FreeMarker

Apache FreeMarker is a template engine for generating any kind of text output from HTML to email and others. The TODAY Framework has built-in integration for using Web MVC with FreeMarker templates.

View Configuration

The following example shows how to configure FreeMarker as a view technology:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

  @Override
  public void configureViewResolvers(ViewResolverRegistry registry) {
    registry.freeMarker();
  }

  // Configure FreeMarker...

  @Bean
  public FreeMarkerConfigurer freeMarkerConfigurer() {
    FreeMarkerConfigurer configurer = new FreeMarkerConfigurer();
    configurer.setTemplateLoaderPath("/WEB-INF/freemarker");
    return configurer;
  }
}

Alternatively, you can also declare the FreeMarkerConfigurer bean for full control over all properties, as the following example shows:

<bean id="freemarkerConfig" class="cn.taketoday.web.view.freemarker.FreeMarkerConfigurer">
  <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/>
</bean>

Your templates need to be stored in the directory specified by the FreeMarkerConfigurer shown in the preceding example. Given the preceding configuration, if your controller returns a view name of welcome, the resolver looks for the /WEB-INF/freemarker/welcome.ftl template.

FreeMarker Configuration

You can pass FreeMarker 'Settings' and 'SharedVariables' directly to the FreeMarker Configuration object (which is managed by Infra) by setting the appropriate bean properties on the FreeMarkerConfigurer bean. The freemarkerSettings property requires a java.util.Properties object, and the freemarkerVariables property requires a java.util.Map. The following example shows how to use a FreeMarkerConfigurer:

<bean id="freemarkerConfig" class="cn.taketoday.web.mockApi.view.freemarker.FreeMarkerConfigurer">
  <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/>
  <property name="freemarkerVariables">
    <map>
      <entry key="xml_escape" value-ref="fmXmlEscape"/>
    </map>
  </property>
</bean>

<bean id="fmXmlEscape" class="freemarker.template.utility.XmlEscape"/>

See the FreeMarker documentation for details of settings and variables as they apply to the Configuration object.

Form Handling

Infra provides a tag library for use in JSPs that contains, among others, a <spring:bind/> element. This element primarily lets forms display values from form-backing objects and show the results of failed validations from a Validator in the web or business tier. Infra also has support for the same functionality in FreeMarker, with additional convenience macros for generating form input elements themselves.

The Bind Macros

A standard set of macros are maintained within the today-web.jar file for FreeMarker, so they are always available to a suitably configured application.

Some of the macros defined in the Infra templating libraries are considered internal (private), but no such scoping exists in the macro definitions, making all macros visible to calling code and user templates. The following sections concentrate only on the macros you need to directly call from within your templates. If you wish to view the macro code directly, the file is called infra.ftl and is in the cn.taketoday.web.mockApi.view.freemarker package.

Simple Binding

In your HTML forms based on FreeMarker templates that act as a form view for a Web MVC controller, you can use code similar to the next example to bind to field values and display error messages for each input field in similar fashion to the JSP equivalent. The following example shows a personForm view:

<!-- FreeMarker macros have to be imported into a namespace.
  We strongly recommend sticking to 'spring'. -->
<#import "/spring.ftl" as spring/>
<html>
  ...
  <form action="" method="POST">
    Name:
    <@spring.bind "personForm.name"/>
    <input type="text"
      name="${spring.status.expression}"
      value="${spring.status.value?html}"/><br />
    <#list spring.status.errorMessages as error> <b>${error}</b> <br /> </#list>
    <br />
    ...
    <input type="submit" value="submit"/>
  </form>
  ...
</html>

<@spring.bind> requires a 'path' argument, which consists of the name of your command object (it is 'command', unless you changed it in your controller configuration) followed by a period and the name of the field on the command object to which you wish to bind. You can also use nested fields, such as command.address.street. The bind macro assumes the default HTML escaping behavior specified by the MockContextImpl parameter defaultHtmlEscape in web.xml.

An alternative form of the macro called <@spring.bindEscaped> takes a second argument that explicitly specifies whether HTML escaping should be used in the status error messages or values. You can set it to true or false as required. Additional form handling macros simplify the use of HTML escaping, and you should use these macros wherever possible. They are explained in the next section.

Input Macros

Additional convenience macros for FreeMarker simplify both binding and form generation (including validation error display). It is never necessary to use these macros to generate form input fields, and you can mix and match them with simple HTML or direct calls to the Infra bind macros that we highlighted previously.

The following table of available macros shows the FreeMarker Template (FTL) definitions and the parameter list that each takes:

Table 1. Table of macro definitions
macro	FTL definition
`message` (output a string from a resource bundle based on the code parameter)	<@spring.message code/>
`messageText` (output a string from a resource bundle based on the code parameter, falling back to the value of the default parameter)	<@spring.messageText code, text/>
`url` (prefix a relative URL with the application’s context root)	<@spring.url relativeUrl/>
`formInput` (standard input field for gathering user input)	<@spring.formInput path, attributes, fieldType/>
`formHiddenInput` (hidden input field for submitting non-user input)	<@spring.formHiddenInput path, attributes/>
`formPasswordInput` (standard input field for gathering passwords. Note that no value is ever populated in fields of this type.)	<@spring.formPasswordInput path, attributes/>
`formTextarea` (large text field for gathering long, freeform text input)	<@spring.formTextarea path, attributes/>
`formSingleSelect` (drop down box of options that let a single required value be selected)	<@spring.formSingleSelect path, options, attributes/>
`formMultiSelect` (a list box of options that let the user select 0 or more values)	<@spring.formMultiSelect path, options, attributes/>
`formRadioButtons` (a set of radio buttons that let a single selection be made from the available choices)	<@spring.formRadioButtons path, options separator, attributes/>
`formCheckboxes` (a set of checkboxes that let 0 or more values be selected)	<@spring.formCheckboxes path, options, separator, attributes/>
`formCheckbox` (a single checkbox)	<@spring.formCheckbox path, attributes/>
`showErrors` (simplify display of validation errors for the bound field)	<@spring.showErrors separator, classOrStyle/>

In FreeMarker templates, formHiddenInput and formPasswordInput are not actually required, as you can use the normal formInput macro, specifying hidden or password as the value for the fieldType parameter.

The parameters to any of the above macros have consistent meanings:

path: The name of the field to bind to (for example, "command.name")
options: A Map of all the available values that can be selected from in the input field. The keys to the map represent the values that are POSTed back from the form and bound to the command object. Map objects stored against the keys are the labels displayed on the form to the user and may be different from the corresponding values posted back by the form. Usually, such a map is supplied as reference data by the controller. You can use any Map implementation, depending on required behavior. For strictly sorted maps, you can use a SortedMap (such as a TreeMap) with a suitable Comparator and, for arbitrary Maps that should return values in insertion order, use a LinkedHashMap or a LinkedMap from commons-collections.
separator: Where multiple options are available as discreet elements (radio buttons or checkboxes), the sequence of characters used to separate each one in the list (such as <br>).
attributes: An additional string of arbitrary tags or text to be included within the HTML tag itself. This string is echoed literally by the macro. For example, in a textarea field, you may supply attributes (such as 'rows="5" cols="60"'), or you could pass style information such as 'style="border:1px solid silver"'.
classOrStyle: For the showErrors macro, the name of the CSS class that the span element that wraps each error uses. If no information is supplied (or the value is empty), the errors are wrapped in <b></b> tags.

The following sections outline examples of the macros.

Input Fields

The formInput macro takes the path parameter (command.name) and an additional attributes parameter (which is empty in the upcoming example). The macro, along with all other form generation macros, performs an implicit Infra bind on the path parameter. The binding remains valid until a new bind occurs, so the showErrors macro does not need to pass the path parameter again — it operates on the field for which a binding was last created.

The showErrors macro takes a separator parameter (the characters that are used to separate multiple errors on a given field) and also accepts a second parameter — this time, a class name or style attribute. Note that FreeMarker can specify default values for the attributes parameter. The following example shows how to use the formInput and showErrors macros:

<@spring.formInput "command.name"/>
<@spring.showErrors "<br>"/>

The next example shows the output of the form fragment, generating the name field and displaying a validation error after the form was submitted with no value in the field. Validation occurs through Infra Validation framework.

The generated HTML resembles the following example:

Name:
<input type="text" name="name" value="">
<br>
	<b>required</b>
<br>
<br>

The formTextarea macro works the same way as the formInput macro and accepts the same parameter list. Commonly, the second parameter (attributes) is used to pass style information or rows and cols attributes for the textarea.

Selection Fields

You can use four selection field macros to generate common UI value selection inputs in your HTML forms:

formSingleSelect
formMultiSelect
formRadioButtons
formCheckboxes

Each of the four macros accepts a Map of options that contains the value for the form field and the label that corresponds to that value. The value and the label can be the same.

The next example is for radio buttons in FTL. The form-backing object specifies a default value of 'London' for this field, so no validation is necessary. When the form is rendered, the entire list of cities to choose from is supplied as reference data in the model under the name 'cityMap'. The following listing shows the example:

...
Town:
<@spring.formRadioButtons "command.address.town", cityMap, ""/><br><br>

The preceding listing renders a line of radio buttons, one for each value in cityMap, and uses a separator of "". No additional attributes are supplied (the last parameter to the macro is missing). The cityMap uses the same String for each key-value pair in the map. The map’s keys are what the form actually submits as POST request parameters. The map values are the labels that the user sees. In the preceding example, given a list of three well known cities and a default value in the form backing object, the HTML resembles the following:

Town:
<input type="radio" name="address.town" value="London">London</input>
<input type="radio" name="address.town" value="Paris" checked="checked">Paris</input>
<input type="radio" name="address.town" value="New York">New York</input>

If your application expects to handle cities by internal codes (for example), you can create the map of codes with suitable keys, as the following example shows:

Java

protected Map<String, ?> referenceData(HttpServletRequest request) throws Exception {
  Map<String, String> cityMap = new LinkedHashMap<>();
  cityMap.put("LDN", "London");
  cityMap.put("PRS", "Paris");
  cityMap.put("NYC", "New York");

  Map<String, Object> model = new HashMap<>();
  model.put("cityMap", cityMap);
  return model;
}

The code now produces output where the radio values are the relevant codes, but the user still sees the more user-friendly city names, as follows:

Town:
<input type="radio" name="address.town" value="LDN">London</input>
<input type="radio" name="address.town" value="PRS" checked="checked">Paris</input>
<input type="radio" name="address.town" value="NYC">New York</input>

HTML Escaping

Default usage of the form macros described earlier results in HTML elements that are HTML 4.01 compliant and that use the default value for HTML escaping defined in your web.xml file, as used by Infra bind support. To make the elements be XHTML compliant or to override the default HTML escaping value, you can specify two variables in your template (or in your model, where they are visible to your templates). The advantage of specifying them in the templates is that they can be changed to different values later in the template processing to provide different behavior for different fields in your form.

To switch to XHTML compliance for your tags, specify a value of true for a model or context variable named xhtmlCompliant, as the following example shows:

<#-- for FreeMarker -->
<#assign xhtmlCompliant = true>

After processing this directive, any elements generated by the Infra macros are now XHTML compliant.

In similar fashion, you can specify HTML escaping per field, as the following example shows:

<#-- until this point, default HTML escaping is used -->

<#assign htmlEscape = true>
<#-- next field will use HTML escaping -->
<@spring.formInput "command.name"/>

<#assign htmlEscape = false in spring>
<#-- all future fields will be bound with HTML escaping off -->