From Request to Response: How Tomcat Processes Your Web Applications

From Request to Response: How Tomcat Processes Your Web Applications

Internals of Apache Tomcat

Are you aware of the request response model that power ups your spring based application ?

Off course, most of us as a developer are using apache tomcat application server to run spring based applications today.

Let’s understand what are the components of Apache tomcat that make a request works and server the purpose with a response.

Youtube Video Link on Apache Tomcat Internals

Components of Apache Tomcat

• Server

  • Represents the entire Catalina servlet container.

• Service

  • Represents combination of one or more connectors that share a single Engine for processing incoming request.

• Engine

  • It receives and process all requests from one or more connectors and returns the response.

  • One engine per service

• HTTP Connector

  • Listens on TCP port number for connections, and forward request to associated engine

    • HTTP/1.1

    • HTTP 2.0

• Executor(Thread Pool)

  • Standard Implementation – (Platform threads to execute tasks)

  • Virtual Thread Implementation (Java 21)

Since we have a some understanding on components of tomcat application server, now let’s have a look on how a request travels through operating system till the time it makes network calls and get our response back.

How synchronous request reaches to Servlet Container “Catalina” ?

• Requests are received on HTTP protocol which is layer-7 protocol.

• HTTP Protocols works on TCP Protocol which is layer-4 protocol.

• That means client creates a TCP connection with server before sending a http call.

• Servlet Container Catalina uses thread pool to assign one thread per request.

• Assigned thread executes the business logic and goes through all spring internal classes, calls external service, database and finally prepares the response back.

• In case none of the thread is available to serve the request at that moment, request will be queued in a queue maintained by Operating system.

So now let’s consolidate everything together and understand the picture along with all tomcat components.

Also, below is the flow of a request from internal’s servlet classes perspective.

Source - https://tomcat.apache.org/tomcat-9.0-doc/config/server.html

For More Information and manual reading you can visit above mentioned sourced url.

So, now by this time we have reached to a conclusion and understanding how a request gets processed by Apache Tomcat application server.

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