Examples for java servlet request and response: Examples for java servlet request and response

Java Servlets:

Java servlets are server-side programs (running inside a web server) that handle clients' requests and return a customized or dynamic response for each request. The dynamic response could be based on user's input (e.g., search, online shopping, online transaction) with data retrieved from databases or other applications, or time-sensitive data (such as news and stock prices).

Java servlets typically run on the HTTP protocol. HTTP is an asymmetrical request-response protocol. The client sends a request message to the server, and the server returns a response message as illustrated.

Server-Side Technologies

There are many (competing) server-side technologies available: Java-based (servlet, JSP, JSF, Struts, Spring, Hibernate), ASP, PHP, CGI Script, and many others.

Pre-requisites

HTML, Java Programming Language, HTTP and Apache Tomcat Server, SQL and MySQL Database System, and many others.

Apache Tomcat Server

Servlets are server-side programs run inside a Java-capable HTTP server. Apache Tomcat Server (@ http://tomcat.apache.org) is the official Reference Implementation (RI) for Java servlet and JSP, provided free by open-source foundation Apache (@ http://www.apache.org).

You need to install Tomcat to try out Java servlets. Read "How to Install Tomcat and Get Started Java Servlet Programming".

I shall denote Tomcat's installed directory as <CATALINA_HOME>, and assume that Tomcat server is running in port 8080.

Tomcat provides many excellent servlet examples in "<CATALINA_HOME>\webapps\examples\servlets". You can run these examples by launching Tomcat and issuing URL http://localhost:8080/examples.

Java Servlet Versions

Java Servlet has these versions: [TODO features and what is new]

J2EE 1.2 (December 12, 1999) (Java Servlet 2.2, JSP 1.1, EJB 1.1, JDBC 2.0)

J2EE 1.3 (September 24, 2001) (Java Servlet 2.3, JSP 1.2, EJB 2.0, JDBC 2.1)

J2EE 1.4 (November 11, 2003) (Java Servlet 2.4, JSP 2.0, EJB 2.1, JDBC 3.0)

Java EE 5 (May 11, 2006) (Java Servlet 2.5, JSP 2.1, JSTL 1.2, JSF 1.2, EJB 3.0, JDBC 3.0)

Java EE 6 (December 10, 2009) (Java Servlet 3.0, JSP 2.2/EL 2.2, JSTL 1.2, JSF 2.0, EJB 3.1, JDBC 4.0)

Java EE 7: expected in end of 2012.

The Java Servlets Home Page is @ http://java.sun.com/products/servlet (http://www.oracle.com/technetwork/java/javaee/servlet/index.html). For developers, check out the Servlet Developers @ http://java.net/projects/servlet/.

Java Servlet is the foundation technology for Java server-side programming. You need to understand Servlet thoroughly before you could proceed to other Java server-side technologies such as JavaServer Pages (JSP) and JavaServer Faces (JSF).

Review of HTTP

A HTTP Servlet runs under the HTTP protocol. It is important to understanding the HTTP protocol in order to understand server-side programs (servlet, JSP, ASP, PHP, etc) running over the HTTP. Read "HTTP Basics", if needed.

The above configuration defines a servlet named "HelloWroldServlet", implemented in "mypkg.HelloServlet.class" (written earlier), and maps to URL "/sayhello", where "/" denotes the context root of this webapp "helloservlet". In other words, the absolute URL for this servlet is http://hostname:port/helloservlet/sayhello

Developing and Deploying Web Applications using IDE

It is a lot more productive and efficient to use an IDE (such as Eclipse or NetBeans) to develop your web application. You could start/stop your servers from IDE directly. You could debug your web application in IDE, like debugging standalone application.

NetBeans: Read "Developing and Deploying Web Applications in Netbeans".

Eclipse: Read "Developing and Deploying Web Applications in Eclipse".

Tomcat's Servlet Examples

Tomcat provides a number of excellent servlet examples in "<CATALINA_HOME>\webapps\examples". The servlet source files are kept under "<CATALINA_HOME>\webapps\examples\WEB-INF\classes", together with the compiled classes. To run the examples, start Tomcat server and issue URL http://localhost:8080/examples.

I strongly encourage you to study the examples, Read "Tomcat's Java Servlet Examples Explained".

Database Servlet

Read "Java Servlet Case Study" and "Java Servlet Case Study Continue".

Servlet API – A Deeper Look

A servlet is a Java web component, managed by a servlet container (such as Apache Tomcat or Glassfish), which generates dynamic content in response to client's request. A servlet container (or servlet engine) is a web server extension which provides servlet functionality. A servlet container contains and manages servlets throughout their lifecycle.

Servlet 3.0

Servlet API 3.0 introduces these annotations to simplify deployment in javax.servlet.annotation package:

@WebServlet: Define a servlet component

@WebInitParam: Define initialization parameters for a servlet

@WebListener: Define a listener

@WebFilter: Define a filter

@MultipartConfig: For multipart file upload

For example,

@WebServlet(

name = "HelloServletExample",

urlPatterns = {"/sayhello"},

initParams = {

@WebInitParam(name = "param1", value = "value1"),

@WebInitParam(name = "param2", value = "value2")}

)

public class HelloServlet extends HttpServlet { ...... }

@WebServlet

@WebServlet defines a servlet component and its metadata, with the following attributes:

String[] urlPatterns: An array of String declaring the url-pattern for servlet-mapping. Default is an empty array {}.

String[] value: urlPatterns.

String name: servlet-name, default is empty string "".

loadOnStartup: The load-on-startup order of the servlet, default is -1.

WebInitParam[] initParams: The init parameters of the servlet, default is an empty array {}.

boolean asyncSupported: Declares whether the servlet supports asynchronous operation mode, default is false.