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9. Example 07 – Form Tags

We will build and use the following form:

Image

Image

We will extend the concept of parameter injection seen for a text input field to other HTML elements in a form.

9.1. The NetBeans project

  • in [1], the project views [Formx.jsp]
  • in [2], the Struts configuration file and internationalized messages
  • in [3], the actions [Formx.java], and another Struts configuration file.

9.2. Struts Configuration

The [struts.xml] file is as follows:


<?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>
  <constant name="struts.custom.i18n.resources" value="messages" />
  
  <include file="example/example.xml"/>

  <package name="default" namespace="/" extends="struts-default">
    <default-action-ref name="index" />
    <action name="index">
      <result type="redirectAction">
        <param name="actionName">Form</param>
        <param name="namespace">/example</param>
      </result>
    </action>
  </package>
</struts>
  • Line 9: Includes another configuration file [example.xml]. This file configures the actions.
  • Lines 11–19: the default package. Defines a redirect address for the URL /. It will be redirected to the URL /example/Form.action.

The [example.xml] file that configures the actions is as follows:


<?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>
  <package name="example" namespace="/example" extends="struts-default">
    <action name="Form" class="example.Form">
      <result name="success">/example/Form.jsp</result>
    </action>
    <action name="Form1" class="example.Form1">
      <result name="success">/example/Form1.jsp</result>
    </action>
    <action name="Form2" class="example.Form2">
      <result name="success">/example/Form2.jsp</result>
    </action>
  </package>
</struts>
  • Lines 7–17: define the actions /example/Form, /example/Form1, /example/Form2, where /example is the namespace (line 7) and Formx are the actions.
  • lines 8-10: executing the Form action will display the /example/Form.jsp view.
  • lines 11-13: executing the Form1 action will display the /example/Form1.jsp view.
  • Lines 14–16: Executing the Form2 action will display the /example/Form2.jsp view.

9.3. Message files

We will not dwell on the internationalization of the project. We have already covered this in Example 01. We provide the contents of the [messages.properties] file so that the reader can understand the views that follow.


Form.francais=French
Form.english=English
Form.title=Struts 2 - Form Tags
Form.message=Struts 2 - form tags
Form.langues=langues
Form.textfield=1-textfield
Form.password=2-password
Form.textarea=3-textarea
Form.select1=4-select (multiple=false, size=1)
Form.select1.header=<-- select1 -->
Form.select2=5-select (multiple=false, size=3)
Form.select3=6-select (multiple=true, size=3)
Form.radio = 7-radio
Form.checkbox = 8-checkbox
Form.checkboxlist=9-checkboxlist
Form.hidden = 10 - hidden
Form.submitText = Submit
Form.buttonRazText=Reset
Confirmation.message=Confirm entered values
Confirmation.field=field
Confirmation.value=value
Confirmation.textfield=1-textfield
Confirmation.password=2-password
Confirmation.textarea=3-textarea
Confirmation.select1=4-select (multiple=false, size=1)
Confirmation.select2=5-select (multiple=false, size=3)
Confirmation.select3=6-select (multiple=true, size=3)
Confirmation.radio=7-radio
Confirmation.checkbox=8-checkbox
Confirmation.checkboxlist=9-checkboxlist
Confirmation.hidden=10-hidden

9.4. The [Form.jsp] view – input section

It looks like this:

Image

It is as follows:


<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
  <head>
    <title><s:text name="Form.title"/></title>
    <s:head/>
  </head>

  <body background="<s:url value="/resources/standard.jpg"/>">
    <h2><s:text name="Form.message"/></h2>
    <h3><s:text name="Form.langues"/></h3>
    <ul>
      <li>
        <s:url id="url" action="Form">
          <s:param name="request_locale">en</s:param>
        </s:url>
        <s:a href="%{url}"><s:text name="Form.english"/></s:a>
      </li>
      <li>
        <s:url id="url" action="Form">
          <s:param name="request_locale">fr</s:param>
        </s:url>
        <s:a href="%{url}"><s:text name="Form.francais"/></s:a>
      </li>
    </ul>
    <s:form name="form">
      <s:textfield name="textfield" key="Form.textfield" />
      <s:password name="password" key="Form.password"/>
      <s:textarea name="textarea" key="Form.textarea" cols="40" rows="5"/>
      <s:select name="select1" list="select1Values" size="1" key="Form.select1" headerValue="<-- select 1 -->" headerKey="-1" />
      <s:select name="select2" size="3" list="select2Values" key="Form.select2"/>
      <s:select name="select3" size="3" list="select3Values" key="Form.select3" multiple="true"/>
      <s:radio name="radio" list="radioValues" key="Form.radio"/>
      <s:checkbox name="checkbox" key="Form.checkbox"/>
      <s:checkboxlist name="checkboxlist" list="checkboxlistValues" key="Form.checkboxlist"/>
      <s:hidden name="hidden" key="Form.hidden"/>
      <s:submit key="Form.submitText" name="submitText"/>
    </s:form>
    <hr/>
 ...
  </body>
</html>
  • The form begins on line 26 and ends on line 38. On line 26, the `action` attribute is missing. This attribute specifies the action to which the form data will be posted. If the `action` attribute is missing, the data will be posted to the action that caused the view to be displayed, in this case the `[Form]` action.
  • Line 27: an input field. The key attribute specifies its label. The name attribute is the name of the parameter that will be posted. The string posted for this field will be in the form:

textfield=text_entered

The parameter name corresponds to a field in the [Form] action. The value of the text_saisi input field will be injected into the textfield field of the [Form] action. Conversely, if the [Form.jsp] view is displayed following the [Form] action, the value of the input field will be that of the textfield field in the [Form] action. This field is therefore used for both reading and writing. The [Form] class must have the getTextField and setTextField methods for this purpose.

This reasoning applies to all subsequent input tags. We will not repeat it.

  • Line 28: password entry. The string posted to the [Form] action will be in the form

password=entered_password

A password field with its get/set methods must exist in the [Form] action.

  • Line 29: Entering multi-line text in a 5-row, 40-column area. The string posted to the [Form] action will be in the form

textarea=input

A textarea field with its get/set methods must exist in the [Form] action.

  • line 30: a single-select dropdown list (size=1). Only one value from the list can be selected. The string posted to the [Form] action will be in the form:

select1=selected_value

A select1 field with its get/set methods must exist in the [Form] action.

The key attribute is the label of the list. The list attribute defines the list of values to be placed in the combo box. Here, the getSelect1Values method of the [Form] action will be called to populate the combo box. This method can return a collection, a dictionary, or an array. Here, it will return an array of strings [string1, string2, ...] which will generate the following HTML code:

<option value="string1">string1</option>

<option value="string2">string2</option>

...

The text between the <option>...</option> tags will be displayed in the combo box. The value attribute specifies the value to be posted if the option is selected by the user. Here, the value attribute and the text displayed in the combo box are identical. Most often, this is not the case. If the second option is selected, the following string will be posted to the [Form] action:

select1=string2

The [Form].select1 field will then receive the value string2. Conversely, if at the time the form is displayed, this field is set to string3, then visually, the third element

<option value="string3">string3</option>

will appear selected in the combo box.

The headerValue attribute sets the text to be displayed as the first option in the combo box, and headerKey sets the value to be submitted if this option is selected by the user.

  • Line 31: again, a list of size 3 (size=3): unlike the previous list where only one item is visible, here 3 items from the list will be visible. The selection mode remains the same. Only one item can be selected.
  • Line 32: another list, but this time with multiple selection (multiple=true). In this case, the value posted to the [Form] action will be in the form:

select3=string2&select3=string5

if the options string2 and string5 have been selected. When multiple values are posted for the same parameter—in this case, select3—the action must have a field with the parameter’s name and be of type array. So, for example, here the [Form] action could have a field like:

String[] select3;

and the corresponding get/set methods. The select3 array will then receive the array of character strings [string2, string5]. Conversely, when the [Form.jsp] view is displayed, the values of the [Form].select3 field determine which options in the select3 list will appear selected. This is always a read/write operation.

  • Line 33: a group of radio buttons. The group label is provided by the key attribute. The labels of the individual buttons are provided by the list attribute. The value of this attribute is the name of a method in the [Form] action that must return a collection, a dictionary, or an array. Here, the [Form].getRadioValues method will return an array of strings [string1, string2, ...] that will generate the following HTML tags:

<input type="radio" name="radio" ... value="string1"/>string1

<input type="radio" name="radio" ... value="string2"/>string2

...

If the radio button string2 is selected, the posted value will be

radio=string2

and this value will be inserted into the [Form].radio field.

  • Line 34: a checkbox. If checked, the following parameter string will be posted to the [Form] action

checkbox=true

If it is not checked, no parameter string is posted. Struts 2 has an internal mechanism that makes everything happen as if the string

checkbox=false

had been posted.

  • Line 35: a list of checkboxes. Multiple checkboxes can be selected. The group label is provided by the key attribute. The labels of the individual checkboxes are provided by the list attribute. The value of this attribute is the name of a method in the [Form] action that must return a collection, a dictionary, or an array. Here, the [Form].getCheckboxlistValues method will return an array of strings [string1, string2, ...] that will generate the following HTML tags:

<input type="checkbox" name="checkboxlist" ... value="string1"/>string1

<input type="checkbox" name="checkboxlist" ... value="string2"/>string2

...

If the user selects the checkboxes labeled string2 and string5, the following string will be posted to the [Form] action:

checkboxlist=string2&checkboxlist=string5

The array [string2, string5] will be assigned to the [Form].checkboxlist field, which must therefore be of the string array type, as with multiple-selection lists. Conversely, when the [Form.jsp] view is displayed, the values of the [Form].checkboxlist field determine which checkboxes will be checked.

  • Line 36: a hidden field. A hidden field is a field that is submitted without being entered by the user. Its value is set by the programmer. Here, the hidden field will take its value from the [Form].hidden field. This same value will be submitted in the form:

hidden=something

and reassigned to the [Form].hidden field.

  • Line 37: a submit button. Clicking this button will post all the form values to the [Form] action. The string of posted parameters will look like this:

textfield=text&password=&textarea=line1%0D%0Aline2%0D%0A&select1=zero&select2=three&select3=zero&select3=two&__multiselect_select3=&radio=blue&checkbox=true&__checkbox_checkbox=true&checkboxlist=v%C3%A9lo&checkboxlist=bus&__multiselect_checkboxlist=&hidden=initial&submitText=Validate

9.5. The [Form] action – input section

Its code is as follows:


package example;

import com.opensymphony.xwork2.ActionSupport;

public class Form extends ActionSupport {

  // constructor without parameters
  public Form() {
  }
  // form fields
  private String textfield = "text";
  private String password = "secret";
  private String textarea = "line1\nline2\n";
  private String select1 = "zero";
  private String[] select1Values = new String[]{"zero", "one", "two"};
  private String select2 = "three";
  private String[] select2Values = new String[]{"zero", "one", "two", "three", "four"};
  private String[] select3 = new String[]{"zero", "two"};
  private String[] select3Values = new String[]{"zero", "one", "two", "three", "four"};
  private String radio = "blue";
  private String[] radioValues = new String[]{"blue", "white", "red"};
  private Boolean checkbox = false;
  private String[] checkboxlist = new String[]{"bike", "bus"};
  private String[] checkboxlistValues = new String[]{"car", "tram", "bike", "bus", "subway"};
  private String hidden = "initial";
  private String submitText;

  // values selected in the select3 field
  public String getSelect3SelectedValues() {
    return getValue(select3);
  }

  // Values selected in the checkboxlist field
  public String getCheckboxListSelectedValues() {
    return getValue(checkboxlist);
  }

  // utility method
  public String getValue(String[] values) {
    String result = "";
    for (String value : values) {
      result += " " + value;
    }
    return result;
  }

// Field getters and setters
  ....
}
  • line 1: the field associated with the form's textfield tag. Used to initialize this input field as well as to retrieve its value. Receives the value entered in this field at the time of the POST request.
  • line 2: the field associated with the form's password tag. Receives the value entered in this field during the POST request.
  • line 13: associated with the form's textarea tag. Receives the text entered in this field during the POST request.
  • Line 14: Associated with the form’s `select1` tag, a single-select list. Its initial value selects an item from the dropdown. The item with a `value` attribute matching this value will be selected. Upon POST, receives the `value` attribute of the option selected in the dropdown.
  • Line 15: The character strings that will populate the select1 dropdown.
  • Lines 16 and 17: Same as select1
  • Line 18: associated with the form’s select1 tag, a multi-select list. The initial values in the array select the corresponding elements in the list. The elements whose value attribute matches one of these values will be selected. Upon POST, it receives the value attributes of the various options selected in the dropdown.
  • Line 19: the character strings that will populate the select3 list
  • Line 20: Associated with the form’s radio tag. Its value is used to select one of the radio buttons—the one whose value attribute matches this value. Receives the value of the selected radio button during the POST request.
  • Line 21: The various labels and values of the radio buttons.
  • Line 22: Associated with the form’s checkbox tag. Its initial value is used to check or uncheck the box. Upon POST, it receives the value true if the box was checked, false otherwise.
  • Line 23: Associated with the form’s checkboxlist tag. The initial values in the array select the corresponding checkboxes. The checkboxes whose value attribute matches one of these initial values will be checked. Upon POST, receives the value attributes of the various checked checkboxes.
  • Line 24: The strings that will populate the labels of the checkboxlist checkboxes.
  • line 25: associated with the hidden field. Its initial value sets the value of the hidden field. Upon POST, it will receive this same value because the user cannot modify it.
  • Line 26: Associated with the submit tag. During the POST request, it receives the button’s label. This field is optional.
  • The methods in lines 29, 34, and 39 will be discussed further below.

9.6. The [Form.jsp] view – Confirmation section

The [Form.jsp] view has a "Confirmation of entries" section that has not yet been covered:

Image

Its code is as follows:


<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
...
    <hr/>
    <h2><s:text name="Confirmation.message"/></h2>
    <table border="1">
      <tr>
        <th><s:text name="Confirmation.field"/></th>
        <th><s:text name="Confirmation.value"/></th>
      </tr>
      <tr>
        <td><s:text name="Form.textfield"/></td>
        <td><s:property value="textfield"/>
      </tr>
      <tr>
        <td><s:text name="Form.password"/></td>
        <td><s:property value="password"/>
      </tr>
      <tr>
        <td><s:text name="Form.textarea"/></td>
        <td><s:property value="textarea"/>
      </tr>
      <tr>
        <td><s:text name="Form.select1"/></td>
        <td><s:property value="select1"/>
      </tr>
      <tr>
        <td><s:text name="Form.select2"/></td>
        <td><s:property value="select2"/>
      </tr>
      <tr>
        <td><s:text name="Form.select3"/></td>
        <td><s:property value="select3SelectedValues"/>
      </tr>
      <tr>
        <td><s:text name="Form.radio"/></td>
        <td><s:property value="radio"/>
      </tr>
      <tr>
        <td><s:text name="Form.checkbox"/></td>
        <td><s:property value="checkbox"/>
      </tr>
      <tr>
        <td><s:text name="Form.checkboxlist"/></td>
        <td><s:property value="checkboxlistSelectedValues"/>
      </tr>
      <tr>
        <td><s:text name="Form.hidden"/></td>
        <td><s:property value="hidden"/>
      </tr>
    </table>
  </body>
</html>
  • Line 13: displays the value of the [Form].textfield field
  • line 17: displays the value of the [Form].password field
  • line 21: displays the value of the [Form].textarea field
  • line 25: displays the value of the [Form].select1 field
  • line 29: displays the value of the [Form].select2 field
  • Line 33: Displays the values of the [Form].select3 array. To do this, it uses the [Form].getSelect3SelectedValues method.
  • line 37: displays the value of the [Form].radio field
  • line 41: displays the value of the [Form].checkbox field
  • Line 45: Displays the values of the [Form].checkboxlist array. To do this, it uses the [Form].getCheckboxlistSelectedValues method.
  • Line 49: Displays the value of the [Form].hidden field

9.7. The [Form] action – confirmation section

The getSelect3SelectedValues and getCheckboxlistSelectedValues methods mentioned above are defined in the [Form] class:


  // selected values in the select3 field
  public String getSelect3SelectedValues() {
    return getValue(select3);
  }

  // values selected in the checkboxlist field
  public String getCheckboxListSelectedValues() {
    return getValue(checkboxlist);
  }

  // utility method
  public String getValue(String[] values) {
    String result = "";
    for (String value : values) {
      result += " " + value;
    }
    return result;
}

They simply concatenate the elements of the arrays they need to display.

9.8. Tests

When the NetBeans project is run, the following initial page is displayed:

The values displayed in [1] and [2] come from the initial values of the fields in the [Form] action. Let’s look at a few examples:


private String textarea = "line1\nline2\n";

The value of the textarea field explains the displays [1A] and [2A].


private String[] select3 = new String[]{"zero", "two"};
private String[] select3Values = new String[]{"zero", "one", "two", "three", "four"};

The value of the select3Values field explains the content of the list in [1B]. The value of the select3 field explains the selected items in [1B] and displayed in [2B].

If we enter other values in the form and submit it, the entered values will be posted to the corresponding fields of the [Form] action. Then, the [Form.jsp] view will be re-displayed. We are therefore in the same situation as before, except that the initial values have been replaced by the posted values. Here is an example:

Image

Image

9.9. The [Form1] action and the [Form1.jsp] view

The configuration file [example.xml] configures the following [Form1] action:


<?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>
  <package name="example" namespace="/example" extends="struts-default">
    <action name="Form" class="example.Form">
      <result name="success">/example/Form.jsp</result>
    </action>
    <action name="Form1" class="example.Form1">
      <result name="success">/example/Form1.jsp</result>
    </action>
    <action name="Form2" class="example.Form2">
      <result name="success">/example/Form2.jsp</result>
    </action>
  </package>
</struts>

Lines 11–13: The call to the [Form1] action generates the [Form1.jsp] view.

The [Form1] action is as follows:


package example;

import com.opensymphony.xwork2.ActionSupport;

public class Form1 extends ActionSupport{

  // constructor without parameters
  public Form1() {
  }
  // form fields
  private Data data = new Data();

  /**
   * @return the data
   */
  public Data getData() {
    return data;
  }

  /**
   * @param data the data to set
   */
  public void setData(Data data) {
    this.data = data;
  }
}

The [Form1] action is identical to the [Form] action, except that its model part has been moved to a separate class, the [Data] class, line 11. The [Data] class is as follows:


package example;

public class Data {

  // constructor without parameters
  public Data() {
  }
  
// form fields
  private String textfield = "text";
  private String password = "secret";
  private String textarea = "line1\nline2\n";
  private String select1 = "zero";
  private String[] select1Values = new String[]{"zero", "one", "two"};
  private String select2 = "three";
  private String[] select2Values = new String[]{"zero", "one", "two", "three", "four"};
  private String[] select3 = new String[]{"zero", "two"};
  private String[] select3Values = new String[]{"zero", "one", "two", "three", "four"};
  private String radio="blue";
  private String[] radioValues = new String[]{"blue", "white", "red"};
  private Boolean checkbox = false;
  private String[] checkboxlist = new String[]{"bike", "bus"};
  private String[] checkboxlistValues = new String[]{"car", "tram", "bike", "bus", "subway"};
  private String hidden = "initial";
  private String submitText;

  // Values selected in the select3 field
  public String getSelect3SelectedValues() {
    return getValue(select3);
  }

  // values selected in the checkboxlist field
  public String getCheckboxListSelectedValues() {
    return getValue(checkboxlist);
  }

  // utility method
  public String getValue(String[] values) {
    String result = "";
    for (String value : values) {
      result += " " + value;
    }
    return result;
  }

  // getters and setters
....

}

We find the fields previously declared in the [Form] action.

Quite logically, the [Form1.jsp] view is similar to the [Form.jsp] view:


<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
  <head>
    <title><s:text name="Form.title"/></title>
    <s:head/>
  </head>

  <body background="<s:url value="/resources/standard.jpg"/>">
    <h2><s:text name="Form.message"/></h2>
    <h3><s:text name="Form.langues"/></h3>
    <ul>
      <li>
        <s:url id="url" action="Form">
          <s:param name="request_locale">en</s:param>
        </s:url>
        <s:a href="%{url}"><s:text name="Form.english"/></s:a>
      </li>
      <li>
        <s:url id="url" action="Form">
          <s:param name="request_locale">fr</s:param>
        </s:url>
        <s:a href="%{url}"><s:text name="Form.francais"/></s:a>
      </li>
    </ul>
    <s:form name="form">
      <s:textfield name="data.textfield" key="Form.textfield" />
      <s:password name="data.password" key="Form.password"/>
      <s:textarea name="data.textarea" key="Form.textarea" cols="40" rows="5"/>
      <s:select name="data.select1" list="data.select1Values" size="1" key="Form.select1" headerValue="<-- select 1 -->" headerKey="-1" />
      <s:select name="data.select2" size="3" list="data.select2Values" key="Form.select2"/>
      <s:select name="data.select3" size="3" list="data.select3Values" key="Form.select3" multiple="true"/>
      <s:radio name="data.radio" list="data.radioValues" key="Form.radio"/>
      <s:checkbox name="data.checkbox" key="Form.checkbox"/>
      <s:checkboxlist name="data.checkboxlist" list="data.checkboxlistValues" key="Form.checkboxlist"/>
      <s:hidden name="data.hidden" key="Form.hidden"/>
      <s:submit key="Form.submitText" name="data.submitText"/>
    </s:form>
    <hr/>
    <h2><s:text name="Confirmation.message"/></h2>
    <table border="1">
      <tr>
        <th><s:text name="Confirmation.field"/></th>
        <th><s:text name="Confirmation.value"/></th>
      </tr>
      <tr>
        <td><s:text name="Form.textfield"/></td>
        <td><s:property value="data.textfield"/>
      </tr>
      <tr>
        <td><s:text name="Form.password"/></td>
        <td><s:property value="data.password"/>
      </tr>
      <tr>
        <td><s:text name="Form.textarea"/></td>
        <td><s:property value="data.textarea"/>
      </tr>
      <tr>
        <td><s:text name="Form.select1"/></td>
        <td><s:property value="data.select1"/>
      </tr>
      <tr>
        <td><s:text name="Form.select2"/></td>
        <td><s:property value="data.select2"/>
      </tr>
      <tr>
        <td><s:text name="Form.select3"/></td>
        <td><s:property value="data.select3SelectedValues"/>
      </tr>
      <tr>
        <td><s:text name="Form.radio"/></td>
        <td><s:property value="data.radio"/>
      </tr>
      <tr>
        <td><s:text name="Form.checkbox"/></td>
        <td><s:property value="data.checkbox"/>
      </tr>
      <tr>
        <td><s:text name="Form.checkboxlist"/></td>
        <td><s:property value="data.checkboxlistSelectedValues"/>
      </tr>
      <tr>
        <td><s:text name="Form.hidden"/></td>
        <td><s:property value="data.hidden"/>
      </tr>
    </table>
  </body>
</html>

The difference between the [Form] and [Form1] views can be illustrated by line 27 shown below:


<s:textfield name="data.textfield" key="Form.textfield" />

The input field is bound for both reading and writing to the data.textfield field of the [Form1] action. Recall that after execution, the properties of the [Form1] action are accessible to the view. Thus, the preceding name attribute will be evaluated as [Form1].getData().getTextField(). Therefore, the two preceding get methods must exist.

9.10. The [Form2] action and the [Form2.jsp] view

The configuration file [example.xml] configures the following [Form2] action:


<?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>
  <package name="example" namespace="/example" extends="struts-default">
    <action name="Form" class="example.Form">
      <result name="success">/example/Form.jsp</result>
    </action>
    <action name="Form1" class="example.Form1">
      <result name="success">/example/Form1.jsp</result>
    </action>
    <action name="Form2" class="example.Form2">
      <result name="success">/example/Form2.jsp</result>
    </action>
  </package>
</struts>

Lines 14–16: The call to the [Form2] action generates the [Form2.jsp] view.

The [Form2] action is as follows:


package example;

import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;

public class Form2 extends ActionSupport implements ModelDriven {

  // constructor without parameters
  public Form2() {
  }
  // action model
  public Object getModel() {
    return new Data();
  }
}
  • Line 6: The [Form2] action implements the [ModelDriven] interface. There is only one method to implement: the getModel method on line 12. This method returns an instance of the [Data] class discussed earlier.

The fact that the [Form2] action implements the [ModelDriven] interface has the following consequence: the view displayed following the [Form2] action has direct access to the properties of the [Form2] action’s model, which is returned by the getModel() method. Thus, the [Form2.jsp] view reverts to what it was with the initial [Form] action:


<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
  <head>
    <title><s:text name="Form.title"/></title>
    <s:head/>
  </head>

  <body background="<s:url value="/resources/standard.jpg"/>">
    <h2><s:text name="Form.message"/></h2>
    <h3><s:text name="Form.langues"/></h3>
    <ul>
      <li>
        <s:url id="url" action="Form">
          <s:param name="request_locale">en</s:param>
        </s:url>
        <s:a href="%{url}"><s:text name="Form.english"/></s:a>
      </li>
      <li>
        <s:url id="url" action="Form">
          <s:param name="request_locale">fr</s:param>
        </s:url>
        <s:a href="%{url}"><s:text name="Form.francais"/></s:a>
      </li>
    </ul>
    <s:form name="form">
      <s:textfield name="textfield" key="Form.textfield" />
      <s:password name="password" key="Form.password"/>
      <s:textarea name="textarea" key="Form.textarea" cols="40" rows="5"/>
      <s:select name="select1" list="select1Values" size="1" key="Form.select1" headerValue="<-- select 1 -->" headerKey="-1" />
      <s:select name="select2" size="3" list="select2Values" key="Form.select2"/>
      <s:select name="select3" size="3" list="select3Values" key="Form.select3" multiple="true"/>
      <s:radio name="radio" list="radioValues" key="Form.radio"/>
      <s:checkbox name="checkbox" key="Form.checkbox"/>
      <s:checkboxlist name="checkboxlist" list="checkboxlistValues" key="Form.checkboxlist"/>
      <s:hidden name="hidden" key="Form.hidden"/>
      <s:submit key="Form.submitText" name="submitText"/>
    </s:form>
    <hr/>
    <h2><s:text name="Confirmation.message"/></h2>
    <table border="1">
      <tr>
        <th><s:text name="Confirmation.field"/></th>
        <th><s:text name="Confirmation.value"/></th>
      </tr>
      <tr>
        <td><s:text name="Form.textfield"/></td>
        <td><s:property value="textfield"/>
      </tr>
      <tr>
        <td><s:text name="Form.password"/></td>
        <td><s:property value="password"/>
      </tr>
      <tr>
        <td><s:text name="Form.textarea"/></td>
        <td><s:property value="textarea"/>
      </tr>
      <tr>
        <td><s:text name="Form.select1"/></td>
        <td><s:property value="select1"/>
      </tr>
      <tr>
        <td><s:text name="Form.select2"/></td>
        <td><s:property value="select2"/>
      </tr>
      <tr>
        <td><s:text name="Form.select3"/></td>
        <td><s:property value="select3SelectedValues"/>
      </tr>
      <tr>
        <td><s:text name="Form.radio"/></td>
        <td><s:property value="radio"/>
      </tr>
      <tr>
        <td><s:text name="Form.checkbox"/></td>
        <td><s:property value="checkbox"/>
      </tr>
      <tr>
        <td><s:text name="Form.checkboxlist"/></td>
        <td><s:property value="checkboxlistSelectedValues"/>
      </tr>
      <tr>
        <td><s:text name="Form.hidden"/></td>
        <td><s:property value="hidden"/>
      </tr>
    </table>
  </body>
</html>

So line 27, which was previously:


<s:textfield name="data.textfield" key="Form.textfield" />

becomes:


<s:textfield name="textfield" key="Form.textfield" />

The advantage of placing the model outside the view is that this architecture more clearly delineates the functionalities of each element of the MVC architecture. The M model is clearly identified by a class. Furthermore, the model may exist prior to the actions. Thus, if a web application manages a database of people, it is likely that the Person class exists. If an action provides an input form to create a new person, the model for this action is obvious: it is the Person class.

We saw how simple it was to switch from the [Form] action to the [Form2] action:

  • the model M of the view V has been encapsulated in a separate class
  • the action that generates the view using this model implements the ModelDriven interface with the getModel method, which returns an instance of the model M. The action can then be viewed as an extension of the Struts 2 controller C, the FilterDispatcher class.

The reader can apply this approach to any action described below.

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This tutorial written by Serge Tahé is made available to the public under the terms of the Creative Commons Attribution – Non-Commercial – ShareAlike 3.0 Unported.