Monday, 3 January 2022

Top 20 Apache Tomcat Interview Questions and Answers

  

       Tomcat is a Java Servlet container and web server developed by the Apache Software Foundation's Jakarta project. Client browsers send queries to a web server, which the server answers to with web pages. Web servers can generate dynamic content based on the user's requests. Because it supports both Java servlet and JavaServerPages (JSP) technologies, Tomcat excels at this. Even if a free servlet and JSP engine is required, Tomcat can be utilised as a web server for a variety of applications. It can run on its own or alongside standard web servers like Apache httpd, delivering static pages while Tomcat handles dynamic servlet and JSP queries.

    Apache Tomcat is an open source Java Servlet, JavaServer Pages, Java Expression Language, and Java WebSocket implementation platform. Many firms are hiring Devops engineers, Apache Tomcat administrators, Linux Apache Tomcat jobs, and Hadoop developers at varying levels of experience. The most popular Web server is Apache, and you must be familiar with it if you plan to work as a Middleware/System/Web administrator. Apache HTTP is a free and open-source web server that runs on Windows and Linux.

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Ques. 1): Who is in charge of Tomcat?

Answer:

The Apache Software Foundation is the correct answer. The Apache Software Foundation is a non-profit organisation that oversees several Open Source projects.

The Apache Software Foundation's Java-based projects are referred to as Jakarta.

Tomcat is an Apache Jakarta project that manages server-side Java (in the form of Servlets and JSPs). Tomcat is the "reference" implementation of the Servlet and JSP specifications, which means that anything that runs in Tomcat should run in any compliant Servlet / JSP container.

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Ques. 2): Difference between apache and apache-tomcat server?

Answer: 

Apache: Apache is mostly used to serve static content, but there are numerous add-on modules (some of which are included with Apache) that allow it to modify the content and serve dynamic content written in Perl, PHP, Python, Ruby, and other languages.

Apache is an HTTP server that serves HTTP requests.

Tomcat is a servlet/JSP container developed by Apache. It's written in the Java programming language. Although it can provide static information, its primary function is to host servlets and JSPs.

JSP files (which are comparable to PHP and older ASP files) are converted into Java code (HttpServlet), which is then compiled into.class files and run by the Java virtual machine by the server.

Apache Tomcat is used to deploy your Java Servlets and JSPs. So in your Java project, you can build your WAR (short for Web ARchive) file, and just drop it in the deploy directory in Tomcat.

Although it is possible to get Tomcat to run Perl scripts and the like, you wouldn’t use Tomcat unless most of your content was Java.

Tomcat is a Servlet and JSP Server serving Java technologies

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Ques. 3):  What exactly is Coyote?

Answer:

Coyote is a Tomcat Connector component that acts as a web server and supports the HTTP 1.1 protocol. This enables Catalina, which is ostensibly a Java Servlet or JSP container, to additionally serve local files as HTTP documents.

Coyote monitors a specific TCP port for incoming connections to the server and transmits the request to the Tomcat Engine, which processes the request and returns a response to the requesting client.

Coyote is Tomcat's HTTP connector, which offers an interface for browsers to connect to.

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Ques. 4): What is a servlet container?

Answer:

A servlet container is a web server component that communicates with Java servlets. The servlet container is in charge of managing servlet lifecycles, mapping URLs to specific servlets, and ensuring that the URL requester has the appropriate access privileges.

Requests to servlets, JavaServer Pages (JSP) files, and other types of files containing server-side code are handled by the servlet container. The Web container generates servlet instances, loads and unloads servlets, creates and manages request and response objects, and handles other servlet-related operations.

The web component contract of the Java EE architecture is implemented by the servlet container, which defines a runtime environment for web components that includes security, concurrency, lifecycle management, transaction, deployment, and other services.

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Ques. 5): How Do I Can Change The Default Home Page Loaded By Tomcat?

Answer :

We can easily override home page via adding welcome-file-list in application $TOMCAT_HOME/webapps//WEB-INF /web.xml file or by editing in container $TOMCAT_HOME/conf/web.xml

In $TOMCAT_HOME/conf/web.xml, it may look like this:

    index.html

    index.htm

    index.jsp

Request URI refers to a directory, the default servlet looks for a "welcome file" within that directory in following order: index.html, index.htm and index.jsp

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Ques. 6): what is a difference between Apache and Nginx web server?

Answer:

Both are classified as Web Servers, but there are a few key differences. Nginx is an event-driven web server, whereas Apache is a process-driven web server.

Nginx has a reputation for being faster than Apache.

Whereas Nginx does not support OpenVMS or IBMi, Apache supports a wide range of operating systems.

Nginx is still catching up to Apache in terms of module interoperability with backend application servers.

Nginx is a lightweight web server that is rapidly gaining market share. If you're new to Nginx, you might be interested in reading some of my Nginx articles.

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Ques. 7): How Do You Create Multiple Virtual Hosts?

Answer :

If you want tomcat to accept requests for different hosts e.g. www.myhostname.com then you must

Create ${catalina.home}/www/appBase , ${catalina.home}/www/deploy, and ${catalina.home}/conf/Catalina/www.myhostname.com

Add a host entry in the server.xml file

Create the the following file under conf/Catalina/www.myhostname.com/ROOT.xml

Add any parameters specific to this hosts webapp to this context file

Put your war file in ${catalina.home}/www/deploy

When tomcat starts, it finds the host entry, then looks for any context files and will start any apps with a context.

 

Ques. 8): In Apache Tomcat, what is Catalina?

Answer:

Once Jasper has completed the compilation, it turns JSP into a servlet, which Catalina can then manage. Catalina is a servlet container for Tomcat. It also implements all of the Java server page and servlet specs. Catalina is a Java engine embedded into Tomcat that provides an efficient environment for servlets to execute in.

 

Ques. 9): What exactly do you mean by Tomcat's default port, and can it be used with SSL?

Answer:

Tomcat uses port 8080 as its default port. Well, you can change it by editing the server.xml file in the Tomcat install directory's conf folder. By adjusting the property to the desired port connection port="8080" and then restarting Tomcat, the modifications will take effect.

Tomcat can use SSL, but it will require some configuration. You must complete the following tasks:

Generate a keystore

Then add a connector in server.xml

Restart Tomcat

 

Ques. 10): What is a mod_evasive module, and what does it do?

Answer:

Mod_evasive is a third-party module that accomplishes one simple task really well. It identifies when your site is under attack by a Denial of Service (DoS) attack and mitigates the harm that the attack causes. When a single client makes repeated requests in a short period of time, mod evasive recognises this and refuses additional requests from that client. The ban can last for a very short time because it is simply reissued the following time a request is discovered from that same host.

 

Ques. 11): Explain Directory Structure Of Tomcat?

Answer :

Directory structure of Tomcat are:

bin - contain startup, shutdown, and other scripts (*.sh for UNIX and *.bat for Windows systems) and some jar files also there.

conf - Server configuration files (including server.xml) and related DTDs. The most important file in here is server.xml. It is the main configuration file for the container.

lib - contains JARs those are used by container and Servlet and JSP application programming interfaces (APIs).

logs - Log and output files.

webapps – deployed web applications reside in it .

work - Temporary working directories for web applications and mostly used during in JSP compilation where JSP is converted to a Java servlet.

temp - Directory used by the JVM for temporary files .

 

Ques. 12): Explain How Running Tomcat As A Windows Service Provides Benefits?

Answer :

Running Tomcat as a windows service provides benefits like:

Automatic startup: It is crucial for environment where you may want to remotely re-start a system after maintenance

Server startup without active user login: Tomcat is run oftenly on blade servers that may not even have an active monitor attached to them. Windows services can be started without an active user

Security: Tomcat under window service enables you to run it under a special system account, which is protected from the rest of the user accounts

 

Ques. 13): How Do Servlet Life Cycles Work?

Answer:

The life-cycle of a typical Tomcat servlet is as follows:

Through one of its connectors, Tom-cat receives a request from a client.

This request will be processed. This request is routed through Tomcat to the proper server.

Tomcat checks that the servlet class has been loaded after the request has been forwarded to the proper servlet. If it isn't, Tomcat wraps the servlet in Java Bytecode, which is executed by the JVM and creates a servlet instance.

The servlet is started by Tomcat by invoking its init method. The servlet includes code that can inspect Tomcat configuration files and take appropriate action, as well as declare any resources it might need.

Once the servlet has been started, Tomcat can call the servlet’s service method to proceed the request

Tomcat and the servlet can co-ordinate or communicate through the use of listener classes during the servlet’s lifecycle, which tracks the servlet for a variety of state changes.

To remove the servlet, Tomcat calls the servlets destroy method.

 

Ques. 14): In Tomcat, what is the difference between a host and a context?

Answer:

In Tomcat, the host is a component. It's a network name association for the server. On the other hand, context is an element that indicates a web application that is running on a certain virtual host. Web applications are built on top of a Web Application Archive (WAR) file or a corresponding directory that contains all of the unpacked content indicated in the servlet description.

 

Ques. 15): What Is The Distinction Between A Webserver And An Application Server?

Answer:

The main distinction between a web server and an application server is that a web server can only execute web applications, such as servlets and JSPs, and has just one container, the Web container, that is used to understand and execute web applications. The application server has the ability to run Enterprise applications, i.e. (servlets, jsps, and EJBs)

it is having two containers:

Web Container(for interpreting/executing servlets and jsps)

EJB container(for executing EJBs).

it can perform operations like load balancing , transaction demarcation etc.

 

Ques. 16): Apart from Apache Tomcat, what are the different kinds of Web Servers?

Answer:

There are many web servers as mentioned below:

LiteSpeed Web Server

GWS Web Server

Microsoft IIS Web Server

Nginx Web Server

Jigsaw Web Server

Sun Java System Web Server

Lighttpd Web Server

 

Ques. 17): How to limit upload size?

Answer:

I have a web application that allows users to upload files such as word documents, pdf and so on.  How do I limit file upload by users?

You can make use of the LimitRequestBody directive to limit upload file size.

<Directory "usr/local/apache2/uploads">

LimitRequestBody 9000

</Directory>

The value assigned to the LimitRequestBody allows Apache to accept and store file uploads of 9000 bytes by users. You can adjust the value based on the requirement.

 

Ques. 18): Explain how to use WAR files to deploy a web application.

Answer:

JSPs, servlets, and their associated files are placed under Tomcat's web applications directory in the appropriate subdirectories. You can combine all of the files in the web apps directory into a single compressed file with the extension.war. A web application can be run by placing a WAR file in the webapps directory. When a web server starts up, it extracts the contents of the WAR file and places them in the proper webapps sub-directories.

 

Ques. 19): How can an Apache Service be stopped by its control script?

Answer:

The Apache Service is controlled using a script called the apachectl.

So, to stop the service, we need to run the below-mentioned commands.

#apachectl stop [for Ubuntu based system]

# /etc/inid.t/httpd.stop [for red hat based system]

 

Ques. 20): What is the purpose of the Listen property in Apache Tomcat?

Listening is very important for Apache Tomcat and the developers.

If a developer has numerous IPs on the server, we must explicitly indicate IP and PORT in the Listen Drive if we want Apache to evaluate only one of them.

For example: 10.10.10.20

 

 

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