[Java] Servlets

A servlet is a class which responds to a particular type of network request (most commonly an HTTP request). Servlets are usually used to implement web applications.

Servlets run in a servlet container, which handles the network side (eg. parsing HTTP request, connection handling.etc). One of the best-known source servlet containers is Tomcat.

Flow of Request

  1. Client sends HTTP request to Web Server
  2. Web Server forwards HTTP request to Web Container
  3. Web Container converts request into valid request object (because servlet cannot understand HTTP; only understands objects)
  4. Web container spins a thread for each request.
  5. All the business logic goes inside doGet() and doPost() methods inside the servlets.
  6. Servlet builds a Java response object and sends it to the container. It converts that to HTTP response again and send it to the client.


Comments

Post a Comment

Popular posts from this blog

[Redis] Redis Cluster vs Redis Sentinel

1) In-Depth Guides to Redis Cluster and Sentinel For more in-depth explanation for Redis Cluster or Redis Sentinel, please read my other posts: Sentinel:  https://notafraidofwong.blogspot.com/2019/05/redis-redis-sentinel.html Cluster:  https://notafraidofwong.blogspot.com/2019/05/redis-redis-cluster.html 2) Deciding between Redis Sentinel and Redis Cluster Similarities : Both solutions provide high availability for your system. 2.1) Redis Cluster 2.1.1) Pros Shards data across multiple nodes Has replication support Has built-in failover of master 2.1.2) Cons Not every library supports it May not be as robust (yet) as Standalone Redis or Sentinel Setup and maintenance is more complicated 2.2) Redis Sentinel 2.2.1) Pros Automatically selects new master in case of failure Easy to setup, (seems) easy to maintain 2.2.2) Cons No data sharding; master might be overutilized. Another distributed system to maintain. 3) So how do I decide? In
Read more

[Unit Testing] Test Doubles (Stubs, Mocks....etc)

Image
In unit testing, isolation is key. The goal of unit testing is to test individual components, and not an entire system . The class/object/function you are testing is System Under Test (SUT) , and the other components of the system are Collaborators or Dependencies. Test Double  is a generic term for any kind of 'pretend' object used in place of a real object for testing purposes.  There are several types of Testing Doubles. We will start with: Fake Stub Mock Command Queries Mocks vs Stubs And then: Dummy Spies Spies vs Mocks I) Basic Testing Doubles a) Fake Fake are objects that have working implementations, but not same as production one. Usually they take some shortcut and have simplified version of production code. Note that Fake is a generic term - that can point to anything; usually mock and stubs. An example of this is an in-memory implementation of a database. This fake implementation will not access the actual database, but will u
Read more

[Node.js] Pending HTTP requests lead to unresponsive nodeJS

This is a recap conclusion to the potential problems of a NodeJS program I worked on previously. The program simulates thousands of clients navigating a website by sending thousands of http requests to a given API . The idea is to load test a particular API to make sure they can handle high traffic. Because we are simulating clients, it's important to keep track of the state of the simulated client as well. The problem with this program is it is buggy and becomes unresponsive from time to time (the only solution is to restart it). The problem was fixed by re-writing the entire program in Java, but it was regretful that I never had enough time to find the exact reason the nodeJS version of it failed. The following are potential causes I suspect: 1. Exceptions The NodeJS program was not written very neatly and stacked callbacks on top of callbacks on top of callbacks. This made it very difficult to keep track of exceptions and unexpected http responses are prone to happen. So
Read more