Http Request Headers

To get client browser information :
String client = request.getHeader("User-Agent");

To get content length :
String content = request.getHeader("Content-Length");

To get router hops allowed for request :
String maxForwards = request.getHeader("Max-Forwards");

To get accepted encoding details :
String encoding = request.getHeader("Accept-Encoding");

To get language details :
String language = request.getHeader("Accept-Language");

To get content-type or mime type details :
String mime = request.getHeader("Accept");

To get character set details :
String characterSet = request.getHeader("Accept-Charset");

To get connection status :
String status = request.getHeader("Connection");

Can I map multiple URLs to single servlet?

Yes, We can map multiple urls to a single servlet.
Here i am providing the three ways :

First : By giving another servlet-mapping entry like:
Second : By giving two different name entries for single servlet

   

Three : By giving another url-pattern in servlet mapping but in not support in all servers

  

TCP (Transmission Control Protocol)

TCP is a 16-bit port number used to identify a specific software program on the server hardware.
Port numbers starts from 0 to 65535 and in this 0 to 1023 are reserved for well known services.

Some import port numbers:
  21 - FTP (File Transfer Protocol)
  23 - Telnet
  25 - SMTP (Simple Mail Transfer Protocol)
  37 - Time
  80 - HTTP (Hyper Text Transfer Protocol)
110 - POP2 (Post Office Protocol 2)
443 - HTTPS (Hypertext Transfer Protocol Secure)

Java : Best way to declare a static list constant

public class MyListConstant {

      public static final List CONSTANT = Collections.unmodifiableList(getConstant());

      private static List getConstant() {

            List constant1 = new ArrayList();

            constant1.add("a");

            constant1.add("b");

            constant1.add("c");

            constant1.add("d");

            return constant1;

      }

}

Note:

1. It is better to use Array constants instead of list constants.
2. List constant need to be created with unmodifiableList method otherwise it will modified with its set method.

CONSTANT.set(1, "replaced");

Java : Phone number validation using regular expression

package com.lnn.regex;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class PhoneNumberValidation {

      private static final Pattern PhoneNumberPattern = Pattern.compile("[0-9]{3}[-]{0,1}[0-9]{4}");

      public static boolean isValidPhoneNumber(String phone) {

            Matcher matcher = PhoneNumberPattern.matcher(phone);

            return matcher.matches();

      }

     

      public static void main(String[] args) {

            System.out.println(isValidPhoneNumber("123-4567"));

            System.out.println(isValidPhoneNumber("1234567"));

      }

}

Java Script Regular Expression to restrict repetitive characters in a string

Following java script regular expression will restrict the numbers that contains 4 repetitive digits in a number.


function verifyAccessCode(){
    var val = document.forms[0].textbox.value;
    var exp1 = new RegExp("1111");
    var exp2 = new RegExp("2222");
    var exp3 = new RegExp("3333");
    var exp4 = new RegExp("4444");
    var exp5 = new RegExp("5555");
    var exp6 = new RegExp("6666");
    var exp7 = new RegExp("7777");
    var exp8 = new RegExp("8888");
    var exp9 = new RegExp("9999");
    var exp10 = new RegExp("0000");
    if(exp1.test(val) || exp2.test(val) || exp3.test(val) || exp4.test(val) || exp5.test(val)
        || exp6.test(val) || exp7.test(val) || exp8.test(val) || exp9.test(val) || exp10.test(val)){
        return false;
    }
    return true;
}