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<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>
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