransient(type, pd)) {
Expression oldGetExp = new Expression(oldInstance, getter.getName(), new Object[]{});
Expression newGetExp = new Expression(newInstance, getter.getName(), new Object[]{});
Object oldValue = oldGetExp.getValue();
Object newValue = newGetExp.getValue();
out.writeExpression(oldGetExp);
if (!equals(newValue, out.get(oldValue))) {
// Search for a static constant with this value;
Object e = (Object[])pd.getValue("enumerationValues");
if (e instanceof Object[] && Array.getLength(e) % 3 == 0) {
Object[] a = (Object[])e;
for(int i = 0; i < a.length; i = i + 3) {
try {
Field f = type.getField((String)a[i]);
if (f.get(null).equals(oldValue)) {
out.remove(oldValue);
out.writeExpression(new Expression(oldValue, f, "get", new Object[]{null}));
}
}
catch (Exception ex) {}
}
}
invokeStatement(oldInstance, setter.getName(), new Object[]{oldValue}, out);
}
}
| | private static boolean | equals(java.lang.Object o1, java.lang.Object o2)
return (o1 == null) ? (o2 == null) : o1.equals(o2);
| | private void | initBean(java.lang.Class type, java.lang.Object oldInstance, java.lang.Object newInstance, java.beans.Encoder out)
// System.out.println("initBean: " + oldInstance);
BeanInfo info = MetaData.getBeanInfo(type);
// Properties
PropertyDescriptor[] propertyDescriptors = info.getPropertyDescriptors();
for (int i = 0; i < propertyDescriptors.length; ++i ) {
try {
doProperty(type, propertyDescriptors[i], oldInstance, newInstance, out);
}
catch (Exception e) {
out.getExceptionListener().exceptionThrown(e);
}
}
// Listeners
/*
Pending(milne). There is a general problem with the archival of
listeners which is unresolved as of 1.4. Many of the methods
which install one object inside another (typically "add" methods
or setters) automatically install a listener on the "child" object
so that its "parent" may respond to changes that are made to it.
For example the JTable:setModel() method automatically adds a
TableModelListener (the JTable itself in this case) to the supplied
table model.
We do not need to explictly add these listeners to the model in an
archive as they will be added automatically by, in the above case,
the JTable's "setModel" method. In some cases, we must specifically
avoid trying to do this since the listener may be an inner class
that cannot be instantiated using public API.
No general mechanism currently
exists for differentiating between these kind of listeners and
those which were added explicitly by the user. A mechanism must
be created to provide a general means to differentiate these
special cases so as to provide reliable persistence of listeners
for the general case.
*/
if (!java.awt.Component.class.isAssignableFrom(type)) {
return; // Just handle the listeners of Components for now.
}
EventSetDescriptor[] eventSetDescriptors = info.getEventSetDescriptors();
for (int e = 0; e < eventSetDescriptors.length; e++) {
EventSetDescriptor d = eventSetDescriptors[e];
Class listenerType = d.getListenerType();
// The ComponentListener is added automatically, when
// Contatiner:add is called on the parent.
if (listenerType == java.awt.event.ComponentListener.class) {
continue;
}
// JMenuItems have a change listener added to them in
// their "add" methods to enable accessibility support -
// see the add method in JMenuItem for details. We cannot
// instantiate this instance as it is a private inner class
// and do not need to do this anyway since it will be created
// and installed by the "add" method. Special case this for now,
// ignoring all change listeners on JMenuItems.
if (listenerType == javax.swing.event.ChangeListener.class &&
type == javax.swing.JMenuItem.class) {
continue;
}
EventListener[] oldL = new EventListener[0];
EventListener[] newL = new EventListener[0];
try {
Method m = d.getGetListenerMethod();
oldL = (EventListener[])MethodUtil.invoke(m, oldInstance, new Object[]{});
newL = (EventListener[])MethodUtil.invoke(m, newInstance, new Object[]{});
}
catch (Throwable e2) {
try {
Method m = type.getMethod("getListeners", new Class[]{Class.class});
oldL = (EventListener[])MethodUtil.invoke(m, oldInstance, new Object[]{listenerType});
newL = (EventListener[])MethodUtil.invoke(m, newInstance, new Object[]{listenerType});
}
catch (Exception e3) {
return;
}
}
// Asssume the listeners are in the same order and that there are no gaps.
// Eventually, this may need to do true differencing.
String addListenerMethodName = d.getAddListenerMethod().getName();
for (int i = newL.length; i < oldL.length; i++) {
// System.out.println("Adding listener: " + addListenerMethodName + oldL[i]);
invokeStatement(oldInstance, addListenerMethodName, new Object[]{oldL[i]}, out);
}
String removeListenerMethodName = d.getRemoveListenerMethod().getName();
for (int i = oldL.length; i < newL.length; i++) {
invokeStatement(oldInstance, removeListenerMethodName, new Object[]{oldL[i]}, out);
}
}
| | protected void | initialize(java.lang.Class type, java.lang.Object oldInstance, java.lang.Object newInstance, java.beans.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.
// System.out.println("DefulatPD:initialize" + type);
super.initialize(type, oldInstance, newInstance, out);
if (oldInstance.getClass() == type) { // !type.isInterface()) {
initBean(type, oldInstance, newInstance, out);
}
| | protected java.beans.Expression | instantiate(java.lang.Object oldInstance, java.beans.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.
int nArgs = constructor.length;
Class type = oldInstance.getClass();
// System.out.println("writeObject: " + oldInstance);
Object[] constructorArgs = new Object[nArgs];
for(int i = 0; i < nArgs; i++) {
/*
1.2 introduces "public double getX()" et al. which return values
which cannot be used in the constructors (they are the wrong type).
In constructors, use public fields in preference to getters
when they are defined.
*/
String name = constructor[i];
Field f = null;
try {
// System.out.println("Trying field " + name + " in " + type);
f = type.getDeclaredField(name);
f.setAccessible(true);
}
catch (NoSuchFieldException e) {}
try {
constructorArgs[i] = (f != null && !Modifier.isStatic(f.getModifiers())) ?
f.get(oldInstance) :
MethodUtil.invoke(ReflectionUtils.getPublicMethod(type, "get" + NameGenerator.capitalize(name),
new Class[0]), oldInstance, new Object[0]);
}
catch (Exception e) {
out.getExceptionListener().exceptionThrown(e);
}
}
return new Expression(oldInstance, oldInstance.getClass(), "new", constructorArgs);
| | static void | invokeStatement(java.lang.Object instance, java.lang.String methodName, java.lang.Object[] args, java.beans.Encoder out)
out.writeStatement(new Statement(instance, methodName, args));
| | private boolean | isTransient(java.lang.Class type, java.beans.PropertyDescriptor pd)
if (type == null) {
return false;
}
// This code was mistakenly deleted - it may be fine and
// is more efficient than the code below. This should
// all disappear anyway when property descriptors are shared
// by the introspector.
/*
Method getter = pd.getReadMethod();
Class declaringClass = getter.getDeclaringClass();
if (declaringClass == type) {
return Boolean.TRUE.equals(pd.getValue("transient"));
}
*/
String pName = pd.getName();
BeanInfo info = MetaData.getBeanInfo(type);
PropertyDescriptor[] propertyDescriptors = info.getPropertyDescriptors();
for (int i = 0; i < propertyDescriptors.length; ++i ) {
PropertyDescriptor pd2 = propertyDescriptors[i];
if (pName.equals(pd2.getName())) {
Object value = pd2.getValue("transient");
if (value != null) {
return Boolean.TRUE.equals(value);
}
}
}
return isTransient(type.getSuperclass(), pd);
| | protected boolean | mutatesTo(java.lang.Object oldInstance, java.lang.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.
// Assume the instance is either mutable or a singleton
// if it has a nullary constructor.
return (constructor.length == 0) || !definesEquals(oldInstance) ?
super.mutatesTo(oldInstance, newInstance) :
oldInstance.equals(newInstance);
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