Category Archives: FreeMarker

Spring Web Flow – displaying your JSR-303 validation messages using FreeMarker

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Instead of creating a custom validator in the traditional sense I’m relying on JSR-303 annotations to specify validation constraints, because, it is the future, and I shouldn’t have to do a load of coding to specify common validation requirements like an email address regular expression or a numeric value that is required to be within a defined range.

Using Spring web flow, I found that binding error messages weren’t available when I called “<@spring.showErrors ‘<br/>’/>” in my freemarker view (after I had bound the field I wanted to show errors for of course).

So where are my error messages?

It turns out that Spring Web Flow has a different way of providing the user with feedback messages. The Spring Web Flow reference documentation says: “Spring Web Flow’s MessageContext is an API for recording messages during the course of flow executions”.

The message context (with all your binding error messages in it) can be found here: flowRequestContext.messageContext. I’ve written a couple of macros to make retrieving error messages from this object a little easier:

<#--
 * Shows flow messages (which reside in flowRequestContext.messageContext)
 *
 * @param source Name of the field that caused the error
 * @param severity String representation of org.springframework.binding.message.Severity
 * @param separator the html tag or other character list that should be used to
 *    separate each option. Typically '<br>'.
 * @param classOrStyle either the name of a CSS class element (which is defined in
 *    the template or an external CSS file) or an inline style. If the value passed in here
 *    contains a colon (:) then a 'style=' attribute will be used, else a 'class=' attribute
 *    will be used.
 * @param tag The HTML tag to wrap the error in
-->
<#macro showFlowMessages source severity separator classOrStyle="" tag="">
  <#assign messages = flowRequestContext.messageContext.getMessagesBySource(source)/>
  <#if (messages?size > 0)>
    <#list messages as message>
      <#if message.severity?string == severity>
        <#if classOrStyle == "" && tag == "">
          ${message.getText()}
        <#else>
          <#if classOrStyle == "">
            <${tag}>${message.getText()}</${tag}>
          <#else>
            <#if tag == ""><#local tag = "span" /></#if>
            <#if classOrStyle?index_of(":") == -1><#local attr="class"><#else><#local attr="style"></#if>
            <${tag} ${attr}="${classOrStyle}">${message.getText()}</${tag}>
          </#if>
        </#if>
        <#if message_has_next>${separator}</#if>
      </#if>
    </#list>
  </#if>
</#macro>

<#--
 * Shows flow messages (which reside in flowRequestContext.messageContext) in an ordered or unordered list
 *
 * @param source Name of the field that caused the error
 * @param severity String representation of org.springframework.binding.message.Severity
 * @param classOrStyle either the name of a CSS class element (which is defined in
 *    the template or an external CSS file) or an inline style. If the value passed in here
 *    contains a colon (:) then a 'style=' attribute will be used, else a 'class=' attribute
 *    will be used.
 * @param ordered Whether or not the macro should output the list as an <ol> or <ul>
-->
<#macro showFlowMessagesList source severity classOrStyle="" ordered=false>
  <#local errorsList><@showFlowMessages source, severity, "", "", "li" /></#local>
  <#if errorsList?trim != "">
    <#if classOrStyle == "">
      <#local attr="">
    <#elseif classOrStyle?index_of(":") == -1>
      <#local attr=" class=" + classOrStyle>
    <#else>
      <#local attr=" style=" + classOrStyle>
    </#if>
    <#if ordered><ol${attr}><#else><ul${attr}></#if>
    ${errorsList}
    <#if ordered></ol><#else></ul></#if>
  </#if>
</#macro>

I’ve added these to my spring extensions, which you can download here: springx.ftl

FreeMarker pagination macros

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I couldn’t find a good set of macros to help navigate through paginated data so I wrote my own. The macro names echo the names of the CakePHP PaginationHelper functions because…well, they’re reasonably sensible.

The macros expect you to add a model attribute called “paginationData” which contains (at least) the following properties:

pageNumber -> The current page number
pageSize -> The number of items in each page
pagesAvailable -> The total number of pages
sortDirection -> The sorting direction (ascending or descending)
sortField -> The field currently sorted by

In my implementation, my paginationData also contains a property called “pageItems” – the actual items in this page.

The macros available to you are:

  • first
    Outputs a link to the first page
  • last
    Outputs a link to the last page
  • next
    Outputs a link to the next page
  • previous
    Outputs a link to the previous page
  • numbers
    Outputs links to other pages. The macro takes a parameter called “maxPages”, which is the maximum number of pages that should be output. There is also a second parameter “separator”, which is the text/html that should be output between each page link.
  • page
    Outputs a link to a particular page. It takes the page number and link text as parameters. If you omit the link text it’ll default to the page number
  • counter
    Outputs the current page number and the total pages e.g. “1 of 20″
  • sort
    Outputs a link to sort by a field. Takes the field to sort by as its first parameter. If field is different to the current sort field, the link will change the sort field but not the sort direction. If the field is the same as the current sort field, the link will change the sort direction. The second parameter is the link text, which defaults to the field name with an upper case first letter. It also takes a parameter called “directions”. This is an an array of two items: the words being used in paginationData.sortDirection to describe the sorting direction of ascending or descending. Default: ["Asc", "Desc"]. So it can compare the current sorting direction and switch to the converse.

Note, ordinarily you’ll probably not need to use the “page” macro.

How to use

In Java, add a model attribute “paginationData” containing the properties I’ve described above. Then, in your view, import the library:

    <#import "pagination.ftl" as pagination />

Call the macros:

    <nav style="float:right;">
        <@pagination.first />
        <@pagination.previous />
        <@pagination.numbers />
        <@pagination.next />
        <@pagination.last />
    </nav>
    <@pagination.counter />

Which’ll give you something like:

For table headings that allow sorting:

    <table>
        <tr>
            <th><@pagination.sort "forename" /></th>
            <th><@pagination.sort "surname" /></th>
            <th><@pagination.sort "email" /></th>
            <th><@pagination.sort "created" "Registration date" /></th>
        </tr>
        ...
    </table>

Download

You can download the pagination macros here.

Simple FreeMarker random number generator

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FreeMarker doesn’t have a random number generator function. I needed a really simple solution that would allow me to pick a random image URL to be displayed on the homepage.

<#--
* Generates a "random" integer between min and max (inclusive)
*
* Note the values this function returns are based on the current
* second the function is called and thus are highly deterministic
* and SHOULD NOT be used for anything other than inconsequential
* purposes, such as picking a random image to display.
-->
<#function rand min max>
  <#local now = .now?long?c />
  <#local randomNum = _rand +
    ("0." + now?substring(now?length-1) + now?substring(now?length-2))?number />
  <#if (randomNum > 1)>
    <#assign _rand = randomNum % 1 />
  <#else>
    <#assign _rand = randomNum />
  </#if>
  <#return (min + ((max - min) * _rand))?round />
</#function>
<#assign _rand = 0.36 />

I’ve added this function to the FreeMarker Spring extensions I’ve been building up. You might use it in your code like so:

<img src="<@spring.url "/images/" + springx.rand(1, 10) + ".jpg" />" />

Note that there are obvious issues with this function. Aside from being based heavily on the second the function is called, you’ll notice that the min and max have less probability of being generated as the other values…what? I said it was simple.

Extensions to Spring’s FreeMarker macro’s (spring.ftl)

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Spring’s FreeMarker macro’s are pretty useful, but there are a couple of things I need from the showErrors macro that simply aren’t there:

  1. Show errors without a HTML tag around them – if you don’t specify a classOrStyle, the showErrors macro will wrap your error message in a <b> tag. If you do, it’ll wrap it in a <span> (understandably)
  2. Pick the tag that surrounds each message – As explained in the first point, you can see we only get the choice of <b> or <span>. What if I wanted to use an <li>? …use the separator? – no good, because unless I write an <#if> statement to check the number of error messages before I call showErrors I’ll end up with redundant <ul>/<ol> and <li>’s in my markup if there aren’t any errors:
    e.g. <ul><li><@spring.showErrors “</li><li>”/></li></ul>
    Which leads me nicely onto the next point:
  3. Show errors in an ordered/unordered list, automatically detecting zero messages and not outputting markup if this is the case
  4. Show errors for multiple bind paths – Spring’s showErrors only shows errors for the currently bound field. However I’ve found that I’ve needed to show errors for 2 or more fields together. This is particularly true of a DOB field where the day/month and year are separate <select>’s
  5. Finally, show errors for multiple bind paths, in an unordered/ordered list

You can download my Spring extensions here: springx.ftl. Inevitably I’ll find more bits and pieces to add and will update them accordingly.