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Posted to commits@zookeeper.apache.org by ph...@apache.org on 2017/11/09 18:14:00 UTC
svn commit: r1814761 [29/45] - in /zookeeper/site/trunk: content/
content/doc/r3.4.11/ content/doc/r3.4.11/api/ content/doc/r3.4.11/api/org/
content/doc/r3.4.11/api/org/apache/ content/doc/r3.4.11/api/org/apache/jute/
content/doc/r3.4.11/api/org/apache...
Added: zookeeper/site/trunk/content/doc/r3.4.11/bookkeeperStream.html
URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.11/bookkeeperStream.html?rev=1814761&view=auto
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--- zookeeper/site/trunk/content/doc/r3.4.11/bookkeeperStream.html (added)
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@@ -0,0 +1,612 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<head>
+<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<meta content="Apache Forrest" name="Generator">
+<meta name="Forrest-version" content="0.9">
+<meta name="Forrest-skin-name" content="pelt">
+<title>Streaming with BookKeeper</title>
+<link type="text/css" href="skin/basic.css" rel="stylesheet">
+<link media="screen" type="text/css" href="skin/screen.css" rel="stylesheet">
+<link media="print" type="text/css" href="skin/print.css" rel="stylesheet">
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+<link rel="shortcut icon" href="images/favicon.ico">
+</head>
+<body onload="init()">
+<script type="text/javascript">ndeSetTextSize();</script>
+<div id="top">
+<!--+
+ |breadtrail
+ +-->
+<div class="breadtrail">
+<a href="http://www.apache.org/">Apache</a> > <a href="http://zookeeper.apache.org/">ZooKeeper</a> > <a href="http://zookeeper.apache.org/">ZooKeeper</a><script src="skin/breadcrumbs.js" language="JavaScript" type="text/javascript"></script>
+</div>
+<!--+
+ |header
+ +-->
+<div class="header">
+<!--+
+ |start group logo
+ +-->
+<div class="grouplogo">
+<a href="http://hadoop.apache.org/"><img class="logoImage" alt="Hadoop" src="images/hadoop-logo.jpg" title="Apache Hadoop"></a>
+</div>
+<!--+
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+ |start Project Logo
+ +-->
+<div class="projectlogo">
+<a href="http://zookeeper.apache.org/"><img class="logoImage" alt="ZooKeeper" src="images/zookeeper_small.gif" title="ZooKeeper: distributed coordination"></a>
+</div>
+<!--+
+ |end Project Logo
+ +-->
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+<div class="searchbox">
+<form action="http://www.google.com/search" method="get" class="roundtopsmall">
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+ <input name="Search" value="Search" type="submit">
+</form>
+</div>
+<!--+
+ |end search
+ +-->
+<!--+
+ |start Tabs
+ +-->
+<ul id="tabs">
+<li>
+<a class="unselected" href="http://zookeeper.apache.org/">Project</a>
+</li>
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+<a class="unselected" href="https://cwiki.apache.org/confluence/display/ZOOKEEPER/">Wiki</a>
+</li>
+<li class="current">
+<a class="selected" href="index.html">ZooKeeper 3.4 Documentation</a>
+</li>
+</ul>
+<!--+
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+ +-->
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+</div>
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+<div id="publishedStrip">
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+document.write("Last Published: " + document.lastModified);
+// --></script>
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+ |breadtrail
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+<!--+
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+<div onclick="SwitchMenu('menu_1.1', 'skin/')" id="menu_1.1Title" class="menutitle">Overview</div>
+<div id="menu_1.1" class="menuitemgroup">
+<div class="menuitem">
+<a href="index.html">Welcome</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperOver.html">Overview</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperStarted.html">Getting Started</a>
+</div>
+<div class="menuitem">
+<a href="releasenotes.html">Release Notes</a>
+</div>
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+<div onclick="SwitchMenu('menu_1.2', 'skin/')" id="menu_1.2Title" class="menutitle">Developer</div>
+<div id="menu_1.2" class="menuitemgroup">
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+</div>
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+</div>
+<div class="menuitem">
+<a href="javaExample.html">Java Example</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperTutorial.html">Barrier and Queue Tutorial</a>
+</div>
+<div class="menuitem">
+<a href="recipes.html">Recipes</a>
+</div>
+</div>
+<div onclick="SwitchMenu('menu_1.3', 'skin/')" id="menu_1.3Title" class="menutitle">BookKeeper</div>
+<div id="menu_1.3" class="menuitemgroup">
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+<a href="bookkeeperStarted.html">Getting started</a>
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+<div id="menu_1.5" class="menuitemgroup">
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+<a href="http://zookeeper.apache.org/mailing_lists.html">Mailing Lists</a>
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+<!--+
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+<div title="Portable Document Format" class="pdflink">
+<a class="dida" href="bookkeeperStream.pdf"><img alt="PDF -icon" src="skin/images/pdfdoc.gif" class="skin"><br>
+ PDF</a>
+</div>
+<h1>Streaming with BookKeeper</h1>
+<div id="front-matter">
+<div id="minitoc-area">
+<ul class="minitoc">
+<li>
+<a href="#bk_StreamSummary">Summary</a>
+</li>
+<li>
+<a href="#bk_LedgerOutputStream">Writing a stream of bytes</a>
+</li>
+<li>
+<a href="#bk_LedgerInputStream">Reading a stream of bytes</a>
+</li>
+</ul>
+</div>
+</div>
+
+
+
+
+<a name="bk_StreamSummary"></a>
+<h2 class="h3">Summary</h2>
+<div class="section">
+<p>
+ When using the BookKeeper API, an application has to split the data to write into entries, each
+ entry being a byte array. This is natural for many applications. For example, when using BookKeeper
+ for write-ahead logging, an application typically wants to write the modifications corresponding
+ to a command or a transaction. Some other applications, however, might not have a natural boundary
+ for entries, and may prefer to write and read streams of bytes. This is exactly the purpose of the
+ stream API we have implemented on top of BookKeeper.
+ </p>
+<p>
+ The stream API is implemented in the package <span class="codefrag computeroutput">Streaming</span>, and it contains two main classes: <span class="codefrag computeroutput">LedgerOutputStream</span> and
+ <span class="codefrag computeroutput">LedgerInputStream</span>. The class names are indicative of what they do.
+ </p>
+</div>
+
+
+<a name="bk_LedgerOutputStream"></a>
+<h2 class="h3">Writing a stream of bytes</h2>
+<div class="section">
+<p>
+ Class <span class="codefrag computeroutput">LedgerOutputStream</span> implements two constructors and five public methods:
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public LedgerOutputStream(LedgerHandle lh)
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<span class="codefrag computeroutput">
+ public LedgerOutputStream(LedgerHandle lh, int size)
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.
+ </p>
+
+</li>
+
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">size</span> is the size of the byte buffer to store written bytes before flushing.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<strong>Closing a stream.</strong> This call closes the stream by flushing the write buffer.
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public void close()
+ </span>
+
+</p>
+<p>
+ which has no parameters.
+ </p>
+<p>
+
+<strong>Flushing a stream.</strong> This call essentially flushes the write buffer.
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized void flush()
+ </span>
+
+</p>
+<p>
+ which has no parameters.
+ </p>
+<p>
+
+<strong>Writing bytes.</strong> There are three calls for writing bytes to a stream.
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized void write(byte[] b)
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">b</span> is an array of bytes to write.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized void write(byte[] b, int off, int len)
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">b</span> is an array of bytes to write.
+ </p>
+
+</li>
+
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">off</span> is a buffer offset.
+ </p>
+
+</li>
+
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">len</span> is the length to write.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized void write(int b)
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">b</span> contains a byte to write. The method writes the least significant byte of the integer four bytes.
+ </p>
+
+</li>
+
+</ul>
+</div>
+
+
+<a name="bk_LedgerInputStream"></a>
+<h2 class="h3">Reading a stream of bytes</h2>
+<div class="section">
+<p>
+ Class <span class="codefrag computeroutput">LedgerOutputStream</span> implements two constructors and four public methods:
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public LedgerInputStream(LedgerHandle lh)
+ throws BKException, InterruptedException
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<span class="codefrag computeroutput">
+ public LedgerInputStream(LedgerHandle lh, int size)
+ throws BKException, InterruptedException
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.
+ </p>
+
+</li>
+
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">size</span> is the size of the byte buffer to store bytes that the application
+ will eventually read.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<strong>Closing.</strong> There is one call to close an input stream, but the call
+ is currently empty and the application is responsible for closing the ledger handle.
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public void close()
+ </span>
+
+</p>
+<p>
+ which has no parameters.
+ </p>
+<p>
+
+<strong>Reading.</strong> There are three calls to read from the stream.
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized int read()
+ throws IOException
+ </span>
+
+</p>
+<p>
+ which has no parameters.
+ </p>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized int read(byte[] b)
+ throws IOException
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">b</span> is a byte array to write to.
+ </p>
+
+</li>
+
+</ul>
+<p>
+
+<span class="codefrag computeroutput">
+ public synchronized int read(byte[] b, int off, int len)
+ throws IOException
+ </span>
+
+</p>
+<p>
+ where:
+ </p>
+<ul>
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">b</span> is a byte array to write to.
+ </p>
+
+</li>
+
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">off</span> is an offset for byte array <span class="codefrag computeroutput">b</span>.
+ </p>
+
+</li>
+
+
+<li>
+
+<p>
+
+<span class="codefrag computeroutput">len</span> is the length in bytes to write to <span class="codefrag computeroutput">b</span>.
+ </p>
+
+</li>
+
+</ul>
+</div>
+
+<p align="right">
+<font size="-2"></font>
+</p>
+</div>
+<!--+
+ |end content
+ +-->
+<div class="clearboth"> </div>
+</div>
+<div id="footer">
+<!--+
+ |start bottomstrip
+ +-->
+<div class="lastmodified">
+<script type="text/javascript"><!--
+document.write("Last Published: " + document.lastModified);
+// --></script>
+</div>
+<div class="copyright">
+ Copyright ©
+ <a href="http://www.apache.org/licenses/">The Apache Software Foundation.</a>
+</div>
+<!--+
+ |end bottomstrip
+ +-->
+</div>
+</body>
+</html>
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+<meta name="Forrest-skin-name" content="pelt">
+<title>ZooKeeper: Because Coordinating Distributed Systems is a Zoo</title>
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+<link rel="shortcut icon" href="images/favicon.ico">
+</head>
+<body onload="init()">
+<script type="text/javascript">ndeSetTextSize();</script>
+<div id="top">
+<!--+
+ |breadtrail
+ +-->
+<div class="breadtrail">
+<a href="http://www.apache.org/">Apache</a> > <a href="http://zookeeper.apache.org/">ZooKeeper</a> > <a href="http://zookeeper.apache.org/">ZooKeeper</a><script src="skin/breadcrumbs.js" language="JavaScript" type="text/javascript"></script>
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+</div>
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+<a href="http://zookeeper.apache.org/"><img class="logoImage" alt="ZooKeeper" src="images/zookeeper_small.gif" title="ZooKeeper: distributed coordination"></a>
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+<!--+
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+<a class="selected" href="index.html">ZooKeeper 3.4 Documentation</a>
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+<div onclick="SwitchMenu('menu_selected_1.1', 'skin/')" id="menu_selected_1.1Title" class="menutitle" style="background-image: url('skin/images/chapter_open.gif');">Overview</div>
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+<div class="menupagetitle">Welcome</div>
+</div>
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+<a href="zookeeperOver.html">Overview</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperStarted.html">Getting Started</a>
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+</div>
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+<a href="javaExample.html">Java Example</a>
+</div>
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+<a class="dida" href="index.pdf"><img alt="PDF -icon" src="skin/images/pdfdoc.gif" class="skin"><br>
+ PDF</a>
+</div>
+<h1>ZooKeeper: Because Coordinating Distributed Systems is a Zoo</h1>
+<div id="front-matter"></div>
+
+<p>ZooKeeper is a high-performance coordination service for
+ distributed applications. It exposes common services - such as
+ naming, configuration management, synchronization, and group
+ services - in a simple interface so you don't have to write them
+ from scratch. You can use it off-the-shelf to implement
+ consensus, group management, leader election, and presence
+ protocols. And you can build on it for your own, specific needs.
+ </p>
+
+
+<p>
+ The following documents describe concepts and procedures to get
+ you started using ZooKeeper. If you have more questions, please
+ ask the <a href="http://zookeeper.apache.org/mailing_lists.html">mailing list</a> or browse the
+ archives.
+ </p>
+
+<ul>
+
+
+<li>
+<strong>ZooKeeper Overview</strong>
+<p>Technical Overview Documents for Client Developers, Adminstrators, and Contributors</p>
+
+<ul>
+<li>
+<a href="zookeeperOver.html">Overview</a> - a bird's eye view of ZooKeeper, including design concepts and architecture</li>
+
+<li>
+<a href="zookeeperStarted.html">Getting Started</a> - a tutorial-style guide for developers to install, run, and program to ZooKeeper</li>
+
+<li>
+<a href="releasenotes.html">Release Notes</a> - new developer and user facing features, improvements, and incompatibilities</li>
+
+</ul>
+
+</li>
+
+
+<li>
+<strong>Developers</strong>
+<p> Documents for Developers using the ZooKeeper Client API</p>
+
+<ul>
+
+<li>
+<a href="api/index.html">API Docs</a> - the technical reference to ZooKeeper Client APIs</li>
+
+<li>
+<a href="zookeeperProgrammers.html">Programmer's Guide</a> - a client application developer's guide to ZooKeeper</li>
+
+<li>
+<a href="javaExample.html">ZooKeeper Java Example</a> - a simple Zookeeper client appplication, written in Java</li>
+
+<li>
+<a href="zookeeperTutorial.html">Barrier and Queue Tutorial</a> - sample implementations of barriers and queues</li>
+
+<li>
+<a href="recipes.html">ZooKeeper Recipes</a> - higher level solutions to common problems in distributed applications</li>
+
+</ul>
+
+</li>
+
+
+<li>
+<strong>Administrators & Operators</strong>
+<p> Documents for Administrators and Operations Engineers of ZooKeeper Deployments</p>
+
+<ul>
+
+<li>
+<a href="zookeeperAdmin.html">Administrator's Guide</a> - a guide for system administrators and anyone else who might deploy ZooKeeper</li>
+
+<li>
+<a href="zookeeperQuotas.html">Quota Guide</a> - a guide for system administrators on Quotas in ZooKeeper. </li>
+
+<li>
+<a href="zookeeperJMX.html">JMX</a> - how to enable JMX in ZooKeeper</li>
+
+<li>
+<a href="zookeeperHierarchicalQuorums.html">Hierarchical quorums</a>
+</li>
+
+<li>
+<a href="zookeeperObservers.html">Observers</a> - non-voting ensemble members that easily improve ZooKeeper's scalability</li>
+
+</ul>
+
+</li>
+
+
+<li>
+<strong>Contributors</strong>
+<p> Documents for Developers Contributing to the ZooKeeper Open Source Project</p>
+
+<ul>
+
+<li>
+<a href="zookeeperInternals.html">ZooKeeper Internals</a> - assorted topics on the inner workings of ZooKeeper</li>
+
+</ul>
+
+</li>
+
+
+<li>
+<strong>Miscellaneous ZooKeeper Documentation</strong>
+
+<ul>
+
+<li>
+<a href="https://cwiki.apache.org/confluence/display/ZOOKEEPER">Wiki</a>
+</li>
+
+<li>
+<a href="https://cwiki.apache.org/confluence/display/ZOOKEEPER/FAQ">FAQ</a>
+</li>
+
+</ul>
+
+</li>
+
+
+<li>
+<strong>BookKeeper Documentation</strong>
+
+<p> BookKeeper is a highly-available system that implements high-performance write-ahead logging. It uses ZooKeeper for metadata,
+ which is the main reason for being a ZooKeeper contrib.
+ </p>
+
+<ul>
+
+<li>
+<a href="bookkeeperOverview.html">henn, what's it again?</a>
+</li>
+
+<li>
+<a href="bookkeeperStarted.html">Ok, now how do I try it out</a>
+</li>
+
+<li>
+<a href="bookkeeperProgrammer.html">Awesome, but how do I integrate it with my app?</a>
+</li>
+
+<li>
+<a href="bookkeeperStream.html">Can I stream bytes instead of entries?</a>
+</li>
+
+</ul>
+
+</li>
+
+</ul>
+
+</div>
+<!--+
+ |end content
+ +-->
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+</div>
+<div id="footer">
+<!--+
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+<script type="text/javascript"><!--
+document.write("Last Published: " + document.lastModified);
+// --></script>
+</div>
+<div class="copyright">
+ Copyright ©
+ <a href="http://www.apache.org/licenses/">The Apache Software Foundation.</a>
+</div>
+<div id="logos"></div>
+<!--+
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+</body>
+</html>
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+++ zookeeper/site/trunk/content/doc/r3.4.11/javaExample.html Thu Nov 9 18:13:55 2017
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+<meta content="Apache Forrest" name="Generator">
+<meta name="Forrest-version" content="0.9">
+<meta name="Forrest-skin-name" content="pelt">
+<title>ZooKeeper Java Example</title>
+<link type="text/css" href="skin/basic.css" rel="stylesheet">
+<link media="screen" type="text/css" href="skin/screen.css" rel="stylesheet">
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+<body onload="init()">
+<script type="text/javascript">ndeSetTextSize();</script>
+<div id="top">
+<!--+
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+ +-->
+<div class="breadtrail">
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+</div>
+<!--+
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+ +-->
+<!--+
+ |start Project Logo
+ +-->
+<div class="projectlogo">
+<a href="http://zookeeper.apache.org/"><img class="logoImage" alt="ZooKeeper" src="images/zookeeper_small.gif" title="ZooKeeper: distributed coordination"></a>
+</div>
+<!--+
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+ +-->
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+</form>
+</div>
+<!--+
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+ +-->
+<!--+
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+ +-->
+<ul id="tabs">
+<li>
+<a class="unselected" href="http://zookeeper.apache.org/">Project</a>
+</li>
+<li>
+<a class="unselected" href="https://cwiki.apache.org/confluence/display/ZOOKEEPER/">Wiki</a>
+</li>
+<li class="current">
+<a class="selected" href="index.html">ZooKeeper 3.4 Documentation</a>
+</li>
+</ul>
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+<!--+
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+<div id="menu">
+<div onclick="SwitchMenu('menu_1.1', 'skin/')" id="menu_1.1Title" class="menutitle">Overview</div>
+<div id="menu_1.1" class="menuitemgroup">
+<div class="menuitem">
+<a href="index.html">Welcome</a>
+</div>
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+</div>
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+<a href="zookeeperStarted.html">Getting Started</a>
+</div>
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+<div onclick="SwitchMenu('menu_selected_1.2', 'skin/')" id="menu_selected_1.2Title" class="menutitle" style="background-image: url('skin/images/chapter_open.gif');">Developer</div>
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+<div class="menuitem">
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+<div class="menupagetitle">Java Example</div>
+</div>
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+</div>
+<div class="menuitem">
+<a href="recipes.html">Recipes</a>
+</div>
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+<div id="menu_1.4" class="menuitemgroup">
+<div class="menuitem">
+<a href="zookeeperAdmin.html">Administrator's Guide</a>
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+<div id="menu_1.5" class="menuitemgroup">
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+<a href="zookeeperInternals.html">ZooKeeper Internals</a>
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+<div id="roundbottom">
+<img style="display: none" class="corner" height="15" width="15" alt="" src="skin/images/rc-b-l-15-1body-2menu-3menu.png"></div>
+<!--+
+ |alternative credits
+ +-->
+<div id="credit2"></div>
+</div>
+<!--+
+ |end Menu
+ +-->
+<!--+
+ |start content
+ +-->
+<div id="content">
+<div title="Portable Document Format" class="pdflink">
+<a class="dida" href="javaExample.pdf"><img alt="PDF -icon" src="skin/images/pdfdoc.gif" class="skin"><br>
+ PDF</a>
+</div>
+<h1>ZooKeeper Java Example</h1>
+<div id="front-matter">
+<div id="minitoc-area">
+<ul class="minitoc">
+<li>
+<a href="#ch_Introduction">A Simple Watch Client</a>
+<ul class="minitoc">
+<li>
+<a href="#sc_requirements">Requirements</a>
+</li>
+<li>
+<a href="#sc_design">Program Design</a>
+</li>
+</ul>
+</li>
+<li>
+<a href="#sc_executor">The Executor Class</a>
+</li>
+<li>
+<a href="#sc_DataMonitor">The DataMonitor Class</a>
+</li>
+<li>
+<a href="#sc_completeSourceCode">Complete Source Listings</a>
+</li>
+</ul>
+</div>
+</div>
+
+
+
+
+
+<a name="ch_Introduction"></a>
+<h2 class="h3">A Simple Watch Client</h2>
+<div class="section">
+<p>To introduce you to the ZooKeeper Java API, we develop here a very simple
+ watch client. This ZooKeeper client watches a ZooKeeper node for changes
+ and responds to by starting or stopping a program.</p>
+<a name="sc_requirements"></a>
+<h3 class="h4">Requirements</h3>
+<p>The client has four requirements:</p>
+<ul>
+<li>
+<p>It takes as parameters:</p>
+
+<ul>
+
+<li>
+<p>the address of the ZooKeeper service</p>
+</li>
+
+<li>
+<p>then name of a znode - the one to be watched</p>
+</li>
+
+<li>
+<p>an executable with arguments.</p>
+</li>
+</ul>
+</li>
+
+<li>
+<p>It fetches the data associated with the znode and starts the executable.</p>
+</li>
+
+<li>
+<p>If the znode changes, the client refetches the contents and restarts the executable.</p>
+</li>
+
+<li>
+<p>If the znode disappears, the client kills the executable.</p>
+</li>
+</ul>
+<a name="sc_design"></a>
+<h3 class="h4">Program Design</h3>
+<p>Conventionally, ZooKeeper applications are broken into two units, one which maintains the connection,
+ and the other which monitors data. In this application, the class called the <strong>Executor</strong>
+ maintains the ZooKeeper connection, and the class called the <strong>DataMonitor</strong> monitors the data
+ in the ZooKeeper tree. Also, Executor contains the main thread and contains the execution logic.
+ It is responsible for what little user interaction there is, as well as interaction with the exectuable program you
+ pass in as an argument and which the sample (per the requirements) shuts down and restarts, according to the
+ state of the znode.</p>
+</div>
+
+
+<a name="sc_executor"></a>
+<h2 class="h3">The Executor Class</h2>
+<div class="section">
+<p>The Executor object is the primary container of the sample application. It contains
+ both the <strong>ZooKeeper</strong> object, <strong>DataMonitor</strong>, as described above in
+ <a href="#sc_design">Program Design</a>. </p>
+<pre class="code">
+ // from the Executor class...
+
+ public static void main(String[] args) {
+ if (args.length < 4) {
+ System.err
+ .println("USAGE: Executor hostPort znode filename program [args ...]");
+ System.exit(2);
+ }
+ String hostPort = args[0];
+ String znode = args[1];
+ String filename = args[2];
+ String exec[] = new String[args.length - 3];
+ System.arraycopy(args, 3, exec, 0, exec.length);
+ try {
+ new Executor(hostPort, znode, filename, exec).run();
+ } catch (Exception e) {
+ e.printStackTrace();
+ }
+ }
+
+ public Executor(String hostPort, String znode, String filename,
+ String exec[]) throws KeeperException, IOException {
+ this.filename = filename;
+ this.exec = exec;
+ zk = new ZooKeeper(hostPort, 3000, this);
+ dm = new DataMonitor(zk, znode, null, this);
+ }
+
+ public void run() {
+ try {
+ synchronized (this) {
+ while (!dm.dead) {
+ wait();
+ }
+ }
+ } catch (InterruptedException e) {
+ }
+ }
+</pre>
+<p>
+ Recall that the Executor's job is to start and stop the executable whose name you pass in on the command line.
+ It does this in response to events fired by the ZooKeeper object. As you can see in the code above, the Executor passes
+ a reference to itself as the Watcher argument in the ZooKeeper constructor. It also passes a reference to itself
+ as DataMonitorListener argument to the DataMonitor constructor. Per the Executor's definition, it implements both these
+ interfaces:
+ </p>
+<pre class="code">
+public class Executor implements Watcher, Runnable, DataMonitor.DataMonitorListener {
+...</pre>
+<p>The <strong>Watcher</strong> interface is defined by the ZooKeeper Java API.
+ ZooKeeper uses it to communicate back to its container. It supports only one method, <span class="codefrag command">process()</span>, and ZooKeeper uses
+ it to communciates generic events that the main thread would be intersted in, such as the state of the ZooKeeper connection or the ZooKeeper session.The Executor
+ in this example simply forwards those events down to the DataMonitor to decide what to do with them. It does this simply to illustrate
+ the point that, by convention, the Executor or some Executor-like object "owns" the ZooKeeper connection, but it is free to delegate the events to other
+ events to other objects. It also uses this as the default channel on which to fire watch events. (More on this later.)</p>
+<pre class="code">
+ public void process(WatchedEvent event) {
+ dm.process(event);
+ }
+</pre>
+<p>The <strong>DataMonitorListener</strong>
+ interface, on the other hand, is not part of the the ZooKeeper API. It is a completely custom interface,
+ designed for this sample application. The DataMonitor object uses it to communicate back to its container, which
+ is also the the Executor object.The DataMonitorListener interface looks like this:</p>
+<pre class="code">
+public interface DataMonitorListener {
+ /**
+ * The existence status of the node has changed.
+ */
+ void exists(byte data[]);
+
+ /**
+ * The ZooKeeper session is no longer valid.
+ *
+ * @param rc
+ * the ZooKeeper reason code
+ */
+ void closing(int rc);
+}
+</pre>
+<p>This interface is defined in the DataMonitor class and implemented in the Executor class.
+ When <span class="codefrag command">Executor.exists()</span> is invoked,
+ the Executor decides whether to start up or shut down per the requirements. Recall that the requires say to kill the executable when the
+ znode ceases to <em>exist</em>. </p>
+<p>When <span class="codefrag command">Executor.closing()</span>
+ is invoked, the Executor decides whether or not to shut itself down in response to the ZooKeeper connection permanently disappearing.</p>
+<p>As you might have guessed, DataMonitor is the object that invokes
+ these methods, in response to changes in ZooKeeper's state.</p>
+<p>Here are Executor's implementation of
+ <span class="codefrag command">DataMonitorListener.exists()</span> and <span class="codefrag command">DataMonitorListener.closing</span>:
+ </p>
+<pre class="code">
+public void exists( byte[] data ) {
+ if (data == null) {
+ if (child != null) {
+ System.out.println("Killing process");
+ child.destroy();
+ try {
+ child.waitFor();
+ } catch (InterruptedException e) {
+ }
+ }
+ child = null;
+ } else {
+ if (child != null) {
+ System.out.println("Stopping child");
+ child.destroy();
+ try {
+ child.waitFor();
+ } catch (InterruptedException e) {
+ e.printStackTrace();
+ }
+ }
+ try {
+ FileOutputStream fos = new FileOutputStream(filename);
+ fos.write(data);
+ fos.close();
+ } catch (IOException e) {
+ e.printStackTrace();
+ }
+ try {
+ System.out.println("Starting child");
+ child = Runtime.getRuntime().exec(exec);
+ new StreamWriter(child.getInputStream(), System.out);
+ new StreamWriter(child.getErrorStream(), System.err);
+ } catch (IOException e) {
+ e.printStackTrace();
+ }
+ }
+}
+
+public void closing(int rc) {
+ synchronized (this) {
+ notifyAll();
+ }
+}
+</pre>
+</div>
+
+<a name="sc_DataMonitor"></a>
+<h2 class="h3">The DataMonitor Class</h2>
+<div class="section">
+<p>
+The DataMonitor class has the meat of the ZooKeeper logic. It is mostly
+asynchronous and event driven. DataMonitor kicks things off in the constructor with:</p>
+<pre class="code">
+public DataMonitor(ZooKeeper zk, String znode, Watcher chainedWatcher,
+ DataMonitorListener listener) {
+ this.zk = zk;
+ this.znode = znode;
+ this.chainedWatcher = chainedWatcher;
+ this.listener = listener;
+
+ // Get things started by checking if the node exists. We are going
+ // to be completely event driven
+ <strong>zk.exists(znode, true, this, null);</strong>
+}
+</pre>
+<p>The call to <span class="codefrag command">ZooKeeper.exists()</span> checks for the existence of the znode,
+sets a watch, and passes a reference to itself (<span class="codefrag command">this</span>)
+as the completion callback object. In this sense, it kicks things off, since the
+real processing happens when the watch is triggered.</p>
+<div class="note">
+<div class="label">Note</div>
+<div class="content">
+
+<p>Don't confuse the completion callback with the watch callback. The <span class="codefrag command">ZooKeeper.exists()</span>
+completion callback, which happens to be the method <span class="codefrag command">StatCallback.processResult()</span> implemented
+in the DataMonitor object, is invoked when the asynchronous <em>setting of the watch</em> operation
+(by <span class="codefrag command">ZooKeeper.exists()</span>) completes on the server. </p>
+
+<p>
+The triggering of the watch, on the other hand, sends an event to the <em>Executor</em> object, since
+the Executor registered as the Watcher of the ZooKeeper object.</p>
+
+
+<p>As an aside, you might note that the DataMonitor could also register itself as the Watcher
+for this particular watch event. This is new to ZooKeeper 3.0.0 (the support of multiple Watchers). In this
+example, however, DataMonitor does not register as the Watcher.</p>
+
+</div>
+</div>
+<p>When the <span class="codefrag command">ZooKeeper.exists()</span> operation completes on the server, the ZooKeeper API invokes this completion callback on
+the client:</p>
+<pre class="code">
+public void processResult(int rc, String path, Object ctx, Stat stat) {
+ boolean exists;
+ switch (rc) {
+ case Code.Ok:
+ exists = true;
+ break;
+ case Code.NoNode:
+ exists = false;
+ break;
+ case Code.SessionExpired:
+ case Code.NoAuth:
+ dead = true;
+ listener.closing(rc);
+ return;
+ default:
+ // Retry errors
+ zk.exists(znode, true, this, null);
+ return;
+ }
+
+ byte b[] = null;
+ if (exists) {
+ try {
+ <strong>b = zk.getData(znode, false, null);</strong>
+ } catch (KeeperException e) {
+ // We don't need to worry about recovering now. The watch
+ // callbacks will kick off any exception handling
+ e.printStackTrace();
+ } catch (InterruptedException e) {
+ return;
+ }
+ }
+ if ((b == null && b != prevData)
+ || (b != null && !Arrays.equals(prevData, b))) {
+ <strong>listener.exists(b);</strong>
+ prevData = b;
+ }
+}
+</pre>
+<p>
+The code first checks the error codes for znode existence, fatal errors, and
+recoverable errors. If the file (or znode) exists, it gets the data from the znode, and
+then invoke the exists() callback of Executor if the state has changed. Note,
+it doesn't have to do any Exception processing for the getData call because it
+has watches pending for anything that could cause an error: if the node is deleted
+before it calls <span class="codefrag command">ZooKeeper.getData()</span>, the watch event set by
+the <span class="codefrag command">ZooKeeper.exists()</span> triggers a callback;
+if there is a communication error, a connection watch event fires when
+the connection comes back up.
+</p>
+<p>Finally, notice how DataMonitor processes watch events: </p>
+<pre class="code">
+ public void process(WatchedEvent event) {
+ String path = event.getPath();
+ if (event.getType() == Event.EventType.None) {
+ // We are are being told that the state of the
+ // connection has changed
+ switch (event.getState()) {
+ case SyncConnected:
+ // In this particular example we don't need to do anything
+ // here - watches are automatically re-registered with
+ // server and any watches triggered while the client was
+ // disconnected will be delivered (in order of course)
+ break;
+ case Expired:
+ // It's all over
+ dead = true;
+ listener.closing(KeeperException.Code.SessionExpired);
+ break;
+ }
+ } else {
+ if (path != null && path.equals(znode)) {
+ // Something has changed on the node, let's find out
+ zk.exists(znode, true, this, null);
+ }
+ }
+ if (chainedWatcher != null) {
+ chainedWatcher.process(event);
+ }
+ }
+</pre>
+<p>
+If the client-side ZooKeeper libraries can re-establish the
+communication channel (SyncConnected event) to ZooKeeper before
+session expiration (Expired event) all of the session's watches will
+automatically be re-established with the server (auto-reset of watches
+is new in ZooKeeper 3.0.0). See <a href="zookeeperProgrammers.html#ch_zkWatches">ZooKeeper Watches</a>
+in the programmer guide for more on this. A bit lower down in this
+function, when DataMonitor gets an event for a znode, it calls
+<span class="codefrag command">ZooKeeper.exists()</span> to find out what has changed.
+</p>
+</div>
+
+
+<a name="sc_completeSourceCode"></a>
+<h2 class="h3">Complete Source Listings</h2>
+<div class="section">
+<div class="note example">
+<div class="label">Executor.java</div>
+<div class="content">
+<title>Executor.java</title>
+<pre class="code">
+/**
+ * A simple example program to use DataMonitor to start and
+ * stop executables based on a znode. The program watches the
+ * specified znode and saves the data that corresponds to the
+ * znode in the filesystem. It also starts the specified program
+ * with the specified arguments when the znode exists and kills
+ * the program if the znode goes away.
+ */
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.WatchedEvent;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.ZooKeeper;
+
+public class Executor
+ implements Watcher, Runnable, DataMonitor.DataMonitorListener
+{
+ String znode;
+
+ DataMonitor dm;
+
+ ZooKeeper zk;
+
+ String filename;
+
+ String exec[];
+
+ Process child;
+
+ public Executor(String hostPort, String znode, String filename,
+ String exec[]) throws KeeperException, IOException {
+ this.filename = filename;
+ this.exec = exec;
+ zk = new ZooKeeper(hostPort, 3000, this);
+ dm = new DataMonitor(zk, znode, null, this);
+ }
+
+ /**
+ * @param args
+ */
+ public static void main(String[] args) {
+ if (args.length < 4) {
+ System.err
+ .println("USAGE: Executor hostPort znode filename program [args ...]");
+ System.exit(2);
+ }
+ String hostPort = args[0];
+ String znode = args[1];
+ String filename = args[2];
+ String exec[] = new String[args.length - 3];
+ System.arraycopy(args, 3, exec, 0, exec.length);
+ try {
+ new Executor(hostPort, znode, filename, exec).run();
+ } catch (Exception e) {
+ e.printStackTrace();
+ }
+ }
+
+ /***************************************************************************
+ * We do process any events ourselves, we just need to forward them on.
+ *
+ * @see org.apache.zookeeper.Watcher#process(org.apache.zookeeper.proto.WatcherEvent)
+ */
+ public void process(WatchedEvent event) {
+ dm.process(event);
+ }
+
+ public void run() {
+ try {
+ synchronized (this) {
+ while (!dm.dead) {
+ wait();
+ }
+ }
+ } catch (InterruptedException e) {
+ }
+ }
+
+ public void closing(int rc) {
+ synchronized (this) {
+ notifyAll();
+ }
+ }
+
+ static class StreamWriter extends Thread {
+ OutputStream os;
+
+ InputStream is;
+
+ StreamWriter(InputStream is, OutputStream os) {
+ this.is = is;
+ this.os = os;
+ start();
+ }
+
+ public void run() {
+ byte b[] = new byte[80];
+ int rc;
+ try {
+ while ((rc = is.read(b)) > 0) {
+ os.write(b, 0, rc);
+ }
+ } catch (IOException e) {
+ }
+
+ }
+ }
+
+ public void exists(byte[] data) {
+ if (data == null) {
+ if (child != null) {
+ System.out.println("Killing process");
+ child.destroy();
+ try {
+ child.waitFor();
+ } catch (InterruptedException e) {
+ }
+ }
+ child = null;
+ } else {
+ if (child != null) {
+ System.out.println("Stopping child");
+ child.destroy();
+ try {
+ child.waitFor();
+ } catch (InterruptedException e) {
+ e.printStackTrace();
+ }
+ }
+ try {
+ FileOutputStream fos = new FileOutputStream(filename);
+ fos.write(data);
+ fos.close();
+ } catch (IOException e) {
+ e.printStackTrace();
+ }
+ try {
+ System.out.println("Starting child");
+ child = Runtime.getRuntime().exec(exec);
+ new StreamWriter(child.getInputStream(), System.out);
+ new StreamWriter(child.getErrorStream(), System.err);
+ } catch (IOException e) {
+ e.printStackTrace();
+ }
+ }
+ }
+}
+</pre>
+
+
+</div>
+</div>
+<div class="note example">
+<div class="label">DataMonitor.java</div>
+<div class="content">
+
+<title>DataMonitor.java</title>
+
+<pre class="code">
+/**
+ * A simple class that monitors the data and existence of a ZooKeeper
+ * node. It uses asynchronous ZooKeeper APIs.
+ */
+import java.util.Arrays;
+
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.WatchedEvent;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.ZooKeeper;
+import org.apache.zookeeper.AsyncCallback.StatCallback;
+import org.apache.zookeeper.KeeperException.Code;
+import org.apache.zookeeper.data.Stat;
+
+public class DataMonitor implements Watcher, StatCallback {
+
+ ZooKeeper zk;
+
+ String znode;
+
+ Watcher chainedWatcher;
+
+ boolean dead;
+
+ DataMonitorListener listener;
+
+ byte prevData[];
+
+ public DataMonitor(ZooKeeper zk, String znode, Watcher chainedWatcher,
+ DataMonitorListener listener) {
+ this.zk = zk;
+ this.znode = znode;
+ this.chainedWatcher = chainedWatcher;
+ this.listener = listener;
+ // Get things started by checking if the node exists. We are going
+ // to be completely event driven
+ zk.exists(znode, true, this, null);
+ }
+
+ /**
+ * Other classes use the DataMonitor by implementing this method
+ */
+ public interface DataMonitorListener {
+ /**
+ * The existence status of the node has changed.
+ */
+ void exists(byte data[]);
+
+ /**
+ * The ZooKeeper session is no longer valid.
+ *
+ * @param rc
+ * the ZooKeeper reason code
+ */
+ void closing(int rc);
+ }
+
+ public void process(WatchedEvent event) {
+ String path = event.getPath();
+ if (event.getType() == Event.EventType.None) {
+ // We are are being told that the state of the
+ // connection has changed
+ switch (event.getState()) {
+ case SyncConnected:
+ // In this particular example we don't need to do anything
+ // here - watches are automatically re-registered with
+ // server and any watches triggered while the client was
+ // disconnected will be delivered (in order of course)
+ break;
+ case Expired:
+ // It's all over
+ dead = true;
+ listener.closing(KeeperException.Code.SessionExpired);
+ break;
+ }
+ } else {
+ if (path != null && path.equals(znode)) {
+ // Something has changed on the node, let's find out
+ zk.exists(znode, true, this, null);
+ }
+ }
+ if (chainedWatcher != null) {
+ chainedWatcher.process(event);
+ }
+ }
+
+ public void processResult(int rc, String path, Object ctx, Stat stat) {
+ boolean exists;
+ switch (rc) {
+ case Code.Ok:
+ exists = true;
+ break;
+ case Code.NoNode:
+ exists = false;
+ break;
+ case Code.SessionExpired:
+ case Code.NoAuth:
+ dead = true;
+ listener.closing(rc);
+ return;
+ default:
+ // Retry errors
+ zk.exists(znode, true, this, null);
+ return;
+ }
+
+ byte b[] = null;
+ if (exists) {
+ try {
+ b = zk.getData(znode, false, null);
+ } catch (KeeperException e) {
+ // We don't need to worry about recovering now. The watch
+ // callbacks will kick off any exception handling
+ e.printStackTrace();
+ } catch (InterruptedException e) {
+ return;
+ }
+ }
+ if ((b == null && b != prevData)
+ || (b != null && !Arrays.equals(prevData, b))) {
+ listener.exists(b);
+ prevData = b;
+ }
+ }
+}
+</pre>
+
+</div>
+</div>
+</div>
+
+
+
+
+<p align="right">
+<font size="-2"></font>
+</p>
+</div>
+<!--+
+ |end content
+ +-->
+<div class="clearboth"> </div>
+</div>
+<div id="footer">
+<!--+
+ |start bottomstrip
+ +-->
+<div class="lastmodified">
+<script type="text/javascript"><!--
+document.write("Last Published: " + document.lastModified);
+// --></script>
+</div>
+<div class="copyright">
+ Copyright ©
+ <a href="http://www.apache.org/licenses/">The Apache Software Foundation.</a>
+</div>
+<!--+
+ |end bottomstrip
+ +-->
+</div>
+</body>
+</html>
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+++ zookeeper/site/trunk/content/doc/r3.4.11/jdiff/changes.html Thu Nov 9 18:13:55 2017
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN""http://www.w3.org/TR/REC-html40/frameset.dtd">
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+<TITLE>
+API Differences between zookeeper 3.1.1 and zookeeper 3.4.11
+</TITLE>
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