TCPServer.java

import java.io.*; 
import java.net.*; 
import java.lang.*;

public class TCPServer { 
    public static void main(String argv[]) throws Exception 
    { 
        String clientSentence; 
		String keyword;
		String getNum;
		String setNum;
        HashMap<String,String> directory = new HashMap<String,String>();

        ServerSocket welcomeSocket = new ServerSocket(6791); 

        Socket connectionSocket = welcomeSocket.accept(); 

        BufferedReader inFromClient = 
            new BufferedReader(new
                InputStreamReader(connectionSocket.getInputStream()));

        DataOutputStream  outToClient = 
            new DataOutputStream(connectionSocket.getOutputStream()); 
            
            
        while(true) {

            clientSentence = inFromClient.readLine().split(" ");			
			keyword = clientSentence[0];
            if (keyword.equals("CHECK:"))
            {
				if (clientSentence.length < 2){
					outToClient.writeBytes(
						"Correct format is CHECK: $NAME\n"); 
				}
				else{
					getNum = directory.get(clientSentence[1]);
					if (getNum != null){
						outToClient.writeBytes(
							clientSentence[1] + "'s number is " + getNum + "\n"); 
					}
					else{
						outToClient.writeBytes(
							"Sorry, name not found, please try again\n"); 
					}
				}
            }
			
            else if (keyword.equals("ADD:"))
            {
				if (clientSentence.length < 3){
					outToClient.writeBytes(
						"Correct format is ADD: $NAME $NUMBER\n"); 
				}
				else{
					setNum = directory.get(clientSentence[1]);
					if (getNum == null){
						directory.put(clientSentence[1], clientSentence[2]);
						outToClient.writeBytes(clientSentence[1] + " added\n"); 	
					}
					else{
						outToClient.writeBytes(
							"Sorry, that name is already in the directory\n");
					}
				}                
            
            }
			
			else if (keyword.equals("LIST")){
				for(Map.Entry<String, HashMap> entry : directory.entrySet()) {
					String key = entry.getKey();
					HashMap value = entry.getValue();
					outToClient.writeBytes(
						key + ": " + value + "\n");
			}
			
			else if (keyword.equals("DELETE")){
				
				
				//Delete an entry
				
			}
			
            else if(keyword.equals("END"))
            {
                break;
            }
			
			else {
				outToClient.writeBytes("Command not recognised, please try again\n");
			}
        } 
    } 
}