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https://github.com/berkeleydb/je.git
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285 lines
13 KiB
HTML
285 lines
13 KiB
HTML
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<?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>Cursor 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="Cursors.html" title="Chapter 9. Using Cursors" />
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<link rel="prev" href="ReplacingEntryWCursor.html" title="Replacing Records Using Cursors" />
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<link rel="next" href="indexes.html" title="Chapter 10. Secondary Databases" />
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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">Cursor 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="ReplacingEntryWCursor.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 9. Using Cursors</th>
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<td width="20%" align="right"> <a accesskey="n" href="indexes.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="cursorUsage"></a>Cursor Example</h2>
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</div>
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</div>
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</div>
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<p>In <a class="xref" href="dbUsage.html" title="Database Example">Database Example</a> we wrote an
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application that loaded two <code class="classname">Database</code> objects with vendor
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and inventory information. In this example, we will use those databases to
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display all of the items in the inventory database. As a part of showing
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any given inventory item, we will look up the vendor who can provide the
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item and show the vendor's contact information.</p>
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<p>To do this, we create the <code class="classname">ExampleInventoryRead</code>
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application. This application reads and displays all inventory records by:</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>Opening the environment and then the inventory, vendor, and
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class catalog <code class="classname">Database</code> objects. We do this using the
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<code class="classname">MyDbEnv</code> class. See <a class="xref" href="dbtUsage.html#dbenvStoredClass" title="Example 8.4 Stored Class Catalog Management with MyDbEnv">Stored Class Catalog Management with MyDbEnv</a>
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for a description of this class.</p>
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</li>
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<li>
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<p>Obtaining a cursor from the inventory <code class="classname">Database</code>.</p>
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</li>
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<li>
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<p>Steps through the <code class="classname">Database</code>, displaying
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each record as it goes.</p>
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</li>
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<li>
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<p>To display the Inventory record, the custom tuple binding that
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we created in <a class="xref" href="dbtUsage.html#InventoryBinding" title="Example 8.3 InventoryBinding.java">InventoryBinding.java</a> is used.</p>
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</li>
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<li>
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<p><code class="methodname">Database.get()</code> is used to obtain the vendor that corresponds to
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the inventory item.</p>
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</li>
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<li>
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<p>A serial binding is used to convert the
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<code class="classname">DatabaseEntry</code> returned
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by the <code class="methodname">get()</code> to a Vendor object.</p>
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</li>
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<li>
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<p>The contents of the Vendor object are displayed.</p>
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</li>
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</ol>
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</div>
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<p>We implemented the <code class="classname">Vendor</code> class in <a class="xref" href="dbtUsage.html#vendor" title="Example 8.2 Vendor.java">Vendor.java</a>. We implemented the
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<code class="classname">Inventory</code> class in <a class="xref" href="dbtUsage.html#inventory" title="Example 8.1 Inventory.java">Inventory.java</a>.</p>
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<p>The full implementation of <code class="classname">ExampleInventoryRead</code>
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can be found in:
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</p>
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<pre class="programlisting"><span class="emphasis"><em>JE_HOME</em></span>/examples/je/gettingStarted/ExampleInventoryRead.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
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distribution.
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</p>
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<div class="example">
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<a id="EIR"></a>
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<p class="title">
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<b>Example 9.1 ExampleInventoryRead.java</b>
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</p>
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<div class="example-contents">
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<p>To begin, we import the necessary classes:</p>
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<a id="je_cursor10"></a>
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<pre class="programlisting">// file ExampleInventoryRead.java
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package je.gettingStarted;
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import com.sleepycat.bind.EntryBinding;
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import com.sleepycat.bind.serial.SerialBinding;
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import com.sleepycat.bind.tuple.TupleBinding;
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import com.sleepycat.je.Cursor;
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import com.sleepycat.je.DatabaseEntry;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.LockMode;
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import com.sleepycat.je.OperationStatus;
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import java.io.File;
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import java.io.IOException; </pre>
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<p>Next we declare our class and set up some global variables. Note a
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<code class="classname">MyDbEnv</code> object is instantiated here. We can do
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this because its constructor never throws an exception. See <a class="xref" href="dbUsage.html" title="Database Example">Database Example</a> for its implementation
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details.</p>
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<a id="je_cursor11"></a>
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<pre class="programlisting">public class ExampleInventoryRead {
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private static File myDbEnvPath =
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new File("/tmp/JEDB");
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// Encapsulates the database environment and databases.
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private static MyDbEnv myDbEnv = new MyDbEnv();
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private static TupleBinding inventoryBinding;
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private static EntryBinding vendorBinding;</pre>
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<p>
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Next we create the <code class="methodname">ExampleInventoryRead.usage()</code> and
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<code class="methodname">ExampleInventoryRead.main()</code> methods.
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We perform almost all of our exception handling from <code class="methodname">ExampleInventoryRead.main()</code>, and so we
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must catch <code class="classname">DatabaseException</code> because the <code class="literal">com.sleepycat.je.*</code>
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APIs throw them.
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</p>
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<a id="je_cursor12"></a>
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<pre class="programlisting"> private static void usage() {
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System.out.println("ExampleInventoryRead [-h <env directory>]");
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System.exit(0);
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}
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public static void main(String args[]) {
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ExampleInventoryRead eir = new ExampleInventoryRead();
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try {
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eir.run(args);
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} catch (DatabaseException dbe) {
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System.err.println("ExampleInventoryRead: " + dbe.toString());
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dbe.printStackTrace();
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} finally {
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myDbEnv.close();
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}
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System.out.println("All done.");
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}</pre>
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<p>In <code class="methodname">ExampleInventoryRead.run()</code>, we call <code class="methodname">MyDbEnv.setup()</code> to
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open our environment and databases. Then we create the bindings that we need for using our data objects with
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<code class="classname">DatabaseEntry</code> objects.
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</p>
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<a id="je_cursor13"></a>
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<pre class="programlisting"> private void run(String args[]) throws DatabaseException {
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// Parse the arguments list
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parseArgs(args);
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myDbEnv.setup(myDbEnvPath, // path to the environment home
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true); // is this environment read-only?
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// Setup our bindings.
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inventoryBinding = new InventoryBinding();
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vendorBinding =
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new SerialBinding(myDbEnv.getClassCatalog(),
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Vendor.class);
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showAllInventory();
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}</pre>
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<p>Now we write the loop that displays the <code class="classname">Inventory</code>
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records. We do this by opening a cursor on the inventory database and
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iterating over all its contents, displaying each as we go.</p>
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<a id="je_cursor14"></a>
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<pre class="programlisting"> private void showAllInventory()
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throws DatabaseException {
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// Get a cursor
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Cursor cursor = myDbEnv.getInventoryDB().openCursor(null, null);
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// DatabaseEntry objects used for reading records
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DatabaseEntry foundKey = new DatabaseEntry();
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DatabaseEntry foundData = new DatabaseEntry();
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try { // always want to make sure the cursor gets closed.
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while (cursor.getNext(foundKey, foundData,
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LockMode.DEFAULT) == OperationStatus.SUCCESS) {
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Inventory theInventory =
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(Inventory)inventoryBinding.entryToObject(foundData);
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displayInventoryRecord(foundKey, theInventory);
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}
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} catch (Exception e) {
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System.err.println("Error on inventory cursor:");
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System.err.println(e.toString());
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e.printStackTrace();
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} finally {
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cursor.close();
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}
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} </pre>
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<p>We use <code class="methodname">ExampleInventoryRead.displayInventoryRecord()</code> to actually show the record. This
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method first displays all the relevant information from the retrieved
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Inventory object. It then uses the vendor database to retrieve and
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display the vendor. Because the vendor database is keyed by vendor name,
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and because each inventory object contains this key, it is trivial to
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retrieve the appropriate vendor record.</p>
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<a id="je_cursor15"></a>
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<pre class="programlisting"> private void displayInventoryRecord(DatabaseEntry theKey,
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Inventory theInventory)
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throws DatabaseException {
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DatabaseEntry searchKey = null;
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try {
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String theSKU = new String(theKey.getData(), "UTF-8");
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System.out.println(theSKU + ":");
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System.out.println("\t " + theInventory.getItemName());
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System.out.println("\t " + theInventory.getCategory());
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System.out.println("\t " + theInventory.getVendor());
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System.out.println("\t\tNumber in stock: " +
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theInventory.getVendorInventory());
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System.out.println("\t\tPrice per unit: " +
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theInventory.getVendorPrice());
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System.out.println("\t\tContact: ");
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searchKey =
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new DatabaseEntry(theInventory.getVendor().getBytes("UTF-8"));
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} catch (IOException willNeverOccur) {}
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DatabaseEntry foundVendor = new DatabaseEntry();
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if (myDbEnv.getVendorDB().get(null, searchKey, foundVendor,
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LockMode.DEFAULT) != OperationStatus.SUCCESS) {
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System.out.println("Could not find vendor: " +
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theInventory.getVendor() + ".");
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System.exit(-1);
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} else {
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Vendor theVendor =
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(Vendor)vendorBinding.entryToObject(foundVendor);
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System.out.println("\t\t " + theVendor.getAddress());
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System.out.println("\t\t " + theVendor.getCity() + ", " +
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theVendor.getState() + " " + theVendor.getZipcode());
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System.out.println("\t\t Business Phone: " +
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theVendor.getBusinessPhoneNumber());
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System.out.println("\t\t Sales Rep: " +
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theVendor.getRepName());
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System.out.println("\t\t " +
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theVendor.getRepPhoneNumber());
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}
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}</pre>
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<p>The remainder of this application provides a utility method used
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to parse the command line options. From the perspective of this
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document, this is relatively uninteresting. You can see how this is
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implemented by looking at:
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</p>
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<pre class="programlisting"><span class="emphasis"><em>JE_HOME</em></span>/examples/je/gettingStarted/ExampleInventoryRead.java</pre>
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<p>
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|||
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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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|||
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</div>
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|||
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</div>
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|||
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<br class="example-break" />
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|||
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</div>
|
|||
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<div class="navfooter">
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|||
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<hr />
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|||
|
|
<table width="100%" summary="Navigation footer">
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|||
|
|
<tr>
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|||
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|
<td width="40%" align="left"><a accesskey="p" href="ReplacingEntryWCursor.html">Prev</a> </td>
|
|||
|
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<td width="20%" align="center">
|
|||
|
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<a accesskey="u" href="Cursors.html">Up</a>
|
|||
|
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</td>
|
|||
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<td width="40%" align="right"> <a accesskey="n" href="indexes.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
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<tr>
|
|||
|
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<td width="40%" align="left" valign="top">Replacing Records Using Cursors </td>
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|||
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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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|||
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</td>
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|||
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<td width="40%" align="right" valign="top"> Chapter 10. Secondary Databases</td>
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</tr>
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</table>
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</div>
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|||
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</body>
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</html>
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