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# Using Tags

This tutorial assumes you’ve completed the Hello World tutorial and have a working helloworld project. The example code for this tutorial, using-tags, is available for checkout from the Struts 2 GitHub repository at struts-examples. The example projects use Maven to manage the artifact dependencies and to build the .war files.

In the Hello World lesson, we added a Struts 2 url tag to the `index.jsp` to create a hyperlink to the `hello.action`. This tutorial will explore the url and other Struts 2 tags further.

Web applications differ from conventional websites in that web applications can create a dynamic response. To make it easier to reference dynamic data from a page, the Struts 2 framework offers a set of tags. Some of the tags mimic standard HTML tag while providing added value. Other tags create non-standard, but useful controls.

To use the Struts 2 tags on the view page, you must include a tag library directive. Typically, the taglib directive is `<%@ taglib prefix="s" uri="/struts-tags" %>`. So the prefix for all the Struts 2 tags will be `s`. If you want to actually read the Struts 2 tag TLD file, you’ll find it in the `META-INF` folder of the Struts 2 core jar.

## Struts 2 url Tag

One use of the Struts 2 Tags is to create links to other web resources, especially to other resources in the local application.

While HTML provides a simple a tag for creating hyperlinks, the HTML tag often requires us to include redundant information. Also the HTML tag cannot easily access dynamic data provided by the framework.

A very common use case in web applications is linking to other pages. In the Hello World tutorial we added a link to `hello.action` inside the `index.jsp` using the Struts 2 url tag. Please refer to the url documentation for more information about the url tag.

index.jsp

    <!DOCTYPE html>
    <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
    <%@ taglib prefix="s" uri="/struts-tags" %>
    <html>
      <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Basic Struts 2 Application - Welcome</title>
      </head>
      <body>
        <h1>Welcome To Struts 2!</h1>
        <p><a href="<s:url action='hello'/>">Hello World</a></p>
      </body>
    </html>

When you run the Hello World tutorial in your Servlet container and then mouse over the Hello World hyperlink created by the Struts 2 url tag you’ll see that the URL created is `hello.action` (relative to the web context’s root folder).

Examine the `struts.xml` configuration in the Hello World tutorial and you will find this:

struts.xml

    ...
    <action name="hello" class="org.apache.struts.helloworld.action.HelloWorldAction" method="execute">
        <result name="success">/HelloWorld.jsp</result>
    </action>
    ...

The action node above maps the `hello.action` to the execute method of class `HelloWorldAction`. If the execute method returns `success`, the view page `HelloWorld.jsp` (in web context root folder) will be returned to the user.

A common use case is that the URL also needs to include a value for a query string parameter such as userName. To add a query string parameter and its value use the Struts 2 param tag, nested inside the url tag.

For the Using Tags tutorial add the following to `index.jsp` just after the link for Hello World.

url tag with param

    ...
    <s:url action="hello" var="helloLink">
      <s:param name="userName">Bruce Phillips</s:param>
    </s:url>

    <p><a href="${helloLink}">Hello Bruce Phillips</a></p>
    ...

Rather than put the url tag as the value for the anchor tag’s href attribute, we’ve separated out the s:url tag into its own code block. Nested inside the url tag is the Struts 2 param tag. This tag lets you specify a parameter name ( e.g. userName) and a value for that parameter (e.g. Bruce Phillips).

Notice the use of the var attribute. The value of the var attribute is a reference we can use later in our code to refer to the url created.

Examine the anchor tag above. Notice the value of the href attribute is `${helloLink}`. The view page will substitute the hyperlink we created using the url tag for the `${helloLink}` reference. Note that the query string parameter will be properly URL-encoded (`Bruce+Phillips`).

In the next tutorial we’ll cover how Struts can access the query string parameter value.

## Struts 2 Form Tag

Most applications will use several data entry forms. The Struts 2 tags make creating input forms easy. Consult the Form Tags Reference for all the details about the Struts 2 form tags.

Each of the Struts 2 form tags has numerous attributes to mimic the normal HTML form tag attributes.

To create the outer shell of the form, use the Struts 2 form tag. The action attribute sets the action name to submit to.

Add the following markup to `index.jsp` after the Hello Bruce Phillips link.

Struts 2 Form

    <p>Get your own personal hello by filling out and submitting this form.</p>

    <s:form action="hello">
      <s:textfield name="userName" label="Your name" />
      <s:submit value="Submit" />
    </s:form>

The Struts 2 textfield tag provides an input html tag of tag text and the submit tag creates a submit button. When the index page is returned by the server to the browser you should see:

The Struts form, textfield, and submit tags were converted to this HTML.

Struts Form Tags Converted To HTML

    <form id="hello" name="hello" action="/using-tags/hello.action;jsessionid=6233ot11na1mtshbr292hu1w" method="post">
      <table class="wwFormTable">
        <tr>
          <td class="tdLabel"><label for="hello_userName" class="label">Your name:</label></td>
          <td class="tdInput"><input type="text" name="userName" value="" id="hello_userName"/></td>
        </tr>
        <tr>
          <td colspan="2">
            <div class="formButton">
              <input type="submit" value="Submit" id="hello_0"/>
            </div>
          </td>
        </tr>
      </table>
    </form>

Note how Struts 2 created a table inside the form to position the form elements. In later tutorials you’ll learn how to specify the layout (table, CSS). The Struts 2 textfield tag created an HTML input tag of type text with a name value that matches the name value of the textfield tag. Struts 2 also created a label HTML tag based on the label value of the textfield tag.

In the next tutorial we’ll cover how to use Struts 2 to process this form submission.

## Struts 2 property tag

In the Hello World tutorial’s example application on JSP `HelloWorld.jsp` was this code:

Struts Property Tag

    <s:property value="messageStore.message" />

The most common use of the property tag is to “get” the value returned by calling a public get method (of the Action class) and then to include that value in the HTML returned to the browser.

As discussed in the Hello World tutorial, the value of `messageStore.message` instructs Struts 2 to first call method `getMessageStore` of the Action class. That method call returns a `MessageStore` object. The `.message` part instructs Struts 2 to call the `getMessage` method of the `MessageStore` object. The `getMessage` method returns a String which will be included in the HTML returned to the browser.

One very useful feature of the Struts 2 property tag is that it will automatically convert the most common data types (int, double, boolean) to their String equivalents. To demonstrate this feature let’s add a static int variable to class `HelloWorldAction`.

Add Static Field

    private static int helloCount = 0;

    public int getHelloCount() {
        return helloCount;
    }

Each time the execute method is called we’ll increase `helloCount` by 1. So add this code to the `execute` method of the `HelloWorldAction` class.

Increase helloCount

    helloCount++;

Whenever a user clicks one of the links on the page index.jsp (or submits the form), method `execute` of class `HelloWorldAction` will be run and the static field `helloCount` will be increased by 1.

To include the value of the `helloCount` attribute in the `HelloWorld.jsp` we can use the Struts 2 property tag. Add the following to `HelloWorld.jsp` after the h2 tag.

Use Property Tag To Display helloCount Value

    <p>I've said hello <s:property value="helloCount" /> times!</p>

So even though the `getHelloCount` method returns an integer type, Struts 2 converted it to type String and placed it into the body of the p tag.

Note that even though `helloCount` is a static field, the get method for `helloCount` is not static. For Struts 2 to call the `getHelloCount` method to get the value of `helloCount`, the `getHelloCount` method cannot be static.

If the value returned by the get method is an object, then the property tag will cause Struts 2 to call the object’s `toString` method. Of course, you should always override Class Object’s `toString` method in your model classes. Add the following `toString` method to the `MessageStore` class:

Add toString Method To Class MessageStore

    public String toString() {
        return message + " (from toString)";
    }

Add the following to `HelloWorld.jsp`

Using Property Tag to Call toString

    <p><s:property value="messageStore" /></p>

Since `getMessageStore` of `HelloWorldAction` class returns a `MessageStore` object, Struts 2 will call the `toString` method of class `MessageStore`. The string returned by that `toString` method will be displayed in the browser.

We covered a lot in this tutorial, but we’ve really only scratched the surface of how to use the Struts 2 tags. Consult the Struts 2 Tag Reference for much more information about all the Struts 2 tags.

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