Writing your first JSP and Servlet using Vim

Moving to Java from scripting languages can be a tedious process. A lot of times, it is hard to understand what the IDE does in the background to serve our web application. Hence, I’m writing these quick bite-sized notes as I learn.

Servlets and JSPs run on a Servlet Container such as Apache Tomcat, Jetty, etc. When we write a Servlet in an IDE such as Eclipse, the IDE takes care of building the class and serving it. This note will help you write your first servlet without an IDE (you can even use notepad to follow along).

Setting up Vim for Java

To begin with, Syntastic is good enough. you can try solutions like Eclim, but I was recommended to move to IDEs once I pick up with the underlying basics since Java needs a lot of configuring and building process.

Tomcat Structure

You can tomcat from here.

Directory	Description
bin	contains all tomcat related scripts such as shutdown, startup, etc.
conf	contains tomcat configuration files such as web.xml and server.xml.
lib	contains tomcat required jars including servlet-api.jar.
logs	all tomcat generated logs are stored here.
temp	JVM writes temporary files here.
work	stores compiled JSPs and other assests.
webapps	contains all webapps deployed by tomcat. .war files placed here are expanded automatically.
WEB-INF	contains application related files that aren’t served such as web.xml, libraries, and servlet class files.

Starting Tomcat

Once you have downloaded tomcat, you can start it by opening your command line/terminal in the directory and running bin/startup.sh. (bin/startup.bat for windows). Now tomcat is started in port 8080.

Similarly, you can quit tomcat by running bin/shutdown.sh or bin/shutdown.bat.

Serving JSPs

By default, your webapps/ROOT is served. replace the default index.jsp with the following:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello World</title>
</head>
<body>
    <%= "Hello World" %>
</body>
</html>

Since JSP files are automatically compiled by Tomcat, you do not need to restart the server.

Compiling and Serving Servlets

Write a simple servlet class

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

public class Hello extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html");

    PrintWriter out = response.getWriter();
    out.println("<h1>Hello World</h1>");
    }
}

Compile the servlet class

To compile the servlet class, you need to include servlet-api.jar to your CLASSPATH.

export CLASSPATH=/path/to/tomcat/lib/servlet-api.jar

Move the generated .class file to WEB-INF/classes.

Add entry to deployment descriptor (web.xml)

Add the following between <web-app> in WEB-INF/web.xml:

<servlet>
<servlet-name>Hello</servlet-name>
<servlet-class>Hello</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>Hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>

Entry to web.xml works like this:

First add the servlet class with a name within <servlet>.
Then map that servlet name to a URL within <servlet-mapping>.

Restart tomcat

./bin/shutdown.sh
./bin/startup.sh

That’s it. Navigate to http://localhost:8080/hello to see your servlet. This note is the first in my JavaBytes series. Hope this had helped you to know what eclipse does under the hood.

So long!