184 lines
6.6 KiB
HTML
184 lines
6.6 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 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 V1.62.4" />
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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="CoreEnvUsage.html" title="Managing Databases in Environments" />
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<link rel="next" href="DBEntry.html" title="Chapter 8. Database Records" />
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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">Database 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="CoreEnvUsage.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="DBEntry.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="CoreJavaUsage"></a>Database Example</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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Throughout this book we will build a couple of applications that load
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and retrieve inventory data from DB databases. While we are not yet ready to
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begin reading from or writing to our databases, we can at least create
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the class that we will use to manage our databases.
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</p>
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<p>
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Note that subsequent examples in this book will build on this code to
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perform the more interesting work of writing to and reading from the
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databases.
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</p>
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<p>
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Note that you can find the complete implementation of these functions
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in:
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</p>
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<pre class="programlisting"><span class="emphasis"><em>DB_INSTALL</em></span>/examples_java/db/GettingStarted</pre>
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<p>
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where <tt class="literal"><span class="emphasis"><em>DB_INSTALL</em></span></tt> is the location where you
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placed your DB distribution.
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</p>
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<div class="example">
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<a id="MyDb"></a>
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<p class="title">
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<b>Example 7.1 MyDbs Class</b>
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</p>
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<p>
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To manage our database open and close activities, we encapsulate them
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in the <tt class="classname">MyDbs</tt> class. There are several good reasons
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to do this, the most important being that we can ensure our databases are
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closed by putting that activity in the <tt class="classname">MyDbs</tt>
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class destructor.
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</p>
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<p>
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To begin, we import some needed classes:
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</p>
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<a id="java_db12"></a>
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<pre class="programlisting">// File: MyDbs.java
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package db.GettingStarted;
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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.DatabaseException;
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import com.sleepycat.db.DatabaseType;
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import java.io.FileNotFoundException; </pre>
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<p>
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And then we write our class declaration and provided some necessary private data members:
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</p>
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<a id="java_db13"></a>
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<pre class="programlisting">public class MyDbs {
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// The databases that our application uses
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private Database vendorDb = null;
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private Database inventoryDb = null;
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private String vendordb = "VendorDB.db";
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private String inventorydb = "InventoryDB.db";
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// Our constructor does nothing
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public MyDbs() {} </pre>
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<p>
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Next we need a <tt class="methodname">setup()</tt> method. This is where
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we configure and open our databases.
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</p>
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<a id="java_db14"></a>
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<pre class="programlisting"> // The setup() method opens all our databases
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// for us.
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public void setup(String databasesHome)
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throws DatabaseException {
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DatabaseConfig myDbConfig = new DatabaseConfig();
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myDbConfig.setErrorStream(System.err);
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myDbConfig.setErrorPrefix("MyDbs");
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myDbConfig.setType(DatabaseType.BTREE);
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myDbConfig.setAllowCreate(true);
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// Now open, or create and open, our databases
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// Open the vendors and inventory databases
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try {
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vendordb = databasesHome + "/" + vendordb;
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vendorDb = new Database(vendordb,
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null,
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myDbConfig);
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inventorydb = databasesHome + "/" + inventorydb;
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inventoryDb = new Database(inventorydb,
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null,
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myDbConfig);
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} catch(FileNotFoundException fnfe) {
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System.err.println("MyDbs: " + fnfe.toString());
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System.exit(-1);
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}
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} </pre>
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<p>
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Finally, we provide some getter methods, and our <tt class="methodname">close()</tt> method.
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</p>
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<a id="java_db15"></a>
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<pre class="programlisting"> // getter methods
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public Database getVendorDB() {
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return vendorDb;
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}
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public Database getInventoryDB() {
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return inventoryDb;
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}
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// Close the databases
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public void close() {
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try {
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if (vendorDb != null) {
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vendorDb.close();
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}
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if (inventoryDb != null) {
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inventoryDb.close();
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}
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} catch(DatabaseException dbe) {
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System.err.println("Error closing MyDbs: " +
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dbe.toString());
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System.exit(-1);
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}
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}
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} </pre>
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</div>
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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="CoreEnvUsage.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="DBEntry.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">Managing Databases in Environments </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"> Chapter 8. Database Records</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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