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POIs it Possible to Populate a Dropdown (In HTML/JSP) From a Servlet?
 

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  1. POIs it Possible to Populate a Dropdown (In HTML/JSP) From a Servlet?
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    <p>Okay, so I had created my first jsp page which basically created 3 drop downs and populated them with information pulled from a database.</p> <p>However, I was told that this was bad code and I should use a servlet for that database function and error handling, and let the jsp strictly do the displaying.</p> <p>The original jsp code is below:</p> <pre><code>&lt;%@page import="java.sql.*"%&gt; &lt;!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"&gt; &lt;html&gt; &lt;head&gt; &lt;meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"&gt; &lt;title&gt;Code Selector&lt;/title&gt; &lt;/head&gt; &lt;body&gt; &lt;h1&gt;Please select the applicable codes:&lt;/h1&gt; &lt;select name='Code' onchange="showState(this.value)"&gt; &lt;option value="none"&gt;Select a code&lt;/option&gt; &lt;% //Pulls the ids and decriptions from the codes table and stores them in the first drop down try { Class.forName("driverName").newInstance(); Connection con = DriverManager.getConnection("serverURL","username","password"); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("select id, descr from codes"); while(rs.next()) { %&gt; &lt;option value="&lt;%=rs.getString(1)%&gt;"&gt;&lt;%=rs.getString(1)%&gt; &lt;%=rs.getString(2)%&gt;&lt;/option&gt; &lt;% } //Closes the database connection stmt.close(); con.close(); } catch (ClassNotFoundException e) { System.err.println("ClassNotFoundException: " + e.getMessage()); } catch (SQLException e) { System.err.println("SQLException: " + e.getMessage()); } catch (Exception e) { System.err.println("Generic Exception: " + e.getMessage()); } %&gt; &lt;/select&gt; &lt;br&gt; &lt;br&gt; &lt;select name='Code2' onchange="showState(this.value)"&gt; &lt;option value="none"&gt;Select a code&lt;/option&gt; &lt;% //Pulls the ids and decriptions from the codes table and stores them in the second drop down try { Class.forName("driverName").newInstance(); Connection con = DriverManager.getConnection("serverURL","username","password"); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("select id, descr from codes"); while(rs.next()) { %&gt; &lt;option value="&lt;%=rs.getString(1)%&gt;"&gt;&lt;%=rs.getString(1)%&gt; &lt;%=rs.getString(2)%&gt;&lt;/option&gt; &lt;% } //Closes the database connection stmt.close(); con.close(); } catch (ClassNotFoundException e) { System.err.println("ClassNotFoundException: " + e.getMessage()); } catch (SQLException e) { System.err.println("SQLException: " + e.getMessage()); } catch (Exception e) { System.err.println("Generic Exception: " + e.getMessage()); } %&gt; &lt;/select&gt; &lt;br&gt; &lt;br&gt; &lt;select name='otherCode' onchange="showState(this.value)"&gt; &lt;option value="none"&gt;Select a other code&lt;/option&gt; &lt;% //Pulls the ids and decriptions from the other codes table and stores them in the third drop down try { Class.forName("driverName").newInstance(); Connection con = DriverManager.getConnection("serverURL","username","password"); Statement stmt = con.createStatement(); ResultSet rs2 = stmt.executeQuery("select id, descr from other_codes"); while(rs2.next()) { %&gt; &lt;option value="&lt;%=rs2.getString(1)%&gt;"&gt;&lt;%=rs2.getString(1)%&gt; &lt;%=rs2.getString(2)%&gt;&lt;/option&gt; &lt;% } //Closes the database connection stmt.close(); con.close(); } catch (ClassNotFoundException e) { System.err.println("ClassNotFoundException: " + e.getMessage()); } catch (SQLException e) { System.err.println("SQLException: " + e.getMessage()); } catch (Exception e) { System.err.println("Generic Exception: " + e.getMessage()); } %&gt; &lt;/select&gt; &lt;br&gt; &lt;br&gt; &lt;form method = "post"&gt; &lt;input type="submit" value="Submit"&gt; &lt;% try { String Code = request.getParameter("Code"); String Code2 = request.getParameter("Code2"); String otherCode = request.getParameter("otherCode"); Class.forName("driverName").newInstance(); Connection con = DriverManager.getConnection("serverURL","username","password"); Statement stmt = con.createStatement(); //ResultSet rs3 = stmt.executeQuery(); System.out.println("This is the first code: " + Code); System.out.println("This is the second code: " + Code2); System.out.println("This is the other code: " + otherCode); con.close(); stmt.close(); } catch (ClassNotFoundException e) { System.err.println("ClassNotFoundException: " + e.getMessage()); } catch (SQLException e) { System.err.println("SQLException: " + e.getMessage()); } catch (Exception e) { System.err.println("Generic Exception: " + e.getMessage()); } %&gt; &lt;script&gt; window.close(); &lt;/script&gt; &lt;/form&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>And so far, this is what I have with the new jsp and servlet page:</p> <p><strong>codes-selector.jsp</strong></p> <pre><code>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"&gt; &lt;HTML&gt; &lt;HEAD&gt; &lt;TITLE&gt; Codes &lt;/TITLE&gt; &lt;/HEAD&gt; &lt;BODY BGCOLOR="#FDF5E6"&gt; &lt;H2 ALIGN="CENTER"&gt; Please select the applicable codes: &lt;/H2&gt; &lt;FORM ACTION="http://localhost:8088/SomeProgram" METHOD="GET"&gt; &lt;CENTER&gt; &lt;select name='code' onchange="showState(this.value)"&gt; &lt;option value="none"&gt;Select a code&lt;/option&gt; &lt;/select&gt; &lt;BR&gt; &lt;BR&gt; &lt;select name='code2' onchange="showState(this.value)"&gt; &lt;option value="none"&gt;Select a code&lt;/option&gt; &lt;/select&gt; &lt;BR&gt; &lt;BR&gt; &lt;select name='otherCode' onchange="showState(this.value)"&gt; &lt;option value="none"&gt;Select an other code&lt;/option&gt; &lt;/select&gt; &lt;BR&gt; &lt;BR&gt; &lt;!-- Press this to submit form --&gt; &lt;INPUT TYPE="SUBMIT" VALUE="Submit"/&gt; &lt;/CENTER&gt; &lt;/FORM&gt; &lt;/BODY&gt; &lt;/HTML&gt; </code></pre> <p><strong>PullCodes.java (servlet)</strong>:</p> <pre><code>package com.firstservlet.alfresco; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.sql.*; /** * Servlet implementation class PullCodes */ @WebServlet("/PullCodes") public class PullCodes extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public PullCodes() { super(); } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String code = request.getParameter("code"); String code2 = request.getParameter("code2"); String otherCode = request.getParameter("otherCode"); try { Class.forName("driverName").newInstance(); Connection con = DriverManager.getConnection("url","username","password"); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("select id, descr from ref_codes"); ResultSet rs2 = stmt.executeQuery("select id, descr from ref_other_codes"); try { while(rs.next()) { //Is this correct? code+=("&lt;option value=\"" + rs.getString(1) + "\"&gt;" + rs.getString(1) + " " + rs.getString(2) + "&lt;/option&gt;"); } //Closes the database connection stmt.close(); con.close(); } catch (Exception e) { System.err.println("Insertion Exception: " + e.getMessage()); } } catch (ClassNotFoundException e) { System.err.println("ClassNotFoundException: " + e.getMessage()); } catch (SQLException e) { System.err.println("SQLException: " + e.getMessage()); } catch (Exception e) { System.err.println("Generic Exception: " + e.getMessage()); } } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } } </code></pre> <p>So now, at this point, I'm not sure how to access that dropdown list element from my html page. And Googling around, I was not seeing anything that appeared to show this being done. Also, from what I read it seems most of the time a servlet is just processing information from the html/jsp page. What I'm doing right now is <code>code+=("&lt;option value=\"" + rs.getString(1) + "\"&gt;" + rs.getString(1) + " " + rs.getString(2) + "&lt;/option&gt;");</code>. Is that correct? And if so, how do I link that with the html/jsp page? Or is it not even possible to access that html page on load and populate it using the servlet?</p>
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    1. USThis 0ne Pr0grammer
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    1. COI'm sorry to say your code looks just ugly. Putting all that database stuff in a JSP makes it bulky and confusing, and it's difficult to look for errors here. Why not let a servlet do all the database stuff and exception handling instead, and focus on displaying on the JSP side?
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    2. COHonestly, this is my first time writing a jsp, so any comments are appreciated. I'll give that a try and re-post my code when I'm done. :)
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    3. COI'm not sure where you learnt HTML/JSP, but all those uppercase HTML tags and `<center>` tag suggest that the book/resource is 10~20 years old. This also implies the old school JSP scriptlet style which is bad for various reasons. I strongly recommend to carefully pay attention to the publication date of the book/resource from where you're trying to learn the new stuff. It should *preferably* not be older than the **current** JSP (2.2) / HTML (5) version. Put your mouse above `[jsp]` and `[servlets]` tags which you placed on the question until a black box shows and click therein *info* link.
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