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MqttPersistable (MQTT v3 Client API)
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org.eclipse.paho.client.mqttv3</FONT>
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Interface MqttPersistable</H2>
<HR>
<DL>
<DT>public interface <B>MqttPersistable</B></DL>
<P>
Represents an object used to pass data to be persisted across the
<A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttClientPersistence.html" title="interface in org.eclipse.paho.client.mqttv3"><CODE>MqttClientPersistence</CODE></A>
interface.
<p>
When data is passed across the interface the header and payload are
separated, so that unnecessary message copies may be avoided.
For example, if a 10 MB payload was published it would be inefficient
to create a byte array a few bytes larger than 10 MB and copy the
MQTT message header and payload into a contiguous byte array.</p>
<p>
When the request to persist data is made a separate byte array and offset
is passed for the header and payload. Only the data between
offset and length need be persisted.
So for example, a message to be persisted consists of a header byte
array starting at offset 1 and length 4, plus a payload byte array
starting at offset 30 and length 40000. There are three ways in which
the persistence implementation may return data to the client on
recovery:
<ul>
<li>It could return the data as it was passed in
originally, with the same byte arrays and offsets.</li>
<li>It could safely just persist and return the bytes from the offset
for the specified length. For example, return a header byte array with
offset 0 and length 4, plus a payload byte array with offset 0 and length
40000</li>
<li>It could return the header and payload as a contiguous byte array
with the header bytes preceeding the payload. The contiguous byte array
should be set as the header byte array, with the payload byte array being
null. For example, return a single byte array with offset 0
and length 40004.
This is useful when recovering from a file where the header and payload
could be written as a contiguous stream of bytes.</li>
</ul>
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<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> byte[]</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderBytes()">getHeaderBytes</A></B>()</CODE>
<BR>
Returns the header bytes in an array.
</TD>
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<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderLength()">getHeaderLength</A></B>()</CODE>
<BR>
Returns the length of the header.</TD>
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<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderOffset()">getHeaderOffset</A></B>()</CODE>
<BR>
Returns the offset of the header within the byte array returned by <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderBytes()"><CODE>getHeaderBytes()</CODE></A>.</TD>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> byte[]</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadBytes()">getPayloadBytes</A></B>()</CODE>
<BR>
Returns the payload bytes in an array.
</TD>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadLength()">getPayloadLength</A></B>()</CODE>
<BR>
Returns the length of the payload.</TD>
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<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadOffset()">getPayloadOffset</A></B>()</CODE>
<BR>
Returns the offset of the payload within the byte array returned by <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadBytes()"><CODE>getPayloadBytes()</CODE></A>.</TD>
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<A NAME="getHeaderBytes()"><!-- --></A><H3>
getHeaderBytes</H3>
<PRE>
public byte[] <B>getHeaderBytes</B>()
throws <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></PRE>
<DL>
<DD>Returns the header bytes in an array.
The bytes start at <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderOffset()"><CODE>getHeaderOffset()</CODE></A>
and continue for <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderLength()"><CODE>getHeaderLength()</CODE></A>.
<P>
<DD><DL>
<DT><B>Returns:</B><DD>the header bytes.
<DT><B>Throws:</B>
<DD><CODE><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></CODE></DL>
</DD>
</DL>
<HR>
<A NAME="getHeaderLength()"><!-- --></A><H3>
getHeaderLength</H3>
<PRE>
public int <B>getHeaderLength</B>()
throws <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></PRE>
<DL>
<DD>Returns the length of the header.
<P>
<DD><DL>
<DT><B>Returns:</B><DD>the header length
<DT><B>Throws:</B>
<DD><CODE><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></CODE></DL>
</DD>
</DL>
<HR>
<A NAME="getHeaderOffset()"><!-- --></A><H3>
getHeaderOffset</H3>
<PRE>
public int <B>getHeaderOffset</B>()
throws <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></PRE>
<DL>
<DD>Returns the offset of the header within the byte array returned by <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getHeaderBytes()"><CODE>getHeaderBytes()</CODE></A>.
<P>
<DD><DL>
<DT><B>Returns:</B><DD>the header offset.
<DT><B>Throws:</B>
<DD><CODE><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></CODE></DL>
</DD>
</DL>
<HR>
<A NAME="getPayloadBytes()"><!-- --></A><H3>
getPayloadBytes</H3>
<PRE>
public byte[] <B>getPayloadBytes</B>()
throws <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></PRE>
<DL>
<DD>Returns the payload bytes in an array.
The bytes start at <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadOffset()"><CODE>getPayloadOffset()</CODE></A>
and continue for <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadLength()"><CODE>getPayloadLength()</CODE></A>.
<P>
<DD><DL>
<DT><B>Returns:</B><DD>the payload bytes.
<DT><B>Throws:</B>
<DD><CODE><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></CODE></DL>
</DD>
</DL>
<HR>
<A NAME="getPayloadLength()"><!-- --></A><H3>
getPayloadLength</H3>
<PRE>
public int <B>getPayloadLength</B>()
throws <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></PRE>
<DL>
<DD>Returns the length of the payload.
<P>
<DD><DL>
<DT><B>Returns:</B><DD>the payload length.
<DT><B>Throws:</B>
<DD><CODE><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></CODE></DL>
</DD>
</DL>
<HR>
<A NAME="getPayloadOffset()"><!-- --></A><H3>
getPayloadOffset</H3>
<PRE>
public int <B>getPayloadOffset</B>()
throws <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></PRE>
<DL>
<DD>Returns the offset of the payload within the byte array returned by <A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistable.html#getPayloadBytes()"><CODE>getPayloadBytes()</CODE></A>.
<P>
<DD><DL>
<DT><B>Returns:</B><DD>the payload offset.
<DT><B>Throws:</B>
<DD><CODE><A HREF="../../../../../org/eclipse/paho/client/mqttv3/MqttPersistenceException.html" title="class in org.eclipse.paho.client.mqttv3">MqttPersistenceException</A></CODE></DL>
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