<?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>Cursor Example</title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Getting Started with Berkeley DB" /> <link rel="up" href="Cursors.html" title="Chapter 9. Using Cursors" /> <link rel="prev" href="ReplacingEntryWCursor.html" title="Replacing Records Using Cursors" /> <link rel="next" href="indexes.html" title="Chapter 10. Secondary Databases" /> </head> <body> <div xmlns="" class="navheader"> <div class="libver"> <p>Library Version 12.1.6.1</p> </div> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Cursor Example</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="ReplacingEntryWCursor.html">Prev</a> </td> <th width="60%" align="center">Chapter 9. Using Cursors</th> <td width="20%" align="right"> <a accesskey="n" href="indexes.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="cursorJavaUsage"></a>Cursor Example</h2> </div> </div> </div> <p>In <a class="xref" href="dbtJavaUsage.html" title="Database Usage Example">Database Usage Example</a> we wrote an application that loaded two <code class="classname">Database</code> objects with vendor and inventory information. In this example, we will use those databases to display all of the items in the inventory database. As a part of showing any given inventory item, we will look up the vendor who can provide the item and show the vendor's contact information.</p> <p>To do this, we create the <code class="classname">ExampleDatabaseRead</code> application. This application reads and displays all inventory records by:</p> <div class="orderedlist"> <ol type="1"> <li> <p>Opening the inventory, vendor, and class catalog <code class="classname">Database</code> objects. We do this using the <code class="classname">MyDbs</code> class. See <a class="xref" href="dbtJavaUsage.html#dbsStoredClass" title="Example 8.4 Stored Class Catalog Management with MyDbs">Stored Class Catalog Management with MyDbs</a> for a description of this class.</p> </li> <li> <p>Obtaining a cursor from the inventory <code class="classname">Database</code>.</p> </li> <li> <p>Steps through the <code class="classname">Database</code>, displaying each record as it goes.</p> </li> <li> <p>To display the Inventory record, the custom tuple binding that we created in <a class="xref" href="dbtJavaUsage.html#InventoryJavaBinding" title="Example 8.3 InventoryBinding.java">InventoryBinding.java</a> is used.</p> </li> <li> <p><code class="methodname">Database.get()</code> is used to obtain the vendor that corresponds to the inventory item.</p> </li> <li> <p>A serial binding is used to convert the <code class="classname">DatabaseEntry</code> returned by the <code class="methodname">get()</code> to a Vendor object.</p> </li> <li> <p>The contents of the Vendor object are displayed.</p> </li> </ol> </div> <p>We implemented the <code class="classname">Vendor</code> class in <a class="xref" href="dbtJavaUsage.html#vendorjava" title="Example 8.2 Vendor.java">Vendor.java</a>. We implemented the <code class="classname">Inventory</code> class in <a class="xref" href="dbtJavaUsage.html#inventoryjava" title="Example 8.1 Inventory.java">Inventory.java</a>.</p> <p>The full implementation of <code class="classname">ExampleDatabaseRead</code> can be found in: </p> <pre class="programlisting"><span class="emphasis"><em>DB_INSTALL</em></span>/examples/java/db/GettingStarted</pre> <p> where <code class="literal"><span class="emphasis"><em>DB_INSTALL</em></span></code> is the location where you placed your DB distribution. </p> <div class="example"> <a id="EDR"></a> <p class="title"> <b>Example 9.1 ExampleDatabaseRead.java</b> </p> <div class="example-contents"> <p>To begin, we import the necessary classes:</p> <a id="java_cursor10"></a> <pre class="programlisting">// file ExampleDatabaseRead.java package db.GettingStarted; import java.io.File; import java.io.IOException; import com.sleepycat.bind.EntryBinding; import com.sleepycat.bind.serial.SerialBinding; import com.sleepycat.bind.tuple.TupleBinding; import com.sleepycat.db.Cursor; import com.sleepycat.db.DatabaseEntry; import com.sleepycat.db.DatabaseException; import com.sleepycat.db.LockMode; import com.sleepycat.db.OperationStatus;</pre> <p>Next we declare our class and set up some global variables. Note a <code class="classname">MyDbs</code> object is instantiated here. We can do this because its constructor never throws an exception. See <a class="xref" href="CoreJavaUsage.html" title="Database Example">Database Example</a> for its implementation details.</p> <a id="java_cursor11"></a> <pre class="programlisting">public class ExampleDatabaseRead { private static String myDbsPath = "./"; // Encapsulates the database environment and databases. private static MyDbs myDbs = new MyDbs(); private static TupleBinding inventoryBinding; private static EntryBinding vendorBinding; </pre> <p> Next we create the <code class="methodname">ExampleDatabaseRead.usage()</code> and <code class="methodname">ExampleDatabaseRead.main()</code> methods. We perform almost all of our exception handling from <code class="methodname">ExampleDatabaseRead.main()</code>, and so we must catch <code class="classname">DatabaseException</code> because the <code class="literal">com.sleepycat.db.*</code> APIs throw them. </p> <a id="java_cursor12"></a> <pre class="programlisting"> private static void usage() { System.out.println("ExampleDatabaseRead [-h <env directory>]" + "[-s <item to locate>]"); System.exit(-1); } public static void main(String args[]) { ExampleDatabaseRead edr = new ExampleDatabaseRead(); try { edr.run(args); } catch (DatabaseException dbe) { System.err.println("ExampleDatabaseRead: " + dbe.toString()); dbe.printStackTrace(); } finally { myDbs.close(); } System.out.println("All done."); }</pre> <p>In <code class="methodname">ExampleDatabaseRead.run()</code>, we call <code class="methodname">MyDbs.setup()</code> to open our databases. Then we create the bindings that we need for using our data objects with <code class="classname">DatabaseEntry</code> objects. </p> <a id="java_cursor13"></a> <pre class="programlisting"> private void run(String args[]) throws DatabaseException { // Parse the arguments list parseArgs(args); myDbs.setup(myDbsPath); // Setup our bindings. inventoryBinding = new InventoryBinding(); vendorBinding = new SerialBinding(myDbs.getClassCatalog(), Vendor.class); showAllInventory(); }</pre> <p>Now we write the loop that displays the <code class="classname">Inventory</code> records. We do this by opening a cursor on the inventory database and iterating over all its contents, displaying each as we go.</p> <a id="java_cursor14"></a> <pre class="programlisting"> private void showAllInventory() throws DatabaseException { // Get a cursor Cursor cursor = myDbs.getInventoryDB().openCursor(null, null); // DatabaseEntry objects used for reading records DatabaseEntry foundKey = new DatabaseEntry(); DatabaseEntry foundData = new DatabaseEntry(); try { // always want to make sure the cursor gets closed while (cursor.getNext(foundKey, foundData, LockMode.DEFAULT) == OperationStatus.SUCCESS) { Inventory theInventory = (Inventory)inventoryBinding.entryToObject(foundData); displayInventoryRecord(foundKey, theInventory); } } catch (Exception e) { System.err.println("Error on inventory cursor:"); System.err.println(e.toString()); e.printStackTrace(); } finally { cursor.close(); } } </pre> <p>We use <code class="methodname">ExampleDatabaseRead.displayInventoryRecord()</code> to actually show the record. This method first displays all the relevant information from the retrieved Inventory object. It then uses the vendor database to retrieve and display the vendor. Because the vendor database is keyed by vendor name, and because each inventory object contains this key, it is trivial to retrieve the appropriate vendor record.</p> <a id="java_cursor15"></a> <pre class="programlisting"> private void displayInventoryRecord(DatabaseEntry theKey, Inventory theInventory) throws DatabaseException { String theSKU = null; try { theSKU = new String(theKey.getData(), "UTF-8"); } catch(java.io.UnsupportedEncodingException e) { /* Handle the exception here. */ } System.out.println(theSKU + ":"); System.out.println("\t " + theInventory.getItemName()); System.out.println("\t " + theInventory.getCategory()); System.out.println("\t " + theInventory.getVendor()); System.out.println("\t\tNumber in stock: " + theInventory.getVendorInventory()); System.out.println("\t\tPrice per unit: " + theInventory.getVendorPrice()); System.out.println("\t\tContact: "); DatabaseEntry searchKey = null; try { searchKey = new DatabaseEntry(theInventory.getVendor().getBytes("UTF-8")); } catch (IOException willNeverOccur) {} DatabaseEntry foundVendor = new DatabaseEntry(); if (myDbs.getVendorDB().get(null, searchKey, foundVendor, LockMode.DEFAULT) != OperationStatus.SUCCESS) { System.out.println("Could not find vendor: " + theInventory.getVendor() + "."); System.exit(-1); } else { Vendor theVendor = (Vendor)vendorBinding.entryToObject(foundVendor); System.out.println("\t\t " + theVendor.getAddress()); System.out.println("\t\t " + theVendor.getCity() + ", " + theVendor.getState() + " " + theVendor.getZipcode()); System.out.println("\t\t Business Phone: " + theVendor.getBusinessPhoneNumber()); System.out.println("\t\t Sales Rep: " + theVendor.getRepName()); System.out.println("\t\t " + theVendor.getRepPhoneNumber()); } }</pre> <p>The remainder of this application provides a utility method used to parse the command line options. From the perspective of this document, this is relatively uninteresting. You can see how this is implemented by looking at: </p> <pre class="programlisting"><span class="emphasis"><em>DB_INSTALL</em></span>/examples/java/db/GettingStarted</pre> <p> where <code class="literal"><span class="emphasis"><em>DB_INSTALL</em></span></code> is the location where you placed your DB distribution. </p> </div> </div> <br class="example-break" /> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="ReplacingEntryWCursor.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="Cursors.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="indexes.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Replacing Records Using Cursors </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Chapter 10. Secondary Databases</td> </tr> </table> </div> </body> </html>