Servlet

|
In Java EE world, Servlet simply is a web technology with which we can receive and handle the HTTP requests, create HTTP response and return that response back to the client.

 Servlet technology makes a basis for other Java web technologies on top of which other frameworks put their extensions. For example JSP, JSF, Spring MVC are such technologies which are uses Servlet technology at behind. 

 Servlets run on a web container such as Tomcat which provides the services on Java EE technology stack. 

What is a servlet ?

Servlet simply makes an object having HTTP-server functionality when its class extends HttpServlet class.
  • A servlet is mapped to a URL to which clients request
  • HTTP requests made to the URL is directed to the corresponding Servlet object
  • Servlet implementation receives the request in the form of GET, POST, PUT or DELETE
  • Servlet implementation runs a business logic and prepares an HTTP response and sends it back to the client just an HTTP server does
  • Lifecycle of the servlet is managed by the web container
In this article, i will not dive into Servlet basics, but mostly the new features come with Java EE 6 and will use this article as umbrella and update it for new coming features of Servlets with upcoming Java EE versions.

1. Servlet 3.0

Servlet 3.0 is specified with JSR 315 under the Java EE 6 specification and added important features to Servlet technology especially annotation-ware usage.

1.1 @WebServlet

@Webservlet annotation has come with Java EE 6. It basically does the mapping of Servlet class with the URLs; instead of doing this job in web.xml file.
@WebServlet(name="Simple Servlet", urlPatterns={"/simpleServlet", "/testServlet"})
public class SimpleServlet extends HttpServlet

1.2 @WebInitParam

@WebInitParam annotation can be used to declare initialization parameters for which we have been using init-param in web.xml, instead.
@WebServlet(name="Simple Servlet", 
          urlPatterns={"/simpleServlet", "/testServlet"},
          initParams={@WebInitParam(name="p1", value="v1"), 
                      @WebInitParam(name="p2", value="v2")})

1.3 @WebFilter

@WebFilter annotation can be used to declare a Servlet Filter.
@WebFilter(servletNames = {"SimpleServlet"})
public class SimpleServletFilter implements Filter

1.4 @WebListener

@WebListener annotation can be used to declare Servlet listener without any decleration in web.xml. Following listeners interfaces are at the scope if implemented:
    - javax.servlet.ServletContextListener
    - javax.servlet.ServletRequestListener
    - javax.servlet.http.HttpSessionIdListener
    - javax.servlet.ServletContextAttributeListener 
    - javax.servlet.ServletRequestAttributeListener
@WebListener
public class SimpleServletContextListener implements ServletContextListener

1.5 Async Servlet

Along with Servlet 3.0, asyncSupported can be used to make long running requests execute on different threads than of threads allocated for Servlets.
@WebServlet(urlPatterns = {"/asynch"}, asyncSupported = true)
public class SimpleAsyncServlet extends HttpServlet

1.6 web.xml

We still need web.xml file for features that are not supported via annotations. Welcome file decleration is one of them. 
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns="http://java.sun.com/xml/ns/javaee"
      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
      id="WebApp_ID" version="3.0">
   <display-name>servlet3</display-name>
   <welcome-file-list>
      <welcome-file>index.html</welcome-file>
      <welcome-file>index.jsp</welcome-file>
   </welcome-file-list>
</web-app>


2. Servlet 3.1

Servlet 3.1 is specified with JSR 340 under the Java EE 7 specification and some behavioural changes have been made to the specification and non-blocking io support is added to the specification.

2.1 Non-Blocking I/O

Along with Servlet 3.0, we can execute long-running jobs within seperate threads so we can prevent the Servlet to be blocked with this long-running tasks. However, that is not the only bottleneck; a block can also be happened while reading the request or writing the response and if so, the Servlet could be again blocked. Therefore, the non-blocking io can be used when reading/writing the streams along with the Servlet 3.1.

 Sample code for this can be found on my github and the below references section.

2.2 References

https://www.ibm.com/support/knowledgecenter/en/SSEQTP_liberty/com.ibm.websphere.wlp.doc/ae/cwlp_servlet31_behavior.html


3. Servlet 4.0

Along with Java EE 8, Servlet 4.0 includes major updates in servlet specification. Two of the most noteworthy are HTTP/2 protocol support and Server Push which is also the most noteworthy HTTP/2 enhancement.

 Major browsers implements HTTP/2 over TLS so https configuration sould be done in your server.
request.newPushBuilder()
    .path("image/javalopment.png")
    .addHeader("content-type", "image/png")
    .push();
response.getWriter()
    .write("<html><body>" + "<img src='image/javalopment.png'>" + "</body></html>");

You can find my Servlet code samples in my github page:

Yorumlar

Yorum Gönder

Popular

Java 14 New Features

|
Java SE 14 was released in March 2020. The full list of new features in JDK 14 can be found here: https://openjdk.org/projects/jdk/14/   In this tutorial, we will look over some of these new features and examine some of them. 1. JEP 305: Pattern Matching for instanceof (Preview) With this JEP, instanceof now allows casting of the checked object to a variable. Before Java 14: if (obj instanceof String) { String s = (String) obj; // use s } With Java 14: if (obj instanceof String s) { // can use s here } else { // can't use s here } 2. JEP 345: NUMA-Aware Memory Allocation for G1 This JEP i mproves G1 performance on large machines by implementing NUMA-aware( non-uniform memory access ) memory allocation. Use the  +XX:+UseNUMA option to enable it. 3. JEP 358: Helpful NullPointerExceptions This JEP  improves the usability of  NullPointerException  generated by the JVM by describing precisely which variable was  null . Let's look over the following code which throw
Devamı

Pretenders, Contenders and Liars

|
Life is a way to the uncertainity. This is an exact fact. In this uncertain journey, we meet kinds of people of having different behaviours, and generally label them according to their behaviours. In this writing, i will try to write my understanding of three of these labels; pretenders, contenders and liars. Pretenders A pretender is a kind of people who pretends :) It does not do what it seems to do. It does what it does not seem to do. We frequently meet pretenders in our daily life. And if we catch a person pretending, then we feel that is not sincere. Okay, then here is a question sincerely to ask yourself; do you ever find yourself pretending ? Contenders A contender is a person who has a goal to reach and do not hesitate to fight for that goal. So a contender is sincere ? Absolutely yes, you may be completely opposite to a contender, but if you know that it's a contender, then you know that it's sincere in its behaviours. And sure it is, if you trus
Devamı

Java 12 New Features

|
Java SE 12 was released in March 2019. The full list of new features in JDK 12 can be found here: https://openjdk.org/projects/jdk/12/   In this tutorial, we will look at some of these new features and examine some of them. 1. JEP 189:  Shenandoah: A Low-Pause-Time Garbage Collector (Experimental) Shenandoah is a new garbage collection (GC) algorithm which reduces GC pause times,  independent of heap size. This GC algorithm is experimental so in order to use it with Java 12, you have to enable it : -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC 2. JEP 325:  Switch Expressions (Preview) This JEP extends the switch statement to be used as either a statement or an expression. Meaning that we can now return a value from a switch expression. Before Java 12, we can return a value by assigning it to a variable: String getColor(int num) { String result = ""; switch (number) { case 1, 2, 3: result = "red, green or blue"; break;
Devamı