Servlet was not written redirection and forwarding, write only alert, the alert belongs to which page ?

below , AgentNewServlet.java

list = ccGroupDAO.findCCGroupList(ccGroupDTO);
  			if(list !=null && list.size() > 0) {
  				out.print("<script>alert('该分组序号已经存在，请重新输入!');</script>");
  				return;
  			}

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Why not try
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jsp at run time , is first compiled into jsp servlet. java run , this time you should know how it 's going
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Thank you for your answer !   
Do you mean that the current page , who calls who is it?  
No, I feel the current page is the servlet.
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AJAX way or return message , response to this new page , and put a message on the request in
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Those who do not return the servlet will have a blank page , it will print out the contents out .
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try. As follows:

hostFrame.jsp is opened by window.showModalDialog way dialog where parameters for the title and name. The page has a frame: to dynamically point to different pages , such as adding pages agentNew.jsp. Save the page and click on submit to AgentNewServlet for processing.

effect you want to achieve is:
servlet based on the passed parameters determine and alert processing , such as additional reasons for the failure, how to ensure that the current dialog box does not add any changes ?

I did not write the jump , only alert the pop-up box , this new dialog box is blank page.
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Thank you for your answer !
Do you mean that the current page , who calls who is it?
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try. As follows:   
  
hostFrame.jsp is opened by window.showModalDialog way dialog where parameters for the title and name. The page has a frame: to dynamically point to different pages , such as adding pages agentNew.jsp. Save the page and click on submit to AgentNewServlet for processing.   
  
effect you want to achieve is:   
servlet based on the passed parameters determine and alert processing , such as additional reasons for the failure, how to ensure that the current dialog box does not add any changes ?   
  
I did not write the jump , only alert the pop-up box , this new dialog box is blank page.  

out.print("没有转发和重定向，这个打印会到哪呢？");

look behind the text. So instead text.jsp not forwarding and redirection , then it should not generated html page, so you should not run the script , but printed directly , as to why not console print text print what is I do not know, rookie
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try. As follows:     
    
hostFrame.jsp is opened by window.showModalDialog way dialog where parameters for the title and name. The page has a frame: to dynamically point to different pages , such as adding pages agentNew.jsp. Save the page and click on submit to AgentNewServlet for processing.     
    
effect you want to achieve is:     
servlet based on the passed parameters determine and alert processing , such as additional reasons for the failure, how to ensure that the current dialog box does not add any changes ?     
    
I did not write the jump , only alert the pop-up box , this new dialog box is blank page.          
  
     
  
  

out.print("没有转发和重定向，这个打印会到哪呢？");

  
  
look behind the text. So instead text.jsp not forwarding and redirection , then it should not generated html page, so you should not run the script , but printed directly , as to why not console print text print what is I do not know, rookie  

Thank you ! I do not agree with your point of view , I learned servlet well, I hope more great God enlighten !
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This is a very old procedure, using asp.net written inside a bit chaotic, I unified with the servlet.
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This is a very old procedure, using asp.net written inside a bit chaotic, I unified with the servlet.  

Can you imagine :