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SipRefreshHelper (JSR180 SIP API for J2ME)
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javax.microedition.sip</FONT>
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Class SipRefreshHelper</H2>
<PRE>
java.lang.Object
<IMG SRC="../../../resources/inherit.gif" ALT="extended by"><B>javax.microedition.sip.SipRefreshHelper</B>
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<DL>
<DT>public class <B>SipRefreshHelper</B><DT>extends java.lang.Object</DL>
<P>
This class implements the functionality that facilitates the handling of refreshing requests on behalf of the application. Some SIP requests (REGISTER, SUBSCRIBE, ...) need to be timely refreshed (binding between end point and server, see RFC 3261 - chapter 10.2.1 page 58). For example the REGISTER request (RFC 3261, chapter 10 page 56) needs to be re-sent to ensure that the originating end point is still well and alive. The request's validity is proposed by the end point in the request and confirmed in the response by the registrar/notifier for example in expires header (RFC 3261, chapter 2 page 5). The handling of such binding would significantly increase application complexity and size. As a consequence the <tt>SipRefreshHelper</tt> can be used to facilitate such operations. The specification does not define the strategy for timely refreshing of registrations and subscriptions, implementations may choose the algorithm of when to send the refresh request.<br> The implementation must support refreshing REGISTER and SUBSCRIBE requests using the features of this class, however it is not mandated that refreshing PUBLISH requests is supported by the refreshHelper mechanism. Note that even if the <tt>SipRefreshHelper</tt> provides no support for PUBLISH, refreshing PUBLISH requests is possible by sending the appropriate SIP request from the application.<br> When the application wants to send a refreshable request it: <p> <UL> <LI>implements <A HREF="./SipRefreshListener.html"><tt>SipRefreshListener</tt> </A> callback interface. <LI>creates a new <A HREF="./SipClientConnection.html"> <tt>SipClientConnection</tt></A> and sets it up. <LI>calls the method <A HREF="./SipClientConnection.html#enableRefresh(javax.microedition.sip.SipRefreshListener)"> <tt>enableRefresh(SipRefreshListener)</tt></A>. A refresh ID is returned. If the request is not refreshable the method returns 0. <LI>if the refresh task fails a failure event is sent to the <A HREF="./SipRefreshListener.html"><tt>SipRefreshListener</tt></A> </UL> </p> A reference to the <tt>SipRefreshHelper</tt> object is obtained by calling the static method <A HREF="./SipRefreshHelper.html#getInstance()"> <tt>SipRefreshHelper.getInstance()</tt></A> (singleton pattern). <br> <br> Finally, using the refresh ID returned from <A HREF="./SipClientConnection.html#enableRefresh(javax.microedition.sip.SipRefreshListener)"> <tt>enableRefresh(SipRefreshListener)</tt></A> the application can: <p> <UL> <LI><A HREF="./SipRefreshHelper.html#stop(int)"><tt>stop()</tt></A> a refresh. The possible binding between end point and server is cancelled (RFC3261, chapter 10.2.2 page 61). <LI><A HREF="./SipRefreshHelper.html#update(int, java.lang.String[], java.lang.String, int, int)"><tt>update(...)</tt></A> the refreshed request with new parameters (Contact info, expires header and new payload). Note that this functionality is limited to the most typical case. A more complex case would require to stop the refresh and to create a new request with the needed updates. </UL> </p> When all refresh tasks belonging to one refresh listener are stopped, the listener reference will be removed from the <tt>SipRefreshHelper</tt>. <p> In case of failure of either the original request or a subsequent refresh request the refreshing is automatically stopped and the failure response is reported in the <tt>refreshEvent()</tt> callback. The corresponding refresh ID is invalidated, so calling <tt>update()</tt> with the same ID will throw an exception. The application has to start a new refresh task if it wishes so and the implementation will assign a new refresh ID. <p> An implementation compliant to this specification MUST report the refresh responses to the <tt>refreshEvent</tt> callback in case of failure response codes (3xx ⌨️ 快捷键说明
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