Edit File: CoreJavaUsage.html
<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>Database Example</title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> <link rel="home" href="index.html" title="Getting Started with Berkeley DB" /> <link rel="up" href="DB.html" title="Chapter 7. Databases" /> <link rel="previous" href="CoreEnvUsage.html" title="Managing Databases in Environments" /> <link rel="next" href="DBEntry.html" title="Chapter 8. Database Records" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Database Example</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="CoreEnvUsage.html">Prev</a> </td> <th width="60%" align="center">Chapter 7. Databases</th> <td width="20%" align="right"> <a accesskey="n" href="DBEntry.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="CoreJavaUsage"></a>Database Example</h2> </div> </div> <div></div> </div> <p> Throughout this book we will build a couple of applications that load and retrieve inventory data from DB databases. While we are not yet ready to begin reading from or writing to our databases, we can at least create the class that we will use to manage our databases. </p> <p> Note that subsequent examples in this book will build on this code to perform the more interesting work of writing to and reading from the databases. </p> <p> Note that you can find the complete implementation of these functions in: </p> <pre class="programlisting"><span class="emphasis"><em>DB_INSTALL</em></span>/examples_java/db/GettingStarted</pre> <p> where <tt class="literal"><span class="emphasis"><em>DB_INSTALL</em></span></tt> is the location where you placed your DB distribution. </p> <div class="example"> <a id="MyDb"></a> <p class="title"> <b>Example 7.1 MyDbs Class</b> </p> <p> To manage our database open and close activities, we encapsulate them in the <tt class="classname">MyDbs</tt> class. There are several good reasons to do this, the most important being that we can ensure our databases are closed by putting that activity in the <tt class="classname">MyDbs</tt> class destructor. </p> <p> To begin, we import some needed classes: </p> <a id="java_db12"></a> <pre class="programlisting">// File: MyDbs.java package db.GettingStarted; import com.sleepycat.db.Database; import com.sleepycat.db.DatabaseConfig; import com.sleepycat.db.DatabaseException; import com.sleepycat.db.DatabaseType; import java.io.FileNotFoundException; </pre> <p> And then we write our class declaration and provided some necessary private data members: </p> <a id="java_db13"></a> <pre class="programlisting">public class MyDbs { // The databases that our application uses private Database vendorDb = null; private Database inventoryDb = null; private String vendordb = "VendorDB.db"; private String inventorydb = "InventoryDB.db"; // Our constructor does nothing public MyDbs() {} </pre> <p> Next we need a <tt class="methodname">setup()</tt> method. This is where we configure and open our databases. </p> <a id="java_db14"></a> <pre class="programlisting"> // The setup() method opens all our databases // for us. public void setup(String databasesHome) throws DatabaseException { DatabaseConfig myDbConfig = new DatabaseConfig(); myDbConfig.setErrorStream(System.err); myDbConfig.setErrorPrefix("MyDbs"); myDbConfig.setType(DatabaseType.BTREE); myDbConfig.setAllowCreate(true); // Now open, or create and open, our databases // Open the vendors and inventory databases try { vendordb = databasesHome + "/" + vendordb; vendorDb = new Database(vendordb, null, myDbConfig); inventorydb = databasesHome + "/" + inventorydb; inventoryDb = new Database(inventorydb, null, myDbConfig); } catch(FileNotFoundException fnfe) { System.err.println("MyDbs: " + fnfe.toString()); System.exit(-1); } } </pre> <p> Finally, we provide some getter methods, and our <tt class="methodname">close()</tt> method. </p> <a id="java_db15"></a> <pre class="programlisting"> // getter methods public Database getVendorDB() { return vendorDb; } public Database getInventoryDB() { return inventoryDb; } // Close the databases public void close() { try { if (vendorDb != null) { vendorDb.close(); } if (inventoryDb != null) { inventoryDb.close(); } } catch(DatabaseException dbe) { System.err.println("Error closing MyDbs: " + dbe.toString()); System.exit(-1); } } } </pre> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="CoreEnvUsage.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="DB.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="DBEntry.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Managing Databases in Environments </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Chapter 8. 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