1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Chapter��2.��Database Environments</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="index.html" title="Getting Started with Berkeley DB" /> 11 <link rel="prev" href="gettingit.html" title="Getting and Using DB" /> 12 <link rel="next" href="EnvClose.html" title="Closing Database Environments" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter��2.��Database Environments</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="gettingit.html">Prev</a>��</td> 22 <th width="60%" align="center">��</th> 23 <td width="20%" align="right">��<a accesskey="n" href="EnvClose.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="chapter" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title"><a id="Env"></a>Chapter��2.��Database Environments</h2> 33 </div> 34 </div> 35 </div> 36 <div class="toc"> 37 <p> 38 <b>Table of Contents</b> 39 </p> 40 <dl> 41 <dt> 42 <span class="sect1"> 43 <a href="Env.html#EnvOpen">Opening Database Environments</a> 44 </span> 45 </dt> 46 <dt> 47 <span class="sect1"> 48 <a href="EnvClose.html">Closing Database Environments</a> 49 </span> 50 </dt> 51 <dt> 52 <span class="sect1"> 53 <a href="EnvProps.html">Environment Properties</a> 54 </span> 55 </dt> 56 <dd> 57 <dl> 58 <dt> 59 <span class="sect2"> 60 <a href="EnvProps.html#envconfig">The EnvironmentConfig Class</a> 61 </span> 62 </dt> 63 <dt> 64 <span class="sect2"> 65 <a href="EnvProps.html#envhandleconfig">EnvironmentMutableConfig</a> 66 </span> 67 </dt> 68 </dl> 69 </dd> 70 </dl> 71 </div> 72 <p> 73 Environments are optional, but very commonly used, for Berkeley DB 74 applications built using the base API. If you are using the DPL, then 75 environments are required. 76 </p> 77 <p> 78 Database environments encapsulate one or more databases. This encapsulation 79 provides your threads with efficient access to your databases by allowing a single 80 in-memory cache to be used for each of the databases contained in the 81 environment. This encapsulation also allows you to group operations performed against 82 multiple databases inside a single 83 transactions (see the <em class="citetitle">Berkeley DB Java Edition Getting Started with Transaction Processing</em> guide for more information). 84 </p> 85 <p> 86 Most commonly you use database environments to create and open 87 databases (you close individual databases using the individual 88 database handles). You can also use environments to delete and rename 89 databases. For transactional applications, you use the environment to start 90 transactions. For non-transactional 91 applications, you use the environment to sync your in-memory cache to disk. 92 </p> 93 <div class="sect1" lang="en" xml:lang="en"> 94 <div class="titlepage"> 95 <div> 96 <div> 97 <h2 class="title" style="clear: both"><a id="EnvOpen"></a>Opening Database Environments</h2> 98 </div> 99 </div> 100 </div> 101 <p>You open a database environment by instantiating an 102 <code class="classname">Environment</code> object. You must provide to the 103 constructor the name of the on-disk directory where the environment is to reside. 104 This directory location must exist or the open will fail.</p> 105 <p>By default, the environment is not created for you if it does not exist. Set the 106 <a class="link" href="EnvProps.html" title="Environment Properties">creation property</a> to <code class="literal">true</code> if 107 you want the environment to be created. For example:</p> 108 <a id="je_env1"></a> 109 <pre class="programlisting"> 110 111import com.sleepycat.je.DatabaseException; 112import com.sleepycat.je.Environment; 113import com.sleepycat.je.EnvironmentConfig; 114 115import java.io.File; 116 117... 118 119// Open the environment. Allow it to be created if it does not already exist. 120Environment myDbEnvironment = null; 121 122try { 123 EnvironmentConfig envConfig = new EnvironmentConfig(); 124 envConfig.setAllowCreate(true); 125 myDbEnvironment = new Environment(new File("/export/dbEnv"), envConfig); 126} catch (DatabaseException dbe) { 127 // Exception handling goes here 128} </pre> 129 <pre class="programlisting">package db.gettingStarted; 130 131import com.sleepycat.db.DatabaseException; 132import com.sleepycat.db.Environment; 133import com.sleepycat.db.EnvironmentConfig; 134 135import java.io.File; 136import java.io.FileNotFoundException; 137 138... 139 140// Open the environment. Allow it to be created if it does not already exist. 141Environment myDbEnvironment = null; 142 143try { 144 EnvironmentConfig envConfig = new EnvironmentConfig(); 145 envConfig.setAllowCreate(true); 146 myDbEnvironment = new Environment(new File("/export/dbEnv"), envConfig); 147} catch (DatabaseException dbe) { 148 // Exception handling goes here 149} catch (FileNotFoundException fnfe) { 150// Exception handling goes here 151} </pre> 152 <p>Your application can open and use as many environments as you have 153 disk and memory to manage, although most applications will use just one 154 environment. Also, you can instantiate multiple <code class="classname">Environment</code> 155 objects for the same physical environment.</p> 156 </div> 157 </div> 158 <div class="navfooter"> 159 <hr /> 160 <table width="100%" summary="Navigation footer"> 161 <tr> 162 <td width="40%" align="left"><a accesskey="p" href="gettingit.html">Prev</a>��</td> 163 <td width="20%" align="center">��</td> 164 <td width="40%" align="right">��<a accesskey="n" href="EnvClose.html">Next</a></td> 165 </tr> 166 <tr> 167 <td width="40%" align="left" valign="top">Getting and Using DB ��</td> 168 <td width="20%" align="center"> 169 <a accesskey="h" href="index.html">Home</a> 170 </td> 171 <td width="40%" align="right" valign="top">��Closing Database Environments</td> 172 </tr> 173 </table> 174 </div> 175 </body> 176</html> 177