before this we have used request.getParameter(String) which is used to get a single request parameter value.
Now if we want to get all parameter names then we have to use request.getParameterNames()
it returns Enumeration of String objects of all parameter names.
After getting all parameter names we can get its value using request.getParameter(String) .
request.getParameterNames() is useful we have large number of parameters are used in request.
Following example is used to explain the above concepts.

Project Explorer:

index.jsp

&lt;%@page contentType="text/html" pageEncoding="UTF-8"%&gt;

1	<%@page contentType="text/html" pageEncoding="UTF-8"%>

Getting all parameters in servlet

AllSerlvet.java

package com.ebhor.servletparameters;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "AllParameters", urlPatterns = {"/allparameters"})
public class AllParameters extends HttpServlet {

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("");
        out.println("");
        out.println("");
        out.println("");
        out.println("");
        out.println("");
        try {
            Enumeration parameterNames = request.getParameterNames();
            while (parameterNames.hasMoreElements()) {
                String parameterName = parameterNames.nextElement();
                String value = request.getParameter(parameterName);
                System.out.println("parameter name is " + parameterName);
                out.println("Parameter name is  <b>" + parameterName + "</b>  value is <b> " + value + "</b>
");
            }

            out.println("");
            out.println("");
        } finally {
            out.close();
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
}

package com.ebhor.servletparameters;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.Enumeration;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "AllParameters", urlPatterns = {"/allparameters"})

public class AllParameters extends HttpServlet {

protected void processRequest(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html;charset=UTF-8");

PrintWriter out = response.getWriter();

out.println("");

try {

Enumeration parameterNames = request.getParameterNames();

while (parameterNames.hasMoreElements()) {

String parameterName = parameterNames.nextElement();

String value = request.getParameter(parameterName);

System.out.println("parameter name is " + parameterName);

out.println("Parameter name is <b>" + parameterName + "</b> value is <b> " + value + "</b>

");

}

out.println("");

} finally {

out.close();

}

@Override

protected void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

processRequest(request, response);

}

@Override

protected void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

processRequest(request, response);

}

pom.xml

    4.0.0

    com.ebhor
    ServletParameters
    1.0-SNAPSHOT
    war

    ServletParameters

    
        ${project.build.directory}/endorsed
        UTF-8
    

    
        
            javax
            javaee-web-api
            6.0
            provided
        
    

    
        
            
                org.apache.maven.plugins
                maven-compiler-plugin
                2.3.2
                
                    1.6
                    1.6
                    
                        ${endorsed.dir}
                    
                
            
            
                org.apache.maven.plugins
                maven-war-plugin
                2.1.1
                
                    false
                
            
            
                org.apache.maven.plugins
                maven-dependency-plugin
                2.1
                
                    
                        validate
                        
                            copy
                        
                        
                            ${endorsed.dir}
                            true
                            
                                
                                    javax
                                    javaee-endorsed-api
                                    6.0
                                    jar

4.0.0

com.ebhor

ServletParameters

1.0-SNAPSHOT

war

ServletParameters

${project.build.directory}/endorsed

UTF-8

javax

javaee-web-api

6.0

provided

org.apache.maven.plugins

maven-compiler-plugin

2.3.2

1.6

${endorsed.dir}

org.apache.maven.plugins

maven-war-plugin

2.1.1

false

org.apache.maven.plugins

maven-dependency-plugin

2.1

validate

copy

${endorsed.dir}

true

javax

javaee-endorsed-api

6.0

jar

Result: