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PersistentProxy (Oracle - Berkeley DB Java API)
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<H2>

com.sleepycat.persist.model
 
Interface PersistentProxy&lt;T&gt;</H2>
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<DL>
<DT><PRE>public interface PersistentProxy&lt;T&gt;</DL>
</PRE>

Implemented by a proxy class to represent the persistent state of a
 (non-persistent) proxied class. Normally classes that are outside the scope
 of the developer's control must be proxied since they cannot be annotated,
 and because it is desirable to insulate the stored format from changes to
 the instance fields of the proxied class. This is useful for classes in the
 standard Java libraries, for example.

<code>PersistentProxy</code> objects are not required to be thread-safe. A
 single thread will create and call the methods of a given <code>PersistentProxy</code> object.

There are three requirements for a proxy class:
 <ol>
 <li>It must implement the <code>PersistentProxy</code> interface.</li>
 <li>It must be specified as a persistent proxy class in the entity model.
 When using the <A HREF="../../../../com/sleepycat/persist/model/AnnotationModel.html" title="class in com.sleepycat.persist.model"><CODE>AnnotationModel</CODE></A>, a proxy class is indicated by the
 <A HREF="../../../../com/sleepycat/persist/model/Persistent.html" title="annotation in com.sleepycat.persist.model"><CODE>Persistent</CODE></A> annotation with the <A HREF="../../../../com/sleepycat/persist/model/Persistent.html#proxyFor()"><CODE>Persistent.proxyFor()</CODE></A>
 property.</li>
 <li>It must be explicitly registered by calling <A HREF="../../../../com/sleepycat/persist/model/EntityModel.html#registerClass(java.lang.Class)"><CODE>EntityModel.registerClass(java.lang.Class)</CODE></A> before opening the store.</li>
 </ol>

In order to serialize an instance of the proxied class before it is
 stored, an instance of the proxy class is created. The proxied instance is
 then passed to the proxy's <A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html#initializeProxy(T)"><CODE>initializeProxy</CODE></A> method.
 When this method returns, the proxy instance contains the state of the
 proxied instance. The proxy instance is then serialized and stored in the
 same way as for any persistent object.

When an instance of the proxy object is deserialized after it is
 retrieved from storage, its <A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html#convertProxy()"><CODE>convertProxy()</CODE></A> method is called. The
 instance of the proxied class returned by this method is then returned as a
 field in the persistent instance.

For example:
 <pre class="code">
 import java.util.Locale;

@Persistent(proxyFor=Locale.class)
  class LocaleProxy implements PersistentProxy&lt;Locale&gt; {

String language;
      String country;
      String variant;

private LocaleProxy() {}

public void initializeProxy(Locale object) {
          language = object.getLanguage();
          country = object.getCountry();
          variant = object.getVariant();
      }

public Locale convertProxy() {
 return new Locale(language, country, variant);
 }
 }</pre>

The above definition allows the <code>Locale</code> class to be used in any
 persistent class, for example:
 <pre class="code">
 @Persistent
 class LocalizedText {
 String text;
 Locale locale;
 }</pre>

A proxy for proxied class P does not handle instances of subclasses of P.
 To proxy subclasses of P, a separate proxy class is needed.

Several <a href="Entity.html#proxyTypes">built in proxy types</a>
 are used implicitly. An application defined proxy will be used instead of a
 built-in proxy, if both exist for the same proxied class.

With respect to class evolution, a proxy instance is no different than
 any other persistent instance. When using a <A HREF="../../../../com/sleepycat/persist/raw/RawStore.html" title="class in com.sleepycat.persist.raw"><CODE>RawStore</CODE></A> or <A HREF="../../../../com/sleepycat/persist/evolve/Converter.html" title="class in com.sleepycat.persist.evolve"><CODE>Converter</CODE></A>, only the raw data of the proxy instance will be visible. Raw
 data for the proxied instance never exists.

Currently a proxied object may not contain a reference to itself. For
 simple proxied objects such as the Locale class shown above, this naturally
 won't occur. But for proxied objects that are containers -- the built-in
 Collection and Map classes for example -- this can occur if the container is
 added as an element of itself. This should be avoided. If an attempt to
 store such an object is made, an <code>IllegalArgumentException</code> will be
 thrown.

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Method Summary</TH>
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<TD ALIGN="right" VALIGN="top" WIDTH="1%">
<CODE>&nbsp;<A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html" title="type parameter in PersistentProxy">T</A></CODE></TD>
<TD><CODE><A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html#convertProxy()">convertProxy</A>()</CODE>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Returns a new proxied class instance to which the state of this proxy
 instance has been copied.</TD>
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<CODE>&nbsp;void</CODE></TD>
<TD><CODE><A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html#initializeProxy(T)">initializeProxy</A>(<A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html" title="type parameter in PersistentProxy">T</A>&nbsp;object)</CODE>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Copies the state of a given proxied class instance to this proxy
 instance.</TD>
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<A NAME="initializeProxy(java.lang.Object)"></A><A NAME="initializeProxy(T)"></A><H3>
initializeProxy</H3>
<PRE>
void initializeProxy(<A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html" title="type parameter in PersistentProxy">T</A>&nbsp;object)</PRE>
<DL>
<DD>Copies the state of a given proxied class instance to this proxy
 instance.

<DD><DL>
</DL>
</DD>
</DL>
<HR>

<A NAME="convertProxy()"></A><H3>
convertProxy</H3>
<PRE>
<A HREF="../../../../com/sleepycat/persist/model/PersistentProxy.html" title="type parameter in PersistentProxy">T</A> convertProxy()</PRE>
<DL>
<DD>Returns a new proxied class instance to which the state of this proxy
 instance has been copied.

<DD><DL>
</DL>
</DD>
</DL>

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