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181 lines
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HTML
181 lines
7.2 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>Database Environment Management Example</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="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="env.html" title="Chapter 2. Database Environments" />
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<link rel="prev" href="envStats.html" title="Environment Statistics" />
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<link rel="next" href="dpl.html" title="Part I. Programming with the Direct Persistence Layer" />
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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">Database Environment Management Example</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="envStats.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2. Database Environments</th>
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<td width="20%" align="right"> <a accesskey="n" href="dpl.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="dbenvUsageExample"></a>Database Environment Management Example</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 example provides a complete class that can open and close an environment. It is
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both extended and used in subsequent examples in this book to open and close both
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environments and databases. We do this so as to make the example code
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shorter and easier to manage. You can find this class in:
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</p>
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<pre class="programlisting"><span class="emphasis"><em>JE_HOME</em></span>/examples/je/gettingStarted/MyDbEnv.java</pre>
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<p>
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where <code class="literal"><span class="emphasis"><em>JE_HOME</em></span></code> is the location where you
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placed your JE distribution.
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</p>
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<div class="example">
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<a id="mydbenv"></a>
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<p class="title">
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<b>Example 2.1 Database Environment Management Class</b>
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</p>
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<div class="example-contents">
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<p>First we write the normal class declarations. We also set up some
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private data members that are used to manage environment creation. We
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use the class constructor to instantiate the <code class="classname">EnvironmentConfig</code>
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object that is used to configure our environment when we open it.</p>
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<a id="je_env6"></a>
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<pre class="programlisting">// File MyDbEnv.java
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package je.gettingStarted;
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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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public class MyDbEnv {
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private Environment myEnv;
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public MyDbEnv() {} </pre>
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<p>Next we need a method to open the environment. This is responsible
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for instantiating our <code class="classname">Environment</code> object.
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Remember that instantiation is what opens the environment (or creates it
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if the creation property is set to <code class="literal">true</code> and the
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environment does not currently exist).
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</p>
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<a id="je_env7"></a>
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<pre class="programlisting"> public void setup(File envHome, boolean readOnly)
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throws DatabaseException {
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// Instantiate an environment configuration object
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EnvironmentConfig myEnvConfig = new EnvironmentConfig();
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// Configure the environment for the read-only state as identified
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// by the readOnly parameter on this method call.
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myEnvConfig.setReadOnly(readOnly);
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// If the environment is opened for write, then we want to be
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// able to create the environment if it does not exist.
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myEnvConfig.setAllowCreate(!readOnly);
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// Instantiate the Environment. This opens it and also possibly
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// creates it.
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myEnv = new Environment(envHome, myEnvConfig);
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} </pre>
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<p>
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Next we provide a getter method that allows us to retrieve the
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<code class="classname">Environment</code> directly. This is needed for later
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examples in this guide.
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</p>
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<a id="je_env8"></a>
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<pre class="programlisting"> // Getter methods
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public Environment getEnv() {
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return myEnv;
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} </pre>
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<p>Finally, we need a method to close our <code class="classname">Environment</code>.
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We wrap this operation in a <code class="literal">try</code> block so that it can
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be used gracefully in a <code class="literal">finally</code> statement.</p>
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<a id="je_env9"></a>
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<pre class="programlisting"> // Close the environment
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public void close() {
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if (myEnv != null) {
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try {
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myEnv.close();
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} catch(DatabaseException dbe) {
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System.err.println("Error closing environment" +
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dbe.toString());
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}
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}
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}
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} </pre>
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<p>
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This completes the <code class="classname">MyDbEnv</code> class. While not particularly useful
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as it currently exists, we will build upon it throughout this book so that it will
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eventually open and close all of the entity stores or databases required by our
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applications.
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</p>
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<p>
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We can now use <code class="classname">MyDbEnv</code> to open and close a database environment
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from the appropriate place in our application. For example:
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</p>
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<a id="je_env10"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.DatabaseEntry;
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import com.sleepycat.je.DatabaseException;
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import java.io.File;
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...
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MyDbEnv exampleDbEnv = new MyDbEnv();
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try {
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exampleDbEnv.setup(new File("/directory/currently/exists"), true);
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...
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} catch(DatabaseException dbe) {
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// Error code goes here
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} finally {
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exampleDbEnv.close();
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} </pre>
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</div>
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</div>
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<br class="example-break" />
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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="envStats.html">Prev</a> </td>
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||
<td width="20%" align="center">
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<a accesskey="u" href="env.html">Up</a>
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||
</td>
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||
<td width="40%" align="right"> <a accesskey="n" href="dpl.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">Environment Statistics </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"> Part I. Programming with the Direct Persistence Layer</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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