Showing all request header in servlet

This tutorial will find the read request header name and values in the servlet.

There are many requests headers present like:

host, connection, user-agent, cookie, etc.

In the below project, we read the request project header names and values.

Technology User

apache-tomcat-9.0.71
javaee-web-api 7.0

Java 1.8

Steps to develop this project

Create a Java with Maven -> Web application project
Give Project Name
Create package com.ebhor.servletheaderes
Create a Servlet with name Header.java
Build and run the project

Creating a project

Assign project name ServletHeader

Project Explorer

Following is the project explorer window for this project.

Inside the source package, all packages and files are kept.

Web Pages are used to store jsp and other files

pom.xml is available in Project Files.

Servlet Header Request page-index.jsp

<!DOCTYPE html>
<html>
    <head>
        <title>Index Page</title>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    </head>
    <body>
        <h1>Servlet Header Example</h1>
        <a href="header">Get Headers</a>
    </body>
</html>

<!DOCTYPE html>

<html>

<head>

<title>Index Page</title>

</head>

<body>

<h1>Servlet Header Example</h1>

<a href="header">Get Headers</a>

</body>

</html>

Servlet header processing -Header.java

On clicking on the header URL it will call header.java servlet.

This will be called by HTTP get request and doGet() method of servlet is get called.

To access all header information request.getHeaderNames() method is used.

This method will return the Enumeration of all header names.

By iterating header enumeration we can get the values of each header.

Here a single request header host is also read in the program, then after all request headers are read.

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 = "Header", urlPatterns = {"/header"})
public class Header extends HttpServlet {
    private static final long serialVersionUID = 1L;
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String hostValue = request.getHeader("host");
        out.println("<h3>Printing a single header</h3>");
        out.println("Header name  <b>host </b> value <b>" + hostValue + "</b>");
        Enumeration<String> headerNames = request.getHeaderNames();
        out.println("<h3>Printing all headers</h3>");
        while (headerNames.hasMoreElements()) {
            String headerName = headerNames.nextElement();
            String headerValue = request.getHeader(headerName);
            out.println("Header name <b>" + headerName + "</b> value <b>" + headerValue + "</b><br/>");
        }
    }
}

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 = "Header", urlPatterns = {"/header"})

public class Header extends HttpServlet {

private static final long serialVersionUID = 1L;

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

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

PrintWriter out = response.getWriter();

String hostValue = request.getHeader("host");

out.println("<h3>Printing a single header</h3>");

out.println("Header name <b>host </b> value <b>" + hostValue + "</b>");

Enumeration<String> headerNames = request.getHeaderNames();

out.println("<h3>Printing all headers</h3>");

while (headerNames.hasMoreElements()) {

String headerName = headerNames.nextElement();

String headerValue = request.getHeader(headerName);

out.println("Header name <b>" + headerName + "</b> value <b>" + headerValue + "</b><br/>");

}

Project Configuration file -pom.xml

This is a Maven configuration file used to configure dependencies and used to build projects.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.ebhor</groupId>
    <artifactId>ServletHeaders</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>ServletHeaders</name>
    <properties>
        <endorsed.dir>${project.build.directory}/endorsed</endorsed.dir>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    
    <dependencies>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-web-api</artifactId>
            <version>7.0</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                    <compilerArguments>
                        <endorseddirs>${endorsed.dir}</endorseddirs>
                    </compilerArguments>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.3</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>2.6</version>
                <executions>
                    <execution>
                        <phase>validate</phase>
                        <goals>
                            <goal>copy</goal>
                        </goals>
                        <configuration>
                            <outputDirectory>${endorsed.dir}</outputDirectory>
                            <silent>true</silent>
                            <artifactItems>
                                <artifactItem>
                                    <groupId>javax</groupId>
                                    <artifactId>javaee-endorsed-api</artifactId>
                                    <version>7.0</version>
                                    <type>jar</type>
                                </artifactItem>
                            </artifactItems>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

<?xml version="1.0" encoding="UTF-8"?>

<groupId>com.ebhor</groupId>

<artifactId>ServletHeaders</artifactId>

<version>1.0-SNAPSHOT</version>

<name>ServletHeaders</name>

<endorsed.dir>${project.build.directory}/endorsed</endorsed.dir>

<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

</properties>

<groupId>javax</groupId>

<artifactId>javaee-web-api</artifactId>

<scope>provided</scope>

</dependency>

</dependencies>

<build>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

<endorseddirs>${endorsed.dir}</endorseddirs>

</compilerArguments>

</configuration>

</plugin>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-war-plugin</artifactId>

<failOnMissingWebXml>false</failOnMissingWebXml>

</configuration>

</plugin>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-dependency-plugin</artifactId>

<phase>validate</phase>

<goals>

</goals>

<outputDirectory>${endorsed.dir}</outputDirectory>

<groupId>javax</groupId>

<artifactId>javaee-endorsed-api</artifactId>

</artifactItem>

</artifactItems>

</configuration>

</execution>

</executions>

</plugin>

</plugins>

</build>

</project>

Result

Index page requesting to get all request header.

First, a host request header is read by its value.

consequently, all request headers are read with values.

Showing all request headers in servlet

for this we have created a JSP file that is not shown in the above project explorer.

You can use any jsp page for this.

code is as below

<%@page import="java.util.Enumeration"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
	pageEncoding="utf-8"%>
<!DOCTYPE html>
<html>
<head>
<title>Servlet Request Headers</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link
	href="https://cdn.jsdelivr.net/npm/bootstrap@5.2.3/dist/css/bootstrap.min.css"
	rel="stylesheet">
<script
	src="https://cdn.jsdelivr.net/npm/bootstrap@5.2.3/dist/js/bootstrap.bundle.min.js"></script>
</head>
<body>
	<div class="container mt-3">
		<h2>Printing All Request Header</h2>

		<table class="table table-striped">
			<thead>
				<tr>
					<th>Sr No</th>
					<th>Header Name</th>
					<th>Header Value</th>
				</tr>
			</thead>
			<tbody>
				<%
				int i = 1;
				Enumeration<String> headerNames = request.getHeaderNames();
				while (headerNames.hasMoreElements()) {
					String headerName = headerNames.nextElement();
					String headerValue = request.getHeader(headerName);
				%>
				<tr>
					<td><%=i++%></td>
					<td><%=headerName%></td>
					<td><%=headerValue%></td>

				</tr>
				<%
				}
				%>
			</tbody>
		</table>
	</div>

</body>
</html>

</body>
</html>

<%@page import="java.util.Enumeration"%>

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"

pageEncoding="utf-8"%>

<!DOCTYPE html>

<html>

<head>

<title>Servlet Request Headers</title>

<link

href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css"

rel="stylesheet">

<script

src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js"></script>

</head>

<body>

<h2>Printing All Request Header</h2>

<thead>

<tr>

<th>Header Name</th>

<th>Header Value</th>

</tr>

</thead>

<tbody>

int i = 1;

Enumeration<String> headerNames = request.getHeaderNames();

while (headerNames.hasMoreElements()) {

String headerName = headerNames.nextElement();

String headerValue = request.getHeader(headerName);

<tr>

</tr>

}

</tbody>

</table>

</div>

</body>

</html>

</body>

</html>

Result

Sending data to servlet using http get method
Submitting data to servlet using http post
Getting parameter values in Servlet getParameterNames
Servlet Annotation WebServlet Example
Servlet url and class mapping using web.xml
Employee Management System Project JSP Servlet

Steps to develop this project

Project Explorer

Servlet header processing -Header.java

Project Configuration file -pom.xml

Result

Showing all request headers in servlet

Read More