2011-09-13 17:44:24 +00:00
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<title>Opening and Closing the Class Catalog</title>
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<link rel="start" href="index.html" title="Berkeley DB Collections Tutorial" />
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<link rel="up" href="BasicProgram.html" title="Chapter 2. The Basic Program" />
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<link rel="prev" href="opendbenvironment.html" title="Opening and Closing the Database Environment" />
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<link rel="next" href="opendatabases.html" title="Opening and Closing Databases" />
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<div class="libver">
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2012-11-14 21:35:20 +00:00
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<p>Library Version 11.2.5.3</p>
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2011-09-13 17:44:24 +00:00
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">
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Opening and Closing the Class Catalog
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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="opendbenvironment.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The Basic Program
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="opendatabases.html">Next</a></td>
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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="openclasscatalog"></a>
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Opening and Closing the Class Catalog
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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 section describes how to open and close the Java class
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catalog. The class catalog is a specialized database store that
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contains the Java class descriptions of the serialized objects that
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are stored in the database. The class descriptions are stored in
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the catalog rather than storing them redundantly in each database
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record. A single class catalog per environment must be opened
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whenever serialized objects will be stored in the database.
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</p>
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<p>
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The <code class="classname">SampleDatabase</code> class is extended to open and close
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the class catalog. The following additional imports and class
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members are needed.
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</p>
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<a id="cb_java_sampledatabase1"></a>
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<pre class="programlisting"><strong class="userinput"><code>import com.sleepycat.bind.serial.StoredClassCatalog;
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import com.sleepycat.bind.serial.ClassCatalog;
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import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseConfig;
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import com.sleepycat.db.DatabaseType;</code></strong>
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import com.sleepycat.db.DatabaseException;
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import com.sleepycat.db.Environment;
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import com.sleepycat.db.EnvironmentConfig;
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import java.io.File;
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import java.io.FileNotFoundException;
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...
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public class SampleDatabase
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{
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private Environment env;
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<strong class="userinput"><code> private static final String CLASS_CATALOG = "java_class_catalog";</code></strong>
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...
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<strong class="userinput"><code> private StoredClassCatalog javaCatalog;</code></strong>
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...
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} </pre>
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<p>
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While the class catalog is itself a database, it contains
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metadata for other databases and is therefore treated specially by
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the DB Java Collections API. The
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<a class="ulink" href="../../java/com/sleepycat/bind/serial/StoredClassCatalog.html" target="_top">StoredClassCatalog</a>
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class encapsulates the catalog store and implements this special
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behavior.
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</p>
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<p>
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The following statements open the class catalog by creating a
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<code class="classname">Database</code> and a <code class="classname">StoredClassCatalog</code> object. The catalog
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database is created if it does not already exist.
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</p>
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<a id="cb_java_sampledatabase2"></a>
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<pre class="programlisting"> public SampleDatabase(String homeDirectory)
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throws DatabaseException, FileNotFoundException
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{
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...
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<strong class="userinput"><code> DatabaseConfig dbConfig = new DatabaseConfig();
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dbConfig.setTransactional(true);
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dbConfig.setAllowCreate(true);
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dbConfig.setType(DatabaseType.BTREE);
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Database catalogDb = env.openDatabase(null, CLASS_CATALOG, null,
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dbConfig);
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javaCatalog = new StoredClassCatalog(catalogDb);</code></strong>
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...
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}
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...
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<strong class="userinput"><code> public final StoredClassCatalog getClassCatalog() {
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return javaCatalog;
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}</code></strong> </pre>
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<p>
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The
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<a class="ulink" href="../../java/com/sleepycat/db/DatabaseConfig.html" target="_top">DatabaseConfig</a>
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class is used to specify configuration parameters when opening a
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database. The first configuration option specified —
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<code class="methodname">setTransactional()</code> — is set to true to create a transactional
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database. While non-transactional databases can also be created,
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the examples in this tutorial use transactional databases.
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</p>
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<p>
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<code class="methodname">setAllowCreate()</code> is set to true to specify
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that the database will be created if it does not already exist. If
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this parameter is not specified, an exception will be thrown if the
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database does not already exist.
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</p>
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<p>
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<code class="methodname">setDatabaseType()</code> identifies the database storage
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type or access method. For opening a catalog database, the
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<code class="literal">BTREE</code> type is required. <code class="literal">BTREE</code> is the
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most commonly used database type and in this tutorial is used for all
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databases.
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</p>
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<p>
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The first parameter of the <code class="methodname">openDatabase()</code> method is an
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optional transaction that is used for creating a new database. If
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null is passed, auto-commit is used when creating a database.
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</p>
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<p>
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The second and third parameters of <code class="methodname">openDatabase()</code>
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specify the filename and database (sub-file) name of the database. The
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database name is optional and is <code class="literal">null</code> in this example.
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</p>
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<p>
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The last parameter of <code class="methodname">openDatabase()</code> specifies the database
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configuration object.
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</p>
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<p>
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Lastly, the <code class="classname">StoredClassCatalog</code> object is created to manage the
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information in the class catalog database. The
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<code class="classname">StoredClassCatalog</code> object will be used in the sections
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following for creating serial bindings.
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</p>
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<p>
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The <code class="methodname">getClassCatalog</code> method returns the catalog object for
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use by other classes in the example program.
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</p>
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<p>
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When the environment is closed, the class catalog is closed
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also.
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</p>
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<a id="cb_close1"></a>
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<pre class="programlisting"> public void close()
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throws DatabaseException
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{
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<strong class="userinput"><code> javaCatalog.close();</code></strong>
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env.close();
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} </pre>
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<p>
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The <code class="methodname">StoredClassCatalog.close()</code> method simply closes the
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underlying class catalog database and in fact the
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<a class="ulink" href="../../java/com/sleepycat/db/Database.html#close()" target="_top">Database.close()</a>
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method may be called instead, if desired. It is recommended that you close the catalog database and
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all other databases, before closing the
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environment.
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</p>
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</div>
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<td width="40%" align="left"><a accesskey="p" href="opendbenvironment.html">Prev</a> </td>
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<a accesskey="u" href="BasicProgram.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="opendatabases.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">
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|
Opening and Closing the Database Environment
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</td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top">
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Opening and Closing Databases
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</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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