A simple servlet that uses Maven, JDBC, and Jetty to say 'Hello world'

Setup The Database

First, make a database, user, table and add a record:

CREATE DATABASE mjjs DEFAULT CHARACTER SET utf8;
GRANT ALL ON mjjs.* TO 'mjjsuser'@'localhost' IDENTIFIED BY 'mjjspassword';
GRANT ALL ON mjjs.* TO 'mjjsuser'@'127.0.0.1' IDENTIFIED BY 'mjjspassword';
CREATE TABLE mjjs (name TEXT) ENGINE = InnoDB DEFAULT CHARSET=utf8;
INSERT INTO mjjs (name) VALUES ('tsugi');

If you have changed any of the values in the example SQL above, edit the file src/main/resources/application.properties and edit these properties:

mjjs.datasource.url=jdbc:mysql://localhost:8889/mjjs
mjjs.datasource.username=mjjsuser
mjjs.datasource.password=mjjspassword
mjjs.datasource.driverClassName=com.mysql.jdbc.Driver

Build / Run

mvn clean compile install jetty:run

Then navigate to

http://localhost:8080/mjjs/hello

If you get this message:

Reading /application.properties ...
Your database is missing or inaccessible

Fire up MAMP, go to localhost:8888/phpMyAdmin, click on SQL tab and copy paste these lines of SQL into the text box and hit "Go"

CREATE DATABASE mjjs DEFAULT CHARACTER SET utf8;
GRANT ALL ON mjjs.* TO 'mjjsuser'@'localhost' IDENTIFIED BY 'mjjspassword';
GRANT ALL ON mjjs.* TO 'mjjsuser'@'127.0.0.1' IDENTIFIED BY 'mjjspassword';

Refresh the phpMyAdmin page, and mjjs now appears on the left. Click on the mjjs database and then click on the SQL tab. Copy paste this command into the text box and hit go

CREATE TABLE mjjs (name TEXT) ENGINE = InnoDB DEFAULT CHARSET=utf8;
INSERT INTO mjjs (name) VALUES ('tsugi');

Refresh this page: http://localhost:8080/mjjs/hello

If all goes well, you will see output like the following:

Welcome to hello world!
Reading /application.properties ...
name=tsugi
Successfully read 1 rows from the database

Looking at the Source Code

• The pom.xml file controls the build process - it tells mvn where the source files are located and what output files to produce. It also tells mvn to download library code for the declared code libraries that this application "depends on".

• The src/main/java/mjjs/HelloServlet.java contains the source code for our Java Servlet. If you look at the code, you will see methods for doGet() and doPost() - these methods are called when there is a GET or POST to the application's URLs. It defines a class called mjjs.HelloServlet that is referenced in the next file. You can debug this program by adding calls to System.out.println() and those print statements will come out on your console.

• The src/main/webapp/WEB-INF/web.xml file tells the servlet container (Jetty in this case) which URLs are to be handed to which classes. If you lok at this file, it has two sections - one defines a servlet and maps it to the java class and the other takes a URL pattern and indicates that it needs to be sent to a particular servlet (i.e. which Java class).

Background Documentation to Read

These are some online resources to read that explain how things in this servlet works:

• How to Write a Hello World Servlet
• HttpServlet interface - javax.servlet.http.HttpServlet
• Request Object interface - javax.servlet.http.HttpServletRequest
• Response Object Interface - javax.servlet.http.HttpServletResponse
• Lesson: JDBC Basics
• Database Connection interfaces - java.sql

Errors

If you end up with this error,

No plugin found for prefix 'jetty' in the current project and in the
plugin groups [org.apache.maven.plugins, org.codehaus.mojo] available
from the repositories