Getting checkbox values from HTML form in Servlet

Environment Used

• JDK 6 (Java SE 6)
• Eclipse Indigo IDE for Java EE Developers (3.7.1)
• Apache Tomcat 6.x
• Java EE 5 API (Servlet 2.5)
• [Optional] For monitoring and analyzing HTTP headers between the browser and web servers, you can use one of these add-ons of Firefox
  • Live HTTP Headers
  • HttpFox

Setting up development environment

If you are new to developing Servlet with Tomcat and Eclipse, you can read this page before proceeding with this example.

Sending multiple values for single parameter

• If the same parameter name appears in the form data more than once, we use getParameterValues (which returns an array of strings) instead of getParameter (which returns a single string corresponding to the first occurrence of the parameter).
  • The <input type=”checkbox”> and <select> allows user to select more than one option.
• The return value of getParameterValues() is null for nonexistent parameter names or none of the choices are selected.
• It is a one-element array when the parameter has only a single value.

HTML Form

Servlet Code

Method signature:

String[] getParameterValues(String name)

• Returns an array of String objects containing all of the values the given request parameter has, or null if the parameter does not exist.
• For Servlets, parameters are contained in the query string (GET request) or request body (POST request).
• This method should be used for the parameter which may have more than one value.
• If the parameter has a single value, the array has a length of 1.

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 				
	xsi:schemaLocation=
	"http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
	id="WebApp_ID" version="2.5">
  <servlet>
    <servlet-name>MultipleValuesSingleParam</servlet-name>
    <servlet-class> 
	com.ibc.multiplevalues.MultipleValuesSingleParamServlet
    </servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>MultipleValuesSingleParam</servlet-name>
    <url-pattern>/multiplevalues.do</url-pattern>
  </servlet-mapping>
</web-app>

Project Folder Structure

The complete directory structure of this project is shown below.

Output

Program Control Flow

• Web client (browser) requests the server/container for the HTML file (multiplevalues.html) through request URL.
• Container responses with the actual content of HTML file along with HTTP response headers.
• When the user submits the form, web client sends request to the Servlet along with form data in the body of HTTP header since it is a POST request.
• Servlet processes the form parameters and responds with the actual HTML content.

The content of HTTP request and response headers can be monitored using browser add-ons such as Live HTTP Headers, HttpFox, etc

Sample HTTP request and response headers using these add-ons is shown below.

HTTP Request

http://localhost:8080/ReqAndResChapter4/multiplevalues.html GET /ReqAndResChapter4/multiplevalues.html HTTP/1.1 Host: localhost:8080 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-gb,en;q=0.5 Accept-Encoding: gzip,deflate Connection: keep-alive ….. …..

HTTP Response

HTTP/1.1 200 OK Server: Apache-Coyote/1.1 Accept-Ranges: bytes Content-Type: text/html Content-Length: 816 Content: HTML Form (multiplevalues.html) …

HTTP Request

Form parameter in Request body, since it is a POST request.

HTTP Response

To develop and run this example with Tomcat and Eclipse, refer this page.