Member Avatar for Kirielson

I have a question about programming Java into HTML using the latest version of Tomcat. I'm trying to get the option values from the HTML to go inside the Java program and print out said values. A friend of mine suggested that I create an array of strings and then print out from there, and I decided to take that advice, however I get the following error after the following code:

<form action="displayMusicChoices" method="post">
 <--...some table code -->
            <td align="right" valign="top">I'm interested in these types of music:</td>
            <td>
                <select name="musicChoices" size="4" multiple>
                    <option name="Rock">Rock</option>
                    <option name="Country">Country</option>
                    <option name="Bluegrass">Bluegrass</option>
                    <option name="Folk">Folk</option>
                </select>
            </td>
        </tr>
    <tr>
      <td></td>
      <td><br><input type="submit" value="Submit"></td>
    </tr>
  </table>
  </form>
String[] choices = request.getParameterValues("musicChoices");
 int select_choices = choices.length;
...///Other code
 out.println(
          "<!doctype html public \"-//W3C//DTD HTML 4.0 Transitional//EN\">\n"
   ///Other ocde
        + "<p>We'll use this email to notify you whenever we have new releases ofr these types of music: </br>"

for (int i =0; i <= select_choices; i++)
out.print(choices[i] + " ");
        ///Print out selections
java.lang.NullPointerException
	DisplayMusicChoicesServlet.doPost(DisplayMusicChoicesServlet.java:61)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

I can understand the NullPointerException, but I don't get HOW I can get it with this code unless it's not getting the option, which in that case I need advice on how to get said options.

Thanks for reading.

  • 5 Contributors
  • 21 Replies
  • 1K Views
  • 1 Day Discussion Span
  • Latest Post Latest Post by mandy011

Recommended Answers

All 21 Replies

Member Avatar for Taywin

I thought that the select tag would send only the value you selected if it is not a multiple selection? Hmm... Haven't played with Servlet for almost a year... Need to recall it...

Member Avatar for Kirielson

Here's the error code I get too:

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception
Member Avatar for Taywin

What's the code at the line (in your servlet) for this error

DisplayMusicChoicesServlet.doPost(DisplayMusicChoicesServlet.java:61)

By the way, where is the 'value' property (not 'name') for each option in your selection???

Edited by Taywin because: n/a
Member Avatar for Kirielson

What's the code at the line (in your servlet) for this error

DisplayMusicChoicesServlet.doPost(DisplayMusicChoicesServlet.java:61)

By the way, where is the 'value' property (not 'name') for each option in your selection???

I tried putting in the values, but I used alphabet names (aka Rock, Folk ect.) instead of numbers

Here's the lines for 60 and 61 to give you context:

+ "button in your browser or the Return button shown <br>\n"
        + "below.</p>\n"
Member Avatar for ztini

Do you have @WebServlet above your class that extends HttpServelet?

@WebServlet("displayMusicChoices")
public class Servlet extends HttpServlet {	

	@Override
	public void doPost(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException {

...

Although you should if you're getting:

DisplayMusicChoicesServlet.doPost(DisplayMusicChoicesServlet.java:61)
Edited by ztini because: n/a
Member Avatar for ztini

Oh,

It may be that you have " <option name="Folk">Folk</option>"

That should be " <option value="Folk">Folk</option>", this is the value for the name "musicChoices".

Member Avatar for Taywin

That's what I asked in my previous post as well...

Member Avatar for Kirielson

That's what I asked in my previous post as well...

Here's what you're looking for:

public class DisplayMusicChoicesServlet extends HttpServlet
{    
    /**
     * @param request servlet request
     * @param response servlet response
     */
    protected void doPost(
        HttpServletRequest request, 
        HttpServletResponse response) 
        throws ServletException, IOException
    {

//More code

 out.close();  
                doPost(request, response);
Member Avatar for ztini

Here's what you're looking for:

public class DisplayMusicChoicesServlet extends HttpServlet
{    
   ..

//More code

 out.close();  
                doPost(request, response);

I disagree with your last 2 lines there. You don't need to call doPost inside of doPost(), this is called automatically.

Also, "out" belongs to the parameter response (PrintWriter out = response.getWriter()). In my opinion, you shouldn't close this writer; that is the responsibility of the class owner...you can't assume it is not needed anymore.

I just tested changing from "name" to "value" for the option in my TomCat and it worked.

Member Avatar for Kirielson

I disagree with your last 2 lines there. You don't need to call doPost inside of doPost(), this is called automatically.

Also, "out" belongs to the parameter response (PrintWriter out = response.getWriter()). In my opinion, you shouldn't close this writer; that is the responsibility of the class owner...you can't assume it is not needed anymore.

I just tested changing from "name" to "value" for the option in my TomCat and it worked.

Unfortunately it's not working on my Tomcat. Though I know it's in bad taste, I'll upload the code I have so far.

I think it should give you a clearer picture. IT might be my web.xml file that's not responding properly.

Here's the HTML since it's not uploading right

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>
    <title>Murach's Java Servlets and JSP</title>
</head>

<body>
  <h1>Join our email list</h1>
  <p>To join our email list, enter your name and
     email address below. <br>
     Then, click on the Submit button.</p>

  <form action="displayMusicChoices" method="post">
  <table cellspacing="5" border="0">
    <tr>
      <td align="right">First name:</td>
      <td><input type="text" name="firstName"></td>
    </tr>
    <tr>
      <td align="right">Last name:</td>
      <td><input type="text" name="lastName"></td>
    </tr>
    <tr>
      <td align="right">Email address:</td>
      <td><input type="text" name="emailAddress"></td>
    </tr>
        <tr>
            <td align="right" valign="top">I'm interested in these types of music:</td>
            <td>
                <select name="musicChoices" size="4" multiple>
                    <option value="Rock">Rock</option>
                    <option value="Country">Country</option>
                    <option value="Bluegrass">Bluegrass</option>
                    <option value="Folk">Folk</option>
                </select>
            </td>
        </tr>
    <tr>
      <td></td>
      <td><br><input type="submit" value="Submit"></td>
    </tr>
  </table>
  </form>
</body>

</html>

Once again, thanks for helping. I will try finding the error to the problem.

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import java.lang.*;

//import User.;
//import UserIO.;

/**
 * @author Joel Murach
 */
public class DisplayMusicChoicesServlet extends HttpServlet
{    
    /**
     * @param request servlet request
     * @param response servlet response
     */
    protected void doPost(
        HttpServletRequest request, 
        HttpServletResponse response) 
        throws ServletException, IOException
    {
        // get parameters from the request
        String firstName = request.getParameter("firstName");
        String lastName = request.getParameter("lastName");
        String emailAddress = request.getParameter("emailAddress");
      String[] musicChoices = request.getParameterValues("musicChoices");
		/*String Country = request.getParameter("Country");
		String Bluegrass = request.getParameter("Bluegrass");
		String Folk = request.getParameter("Folk");
		String Rock = request.getParameter("Rock");*/
		
        // send response to browser
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
		//int select_choices = musicChoices.length;
		int i;
        out.println(
          "<!doctype html public \"-//W3C//DTD HTML 4.0 Transitional//EN\">\n"
        + "<html>\n"
        + "<head>\n"
        + "  <title>Murach's Java Servlets and JSP</title>\n"
        + "</head>\n"
        + "<body>\n"
        + "<h1>Thanks for joining our email list</h1>\n"
        + "<p>Here is the information that you entered:</p>\n"
        + "  <table cellspacing=\"5\" cellpadding=\"5\" border=\"1\">\n"
        + "  <tr><td align=\"right\">First name:</td>\n"
        + "      <td>" + firstName + "</td>\n"
        + "  </tr>\n"
        + "  <tr><td align=\"right\">Last name:</td>\n"
        + "      <td>" + lastName + "</td>\n"
        + "  </tr>\n"
        + "  <tr><td align=\"right\">Email address:</td>\n"
        + "      <td>" + emailAddress + "</td>\n"
        + "  </tr>\n"
        + "  </table>\n" 
        + "<p>We'll use this email to notify you whenever we have new releases of these types of music: </br>"
					);
			out.print(musicChoices[0] + " ");
		
        out.print("</p> " + "<p>To enter another email address, click on the Back <br>\n"
        + "button in your browser or the Return button shown <br>\n"
        + "below.</p>\n"
        + "<form action=\"join_email_list.html\" "
        + "      method=\"post\">\n"
        + "  <input type=\"submit\" value=\"Return\">\n"
        + "</form>\n"
        + "</body>\n"
        + "</html>\n");
        }
        
}
<?xml version="1.0" encoding="ISO-8859-1"?>
<!--
  Copyright 2004 The Apache Software Foundation

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->

<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>

    <display-name>Servlet 2.4 Examples</display-name>
    <description>
      Servlet 2.4 Examples.
    </description>

    <!-- Define servlet-mapped and path-mapped example filters -->
    <filter>
        <filter-name>Servlet Mapped Filter</filter-name>
        <filter-class>filters.ExampleFilter</filter-class>
	<init-param>
	    <param-name>attribute</param-name>
	    <param-value>filters.ExampleFilter.SERVLET_MAPPED</param-value>
	</init-param>
    </filter>
    <filter>
        <filter-name>Path Mapped Filter</filter-name>
        <filter-class>filters.ExampleFilter</filter-class>
	<init-param>
	    <param-name>attribute</param-name>
	    <param-value>filters.ExampleFilter.PATH_MAPPED</param-value>
	</init-param>
    </filter>
    <filter>
        <filter-name>Request Dumper Filter</filter-name>
        <filter-class>filters.RequestDumperFilter</filter-class>
    </filter>

    <!-- Example filter to set character encoding on each request -->
    <filter>
        <filter-name>Set Character Encoding</filter-name>
        <filter-class>filters.SetCharacterEncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>EUC_JP</param-value>
        </init-param>
    </filter>

    <filter>
        <filter-name>Compression Filter</filter-name>
        <filter-class>compressionFilters.CompressionFilter</filter-class>

        <init-param>
          <param-name>compressionThreshold</param-name>
          <param-value>10</param-value>
        </init-param>
        <init-param>
          <param-name>debug</param-name>
          <param-value>0</param-value>
        </init-param>
    </filter>

    <!-- Define filter mappings for the defined filters -->
    <filter-mapping>
        <filter-name>Servlet Mapped Filter</filter-name>
	<servlet-name>invoker</servlet-name>
    </filter-mapping>
    <filter-mapping>
        <filter-name>Path Mapped Filter</filter-name>
	<url-pattern>/servlet/*</url-pattern>
    </filter-mapping>


<!-- Example filter mapping to apply the "Set Character Encoding" filter
     to *all* requests processed by this web application -->
<!--
    <filter-mapping>
        <filter-name>Set Character Encoding</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
-->

<!--
    <filter-mapping>
      <filter-name>Compression Filter</filter-name>
      <url-pattern>/CompressionTest</url-pattern>
    </filter-mapping>
-->

<!--
    <filter-mapping>
        <filter-name>Request Dumper Filter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
-->

    <!-- Define example application events listeners -->
    <listener>
        <listener-class>listeners.ContextListener</listener-class>
    </listener>
    <listener>
        <listener-class>listeners.SessionListener</listener-class>
    </listener>

    <!-- Define servlets that are included in the example application -->

    <servlet>
        <servlet-name>CompressionFilterTestServlet</servlet-name>
        <servlet-class>compressionFilters.CompressionFilterTestServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>HelloWorldExample</servlet-name>
        <servlet-class>HelloWorldExample</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>RequestInfoExample</servlet-name>
        <servlet-class>RequestInfoExample</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>RequestHeaderExample</servlet-name>
        <servlet-class>RequestHeaderExample</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>RequestParamExample</servlet-name>
        <servlet-class>RequestParamExample</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>CookieExample</servlet-name>
        <servlet-class>CookieExample</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>SessionExample</servlet-name>
        <servlet-class>SessionExample</servlet-class>
    </servlet>
    
     <servlet>
        <servlet-name>DisplayMusicChoicesServlet</servlet-name>
        <servlet-class>DisplayMusicChoicesServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>CompressionFilterTestServlet</servlet-name>
        <url-pattern>/CompressionTest</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>HelloWorldExample</servlet-name>
        <url-pattern>/servlet/HelloWorldExample</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>RequestInfoExample</servlet-name>
        <url-pattern>/servlet/RequestInfoExample/*</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>RequestHeaderExample</servlet-name>
        <url-pattern>/servlet/RequestHeaderExample</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>RequestParamExample</servlet-name>
        <url-pattern>/servlet/RequestParamExample</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>CookieExample</servlet-name>
        <url-pattern>/servlet/CookieExample</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>SessionExample</servlet-name>
        <url-pattern>/servlet/SessionExample</url-pattern>
    </servlet-mapping>
    
    <servlet-mapping>
        <servlet-name>DisplayMusicChoicesServlet</servlet-name>
        <url-pattern>/displayMusicChoices</url-pattern>
    </servlet-mapping>
    
    
    <security-constraint>
      <display-name>Example Security Constraint</display-name>
      <web-resource-collection>
         <web-resource-name>Protected Area</web-resource-name>
	 <!-- Define the context-relative URL(s) to be protected -->
         <url-pattern>/jsp/security/protected/*</url-pattern>
	 <!-- If you list http methods, only those methods are protected -->
	 <http-method>DELETE</http-method>
         <http-method>GET</http-method>
         <http-method>POST</http-method>
	 <http-method>PUT</http-method>
      </web-resource-collection>
      <auth-constraint>
         <!-- Anyone with one of the listed roles may access this area -->
         <role-name>tomcat</role-name>
	 <role-name>role1</role-name>
      </auth-constraint>
    </security-constraint>

    <!-- Default login configuration uses form-based authentication -->
    <login-config>
      <auth-method>FORM</auth-method>
      <realm-name>Example Form-Based Authentication Area</realm-name>
      <form-login-config>
        <form-login-page>/jsp/security/protected/login.jsp</form-login-page>
        <form-error-page>/jsp/security/protected/error.jsp</form-error-page>
      </form-login-config>
    </login-config>

    <!-- Security roles referenced by this web application -->
    <security-role>
      <role-name>role1</role-name>
    </security-role>
    <security-role>
      <role-name>tomcat</role-name>
    </security-role>

    <!-- Environment entry examples -->
    <!--env-entry>
      <env-entry-description>
         The maximum number of tax exemptions allowed to be set.
      </env-entry-description>
      <env-entry-name>maxExemptions</env-entry-name>
      <env-entry-value>15</env-entry-value>
      <env-entry-type>java.lang.Integer</env-entry-type>
    </env-entry-->
    <env-entry>
      <env-entry-name>minExemptions</env-entry-name>
      <env-entry-value>1</env-entry-value>
      <env-entry-type>java.lang.Integer</env-entry-type>
    </env-entry>
    <env-entry>
      <env-entry-name>foo/name1</env-entry-name>
      <env-entry-value>value1</env-entry-value>
      <env-entry-type>java.lang.String</env-entry-type>
    </env-entry>
    <env-entry>
      <env-entry-name>foo/bar/name2</env-entry-name>
      <env-entry-value>true</env-entry-value>
      <env-entry-type>java.lang.Boolean</env-entry-type>
    </env-entry>
    <env-entry>
      <env-entry-name>name3</env-entry-name>
      <env-entry-value>1</env-entry-value>
      <env-entry-type>java.lang.Integer</env-entry-type>
    </env-entry>
    <env-entry>
      <env-entry-name>foo/name4</env-entry-name>
      <env-entry-value>10</env-entry-value>
      <env-entry-type>java.lang.Integer</env-entry-type>
    </env-entry>

</web-app>
Edited by Kirielson because: n/a
Member Avatar for ztini

Add

@WebServlet("/displayMusicChoices")

above your class declaration:

@WebServlet("/displayMusicChoices")
public class DisplayMusicChoicesServlet extends HttpServlet {
Member Avatar for Kirielson

Add

@WebServlet("/displayMusicChoices")

above your class declaration:

@WebServlet("/displayMusicChoices")
public class DisplayMusicChoicesServlet extends HttpServlet {

I did what you said and I got this error now

DisplayMusicChoicesServlet.java:13: cannot find symbol
symbol: class WebServlet
      @WebServlet("/displayMusicChoices")
       ^
1 error
Member Avatar for ztini 
import javax.servlet.annotation.WebServlet;
Member Avatar for Kirielson

I have to applogize, I thought I was using the latest release of Tomcat when I've been using the 5x version.

Member Avatar for Kirielson

I have to applogize, I thought I was using the latest release of Tomcat when I've been using the 5x version.

Okay, I did go and install 7.0.8 and now I'm getting this error:

type Status report

message /examples/servlets/displayMusicChoices

description The requested resource (/examples/servlets/displayMusicChoices) is not available.
Member Avatar for mKorbel

Java upTo latest 1.6.24 implements just up to Html <= 3.2

Member Avatar for Taywin

By the way, when you do doPost() inside a servlet, you could simply pass all variable to doGet(). Do not call its own function or you are creating a recursive call. Both doPost() and doGet() methods should not be recursive...

Member Avatar for mandy011

dude it's damn easy problem. Just give every option value attribute,
You can select one option at a time then:
assuming following:

<select name='hmm'>
<option value='one'>one</option>

Assuming you are submitting form via post

//inside doPost()
String selectValue=request.getParameter("hmm");
//selectValue variable would contain one now

This should help you :) sorry for any mistakes I am standing in train and typing :/

Edited by mandy011 because: had forgotten to write something
Member Avatar for mandy011

why do you people suggest to call doPost() or doGet() from other methods?? Frankly it's not worth, not needed. And @threadstarter check your web.xml file for configuration. If you have configured properly then afterwards try reloading the folder via tomcat manager.

<web-app>
<servlet>
<servlet-name>MusicStore</servlet-name>
<servlet-class>MusicStore <!--put ur class file name--></servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>MusicStore</servlet-name>
<url-pattern>/MusicStore</url-pattern>
</servlet-mapping>
</web-app>

put this file in a folder along with your servlet class file in classes folder. Please ones check web-app tag i am not able to recollect it. Your servlet should be accessible via localhost:8080/urfolder/MusicStore don't forget to reload the folder from tomcat manager

Member Avatar for Taywin

@mandy011
Your first post is exactly the same as ztini and I asked for. Not new. Your second post is rude by calling 'who do you people'. Also, post & get methods actually works the same way. Why do you need to implement them separately? By using one to call the other is simple enough.

Anyway, the problem in his code tends to be more from recursive call because his doPost() calls doPost() again. That's the problem.

Edited by Taywin because: n/a
Member Avatar for mandy011

I didn't mean it rudely.. I was asking Why you people suggest! and another thing i was in train so i couldn't see the replies before mine.. I mean I couldn't check all replies Bcoz I was in train. And the topic wasn't solved topic thus I replied. If you felt I was rude sorry for that. But I didn't mean rudely.
Frankly speaking , Both methods doesn't work same way as such. Cause if it would have been Why java developers implemented separate methods for both purposes? Both take same arguments .. And specially optimized methods are written for the form method i.e. get and post

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