Tomcat/Servlets/JSP with NetBeans
— print (last updated: Oct 31, 2009) — print

Server-side web programming

protocol://data_source

file://file
http://server/dir1/dir2/file
http://server/dir1/program
http://server:port/file       (server running on alternate port)

• HTML code generated by programming: (e.g. Perl/CGI, Servlets)
• program code embedded within HTML code: (e.g., PHP, ASP, JSP)

Apache Tomcat

C:\apache-tomcat-6.0.20\

Configure Tomcat Manager

apache-tomcat-6.0.20/conf/tomcat-users.xml

<user username="admin" password="" roles="manager"/>

Configure Tomcat Ports

apache-tomcat-6.0.20/conf/server.xml

<Connector port="8080" protocol="HTTP/1.1"
           connectionTimeout="20000" redirectPort="8443" />
<Server port="8005" shutdown="SHUTDOWN">
<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

<Connector port="8180" protocol="HTTP/1.1"
           connectionTimeout="20000" redirectPort="8443" />

NetBeans Setup

Tools Plugins Available Plugins

Java Web Applications

1. Open the Services window on the left. If necessary bring it up from Windows Services:
2. Right-click on Servers and select Add Server.
3. Choose Tomcat 6.0 from the list in the Choose Server popup. Click Next.
4. In the Add Server Instance window, add this information:

   CataLina Home:  <the Tomcat installation directory>
   UserName:       admin
   Password:       <leave blank>
   
    Create user if it does not exist. (unchecked)
   

   Click Finish.

1. Test startup: Right-click on the Tomcat 6.0 server entry and select Start. If it failed read the failure message closely and try to fix it.
2. Test shutdown: Right-click on the Tomcat 6.0 server entry and select Stop.

Hello World web application

1. From the Projects window, follow New Project Java Web Web Application.
2. Set the Project Name to WebHello. Click Next.
3. Take the default selections:

   Project Name:    WebHello 
   Server:          Tomcat 6.0
   Java EE version: Java EE 5
   Context Path:    /WebHello 
   

   Click Finish (skip the Frameworks dialog).
4. The root file, index.jsp, is automatically brought up in the editor. The Palette window appears on the right. For the most part, I find the Palette not very helpful, and delete it to get more editor space.
5. Edit index.jsp, changing the title tags to:

   <title>Web Hello</title>
   

   Change the header tag (in the body) to

   <h2>Web Hello</h2> 
   

6. Run the project in the usual way you'd run any project. It most likely will use the system default browser and bring up a new browser window or a new tab in an existing browser with the URL:

   http://localhost:8080/WebHello/
   

   displaying what you just created.
   This is the point at which NetBeans accesses the Tomcat Manager. If you see a popup asking for access to the manager, you've made a mistake in the Tomcat server configuration. Go back to the Configure Tomcat Manage section and check your settings.
7. See the project registered in the Tomcat manager. Open

   http://localhost:8080/
   

   and select the Manager hyperlink. Enter the manager username/password in the authentication popup and look for WebHello in the list.
8. Run the Clean and Build choice and observe the output. When you build a Web Application, Tomcat creates a ".war" (web archive) file in the dist directory which can be used to upload to other Java-based web servers such as, perhaps, the "production" version of Tomcat running on a different port or different server.

Create a Hello Servlet

1. Select New Servlet (you may have to go through Other initially).
2. In the Name and Location window, enter this information:

   Class Name:  Hello
   package:     servlet
   

   Click Finish (skip the Configure Servlet Deployment step).

3. Modify the code in processRequest by simply removing the comment lines

     /* TODO output your page here
   

   and

      */
   

4. Run this servlet by itself by selecting Hello.java from the project, right-clicking, and selecting Run File. Click OK in the Set Servlet Execution popup.

http://localhost:8080/WebHello/Hello

The structure of a Servlet

The activation of a servlet is initiated by a client-side (browser) request. There are two types of requests: GET and POST. GET requests are most standard and always activated by typing any URL into a browser. GET requests are also those in which you see parameters delivered in the URL itself after the "?" character, a portion called the query string. POST requests are less frequent and are normally initiated by HTML forms.

NetBeans Servlet template

package servlet;

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

public class Hello extends HttpServlet {
   
  protected void processRequest(
    HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    try {
      /* TODO output your page here
      out.println("<html>");
      out.println("<head>");
      out.println("<title>Servlet Hello</title>");  
      out.println("</head>");
      out.println("<body>");
      out.println(
        "<h1>Servlet Hello at " + request.getContextPath () + "</h1>");
      out.println("</body>");
      out.println("</html>");
      */
    } finally { 
       out.close();
    }
  } 

  protected void doGet(
    HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
    processRequest(request, response);
  } 

  protected void doPost(
    HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
    processRequest(request, response);
  }

  public String getServletInfo() {
    return "Short description";
  }
}

Further Modifications

Add a link to the servlet

<a href="Hello">Hello Servlet</a>

Changes in JSP vs. changes in Servlets

1. Change the line in index.jsp to:

   <a href="Hello">A Hello Servlet Link</a>
   

   Then simply refresh the browser window (not re-run) to observe that you've picked up the change. Click on the servlet hyperlink again.
2. Now edit the Hello servlet. Add this line:

   out.println("Test addition");
   

   Just before the line:

   out.println("</body>");
   

   Then Save and refresh the browser and observe that the change is (hopefully) picked up as well.

Create a dynamic JSP hello script

New JSP

JSP File Name:  hello        (the .jsp extension is automatically added)

<%@page contentType="text/html"%>
<%@page pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">
<% String title = "JSP Hello"; %>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title><%= title %></title>
  </head>
  <body>
  <h2><%= title %></h2>
  <% out.println("Hello Again"); %>
  </body>
</html>

<br /><a href="hello.jsp">Hello JSP</a>

• The tags <% ... %> are points for entry of Java code.
• The tags <%= ... %> allow for the printing of a Java expression.
• The variable out used in the last tag pair is a predefined variable for JSP scripts which has the same effect as in servlets which specifically define it as:

      PrintWriter out = response.getWriter();
  

Discussion

Tomcat Web configuration file

Web Pages/WEB-INF/web.xml

• The welcome-file-list element. The welcome-file entries are automatically used when a browser accesses a directory. NetBeans only has one initially, index.jsp, but you can add other likely choices such as index.html, index.htm, etc.
• The servlet and servlet-mapping elements. Tomcat uses these and three other elements to map the URL /WebHello/Hello to the servlet.Hello class:
  • url-pattern: /Hello, meaning that the URL /WebHello/Hello activates the servlet
  • servlet-name: Hello, this relates the servlet and servlet-mapping groups.
  • servlet-class: servlet.Hello, the actual class that is executed

JSP usage

<%  
  /* Java code here */
%>

for (int i=0; ... ) {
  %>
  <!-- HTML code -->
  <%
}

<% for (String s: some_list) { %>
  <!-- HTML code -->
<% } %>

<% if (x == 5) { %>
  <!-- HTML code -->
<% else if (x == 6) { %>
  <!-- HTML code -->
<% } %>

HttpServletRequest  request
HttpServletResponse response
JspWriter           out          (like PrintWriter in servlets)
HttpSession         session

public void _jspService(HttpServletRequest request, 
                        HttpServletResponse response)
        throws java.io.IOException, ServletException {
  // converted HTML + Java code
}

JSP vs. Servlets