mirror of
https://github.com/yasuhirokimura/db18
synced 2026-06-08 18:29:23 +00:00
Yasuhiro KIMURA
146 lines
7.6 KiB
HTML
146 lines
7.6 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>Java programming notes</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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="java.html" title="Chapter 5. Java API" />
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<link rel="prev" href="java_compat.html" title="Compatibility" />
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<link rel="next" href="java_faq.html" title="Java FAQ" />
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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 18.1.40</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">Java programming notes</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="java_compat.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5. Java API </th>
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<td width="20%" align="right"> <a accesskey="n" href="java_faq.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="java_program"></a>Java programming notes</h2>
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</div>
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</div>
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</div>
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<p>
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Although the Java API parallels the Berkeley DB C++/C
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interface in many ways, it differs where the Java language
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requires. For example, the handle method names are camel-cased
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and conform to Java naming patterns. (The C++/C method names
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are currently provided, but are deprecated.)
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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The Java runtime does not automatically close
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Berkeley DB objects on finalization. There are several
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reasons for this. One is that finalization is generally
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run only when garbage collection occurs, and there is no
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guarantee that this occurs at all, even on exit. Allowing
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specific Berkeley DB actions to occur in ways that cannot
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be replicated seems wrong. Second, finalization of objects
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may happen in an arbitrary order, so we would have to do
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extra bookkeeping to make sure that everything was closed
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in the proper order. The best word of advice is to always
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do a close() for any matching open() call. Specifically,
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the Berkeley DB package requires that you explicitly call
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close on each individual <a class="ulink" href="../java/com/sleepycat/db/Database.html" target="_top">Database</a> and <a class="ulink" href="../java/com/sleepycat/db/Cursor.html" target="_top">Cursor</a> object
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that you opened. Your database
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activity may not be synchronized to disk unless you do
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so.
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</li>
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<li>
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Some methods in the Java API have no return type,
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and throw a <a class="ulink" href="../java/com/sleepycat/db/DatabaseException.html" target="_top">DatabaseException</a>
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when an severe error
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arises. There are some notable methods that do have a
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return value, and can also throw an exception. The "get"
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methods in <a class="ulink" href="../java/com/sleepycat/db/Database.html" target="_top">Database</a> and <a class="ulink" href="../java/com/sleepycat/db/Cursor.html" target="_top">Cursor</a> both
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return 0 when a get succeeds,
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<a class="link" href="program_errorret.html#program_errorret.DB_NOTFOUND">DB_NOTFOUND</a>
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when the key is not found, and throw an error when there is a severe
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error. This approach allows the programmer to check for typical data-driven
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errors by watching return values without special casing
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exceptions.
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<p>
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An object of type <a class="ulink" href="../java/com/sleepycat/db/MemoryException.html" target="_top">
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MemoryException</a> is thrown when a Dbt is
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too small to hold the corresponding key or data
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item.
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</p><p>
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An object of type <a class="ulink" href="../java/com/sleepycat/db/DeadlockException.html" target="_top">
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DeadlockException</a> is thrown when a
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deadlock would occur.
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</p><p>
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An object of type <a class="ulink" href="../java/com/sleepycat/db/RunRecoveryException.html" target="_top">
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RunRecoveryException</a>, a subclass of
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<a class="ulink" href="../java/com/sleepycat/db/DatabaseException.html" target="_top">
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DatabaseException</a>, is thrown when there
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is an error that requires a recovery of the database
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using <a href="../api_reference/C/db_recover.html" class="olink">db_recover</a> utility.
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</p><p>
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An object of type <a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/IllegalArgumentException.html" target="_top">
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IllegalArgumentException</a> a standard Java
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Language exception, is thrown when there is an error
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in method arguments.</p><p>
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An object of type <a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/api/java/lang/OutOfMemoryError.html" target="_top">
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OutOfMemoryError</a> is thrown when the
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system cannot provide enough memory to complete the
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operation (the ENOMEM system error on
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UNIX).
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</p></li>
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<li>
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If there are embedded nulls in the <span class="bold"><strong>curslist</strong></span> argument for <a class="ulink" href="../java/com/sleepycat/db/Database.html#join(com.sleepycat.db.Cursor[], com.sleepycat.db.JoinConfig)" target="_top">
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Database.join(com.sleepycat.db.Cursor[],
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com.sleepycat.db.JoinConfig)</a>, they will be
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treated as the end of the list of cursors, even if you may
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have allocated a longer array. Fill in all the cursors in
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your array unless you intend to cut it short.
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</li>
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<li>
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If you are using custom class loaders in your
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application, make sure that the Berkeley DB classes are
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loaded by the system class loader, not a custom class
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loader. This is due to a JVM bug that can cause an access
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violation during finalization (see the bug 4238486 in Sun
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Microsystem's Java Bug Database).
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</li>
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</ol>
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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="java_compat.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="java.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="java_faq.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">Compatibility </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"> Java FAQ</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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