如何从JSP页面获取参数到Java Helper函数

Question

I'm trying to get the a parameter from a drop down menu that's on the jsp file, onto my helper function which is in a java file. I'm checking to see if the user clicks a button and then I want to take the "rows" parameter. This is what the drop down menu looks like ...

<div class="panel panel-default">
    <div class="panel-body">
        <div class="bottom-nav">
            <h4> Options </h4>
            <form action="AnalysisHelper.java"> 
                    <div>
                Rows: 
                    <select name="rows">
                        <option value="users">users</option>
                        <option value="states">states</option>
                    </select>
                </div>

                    <div>
                    <input type="submit" value="Next 20 Users" name="nextUsers">
                    <input type="submit" value="Next 10 products" name="nextProd">
                    <input type="submit" value="RUN QUERY!" name="run">
                </div>

and this is my helper function:

package helpers;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.http.HttpServletRequest;

public class AnalysisHelper {

    public static List<AnalysisWithCategories> listAnalysis() {

        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        // list object holding data
        List<AnalysisWithCategories> analysis = new ArrayList<AnalysisWithCategories>();

        try {
            try {

                // connect to DB
                conn = HelperUtils.connect();

            } catch (Exception e) {

                // error
                System.err.println("Internal Server Error. This shouldn't happen.");
                return new ArrayList<AnalysisWithCategories>();
            }

            // get all the products
            stmt = conn.createStatement();

                        // check if user wants to filter results
            String runQuery = request.getParameter("run");
            if()

            // might need indexes on userandstates(u_id), userandproductsales(u_id), userandproductsales(p_id), product(p_id)
            rs = stmt.executeQuery("SELECT s.p_name, s.p_id, s.u_name, s.u_id, s.s_price, s.quantity, s.name, s.c_name, u.u_totalSales, p.p_totalSales" 
                    + " FROM userAndProductSales s" 
                    + " left outer join usersandstates u on u.u_id = s.u_id" 
                    + " join product p on p.p_id = s.p_id"
                    + " ORDER BY u_name, p_name LIMIT 20");

I've tried request.getParameter("run") and request.getParameter("rows") but I get an error saying that "request is not resolved" . How do I map the request to my jsp file? Or if there's another way to get the parameter, can you please show me.

Answer 1

It's more than architectural problem.

What you must remember is that JSP is compiled into HTML and sent to the client - once there (or actually after compiling is done), it has no idea what happens on the server. It is no longer JSP and knows nothing of Java.

If you want to call a function on the server, you need to expose the function (servlet, REST, etc.) and call it via Javascript on the client. The client does not (and should not) know the internals of your server - even if you, as the programmer, do.

Specifically as to request not being resolved:

You need to write a function which will get as one of its parameters an httprequest, which is injected by the network communication framework (JEE, Spring, another servlet) - upon which you can request parameters which you pass from client (!). It does not happen by magic. :-)