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POjava run only one instance at a time
 

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    <p>I am using Java(Servlet,JSP) to develop a web application.</p> <p>I have a class which send emails.</p> <p>Class looks like:</p> <pre><code>public class EmailSender { String SendEmail(String from,Session session,String To,String CC, String BCC, String Subject,String Body) { //Actual code for sending emails } } </code></pre> <p><code>EmailSender</code> class is called from another class:</p> <pre><code>public class InvokeSender { public InvokeSender(String dbFileName) { //get emails from database for sending who has STATUS='NOTSENT' //statements to get all required parameter to pass to SendEmail() EmailSender sender = new EmailSender(); String msg = sender.SendEmail(fromEmail,session,To,CC,BCC,SUBJECT,BODY); } } </code></pre> <p>And <code>InvokeSender</code> is called from servlet when the used clicks the button.</p> <p>When user clicks on button the InvokeSender is called, which takes emails to be send from database and forms them and then pass those parameters to <code>SendEmail()</code> of <code>EmailSender</code> class.</p> <p>I want only one instance of <code>InvokeSender</code> to run at a time to avoid same emails going twice if the button is pressed twice. How this can be handled? Will <code>multithreading</code> useful in this case? </p> <p>Any suggestion will be appreciated.</p> <p><strong>Update1</strong> I can't disable the button after user clicks it. Because if user refresh the page then that button will be enabled by default.</p> <p><strong>Update2</strong> First user selects customers, template etc. for sending emails and after that email parameters are stored in database. <code>InvokeSender</code> class get all emails to be sent. Number of emails to be sent can't be predicted. It can be 1 or 500 or more than that. I want only one instance of <code>InvokeSender</code> to run until previous instance is completed sending emails. Functionality (Button to generate and send email) will be exposed to 5-7 users.</p>
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    1. COWhat about simply disabling the button after the user clicks it?
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      1. USJoe
    2. CODisabling the button is a good idea, however I think the intent is to build a robust server component that has no dependency on the UI. For example, one may want to expose this functionality via a web service interface.
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    3. CO@Joe Please see `update1`
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