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Hard time learning Servlets

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posted 13 years ago

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My config look like this:
/webapps/index/WEB-INF/classes/

My /index/WEB-INF/web.xml look like this:

In index/WEB-INF/classes/ i have

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class zjat extends HttpServlet {

public void doGet(HttpServletRequest inRequest,
      HttpServletResponse outResponse) throws ServletException,
      IOException {

PrintWriter out = null;

Connection connection = null;
    Statement statement;
    ResultSet rs;

try {
      Class.forName("com.mysql.jdbc.Driver");

connection = DriverManager
          .getConnection("jdbc:mysql://localhost/zjat", "root", "****");
      statement = connection.createStatement();

outResponse.setContentType("test/html");
      out = outResponse.getWriter();

rs = statement.executeQuery("SELECT * FROM `message`");

out.println("<HTML><HEAD><TITLE>Products</TITLE></HEAD>");
      out.println("<BODY>");
      out.println("<UL>");

while (rs.next()) {
        out.println("<LI>" + rs.getString("id") + " "
            + rs.getString("nick") + " " + rs.getString("message"));
      }

out.println("</UL>");
      out.println("</BODY></HTML>");
    } catch (ClassNotFoundException e) {
      out.println("Driver Error");
    } catch (SQLException e) {
      out.println("SQLException: " + e.getMessage());
    }
  }

public void doPost(HttpServletRequest inRequest,
      HttpServletResponse outResponse) throws ServletException,
      IOException {
    doGet(inRequest, outResponse);
  }
}

Witch is just a test servlet i have download.

I cant load Index/ or my servlet it gives class not found and somehow tries to load my servlet as index/ in manager.
I'm using Ubuntu Lucid and Tomcat 6 please help i have been trying for hours and my head hurts.
What i'm i doing wrong ???
Thank you

Bear Bibeault

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posted 13 years ago

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You're doing a number of things wrong which lead me to believe that you are using some very old information:

You are using the invoker. Stop. Don't.

All classes used in a web application must in a package other than the default.

Your web app is declared as a 2.3 DTD web app. For Tomcat 6 it should be using the 2.5 schema.

What are you using for a reference. It's either very old or very bad.

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Carsten Rasmussen

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posted 13 years ago

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I changed my web.xml to:

Same error, it tries to employ the applet as default page and dont starts.
/index Zjat Beta false 0 Start Stop Reload Undeploy

Bear Bibeault

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posted 13 years ago

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Applet?

Your servlet is still not in a non-default package.
Your deployment descriptor has no mapping for the servlet.

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Virendrasinh Gohil

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posted 13 years ago

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Carsten Rasmussen wrote:I changed my web.xml to:<?xml version="1.0" encoding="ISO-8859-1"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" ..... <servlet-name>zjat</servlet-name> <servlet-class>zjat</servlet-class> <display-name>Zjat Beta</display-name> </servlet> </web-app> Same error, it tries to employ the applet as default page and dont starts.
/index Zjat Beta false 0 Start Stop Reload Undeploy

Also, the </servlet> must have starting <servlet> tag. Incorrect indentation leads to such problems. And as Bear Bibeault said, where is servlet-mapping?

Carsten Rasmussen

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posted 13 years ago

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Im not so god at english terms will someone please give an examble

Carsten Rasmussen

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posted 13 years ago

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I changed my web.xml to:

And it loads the page in Manager but i cannot see index.jsp and servlet gives this error:

Why oh why must it be, please help

Lester Burnham

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posted 13 years ago

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What object is null at line 42 in zjat.java? Why is it null? Why is the code assuming that it would not be null?

Carsten Rasmussen

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posted 13 years ago

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Sorry my bad, i had change something i shouldent had change, the script is ok.
But why can't i see front page in index/

Mike London

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posted 13 years ago

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I'd recommend using MyEclipse, Intellij IDEA, or a tool that helps you get the configuration correct so you don't have most of these problems.

Try a simple Servlet example first. Look at "Coreservlets.com" or pick up a copy of Marty Hall's book "Core Servlets and JavaServer Pages".

Once you get one working, with a good IDE, it's simple from there.

- mike

William Brogden

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posted 13 years ago

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Wrong

Right

That is what was meant by the earlier comment that ALL Java classes used in servlets MUST be in a package.

A class without a package is in the "default" package - a JVM looks for default classes in the "current" directory, something you have no control over. By using a package you force Tomcat to look in the web application for the class file.

Tomcat usually come with a file "class-loader-howto.html" which explains how Tomcat locates classes.

Bill

colin shuker

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posted 13 years ago

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Netbeans is pretty good, I like the deployment descriptor, its easy to add servlets, you don't need to see the xml, but you can if you want.

Bear Bibeault

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colin shuker wrote:Netbeans is pretty good, I like the deployment descriptor, its easy to add servlets, you don't need to see the xml, but you can if you want.

Which is why I think it's a very bad idea to rely upon IDE's at the outset. If it hides things from you, how are you going to learn how to do it without the crutch?

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Carsten Rasmussen

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Please show a whole example of that package thing please be so kind.

Mike London

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Bear Bibeault wrote:

colin shuker wrote:Netbeans is pretty good, I like the deployment descriptor, its easy to add servlets, you don't need to see the xml, but you can if you want.

Which is why I think it's a very bad idea to rely upon IDE's at the outset. If it hides things from you, how are you going to learn how to do it without the crutch?

I partly agree with Bear, but if you're under pressure to produce code (and why we're, as developers, subjected to "XML-Configuration-Hell" with all the Java components I don't know...), then an IDE is a good way to get a *working* example.....THEN look at the code to see how it's put together if you need/want to. Otherwise, just deliver your code unless you're being paid to explain the XML configuration files! ;)

A clear Java book with good examples where you're not typing in code, but trying to understand concepts separately is also something I do.

Also, if you're a student, then Bear is right, but in that case, I'd still recommend at least using TextPad so you have a somewhat Java-aware editor.

Eclipse can be a little overwhelming if you're new to everything.

HTH

-- Mike

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