print barcode labels vb.net The AJAX UI Component for the DirectorySearch Example in Java

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The AJAX UI Component for the DirectorySearch Example
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In addition to rendering the AJAX script, the component also renders the core UI element(s) of the component For the DirectorySearch example this is done by using the encodeInputField( ) method, which is also in the component s encodeBegin( ) method
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encodeInputField(context, clientId);
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Part II:
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Extending JavaServer Faces
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The UI for DirectorySearch is very basic because it is just an input field along with a <DIV>, which will serve as the write location for the results from the AJAX transaction
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public void encodeInputField(FacesContext context, String clientId) throws IOException { // render a standard HTML input field along with a DIV ResponseWriter writer = contextgetResponseWriter(); writerstartElement("p", this); writerstartElement("input", this); writerwriteAttribute("type", "text", null); writerwriteAttribute("id", clientId, "clientId"); writerwriteAttribute("size", "20", null); writerwriteAttribute("onkeyup", "lookup('" + clientId + "');", null); writerendElement("input"); writerendElement("p"); writerstartElement("div", this); writerwriteAttribute("id", clientId + ":table", null); writerendElement("div"); }
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Notice that the lookup( ) JavaScript function is included as an attribute of the input field
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The AJAX Server Component for the DirectorySearch Example
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As an alternative to using an external servlet to serve as the AJAX server component, the DirectorySearch example will embed this functionality inside the component s decode( ) method, as shown here
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public void decode(FacesContext context) { Map requestMap = contextgetExternalContext()getRequestMap(); HttpServletResponse response = (HttpServletResponse) contextgetExternalContext()getResponse(); HttpServletRequest request = (HttpServletRequest) contextgetExternalContext()getRequest(); if (requestMapcontainsKey("ajaxreq")) { // set the header information for the response responsesetContentType("text/xml"); responsesetHeader("Cache-Control", "no-cache"); responsesetCharacterEncoding("UTF-8"); try { XmlGenerator myXmlGenerator = new XmlGenerator(requestgetParameter("input")); String xmlout = myXmlGeneratorgetXmlResponse(); responsegetWriter()write(xmlout); responsegetWriter()close(); } catch (IOException e) { eprintStackTrace(); } contextresponseComplete(); } // Place non-AJAX decode code here }
11:
Building AJAX JSF Components
The first thing to notice about this decode( ) method is the code to check if a certain ajaxreq (AJAX Request) is one of the request parameters:
if (null != requestgetParameter("ajaxreq")) {
This check allows the decode( ) method to distinguish between AJAX requests (XMLHttpRequest) and regular page requests This approach requires that the JavaScript function making this request must supply this parameter Another very important request parameter requirement is that the form name must also be passed as a parameter to the JSF application If this value if not passed, the JSF application will interpret the request as a non-post-back request and the decode( ) method will not be entered Therefore, the resulting response will be a non-AJAX, complete HTML page The form name value can be obtained on the client by using windowdocumentforms[0]id
PART II
NOTE This actually just retrieves the ID of the first form in the page, but this is sufficient to allow
the JSF runtime to identify it as a non-post-back request Placing the formName along with the ajaxreq parameter can be combined with the following JavaScript client code:
var formdata = "formName=" + windowdocumentforms[0]id + "&ajaxreq=true";
The formdata data is then passed in the XmlHttpRequest s send( ) call with req send(formdata) Also, because submitting a form always issues a post-back, a different URL (such as ajaxdirectoryservice ) is not needed for the form s action Another important bit of information that is often passed as a set of parameters is the current status of the components in the page, or view state This is only needed when the AJAX server component needs access to the UI components of the original view to which the user is now posting back The next AJAX JSF example in the chapter does, however, show how to do this The other key thing to notice in the decode( ) method example is the usage of the HttpServletResponsegetWriter( ) method to write the XML directly to the response Another approach would be to create a custom ResponseWriter that is suitable for writing XML The final thing to notice is that once the content for the request has been fulfilled, the JSF lifecycle can complete the response immediately so as not to render an entire page by using contextresponseComplete( ) The other task of the AJAX DirectorySearch JSF component is to render the same JavaScript code that was hard-coded directly into the HTML page in the original AJAX-only version This is accomplished by using the ResponseWriter object in the component s encode( ) method Since this portion is trivial, it is not included in the text but is available on the web site In addition to the rendering code, the only remaining sub-component is the JSP tag handler that exposes the UI component to the JSP page This is also a fairly straightforward step and its code is also available on the web site Our next AJAX JSF component example builds on the concepts shown in the DirectorySearch example but also shows alternative methods for rendering JavaScript on the client as well as how to process AJAX requests
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