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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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