171 lines
6.1 KiB
HTML
171 lines
6.1 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>Managing Databases in Environments</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 V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB" />
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<link rel="up" href="DB.html" title="Chapter 7. Databases" />
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<link rel="previous" href="dbErrorReporting.html" title="Error Reporting Functions" />
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<link rel="next" href="CoreJavaUsage.html" title="Database Example" />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Managing Databases in Environments</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbErrorReporting.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 7. Databases</th>
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<td width="20%" align="right"> <a accesskey="n" href="CoreJavaUsage.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="CoreEnvUsage"></a>Managing Databases in Environments</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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In
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<span>
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<a href="Env.html">Database Environments</a>,
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</span>
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we introduced
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environments. While environments are not used in the example built in this book,
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they are so commonly used for a wide class of DB applications that it is
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necessary to show their basic usage, if only from a completeness perspective.
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</p>
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<p>
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To use an environment, you must first
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open it. At open time, you must identify the directory in
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which it resides. This directory must exist prior to the open attempt.
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You can also identify open properties, such as whether the environment can be
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created if it does not already exist.
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</p>
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<p>
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You will also need to initialize the in-memory cache when you open your environment.
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</p>
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<p>
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For example, to
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<span>create an environment handle and</span>
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open an environment:
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</p>
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<a id="java_env1"></a>
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<pre class="programlisting">package db.GettingStarted;
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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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Environment myEnv = null;
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File envHome = new File("/export1/testEnv");
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try {
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EnvironmentConfig envConf = new EnvironmentConfig();
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envConf.setAllowCreate(true); // If the environment does not
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// exist, create it.
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envConf.setInitializeCache(true); // Initialize the in-memory
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// cache.
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myEnv = new Environment(envHome, envConf);
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} catch (DatabaseException de) {
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// Exception handling goes here
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} catch (FileNotFoundException fnfe) {
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// Exception handling goes here
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} </pre>
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<p>
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Once an environment is opened, you can open databases in it. Note that by default databases
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are stored in the environment's home directory, or relative to that directory if you
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provide any sort of a path in the database's file name:
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</p>
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<a id="java_env2"></a>
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<pre class="programlisting">package db.GettingStarted;
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<b class="userinput"><tt>import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseConfig;
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import com.sleepycat.db.DatabaseType;</tt></b>
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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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Environment myEnv = null;
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Database myDb = null;
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File envHome = new File("/export1/testEnv");
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String dbFileName = new String("mydb.db", "UTF-8");
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try {
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EnvironmentConfig envConf = new EnvironmentConfig();
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envConf.setAllowCreate(true);
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DatabaseConfig dbConfig = new DatabaseConfig();
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<b class="userinput"><tt>dbConfig.setAllowCreate(true);
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dbConfig.setType(DatabaseType.BTREE);</tt></b>
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myEnv = new Environment(envHome, envConf);
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<b class="userinput"><tt>myDb = myEnv.openDatabase(null, dbFileName, null, dbConfig);</tt></b>
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} catch (DatabaseException de) {
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// Exception handling goes here
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} catch (FileNotFoundException fnfe) {
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// Exception handling goes here
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} </pre>
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<p>
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When you are done with an environment, you must close it. Before you close an environment,
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make sure you close any opened databases.
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</p>
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<a id="java_env3"></a>
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<pre class="programlisting">finally {
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try {
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if (myDb != null) {
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myDb.close();
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}
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if (myEnv != null) {
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myEnv.close();
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}
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} catch (DatabaseException de) {
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// Exception handling goes here
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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="dbErrorReporting.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="DB.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="CoreJavaUsage.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">Error Reporting Functions </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"> Database Example</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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