# JSP & JSTL - Java-Springs

Spring provides a couple of out-of-the-box solutions for JSP and JSTL views. Using JSP or JSTL is done using a normal view resolver defined in the WebApplicationContext. Furthermore, of course you need to write some JSPs that will actually render the view.

View resolvers
Just as with any other view technology you're integrating with Spring, for JSPs you'll need a view resolver that will resolve your views. The most commonly used view resolvers when developing with JSPs are the InternalResourceViewResolver and the ResourceBundleViewResolver. Both are declared in the WebApplicationContext:

<!-- the ResourceBundleViewResolver -->
<bean id="viewResolver" class="org.springframework.web.servlet .view.ResourceBundleViewResolver">
<property name="basename" value="views"/>
</bean>
# And a sample properties file is uses (views.properties in WEB-INF/classes):
welcome.(class)=org.springframework.web.servlet.view.JstlView
welcome.url=/WEB-INF/jsp/welcome.jsp
productList.(class)=org.springframework.web.servlet.view.JstlView
productList.url=/WEB-INF/jsp/productlist.jsp

As you can see, the ResourceBundleViewResolver needs a properties file defining the view names mapped to 1) a class and 2) a URL. With a ResourceBundleViewResolver you can mix different types of views using only one resolver.

<bean id="viewResolver" class="org.springframework.web. servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework. web.servlet.view.JstlView"/>
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>

The InternalResourceBundleViewResolver can be configured for using JSPs as described above. As a best practice, we strongly encourage placing your JSP files in a directory under the 'WEB-INF' directory, so there can be no direct access by clients.

'Plain-old' JSPs versus JSTL
When using the Java Standard Tag Library you must use a special view class, the JstlView, as JSTL needs some preparation before things such as the I18N features will work.

Spring provides data binding of request parameters to command objects. To facilitate the development of JSP pages in combination with those data binding features, Spring provides a few tags that make things even easier. All Spring tags have HTML escaping features to enable or disable escaping of characters.

The tag library descriptor (TLD) is included in the spring-webmvc.jar. Further information about the individual tags can be found in the appendix entitled Appendix F, spring.tld.

Using Spring's form tag library
As of version 2.0, Spring provides a comprehensive set of data binding-aware tags for handling form elements when using JSP and Spring Web MVC. Each tag provides support for the set of attributes of its corresponding HTML tag counterpart, making the tags familiar and intuitive to use. The tag-generated HTML is HTML 4.01/XHTML 1.0 compliant.

Unlike other form/input tag libraries, Spring's form tag library is integrated with Spring Web MVC, giving the tags access to the command object and reference data your controller deals with. As you will see in the following examples, the form tags make JSPs easier to develop, read and maintain. Let's go through the form tags and look at an example of how each tag is used. We have included generated HTML snippets where certain tags require further commentary.

Configuration
The form tag library comes bundled in spring-webmvc.jar. The library descriptor is called spring-form.tld. where form is the tag name prefix you want to use for the tags from this library.

1. The form tag
This tag renders an HTML 'form' tag and exposes a binding path to inner tags for binding. It puts the command object in the PageContext so that the command object can be accessed by inner tags. All theother tags in this library are nested tags of the form tag.

Let's assume we have a domain object called User. It is a JavaBean with properties such as firstName and lastName. We will use it as the form backing object of our form controller which returns form.jsp. Below is an example of what form.jsp would look like:

<form:form>
<table>
<tr>
<td>First Name:</td>
<td><form:input path="firstName" /></td>
</tr>
<tr>
<td>Last Name:</td>
<td><form:input path="lastName" /></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form:form>

The firstName and lastName values are retrieved from the command object placed in the PageContext by the page controller. Keep reading to see more complex examples of how inner tags are used with the form tag.

The generated HTML looks like a standard form:

<form method="POST">
<table>
<tr>
<td>First Name:</td>
<td><input name="firstName" type="text" value="Harry"/></td>
</tr>
<tr>
<td>Last Name:</td>
<td><input name="lastName" type="text" value="Potter"/></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form>

The preceding JSP assumes that the variable name of the form backing object is 'command'. If you have put the form backing object into the model under another name (definitely a best practice), then you can bind the form to the named variable like so:

<form:form commandName="user">
<table>
<tr>
<td>First Name:</td>
<td><form:input path="firstName" /></td>
</tr>
<tr>
<td>Last Name:</td>
<td><form:input path="lastName" /></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form:form>

2. The input tag
This tag renders an HTML 'input' tag with type 'text' using the bound value.

3. The checkbox tag
This tag renders an HTML 'input' tag with type 'checkbox'.
Let's assume our User has preferences such as newsletter subscription and a list of hobbies. Below is an example of the Preferences class:

public class Preferences {
private String[] interests;
private String favouriteWord;
}
}
public String[] getInterests() {
return interests;
}
public void setInterests(String[] interests) {
this.interests = interests;
}
public String getFavouriteWord() {
return favouriteWord;
}
public void setFavouriteWord(String favouriteWord) {
this.favouriteWord = favouriteWord;
}
} The form.jsp would look like:
<form:form>
<table>
<tr>
<%-- Approach 1: Property is of type java.lang.Boolean --%>
</tr>
<tr>
<td>Interests:</td>
<td>
<%-- Approach 2: Property is of an array or of type java.util.Collection --%>
Quidditch: <form:checkbox path="preferences.interests" value="Quidditch"/>
Herbology: <form:checkbox path="preferences.interests" value="Herbology"/>
Defence Against the Dark Arts: <form:checkbox path="preferences.interests"
value="Defence Against the Dark Arts"/>
</td>
</tr>
<tr>
<td>Favourite Word:</td>
<td>
<%-- Approach 3: Property is of type java.lang.Object --%>
Magic: <form:checkbox path="preferences.favouriteWord" value="Magic"/>
</td>
</tr>
</table>
</form:form>

There are 3 approaches to the checkbox tag which should meet all your checkbox needs.

• Approach One - When the bound value is of type java.lang.Boolean, the input(checkbox) is marked as 'checked' if the bound value is true. The value attribute corresponds to the resolved value of the setValue(Object) value property.
• Approach Two - When the bound value is of type array or java.util.Collection, the input(checkbox) is marked as 'checked' if the configured setValue(Object) value is present in the bound Collection.
• Approach Three - For any other bound value type, the input(checkbox) is marked as 'checked' if the configured setValue(Object) is equal to the bound value.

Note that regardless of the approach, the same HTML structure is generated. Below is an HTML snippet of some checkboxes:

<tr>
<td>Interests:</td>
<td>
Quidditch: <input name="preferences.interests" type="checkbox" value="Quidditch"/>
<input type="hidden" value="1" name="_preferences.interests"/>
Herbology: <input name="preferences.interests" type="checkbox" value="Herbology"/>
<input type="hidden" value="1" name="_preferences.interests"/>
Defence Against the Dark Arts: <input name="preferences.interests" type="checkbox"
value="Defence Against the Dark Arts"/>
<input type="hidden" value="1" name="_preferences.interests"/>
</td>
</tr>

What you might not expect to see is the additional hidden field after each checkbox. When a checkbox in an HTML page is not checked, its value will not be sent to the server as part of the HTTP request parameters once the form is submitted, so we need a workaround for this quirk in HTML in order for Spring form data binding to work. The checkbox tag follows the existing Spring convention of including a hidden parameter prefixed by an underscore ("_") for each checkbox. By doing this, you are effectively telling Spring that “ the checkbox was visible in the form and I want my object to which theform data will be bound to reflect the state of the checkbox no matter what ”.

4. The checkboxes tag
This tag renders multiple HTML 'input' tags with type 'checkbox'.
Building on the example from the previous checkbox tag section. Sometimes you prefer not to have to list all the possible hobbies in your JSP page. You would rather provide a list at runtime of the available options and pass that in to the tag. That is the purpose of the checkboxes tag. You pass in an Array, a List or a Map containing the available options in the "items" property. Typically the bound property is a collection so it can hold multiple values selected by the user. Below is an example of the JSP using this tag:

<form:form>
<table>
<tr>
<td>Interests:</td>
<td>
<%-- Property is of an array or of type java.util .Collection --%>
<form:checkboxes path="preferences.interests" items="${interestList}"/> </td> </tr> </table> </form:form> This example assumes that the "interestList" is a List available as a model attribute containing strings of the values to be selected from. In the case where you use a Map, the map entry key will be used as the value and the map entry's value will be used as the label to be displayed. You can also use a custom object where you can provide the property names for the value using "itemValue" and the label using "itemLabel". 5. The radiobutton tag This tag renders an HTML 'input' tag with type 'radio'. A typical usage pattern will involve multiple tag instances bound to the same property but with different values. <tr> <td>Sex:</td> <td>Male: <form:radiobutton path="sex" value="M"/> <br/> Female: <form:radiobutton path="sex" value="F"/> </td> </tr> 6. The radiobuttons tag This tag renders multiple HTML 'input' tags with type 'radio'. Just like the checkboxes tag above, you might want to pass in the available options as a runtime variable. For this usage you would use the radiobuttons tag. You pass in an Array, a List or a Map containing the available options in the "items" property. In the case where you use a Map, the map entry key will be used as the value and the map entry's value will be used as the label to be displayed. You can also use a custom object where you can provide the property names for the value using "itemValue" and the label using "itemLabel". <tr> <td>Sex:</td> <td><form:radiobuttons path="sex" items="$ {sexOptions}"/></td>
</tr>

This tag renders an HTML 'input' tag with type 'password' using the bound value.

<tr>
<td>
</td>
</tr>

Please note that by default, the password value is not shown. If you do want the password value to be shown, then set the value of the 'showPassword' attribute to true, like so.

<tr>
<td>
</td>
</tr>

8. The select tag
This tag renders an HTML 'select' element. It supports data binding to the selected option as well as the use of nested option and options tags.
Let's assume a User has a list of skills.

<tr>
<td>Skills:</td>
<td><form:select path="skills" items="${skills}"/></td> </tr> If the User's skill were in Herbology, the HTML source of the 'Skills' row would look like: <tr> <td>Skills:</td> <td><select name="skills" multiple="true"> <option value="Potions">Potions</option> <option value="Herbology" selected="selected"> Herbology</option> <option value="Quidditch">Quidditch</option></select> </td> </tr> 9. The option tag This tag renders an HTML 'option'. It sets 'selected' as appropriate based on the bound value. <tr> <td>House:</td> <td> <form:select path="house"> <form:option value="Gryffindor"/> <form:option value="Hufflepuff"/> <form:option value="Ravenclaw"/> <form:option value="Slytherin"/> </form:select> </td> </tr> If the User's house was in Gryffindor, the HTML source of the 'House' row would look like: <tr> <td>House:</td> <td> <select name="house"> <option value="Gryffindor" selected="selected">Gryffindor</option> <option value="Hufflepuff">Hufflepuff</option> <option value="Ravenclaw">Ravenclaw</option> <option value="Slytherin">Slytherin</option> </select> </td> </tr> 10. The options tag This tag renders a list of HTML 'option' tags. It sets the 'selected' attribute as appropriate based on the bound value. <tr> <td>Country:</td> <td> <form:select path="country"> <form:option value="-" label="--Please Select"/> <form:options items="${countryList}" itemValue="code" itemLabel="name"/>
</form:select>
</td>
</tr> If the User lived in the UK, the HTML source of the 'Country' row would look like:
<tr>
<td>Country:</td>
<td>
<select name="country">
<option value="AT">Austria</option>
<option value="UK" selected="selected">United Kingdom</option>
<option value="US">United States</option>
</select>
</td>
</tr>

As the example shows, the combined usage of an option tag with the options tag generates the same standard HTML, but allows you to explicitly specify a value in the JSP that is for display only (where it belongs) such as the default string in the example: "-- Please Select".

The items attribute is typically populated with a collection or array of item objects. itemValue and itemLabel simply refer to bean properties of those item objects, if specified; otherwise, the item objects themselves will be stringified. Alternatively, you may specify a Map of items, in which case the map keys are interpreted as option values and the map values correspond to option labels. If itemValue and/or itemLabel happen to be specified as well, the item value property will apply to the map key and the item label property will apply to the map value.

11. The textarea tag
This tag renders an HTML 'textarea'.

<tr>
<td>Notes:</td>
<td><form:textarea path="notes" rows="3" cols="20" /></td>
<td><form:errors path="notes" /></td>
</tr>

12. The hidden tag
This tag renders an HTML 'input' tag with type 'hidden' using the bound value. To submit an unbound hidden value, use the HTML input tag with type 'hidden'.

<form:hidden path="house" />
If we choose to submit the 'house' value as a hidden one, the HTML would look like:
<input name="house" type="hidden" value="Gryffindor"/>

13. The errors tag
This tag renders field errors in an HTML 'span' tag. It provides access to the errors created in your controller or those that were created by any validators associated with your controller.

Let's assume we want to display all error messages for the firstName and lastName fields once we submit the form. We have a validator for instances of the User class called UserValidator.

public class UserValidator implements Validator {
public boolean supports(Class candidate) {
return User.class.isAssignableFrom(candidate);
}
public void validate(Object obj, Errors errors) {
ValidationUtils.rejectIfEmptyOrWhitespace(errors,"firstName", "required", "Field is required.");
ValidationUtils.rejectIfEmptyOrWhitespace(errors, "lastName", "required", "Field is required.");
}
}
The form.jsp would look like:
<form:form>
<table>
<tr>
<td>First Name:</td>
<td><form:input path="firstName" /></td>
<%-- Show errors for firstName field --%>
<td><form:errors path="firstName" /></td>
</tr>
<tr>
<td>Last Name:</td>
<td><form:input path="lastName" /></td>
<%-- Show errors for lastName field --%>
<td><form:errors path="lastName" /></td>
</tr>
<tr>
<td colspan="3">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form:form>

If we submit a form with empty values in the firstName and lastName fields, this is what the HTML would look like:

<form method="POST">
<table>
<tr>
<td>First Name:</td>
<td><input name="firstName" type="text" value=""/></td>
<%-- Associated errors to firstName field displayed --%>
<td><span name="firstName.errors">Field is required.</span></td>
</tr>
<tr>
<td>Last Name:</td>
<td><input name="lastName" type="text" value=""/></td>
<%-- Associated errors to lastName field displayed --%>
<td><span name="lastName.errors">Field is required.</span></td>
</tr>
<tr>
<td colspan="3">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form>

What if we want to display the entire list of errors for a given page? The example below shows that the errors tag also supports some basic wildcarding functionality.

• path="*" - displays all errors
• path="lastName" - displays all errors associated with the lastName field

The example below will display a list of errors at the top of the page, followed by field-specific errors next to the fields:

<form:form>
<form:errors path="*" cssClass="errorBox" />
<table>
<tr>
<td>First Name:</td>
<td><form:input path="firstName" /></td>
<td><form:errors path="firstName" /></td>
</tr>
<tr>
<td>Last Name:</td>
<td><form:input path="lastName" /></td>
<td><form:errors path="lastName" /></td>
</tr>
<tr>
<td colspan="3">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form:form>

The HTML would look like:

<form method="POST">
<span name="*.errors" class="errorBox">Field is required.<br/>Field is required.</span>
<table>
<tr>
<td>First Name:</td>
<td><input name="firstName" type="text" value=""/></td>
<td><span name="firstName.errors">Field is required.</span></td>
</tr>
<tr>
<td>Last Name:</td>
<td><input name="lastName" type="text" value=""/></td>
<td><span name="lastName.errors">Field is required.</span></td>
</tr>
<tr>
<td colspan="3">
<input type="submit" value="Save Changes" />
</td>
</tr>
</form>

HTTP Method Conversion
A key principle of REST is the use of the Uniform Interface. This means that all resources (URLs) can be manipulated using the same four HTTP methods: GET, PUT, POST, and DELETE. For each method, the HTTP specification defines the exact semantics. For instance, a GET should always be a safe operation, meaning that is has no side effects, and a PUT or DELETE should be idempotent, meaning that you can repeat these operations over and over again, but the end result should be the same. While HTTP defines these four methods, HTML only supports two: GET and POST. Fortunately, there are two possible workarounds: you can either use JavaScript to do your PUT or DELETE, or simply do a POST with the 'real' method as an additional parameter (modeled as a hidden input field in an HTML form). This latter trick is what Spring's Hidden Http MethodFilter does. This filter is a plain Servlet Filter and therefore it can be used in combination with any web framework (not just Spring MVC). Simply add this filter to your web.xml, and a POST with a hidden _method parameter will be converted into the corresponding HTTP method request.

To support HTTP method conversion the Spring MVC form tag was updated to support setting the HTTP method. For example, the following snippet taken from the updated Petclinic sample

<form:form method="delete">
<p class="submit"><input type="submit" value="Delete Pet"/></p>
</form:form>

This will actually perform an HTTP POST, with the 'real' DELETE method hidden behind a request parameter, to be picked up by the HiddenHttpMethodFilter, as defined in web.xml:

<filter>
<filter-name>httpMethodFilter</filter-name>
<filter-class>org.springframework.web.filter. HiddenHttpMethodFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>httpMethodFilter</filter-name>
<servlet-name>petclinic</servlet-name>
</filter-mapping> The corresponding @Controller method is shown below:
@RequestMapping(method = RequestMethod.DELETE)
public String deletePet(@PathVariable int ownerId, @PathVariable int petId) {
this.clinic.deletePet(petId);
return "redirect:/owners/" + ownerId;
}