Check Valid WWW Domain And HostName Java Examples

This example include java code to check whether a given www domain or a host name string is a valid domain or not. You can see code comments for detail explanation.

1. Check Valid Domain Example

	/*
	 * addStr : A domain string.
	 * return : true means addStr is a valid domain name, false means addStr is not a valide domain name.
	 * */
	public static boolean isValidDomain(String addStr)
	{
		boolean ret = true;
		
		if("".equals(addStr) || addStr==null)
		{
			ret = false;
		}else if(addStr.startsWith("-")||addStr.endsWith("-"))
		{
			ret = false;
		}else if(addStr.indexOf(".")==-1)
		{
			ret = false;
		}else			
		{		
			// Split domain into String array.
			String domainEle[] = addStr.split("\\.");
			int size = domainEle.length;
			// Loop in the domain String array.
			for(int i=0;i<size;i++)
			{
				// If one domain part string is empty, then reutrn false.
				String domainEleStr = domainEle[i];
				if("".equals(domainEleStr.trim()))
				{
					return false;
				}
			}
			
			// Get domain char array.
			char[] domainChar = addStr.toCharArray();			
			size = domainChar.length;
			// Loop in the char array.
			for(int i=0;i<size;i++)
			{
				// Get each char in the array.
				char eleChar = domainChar[i];
				String charStr = String.valueOf(eleChar);
				
				// If char value is not a valid domain character then return false.
				if(!".".equals(charStr) && !"-".equals(charStr) && !charStr.matches("[a-zA-Z]") && !charStr.matches("[0-9]"))
				{
					ret = false;
					break;
				}				
			}
		}		
		return ret;
	}

2. Check Valid HostName Example

	/*
	 * This method is used to verify whether hostName is valid or not.
	 * hostName : Given host name being checked.
	 * return : true means hostName is valid, false means hostName is not valid.
	 * */
	public static boolean isValidHostName(String hostName)
	{
		boolean ret = true;
		if(hostName==null) 
		{
			return false;
		}		
		hostName = hostName.trim();
		if("".equals(hostName) || hostName.indexOf(" ")!=-1)
		{
			ret = false;
		}else
		{
			// Use regular expression to verify host name.
			Pattern p = Pattern.compile("[a-zA-Z0-9\\.\\-\\_]+");  
			Matcher m = p.matcher(hostName);  
			ret = m.matches();
			
			if(ret)
			{
				String tmp = hostName;
				if(hostName.length()>15)
				{
					tmp = hostName.substring(0, 15);					
				}
				// Use another regular expression to verify the first 15 charactor.
				p = Pattern.compile("((.)*[a-zA-Z\\-\\_]+(.)*)+");  
				m = p.matcher(tmp);  
				ret = m.matches();
			}
		}
		return ret;
	}
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