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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Appendix A. API Notes and Details</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Java Edition Collections Tutorial" />
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<link rel="up" href="index.html" title="Berkeley DB Java Edition Collections Tutorial" />
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<link rel="prev" href="Summary.html" title="Chapter 7. Summary" />
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<link rel="next" href="UsingCollectionsAPI.html" title="Using the JE JE Collections API" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Appendix A.
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API Notes and Details
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="Summary.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="UsingCollectionsAPI.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="appendix" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title"><a id="collectionOverview"></a>Appendix A.
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||
API Notes and Details
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</h2>
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</div>
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</div>
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</div>
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<p>
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This appendix contains information useful to the collections programmer
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that is too detailed to easily fit into the format of a tutorial.
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||
Specifically, this appendix contains the following information:
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||
</p>
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<div class="itemizedlist">
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<ul type="disc">
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||
<li>
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<p>
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<a class="xref" href="collectionOverview.html#UsingDataBindings" title="Using Data Bindings">
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Using Data Bindings
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</a>
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</p>
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</li>
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<li>
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<p>
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<a class="xref" href="UsingCollectionsAPI.html" title="Using the JE JE Collections API">
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Using the JE JE Collections API
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</a>
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</p>
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</li>
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<li>
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<p>
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<a class="xref" href="UsingStoredCollections.html" title="Using Stored Collections">
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Using Stored Collections
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</a>
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</p>
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</li>
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<li>
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<p>
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<a class="xref" href="SerializedObjectStorage.html" title="Serialized Object Storage">
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Serialized Object Storage
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</a>
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</p>
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</li>
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</ul>
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="UsingDataBindings"></a>
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Using Data Bindings
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</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<dl>
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<dt>
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<span class="sect2">
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<a href="collectionOverview.html#SelectingBindingFormats">
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Selecting Binding Formats
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</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="collectionOverview.html#SelectingDataBindings">
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Selecting Data Bindings
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</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="collectionOverview.html#ImplementingBindings">
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Implementing Bindings
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</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="collectionOverview.html#UsingBindings">
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Using Bindings
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</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="collectionOverview.html#SecondaryKeyCreators">
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Secondary Key Creators
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</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>
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Data bindings determine how keys and values are represented as
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stored data (byte arrays) in the database, and how stored data is
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converted to and from Java objects.
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</p>
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<p>
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The selection of data bindings is, in general, independent of
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the selection of
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collection views. In other
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words, any binding can be used with any
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collection.
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</p>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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In this document, bindings are described in the
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context of their use for stored data in a database. However,
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bindings may also be used independently of a database to operate on
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an arbitrary byte array. This allows using bindings when data is to
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be written to a file or sent over a network, for example.
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="SelectingBindingFormats"></a>
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Selecting Binding Formats
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</h3>
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</div>
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</div>
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</div>
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<p>
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For the key and value of each stored collection, you may select
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one of the following types of bindings.
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</p>
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<div class="informaltable">
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<table border="1" width="80%">
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<colgroup>
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<col />
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<col />
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<col />
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</colgroup>
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<thead>
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<tr>
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<th>Binding Format</th>
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<th>Ordered</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>
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</td>
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<td>No</td>
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<td>
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The data is stored using a compact form of Java serialization,
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where the class descriptions are stored separately in a catalog
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database. Arbitrary Java objects are supported.
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</td>
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</tr>
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<tr>
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||
<td>
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleBinding.html" target="_top">TupleBinding</a>
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</td>
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<td>Yes</td>
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<td>
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The data is stored using a series of fixed length primitive
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values or zero terminated character arrays (strings). Class/type
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evolution is not supported.
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</td>
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</tr>
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<tr>
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<td>Custom binding format</td>
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<td>User-defined</td>
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<td>
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The data storage format and ordering is determined by the
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custom binding implementation.
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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<p>
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As shown in the table above, the tuple format supports built-in ordering
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(without specifying a custom comparator), while the serial format does
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not. This means that when a specific key order is needed, tuples should
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be used instead of serial data. Alternatively, a custom Btree comparator should be
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specified using
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<code class="methodname">DatabaseConfig.setBtreeComparator()</code>. Note that
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a custom Btree comparator will usually execute more slowly than the
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default byte-by-byte comparison. This makes using tuples an attractive
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option, since they provide ordering along with optimal performance.
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</p>
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<p>
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The tuple binding uses less space and executes faster than the
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serial binding. But once a tuple is written to a database, the
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order of fields in the tuple may not be changed and fields may not
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be deleted. The only type evolution allowed is the addition of
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fields at the end of the tuple, and this must be explicitly
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supported by the custom binding implementation.
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</p>
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<p>
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The serial binding supports the full generality of Java
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serialization including type evolution. But serialized data can
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only be accessed by Java applications, its size is larger, and its
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bindings are slower to execute.
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||
</p>
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||
</div>
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||
<div class="sect2" lang="en" xml:lang="en">
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||
<div class="titlepage">
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||
<div>
|
||
<div>
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||
<h3 class="title"><a id="SelectingDataBindings"></a>
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||
Selecting Data Bindings
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</h3>
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||
</div>
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</div>
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</div>
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<p>
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There are two types of binding interfaces. Simple entry bindings
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implement the
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<a class="ulink" href="../../java/com/sleepycat/bind/EntryBinding.html" target="_top">EntryBinding</a>
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interface and can be used for key or value objects. Entity bindings
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implement the
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<a class="ulink" href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>
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interface and are used for combined key and value objects called
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entities.
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||
</p>
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<p>
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Simple entry bindings map between the key or value data stored
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by Berkeley DB and a key or value object. This is a simple
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one-to-one mapping.
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</p>
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<p>
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Simple entry bindings are easy to implement and in some cases
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require no coding. For example, a
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/SerialBinding.html" target="_top">SerialBinding</a>
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can be used for keys or values without writing any additional
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code. A tuple binding for a single-item tuple can also be used without
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writing any code; see the
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleBinding.html#getPrimitiveBinding(java.lang.Class)" target="_top">TupleBinding.getPrimitiveBinding</a>
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method.
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</p>
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<p>
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Entity bindings must divide an entity object into its key and
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value data, and then combine the key and value data to re-create
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||
the entity object. This is a two-to-one mapping.
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||
</p>
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<p>
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Entity bindings are useful when a stored application object
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naturally has its primary key as a property, which is very common.
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For example, an Employee object would naturally have an
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EmployeeNumber property (its primary key) and an entity binding
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||
would then be needed. Of course, entity bindings are more complex
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to implement, especially if their key and data formats are
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||
different.
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</p>
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<p>
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Note that even when an entity binding is used a key binding is
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also usually needed. For example, a key binding is used to create
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key objects that are passed to the
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<a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/util/Map.html#get" target="_top">Map.get()</a>
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method. A key object is passed to this method even though it may
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||
return an entity that also contains the key.
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||
</p>
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||
</div>
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||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
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||
<h3 class="title"><a id="ImplementingBindings"></a>
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||
Implementing Bindings
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</h3>
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||
</div>
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</div>
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</div>
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<p>
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There are two ways to implement bindings. The first way is to
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create a binding class that implements one of the two binding
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interfaces,
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<a class="ulink" href="../../java/com/sleepycat/bind/EntryBinding.html" target="_top">EntryBinding</a>
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or
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<a class="ulink" href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>.
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For tuple bindings and serial bindings there are a number of
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||
abstract classes that make this easier. For example, you can extend
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleBinding.html" target="_top">TupleBinding</a>
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to implement a simple binding for a tuple key or value. Abstract
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||
classes are also provided for entity bindings and are named after
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the format names of the key and value. For example, you can extend
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/TupleSerialBinding.html" target="_top">TupleSerialBinding</a>
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to implement an entity binding with a tuple key and serial
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value.
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</p>
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<p>
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Another way to implement bindings is with marshalling
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interfaces. These are interfaces which perform the binding
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operations and are implemented by the key, value or entity classes
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themselves. With marshalling you use a binding which calls the
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marshalling interface and you implement the marshalling interface
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for each key, value or entity class. For example, you can use
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<a class="ulink" href="../../java/com/sleepycat/bind/tuple/TupleMarshalledBinding.html" target="_top">TupleMarshalledBinding</a>
|
||
|
||
along with key or value classes that implement the
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||
<a class="ulink" href="../../java/com/sleepycat/bind/tuple/MarshalledTupleEntry.html" target="_top">MarshalledTupleEntry</a>
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||
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interface.
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||
</p>
|
||
</div>
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||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="UsingBindings"></a>
|
||
Using Bindings
|
||
</h3>
|
||
</div>
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||
</div>
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||
</div>
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||
<p>
|
||
Bindings are specified whenever a stored collection is created.
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||
A key binding must be specified for map, key set and entry set
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||
views. A value binding or entity binding must be specified for map,
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||
value set and entry set views.
|
||
</p>
|
||
<p>
|
||
Any number of bindings may be created for the same stored data.
|
||
This allows multiple views over the same data. For example, a tuple
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||
might be bound to an array of values or to a class with properties
|
||
for each object.
|
||
</p>
|
||
<p>
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||
It is important to be careful of bindings that only use a subset
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||
of the stored data. This can be useful to simplify a view or to
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||
hide information that should not be accessible. However, if you
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||
write records using these bindings you may create stored data that
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||
is invalid from the application's point of view. It is up to the
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||
application to guard against this by creating a read-only
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||
collection when such bindings are used.
|
||
</p>
|
||
</div>
|
||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="SecondaryKeyCreators"></a>
|
||
Secondary Key Creators
|
||
</h3>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
Secondary Key Creators are needed whenever database indices are
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||
used. For each secondary index
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||
<span>
|
||
(<a class="ulink" href="../../java/com/sleepycat/je/SecondaryDatabase.html" target="_top">SecondaryDatabase</a>)
|
||
</span>
|
||
|
||
a key creator is used to derive index key data from key/value data.
|
||
Key creators are objects whose classes implement the
|
||
<a class="ulink" href="../../java/com/sleepycat/je/SecondaryKeyCreator.html" target="_top">SecondaryKeyCreator</a>
|
||
|
||
|
||
interface.
|
||
</p>
|
||
<p>
|
||
Like bindings, key creators may be implemented using a separate
|
||
key creator class or using a marshalling interface. Abstract key
|
||
creator classes and marshalling interfaces are provided in the
|
||
com.sleepycat.bind.tuple and com.sleepycat.bind.serial
|
||
packages.
|
||
</p>
|
||
<p>
|
||
Unlike bindings, key creators fundamentally operate on key and
|
||
value data, not necessarily on the objects derived from the data by
|
||
bindings. In this sense key creators are a part of a database
|
||
definition, and may be independent of the various bindings that may
|
||
be used to view data in a database. However, key creators are not
|
||
prohibited from using higher level objects produced by bindings,
|
||
and doing so may be convenient for some applications. For example,
|
||
marshalling interfaces, which are defined for objects produced by
|
||
bindings, are a convenient way to define key creators.
|
||
</p>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="Summary.html">Prev</a> </td>
|
||
<td width="20%" align="center"> </td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="UsingCollectionsAPI.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Chapter 7.
|
||
Summary
|
||
</td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top">
|
||
Using the JE JE Collections API
|
||
</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|