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This chapter will explain the way in which we can set (or modify) values of attributes in our markup.

5.1 Setting the value of any attribute

Say our website publishes a newsletter, and we want our users to be able to subscribe to it, so we create a /WEB-INF/templates/subscribe.html template with a form:

<form action="subscribe.html">
  <fieldset>
    <input type="text" name="email" />
    <input type="submit" value="Subscribe!" />
  </fieldset>
</form>

As with Thymeleaf, this template starts off more like a static prototype than it does a template for a web application. First, the action attribute in our form statically links to the template file itself, so that there is no place for useful URL rewriting. Second, the value attribute in the submit button makes it display a text in English, but we’d like it to be internationalized.

Enter then the th:attr attribute, and its ability to change the value of attributes of the tags it is set in:

<form action="subscribe.html" th:attr="action=@{/subscribe}">
  <fieldset>
    <input type="text" name="email" />
    <input type="submit" value="Subscribe!" th:attr="value=#{subscribe.submit}"/>
  </fieldset>
</form>

The concept is quite straightforward: th:attr simply takes an expression that assigns a value to an attribute. Having created the corresponding controller and messages files, the result of processing this file will be:

<form action="/gtvg/subscribe">
  <fieldset>
    <input type="text" name="email" />
    <input type="submit" value="¡Suscríbe!"/>
  </fieldset>
</form>

Besides the new attribute values, you can also see that the application context name has been automatically prefixed to the URL base in /gtvg/subscribe, as explained in the previous chapter.

But what if we wanted to set more than one attribute at a time? XML rules do not allow you to set an attribute twice in a tag, so th:attr will take a comma-separated list of assignments, like:

<img src="../../images/gtvglogo.png" 
     th:attr="src=@{/images/gtvglogo.png},title=#{logo},alt=#{logo}" />

Given the required messages files, this will output:

<img src="/gtgv/images/gtvglogo.png" title="Logo de Good Thymes" alt="Logo de Good Thymes" />

5.2 Setting value to specific attributes

By now, you might be thinking that something like:

<input type="submit" value="Subscribe!" th:attr="value=#{subscribe.submit}"/>

…is quite an ugly piece of markup. Specifying an assignment inside an attribute’s value can be very practical, but it is not the most elegant way of creating templates if you have to do it all the time.

Thymeleaf agrees with you, and that’s why th:attr is scarcely used in templates. Normally, you will be using other th:* attributes whose task is setting specific tag attributes (and not just any attribute like th:attr).

For example, to set the value attribute, use th:value:

<input type="submit" value="Subscribe!" th:value="#{subscribe.submit}"/>

This looks much better! Let’s try and do the same to the action attribute in the form tag:

<form action="subscribe.html" th:action="@{/subscribe}">

And do you remember those th:href we put in our home.html before? They are exactly this same kind of attributes:

<li><a href="product/list.html" th:href="@{/product/list}">Product List</a></li>

There are quite a lot of attributes like these, each of them targeting a specific HTML5 attribute:

th:abbr	th:accept	th:accept-charset
th:accesskey	th:action	th:align
th:alt	th:archive	th:audio
th:autocomplete	th:axis	th:background
th:bgcolor	th:border	th:cellpadding
th:cellspacing	th:challenge	th:charset
th:cite	th:class	th:classid
th:codebase	th:codetype	th:cols
th:colspan	th:compact	th:content
th:contenteditable	th:contextmenu	th:data
th:datetime	th:dir	th:draggable
th:dropzone	th:enctype	th:for
th:form	th:formaction	th:formenctype
th:formmethod	th:formtarget	th:fragment
th:frame	th:frameborder	th:headers
th:height	th:high	th:href
th:hreflang	th:hspace	th:http-equiv
th:icon	th:id	th:inline
th:keytype	th:kind	th:label
th:lang	th:list	th:longdesc
th:low	th:manifest	th:marginheight
th:marginwidth	th:max	th:maxlength
th:media	th:method	th:min
th:name	th:onabort	th:onafterprint
th:onbeforeprint	th:onbeforeunload	th:onblur
th:oncanplay	th:oncanplaythrough	th:onchange
th:onclick	th:oncontextmenu	th:ondblclick
th:ondrag	th:ondragend	th:ondragenter
th:ondragleave	th:ondragover	th:ondragstart
th:ondrop	th:ondurationchange	th:onemptied
th:onended	th:onerror	th:onfocus
th:onformchange	th:onforminput	th:onhashchange
th:oninput	th:oninvalid	th:onkeydown
th:onkeypress	th:onkeyup	th:onload
th:onloadeddata	th:onloadedmetadata	th:onloadstart
th:onmessage	th:onmousedown	th:onmousemove
th:onmouseout	th:onmouseover	th:onmouseup
th:onmousewheel	th:onoffline	th:ononline
th:onpause	th:onplay	th:onplaying
th:onpopstate	th:onprogress	th:onratechange
th:onreadystatechange	th:onredo	th:onreset
th:onresize	th:onscroll	th:onseeked
th:onseeking	th:onselect	th:onshow
th:onstalled	th:onstorage	th:onsubmit
th:onsuspend	th:ontimeupdate	th:onundo
th:onunload	th:onvolumechange	th:onwaiting
th:optimum	th:pattern	th:placeholder
th:poster	th:preload	th:radiogroup
th:rel	th:rev	th:rows
th:rowspan	th:rules	th:sandbox
th:scheme	th:scope	th:scrolling
th:size	th:sizes	th:span
th:spellcheck	th:src	th:srclang
th:standby	th:start	th:step
th:style	th:summary	th:tabindex
th:target	th:title	th:type
th:usemap	th:value	th:valuetype
th:vspace	th:width	th:wrap
th:xmlbase	th:xmllang	th:xmlspace

5.3 Setting more than one value at a time

There are two rather special attributes called th:alt-title and th:lang-xmllang which can be used for setting two attributes to the same value at the same time. Specifically:

• th:alt-title will set alt and title.
• th:lang-xmllang will set lang and xml:lang.

For our GTVG home page, this will allow us to substitute this:

<img src="../../images/gtvglogo.png" 
     th:attr="src=@{/images/gtvglogo.png},title=#{logo},alt=#{logo}" />

…or this, which is equivalent:

<img src="../../images/gtvglogo.png" 
     th:src="@{/images/gtvglogo.png}" th:title="#{logo}" th:alt="#{logo}" />

…with this:

<img src="../../images/gtvglogo.png" 
     th:src="@{/images/gtvglogo.png}" th:alt-title="#{logo}" />

5.4 Appending and prepending

Thymeleaf also offers the th:attrappend and th:attrprepend attributes, which append (suffix) or prepend (prefix) the result of their evaluation to the existing attribute values.

For example, you might want to store the name of a CSS class to be added (not set, just added) to one of your buttons in a context variable, because the specific CSS class to be used would depend on something that the user did before:

<input type="button" value="Do it!" class="btn" th:attrappend="class=${' ' + cssStyle}" />

If you process this template with the cssStyle variable set to "warning", you will get:

<input type="button" value="Do it!" class="btn warning" />

There are also two specific appending attributes in the Standard Dialect: the th:classappend and th:styleappend attributes, which are used for adding a CSS class or a fragment of style to an element without overwriting the existing ones:

<tr th:each="prod : ${prods}" class="row" th:classappend="${prodStat.odd}? 'odd'">

(Don’t worry about that th:each attribute. It is an iterating attribute and we will talk about it later.)

5.5 Fixed-value boolean attributes

HTML has the concept of boolean attributes, attributes that have no value and the presence of one means that value is “true”. In XHTML, these attributes take just 1 value, which is itself.

For example, checked:

<input type="checkbox" name="option2" checked /> <!-- HTML -->
<input type="checkbox" name="option1" checked="checked" /> <!-- XHTML -->

The Standard Dialect includes attributes that allow you to set these attributes by evaluating a condition, so that if evaluated to true, the attribute will be set to its fixed value, and if evaluated to false, the attribute will not be set:

<input type="checkbox" name="active" th:checked="${user.active}" />

The following fixed-value boolean attributes exist in the Standard Dialect:

th:async	th:autofocus	th:autoplay
th:checked	th:controls	th:declare
th:default	th:defer	th:disabled
th:formnovalidate	th:hidden	th:ismap
th:loop	th:multiple	th:novalidate
th:nowrap	th:open	th:pubdate
th:readonly	th:required	th:reversed
th:scoped	th:seamless	th:selected

5.6 Setting the value of any attribute (default attribute processor)

Thymeleaf offers a default attribute processor that allows us to set the value of any attribute, even if no specific th:* processor has been defined for it at the Standard Dialect.

So something like:

<span th:whatever="${user.name}">...</span>

Will result in:

<span whatever="John Apricot">...</span>

5.7 Support for HTML5-friendly attribute and element names

It is also possible to use a completely different syntax to apply processors to your templates in a more HTML5-friendly manner.

<table>
    <tr data-th-each="user : ${users}">
        <td data-th-text="${user.login}">...</td>
        <td data-th-text="${user.name}">...</td>
    </tr>
</table>

The data-{prefix}-{name} syntax is the standard way to write custom attributes in HTML5, without requiring developers to use any namespaced names like th:*. Thymeleaf makes this syntax automatically available to all your dialects (not only the Standard ones).

There is also a syntax to specify custom tags: {prefix}-{name}, which follows the W3C Custom Elements specification (a part of the larger W3C Web Components spec). This can be used, for example, for the th:block element (or also th-block), which will be explained in a later section.

Important: this syntax is an addition to the namespaced th:* one, it does not replace it. There is no intention at all to deprecate the namespaced syntax in the future.