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>Transactional Cursors</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 Transaction Processing" /> 10 <link rel="up" href="usingtxns.html" title="Chapter��3.��Transaction Basics" /> 11 <link rel="prev" href="nestedtxn.html" title="Nested Transactions" /> 12 <link rel="next" href="txnindices.html" title="Secondary Indices with Transaction Applications" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Transactional Cursors</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��3.��Transaction Basics</th> 23 <td width="20%" align="right">��<a accesskey="n" href="txnindices.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="sect1" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title" style="clear: both"><a id="txncursor"></a>Transactional Cursors</h2> 33 </div> 34 </div> 35 </div> 36 <div class="toc"> 37 <dl> 38 <dt> 39 <span class="sect2"> 40 <a href="txncursor.html#dplcursors">Using Transactional DPL Cursors</a> 41 </span> 42 </dt> 43 </dl> 44 </div> 45 <p> 46 You can transaction-protect your cursor operations by 47 specifying a transaction handle at the time that you create 48 your cursor. Beyond that, you do not ever 49 provide a transaction handle directly to a cursor method. 50 </p> 51 <p> 52 Note that if you transaction-protect a cursor, then you must 53 make sure that the cursor is closed before you either commit or 54 abort the transaction. For example: 55 </p> 56 <pre class="programlisting">package db.txn; 57 58import com.sleepycat.db.Cursor; 59import com.sleepycat.db.Database; 60import com.sleepycat.db.DatabaseConfig; 61import com.sleepycat.db.DatabaseEntry; 62import com.sleepycat.db.DatabaseException; 63import com.sleepycat.db.Environment; 64import com.sleepycat.db.EnvironmentConfig; 65import com.sleepycat.db.LockMode; 66import com.sleepycat.db.OperationStatus; 67import com.sleepycat.db.Transaction; 68 69import java.io.File; 70import java.io.FileNotFoundException; 71 72... 73 74Database myDatabase = null; 75Environment myEnv = null; 76try { 77 78 // Database and environment opens omitted 79 80 String replacementData = "new data"; 81 82 Transaction txn = myEnv.beginTransaction(null, null); 83 Cursor cursor = null; 84 try { 85 // Use the transaction handle here 86 cursor = db.openCursor(txn, null); 87 DatabaseEntry key, data; 88 89 DatabaseEntry key, data; 90 while(cursor.getNext(key, data, LockMode.DEFAULT) == 91 OperationStatus.SUCCESS) { 92 93 data.setData(replacementData.getBytes("UTF-8")); 94 // No transaction handle is used on the cursor read or write 95 // methods. 96 cursor.putCurrent(data); 97 } 98 99 cursor.close(); 100 cursor = null; 101 txn.commit(); 102 txn = null; 103 } catch (Exception e) { 104 if (cursor != null) { 105 cursor.close(); 106 } 107 if (txn != null) { 108 txn.abort(); 109 txn = null; 110 } 111 } 112 113} catch (DatabaseException de) { 114 // Exception handling goes here 115} </pre> 116 <div class="sect2" lang="en" xml:lang="en"> 117 <div class="titlepage"> 118 <div> 119 <div> 120 <h3 class="title"><a id="dplcursors"></a>Using Transactional DPL Cursors</h3> 121 </div> 122 </div> 123 </div> 124 <p> 125 When using the DPL, you create the cursor using the entity 126 class's primary or secondary index (see the 127 128 <em class="citetitle">Getting Started with Berkeley DB for Java</em> 129 guide for details). At the time that you create the cursor, you 130 pass a transaction handle to the <code class="methodname">entities()</code> 131 method, and this causes all subsequent operations performed 132 using that cursor to be performed within the scope of the 133 transaction. 134 </p> 135 <p> 136 Note that if you are using a transaction-enabled store, 137 then you must provide a transaction handle when you open 138 your cursor. 139 </p> 140 <p> 141 For example: 142 </p> 143 <pre class="programlisting">package persist.txn; 144 145import com.sleepycat.db.DatabaseException; 146import com.sleepycat.db.Environment; 147import com.sleepycat.db.EnvironmentConfig; 148import com.sleepycat.db.Transaction; 149 150import com.sleepycat.persist.EntityCursor; 151import com.sleepycat.persist.EntityStore; 152import com.sleepycat.persist.PrimaryIndex; 153 154import java.io.File; 155import java.io.FileNotFoundException; 156 157... 158 159Environment myEnv = null; 160EntityStore store = null; 161 162... 163 164 165 // Store and environment open omitted, as is the DataAccessor 166 // instantiation. 167 168... 169 170 Transaction txn = myEnv.beginTransaction(null, null); 171 PrimaryIndex<String,Inventory> pi = 172 store.getPrimaryIndex(String.class, Inventory.class); 173 EntityCursor<Inventory> pi_cursor = pi.entities(txn, null); 174 175 try { 176 for (Inventory ii : pi_cursor) { 177 // do something with each object "ii" 178 // A transactional handle is not required for any write operations. 179 // All operations performed using this cursor will be done within 180 // the scope of the transaction, txn. 181 } 182 pi_cursor.close(); 183 pi_cursor = null; 184 txn.commit(); 185 txn = null; 186 // Always make sure the cursor is closed when we are done with it. 187 } catch (Exception e) { 188 if (pi_cursor != null) { 189 pi_cursor.close(); 190 } 191 if (txn != null) { 192 txn.abort(); 193 txn = null; 194 } 195 } </pre> 196 </div> 197 </div> 198 <div class="navfooter"> 199 <hr /> 200 <table width="100%" summary="Navigation footer"> 201 <tr> 202 <td width="40%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a>��</td> 203 <td width="20%" align="center"> 204 <a accesskey="u" href="usingtxns.html">Up</a> 205 </td> 206 <td width="40%" align="right">��<a accesskey="n" href="txnindices.html">Next</a></td> 207 </tr> 208 <tr> 209 <td width="40%" align="left" valign="top">Nested Transactions��</td> 210 <td width="20%" align="center"> 211 <a accesskey="h" href="index.html">Home</a> 212 </td> 213 <td width="40%" align="right" valign="top">��Secondary Indices with Transaction Applications</td> 214 </tr> 215 </table> 216 </div> 217 </body> 218</html> 219