| <html><head> |
| <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> |
| <title>2.5. Page Navigation</title><link rel="stylesheet" href="css/stylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.75.0"><link rel="home" href="index.html" title="Apache Click"><link rel="up" href="ch02.html" title="Chapter 2. Pages"><link rel="prev" href="ch02s04.html" title="2.4. Security"><link rel="next" href="ch02s06.html" title="2.6. Page Templating"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.5. Page Navigation</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s04.html">Prev</a> </td><th width="60%" align="center">Chapter 2. Pages</th><td width="20%" align="right"> <a accesskey="n" href="ch02s06.html">Next</a></td></tr></table><hr></div><div class="sect1" title="2.5. Page Navigation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="page-navigation"></a>2.5. Page Navigation</h2></div></div></div><p> Navigation between pages is achieved by using forwards, redirects |
| and by setting the page template path. |
| </p><div class="sect2" title="2.5.1. Forward"><div class="titlepage"><div><div><h3 class="title"><a name="forward"></a>2.5.1. Forward</h3></div></div></div><p> To forward to another page using the servlet |
| <a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="http://java.sun.com/products/servlet/2.3/javadoc/javax/servlet/RequestDispatcher.html" target="_blank">RequestDispatcher</a>, |
| set the Page's forward property. For example to forward to a page with a |
| path <code class="varname">index.htm</code>: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">/** |
| * @see Page#onPost() |
| */</span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">void</span> onPost() { |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Process form post</span> |
| .. |
| |
| setForward(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"index.htm"</span>); |
| }</pre><p>This will invoke a new Page class instance mapped to the path |
| <code class="varname">index.htm</code>. |
| </p><p><span class="bold"><strong>Please note</strong></span> when a request is |
| forwarded to another Page, the controls on the second page will not be |
| processed. This prevents confusion and bugs, like a form on the second page |
| trying to process a POST request from the first page. |
| </p><div class="sect3" title="2.5.1.1. Forward Parameter Passing"><div class="titlepage"><div><div><h4 class="title"><a name="forward-parameter-passing"></a>2.5.1.1. Forward Parameter Passing</h4></div></div></div><p>When you forward to another page the request parameters are |
| maintained. This is a handy way of passing through state information |
| with the request. For example you could add a customer object as a |
| request parameter which is displayed in the template of the forwarded |
| page. |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onViewClick() { |
| Long id = viewLink.getValueLong(); |
| Customer customer = CustomerDAO.findByPK(id); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Set the customer object as a request parameter</span> |
| getContext().setRequestAttribute(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"customer"</span>, customer); |
| setForward(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"view-customer.htm"</span>); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><p>The snippet above forwards to the page template |
| <code class="varname">view-customer.htm</code>: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"><html></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"><head></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"><title></span>Customer Details<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"></title></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"></head></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"><body></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"><h1></span>Customer Details<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"></h1></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"><pre></span> |
| Full Name: <code class="varname">$customer.fullName</code> |
| Email: <code class="varname">$customer.email</code> |
| Telephone: <code class="varname">$customer.telephone</code> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"></pre></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"></body></span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="tag"></html></span></pre><p>Request attributes are automatically added to the Velocity Context |
| object so are available in the page template. |
| </p></div><div class="sect3" title="2.5.1.2. Page Forwarding"><div class="titlepage"><div><div><h4 class="title"><a name="page-forwarding"></a>2.5.1.2. Page Forwarding</h4></div></div></div><p>Page forwarding is another way of passing information between |
| pages. In this case you create the page to be forwarded to using the |
| Context <a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="../../click-api/org/apache/click/Context.html#createPage(java.lang.String)" target="_blank">createPage(String)</a> |
| method and then set properties directly on the Page. Finally set this |
| page as the page to forward the request to. For example: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onEditClick() { |
| Long id = viewLink.getValueLong(); |
| Customer customer = CustomerDAO.findByPK(id); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Create a new EditPage instance based on the specified path</span> |
| EditPage editPage = (EditPage) getContext().createPage(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"/edit-customer.htm"</span>); |
| editPage.setCustomer(customer); |
| setForward(editPage); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><p>When creating a page with the <code class="methodname">createPage()</code> |
| method, ensure you prefix the page path with the <code class="varname">"/"</code> |
| character. |
| </p><p>You can also specify the target page using its class as long as |
| the Page has a unique path. Using this technique the above code becomes: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onEditClick() { |
| Long id = viewLink.getValueLong(); |
| Customer customer = CustomerDAO.findByPK(id); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Create a new EditPage instance based on its class</span> |
| EditPage editPage = (EditPage) getContext().createPage(EditPage.<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">class</span>); |
| editPage.setCustomer(customer); |
| setForward(editPage); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><p>This Page forwarding technique is best practice as it provides you |
| with compile time safety and alleviates you from having to specify page |
| paths in your code. Please always use the Context |
| <code class="methodname">createPage()</code> methods to allow Click to inject |
| Page dependencies. |
| </p><p>Although uncommon it is possible to map more than one path to the |
| same class. In these cases invoking Context |
| <code class="methodname">createPage(Class)</code> will throw an exception, because |
| Click will not be able to determine which path to use for the Page. |
| </p></div></div><div class="sect2" title="2.5.2. Template Path"><div class="titlepage"><div><div><h3 class="title"><a name="template-path"></a>2.5.2. Template Path</h3></div></div></div><p>An alternative method of forwarding to a new page is to simply set |
| the current Page's path to the new page template to render. With this |
| approach the page template being rendered must have everything it needs |
| without having its associated Page object created. Our modified example |
| would be: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onViewClick() { |
| Long id = viewLink.getValueLong(); |
| Customer customer = CustomerDAO.findByPK(id); |
| |
| addModel(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"customer"</span>, customer); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Set the Page's path to a new value</span> |
| setPath(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"view-customer.htm"</span>); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><p>Note how the <code class="varname">customer</code> object is passed through to |
| the template in the Page model. This approach of using the Page model is |
| not available when you forward to another Page, as the first Page object is |
| "<a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="../../click-api/org/apache/click/Page.html#onDestroy()" target="_blank">destroyed</a>" |
| before the second Page object is created and any model values would be lost. |
| </p></div><div class="sect2" title="2.5.3. Redirect"><div class="titlepage"><div><div><h3 class="title"><a name="redirect"></a>2.5.3. Redirect</h3></div></div></div><p>Redirects are another very useful way to navigate between pages. |
| See HttpServletResponse. |
| <a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="http://java.sun.com/products/servlet/2.3/javadoc/javax/servlet/http/HttpServletResponse.html#sendRedirect(java.lang.String)" target="_blank">sendRedirect</a> |
| (location) for details. |
| </p><p>The great thing about redirects are that they provide a clean URL in |
| the users browser which matches the page that they are viewing. This is |
| important for when users want to bookmark a page. The downside of |
| redirects are that they involve a communications round trip with the users |
| browser which requests the new page. Not only does this take time, it also |
| means that all the page and request information is lost. |
| </p><p>An example of a redirect to a <code class="varname">logout.htm</code> page is |
| provided below: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onLogoutClick() { |
| setRedirect(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"/logout.htm"</span>); |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><p>If the redirect location begins with a <span class="symbol">"/"</span> character |
| the redirect location will be prefixed with the web applications context |
| path. For example if an application is deployed to the context |
| <code class="varname">"mycorp"</code> calling |
| <code class="methodname">setRedirect(<code class="varname">"/customer/details.htm"</code>)</code> |
| will redirect the request to: <code class="varname">"/mycorp/customer/details.htm"</code>. |
| </p><p>You can also obtain the redirect path via the target Page's class. |
| For example: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onLogoutClick() { |
| String path = getContext().getPagePath(Logout.<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">class</span>); |
| setRedirect(path); |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><p>Note when using this redirect method, the target Page class must have |
| a unique path. |
| </p><p>A short hand way of redirecting is to simply specify the target Page |
| class in the redirect method. For example: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onLogoutClick() { |
| setRedirect(Logout.<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">class</span>); |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| }</pre><div class="sect3" title="2.5.3.1. Redirect Parameter Passing"><div class="titlepage"><div><div><h4 class="title"><a name="redirect-parameter-passing"></a>2.5.3.1. Redirect Parameter Passing</h4></div></div></div><p>You can pass information between redirected pages using URL |
| request parameters. The ClickServlet will encode the URL for you using |
| HttpServletResponse.<a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="http://java.sun.com/products/servlet/2.3/javadoc/javax/servlet/http/HttpServletResponse.html#encodeRedirectURL(java.lang.String)" target="_blank">encodeRedirectURL</a> |
| (url). |
| </p><p>In the example below a user will click on an OK button to confirm |
| a payment. The <code class="methodname">onOkClick()</code> button handler |
| processes the payment, gets the payment transaction id, and then |
| redirects to the <code class="varname">trans-complete.htm</code> page with the |
| transaction id encoded in the URL. |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">class</span> Payment <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">extends</span> Page { |
| .. |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">boolean</span> onOkClick() { |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">if</span> (form.isValid()) { |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Process payment</span> |
| .. |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Get transaction id</span> |
| Long transId = OrderDAO.purchase(order); |
| |
| setRedirect(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"trans-complete.htm?transId="</span> + transId); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> false; |
| } |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">return</span> true; |
| } |
| }</pre><p>The Page class for the trans-complete.htm page can then get the |
| transaction id through the request parameter <code class="varname">"transId"</code>: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">class</span> TransComplete <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">extends</span> Page { |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">/** |
| * @see Page#onInit() |
| */</span> |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">void</span> onInit() { |
| String transId = getContext().getRequest().getParameter(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"transId"</span>); |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">if</span> (transId != null) { |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="com">// Get order details</span> |
| Order order = OrderDAO.findOrderByPK(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">new</span> Long(transId)); |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">if</span> (order != null) { |
| addModel(<span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="str">"order"</span>, order); |
| } |
| } |
| } |
| }</pre></div><div class="sect3" title="2.5.3.2. Post Redirect"><div class="titlepage"><div><div><h4 class="title"><a name="post-redirect"></a>2.5.3.2. Post Redirect</h4></div></div></div><p>The parameter passing example above is also an example of a Post |
| Redirect. The Post Redirect technique is a very useful method of |
| preventing users from submitting a form twice by hitting the refresh |
| button. |
| </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s04.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s06.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2.4. Security </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 2.6. Page Templating</td></tr></table></div></body></html> |
