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I am less acquainted with front end and am just a beginner in back end. I am creating a webpage using servlets that reads data of a person from the database and displays it on the page in a form of a list. Each row of the list, consists of a button to contact. When clicked on the button, a message is sent to the person whose data has been selected. My question is- how do we create a unique id from the button click to generate a message id in the message table of the database awaiting a response from the selected person?

BalusC
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meowth
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  • This is usually a job for timestamps. If you have a large number of users, maybe a user_id of some sort concatenated with the timestamp to make it more unique. – sorak Feb 16 '18 at 08:31
  • Timestamps are not so 100% sure to be unique, even when using a prefix. I would consider them a workaround. – dr0i Feb 16 '18 at 08:36

2 Answers2

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All decent databases provide a way to generate unique IDs. A common way is through the usage of sequences, but it can even be simpler, PostgreSQL for example provides the SERIAL and BIGSERIAL types that automatically create a new id for each inserted row.

Long story made short: if you only need a different id for each row, use the equivalent of SERIAL provided by your database, and if you need greater control directly use a SEQUENCE (or its equivalent).

Serge Ballesta
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Use UUID Generator

Starting with Java 5, the UUID class provides a simple means for generating unique ids. The identifiers generated by UUID are actually universally unique identifiers. Example 

import java.util.UUID;

public class GenerateUUID {

  public static final void main(String... aArgs){
    //generate random UUIDs
    UUID idOne = UUID.randomUUID();
    UUID idTwo = UUID.randomUUID();
    log("UUID One: " + idOne);
    log("UUID Two: " + idTwo);
  }

  private static void log(Object aObject){
    System.out.println( String.valueOf(aObject) );
  }
} 

Example run:
>java -cp . GenerateUUID
UUID One: 067e6162-3b6f-4ae2-a171-2470b63dff00 
UUID Two: 54947df8-0e9e-4471-a2f9-9af509fb5889

Please refer : http://www.javapractices.com/topic/TopicAction.do?Id=56

I hope this will help.

Sumesh TG
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