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POHow can I easily call a java class (which queries a database) and return usable results to a JSP?
 

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  1. POHow can I easily call a java class (which queries a database) and return usable results to a JSP?
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    <p>I'm new to learning JSPs and Servlets. I have a Java class which calls a stored procedure and return a list of states from a database (this is my test case while I learn, other more complex actions will come later). The list of states should be returned to a JSP for display/use in a form, etc... For now, I'm happy to just get the data printing via the JSP page to know it is there.</p> <p>However, when I call the Java code from the JSP, it appears that the result object is returned as null and thus no data is accessible. I've tried to return the data as a ResultSet object as well, but the results are the same. I do know the stored procedure works when called from SQL. Additionally I have the Java code as a servlet that responds to a doPost request and that works fine...</p> <p>What might I be missing / failing to understand? Is this possible? </p> <pre><code>package edu.XXXX.ais.userapp; import java.sql.*; import java.util.*; public class DBQueries { public static Vector&lt;String&gt; getStatesList() { Vector&lt;String&gt; results = new Vector&lt;String&gt;(); Connection con = null; try { // Example of executing a stored procedure Class.forName("com.mysql.jdbc.Driver"); con = DriverManager.getConnection ("jdbc:mysql://hostname:3306/dbName","username","password"); CallableStatement cs = con.prepareCall("{call getStatesList()}"); ResultSet rs = cs.getResultSet(); while (rs.next()) { results.add(rs.getString(1)); } } catch (SQLException e) { System.err.println("Servlet could not display records." + e); } catch (ClassNotFoundException e) { System.err.println("JDBC driver not found." + e); } finally { try { if (con != null) { con.close(); con = null; } } catch (SQLException e) { System.err.println(e); } } return results; } } </code></pre> <p>JSP page that calls the above Java code (expects to be able to receive results...)</p> <pre><code>&lt;html&gt; &lt;head&gt; &lt;title&gt;Foo&lt;/title&gt; &lt;/head&gt; &lt;body&gt; &lt;h3&gt;List of states via a servlet call to the database&lt;/h3&gt; &lt;%@ page import="java.util.*" %&gt; &lt;%@ page import="edu.XXXX.ais.userapp.DBQueries" %&gt; &lt;% Vector rs = DBQueries.getStatesList(); if (rs != null) for (int index = 0; index &lt; rs.size(); index++) { out.println("Name : " + (String) rs.get(index)); } %&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>The resulting Tomcat errors are as follows:</p> <pre><code>org.apache.jasper.JasperException: An exception occurred processing JSP page /states.jsp at line 12 9: &lt;%@ page import="edu.XXXX.ais.userapp.DBQueries" %&gt; 10: 11: &lt;% 12: Vector rs = DBQueries.getStatesList(); 13: if (rs != null) 14: for (int index = 0; index &lt; rs.size(); index++) { 15: out.println("Name : " + (String) rs.get(index)); Stacktrace: org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) root cause java.lang.NullPointerException edu.XXXX.ais.userapp.DBQueries.getStatesList(Unknown Source) org.apache.jsp.states_jsp._jspService(states_jsp.java:75) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) </code></pre>
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