Struts 2 > Home > Tutorials > Step by Step > Understanding Actions |

Struts 2
Understanding Actions
Edit Page Browse Space Add Page Add News
Added by victorsosa, last edited by Ted Husted on Aug 25, 2006 (view change)

In the Hello World lesson, we implemented a use case that displayed a message with a dynamic timestamp. In this lesson, we create a workflow that displays input from a data-entry form.

The form will ask for your name. If you enter "Zaphod" and click the submit button, the page will display "Hello, Zaphod!". If you don't enter a name, the page will display: "Hmmm, you did not enter a name. Please try again!"

## HTML Form With Data, Using Getters and Setters

In the Hello World lesson, there were three components: the Action class, the result page, and the action mapping. In this lesson, we will add a fourth component: an input form.

### Create a HTML input form

The framework includes a library of special tags that you can use to write dynamic forms, but "plain old HTML" forms work just fine too.

HelloName.html

    <html>
    <head>
        <title>A simple HTML form with data</title>
    </head>
    <body>
        <p>What is your name?</p>

        <form action="HelloName.action" method="post">
            <p><input type="text" name="name"></p>
            <p><input type="submit" value="Submit your name." /></p>
        </form>

    </body>
    </html>

### Create the Action class

The HTML form submits an attribute called "name", and the Action class provides a corresponding JavaBean property.

HelloName.java

    package tutorial;

    import com.opensymphony.xwork2.ActionSupport;

    public class HelloName extends ActionSupport {

        public String execute() throws Exception {
            if (getName() == null || getName().length() == 0)
                return ERROR;
            else
                return SUCCESS;
        }

        private String name;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }
    }

### Create the action mapping

We can just add a new action mapping to the file we started in the Hello World lesson.

struts.xml

    <!DOCTYPE struts PUBLIC
        "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
        "http://struts.apache.org/dtds/struts-2.0.dtd">

    <struts>
      <include file="struts-default.xml" />
        <package name="actions" extends="struts-default">

            <action name="HelloName" class="tutorial.HelloName">
                <result name="success">HelloName-success.jsp</result>
                <result name="error">HelloName-error.html</result>
            </action>

        </package>
    </struts>

### Create the success and error pages

The Action can select between two outcomes, "success" and "failure".

HelloName-success.jsp

    <%@ taglib prefix="s" uri="/struts-tags" %>
    <html>
    <head>
        <title>Success Page</title>
    </head>
    <body>
        <p>
          Hello, <s:property value="name" />!
        </p>
    </body>
    </html>

HelloName-error.html

    <html>
    <head>
        <title>Error Page</title>
    </head>
    <body>
        <p>
            Hmmm, you did not enter a name. Please try again!
        </p>
    </body>
    </html>

### Try it!

If you are coding along, go ahead and try your form now. Open the input page (http://localhost:8080/tutorial/HelloName.html), and click the submit button to see what happens. Try it with and without entering a name.

| Don't forget! Compile your Action to `WEB-INF/classes` and restart your container if necessary.

### How the code works

There are two differences between this example and the previous Hello World lesson.

1. When the Action is called, `setName` is passed the contents of the `name` form field.
2. When the Action's `execute` method returns, the framework has two options. If the string "error" returns, the framework will select `HelloName-error.html` as the result. If the string "success" returns, then `HelloName-success.jsp` is selected.

Let's try a slightly different approach to solve the same use case.

## HTML Form With Data, Without Using Getters and Setters

In our first form, we needed to capture the field `name`. To do that, we added the getters and setters `getName` and `setName` to the Action class, as well as the private variable `name`. A larger application with dozens of forms and hundreds of form fields could need several hundred getters and setters. Let's try that same use case again, but without the JavaBean methods.

### Create the HTML form

Let's use the same HTML form, but change the form Action to `HelloName2.action`:

HelloName2.html

    <html>
    <head>
      <title>A simple form with data</title>
    </head>
    <body>
        <p>What is your name?</p>

        <form action="HelloName2.action" method="post">
            <p><input type="text" name="name"></p>
            <p><input type="submit" value="Submit your name." /></p>
        </form>
    </body>
    </html>

### Create the Action class

HelloName2.java

    package tutorial;

    import com.opensymphony.xwork2.ActionSupport;
    import org.apache.struts2.interceptor.ParameterAware;
    import java.util.Map;

    public class HelloName2 extends ActionSupport implements ParameterAware {

        public static String NAME = "name";

        public String execute() {
            String[] name = (String[]) parameters.get(NAME);
            if (name == null || name[0] == null || name[0].length() == 0)
                return ERROR;
            else
                return SUCCESS;
        }

        Map parameters;

        public Map getParameters() {
            return parameters;
        }

        public void setParameters(Map parameters) {
            this.parameters = parameters;
        }
    }

### Create the action mapping

struts.xml

    <?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE struts PUBLIC
            "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
            "http://struts.apache.org/dtds/struts-2.0.dtd">
    <struts>
        <include file="struts-default.xml"/>
        <package name="actions" extends="struts-default">

            <action name="HelloName" class="tutorial.HelloName">
                <result name="success">/HelloName-success.jsp</result>
                <result name="error">HelloName-error.html</result>
            </action>

            <action name="HelloName2" class="tutorial.HelloName2">
                <result name="success">HelloName2-success.jsp</result>
                <result name="error">HelloName-error.html</result>
            </action>

        </package>
    </struts>

### Create the success and error pages

We can use the same error page, but we'll need a slightly different success page `HelloName2-success.jsp`. The only difference is the `<s:property>` tag.

HelloName2-success.jspl

    <%@ taglib prefix="s" uri="/tags" %>
    <html>
    <head>
        <title>Success Page - Without Using Getters and Setters</title>
    </head>

    <body>
    <p>
        Hello, <s:property value="parameters.name"/>!
    </p>
    </body>
    </html>

### Try it!

Go ahead and try it now. Load (http://localhost:8080/tutorial/HelloName2.html), enter "Zaphod" in the text field, and click the form `submit` button. You should see `HelloName2-success.jsp` saying "Hello, Zaphod!"

| Don't forget! Compile your Action to `WEB-INF/classes` and restart your container if necessary.

## How the code works

Instead of a setter `setName` accessing a private variable `name` in the Action class, `setParameters` magically extracts everything from the `request` object and puts the attributes into a private local Map, `parameters`. In the `execute` method, we can get the value from the `parameters` Map instead of looking for a `name` property. So far so good.

Back on the `HelloName2-success.jsp` page, `<s:property value="name" />` isn't going to work any more, because there is no `getName()` method in the Action. Instead, `<s:property value="parameters.name" />` calls the `getParameters` method, and is able to get the value of the "name" field. Pretty neat!

## Summary

Before processing an Action, the framework matches any Action properties with request attributes. If a match is found, the attribute value is set to the Action property. The Action can process the value, and the Struts tags can present the value too. Rather than define a separate property for each attribute, you can define a single Map property instead. In that case, all the request attributes will be set to the Map automatically.

Next | Onward to Understanding Results
Prev | Return to Hello World