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198 lines
7.3 KiB
HTML
<?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>Opening and Closing the Database Environment</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="BasicProgram.html" title="Chapter 2. The Basic Program" />
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<link rel="prev" href="BasicProgram.html" title="Chapter 2. The Basic Program" />
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<link rel="next" href="openclasscatalog.html" title="Opening and Closing the Class Catalog" />
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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">
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Opening and Closing the Database Environment
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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="BasicProgram.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="openclasscatalog.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="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="opendbenvironment"></a>
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Opening and Closing the Database Environment
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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 of the tutorial describes how to open and close the
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database environment. The database environment manages resources
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(for example, memory, locks and transactions) for any number of
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databases. A single environment instance is normally used for all
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databases.
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</p>
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<p>
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The <code class="classname">SampleDatabase</code> class is used to open and close the
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environment. It will also be used in following sections to open and
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close the class catalog and other databases. Its constructor is
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used to open the environment and its <code class="classname">close()</code> method is used
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to close the environment. The skeleton for the
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<code class="classname">SampleDatabase</code> class follows.
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</p>
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<a id="cb_je_sampledatabase"></a>
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<pre class="programlisting"><strong class="userinput"><code>import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.Environment;
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import com.sleepycat.je.EnvironmentConfig;
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import java.io.File;
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import java.io.FileNotFoundException;
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public class SampleDatabase
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{
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private Environment env;
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public SampleDatabase(String homeDirectory)
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throws DatabaseException, FileNotFoundException
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{
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}
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public void close()
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throws DatabaseException
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{
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}
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}</code></strong> </pre>
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<p>
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The first thing to notice is that the Environment class is in
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the
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<span>com.sleepycat.je</span>
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package, not the com.sleepycat.collections
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package. The
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<span>com.sleepycat.je</span>
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package contains all core Berkeley DB
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functionality. The com.sleepycat.collections package contains
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extended functionality that is based on the Java Collections API.
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The collections package is layered on top of the
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<span>com.sleepycat.je</span>
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package. Both packages are needed to create a complete application
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based on the JE JE Collections API.
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</p>
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<p>
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The following statements create an
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<a class="ulink" href="../../java/com/sleepycat/je/Environment.html" target="_top">Environment</a>
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object.
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</p>
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<a id="cb_je_sampledatabaseconstructor"></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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<strong class="userinput"><code> System.out.println("Opening environment in: " + homeDirectory);
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EnvironmentConfig envConfig = new EnvironmentConfig();
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envConfig.setTransactional(true);
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envConfig.setAllowCreate(true);
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env = new Environment(new File(homeDirectory), envConfig);</code></strong>
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} </pre>
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<p>
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The
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<a class="ulink" href="../../java/com/sleepycat/je/EnvironmentConfig.html" target="_top">EnvironmentConfig</a>
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class is used to specify environment configuration parameters. The
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first configuration option specified — <code class="methodname">setTransactional()</code> —
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is set to true to create an environment where transactional (and
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non-transactional) databases may be opened. While non-transactional
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environments can also be created, the examples in this tutorial use
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a transactional environment.
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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 environment's files will be created if they don't already
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exist. If this parameter is not specified, an exception will be
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thrown if the environment does not already exist. A similar
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parameter will be used later to cause databases to be created if
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they don't exist.
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</p>
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<p>
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When an <code class="classname">Environment</code> object is constructed, a home
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directory and the environment configuration object are specified.
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The home directory is the location of the environment's log files
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that store all database information.
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</p>
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<p>
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The following statement closes the environment. The environment
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must be closed when database work is completed to free
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allocated resources and to avoid having to run recovery later.
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It is recommended that databases are closed before closing the
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environment.
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</p>
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<a id="cb_close"></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> env.close();</code></strong>
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} </pre>
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<p>
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The following getter method returns the environment for use by
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other classes in the example program. The environment is used for
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opening databases and running transactions.
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</p>
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<a id="cb_getenvironment"></a>
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<pre class="programlisting">public class SampleDatabase
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{
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...
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<strong class="userinput"><code> public final Environment getEnvironment()
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{
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return env;
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}</code></strong>
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...
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} </pre>
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</div>
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<div class="navfooter">
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<hr />
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||
<table width="100%" summary="Navigation footer">
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||
<tr>
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||
<td width="40%" align="left"><a accesskey="p" href="BasicProgram.html">Prev</a> </td>
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||
<td width="20%" align="center">
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||
<a accesskey="u" href="BasicProgram.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="openclasscatalog.html">Next</a></td>
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||
</tr>
|
||
<tr>
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<td width="40%" align="left" valign="top">Chapter 2.
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||
The Basic Program
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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>
|
||
<td width="40%" align="right" valign="top">
|
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Opening and Closing the Class Catalog
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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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