What are Spring Tags?

Spring MVC Form Tags are the reusable building blocks of a web page. These Spring tags are used for data binding that automatically sets data to Java object/bean and retrieves from it. It makes an application easy to develop, read, and maintain.

There are various tags available in Spring MVC:

• The form tag
• The input tag
• The checkbox tag
• The checkboxes tag
• The radiobutton tag
• The radiobuttons tag
• The password tag
• The select tag
• The option tag
• The options tag
• The textarea tag
• The hidden tag
• The errors tag

These tags come under spring-webmvc.jar. You need to add the following directive at the beginning of the JSP page:

<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>  

The form tag: It is a parent tag that contains all the other tags.

<form:form action="nextFormPath" modelAttribute=?abc?>  

This will generate an HTML form tag and exposes a binding path to inner tags.

The input tag: It generates an HTML input tag.

<form:input path="name" />  

It also provides other input types such as email, date, tel, etc.

For email:

<form:input type=?email? path="email" /> 

For date:

<form:input type=?date? path="date" />

The password tag: This tag generates an HTML tag with type=’password’.

<form:password path="password" />

The textarea tag: It generates an HTML textarea.

<form:textarea path="notes" rows="3" cols="20"/>

Number of rows and columns can be specified as required.

<form:checkbox path="receiveNewsletter" />

The above is applicable for a single checkbox whose return type is Boolean. After setting the value as true, the checkbox will be checked by default.

For Multiple Checkboxes:

Bird watching: <form:checkbox path="hobbies" value="Bird watching"/>
Astronomy: <form:checkbox path="hobbies" value="Astronomy"/>
Snowboarding: <form:checkbox path="hobbies" value="Snowboarding"/>

The radiobutton and radiobuttons tag: This will generate the HTML input tag with type=’radio’.

For Single Radiobutton:

Male: <form:radiobutton path="sex" value="M"/>
Female: <form:radiobutton path="sex" value="F"/>
For Multiple Radiobutton:
<form:radiobuttons path="sex" items="${sexOptions}" />

The select tag: This will generate the HTML select tag.

<form:select path="country" items="${countryItems}" />

The hidden tag: This will generate the HTML input tag with type=’hidden’.

<form:hidden path="id" value="12345" />

The option and options tag: This is used to select option from a drop-down option containing a list of elements.

To generate single option tag:
<form:option value="abc" label="xyz"/>  
To generate multiple option tag:
<form:options items="${elementList}" itemValue="abc" itemLabel="xyz"/> 

The errors tag: This is used to represent the HTML errors in the JSP page created by Validators.

<form:errors path="name" cssClass="error" />

Example of Validator in error tag:

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.");
    }
}

Form.jsp will 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>

The HTML file will 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>