Tomcat Interview Questions and Answers

Ques 1. What is Tomcat?

• Tomcat is a Java Servlet container and web server from the Jakarta project of the Apache software foundation.
• A web server responds with web pages to requests from client browsers.
• Web servers can provide dynamic content based on the requests sent by the user.
• Tomcat is very good to provide dynamic content because it provides both Java servlet and JavaServerPages (JSP) technologies.
• Tomcat can also be used as a web server for many applications even if free servlet and JSP engine is wanted.
• It can be used standalone or used behind traditional web servers such as Apache httpd, with the traditional server serving static pages and Tomcat serving dynamic servlet and JSP requests.

Ques 2. What is WebServers? Why it is used?

Transaction with HTTP request and HTTP response is called webserver.
rnUsing the internet listening the HTTP request and providing the HTTP response is also called webserver. It gives only html output. It will not process business logic .They can provide Http server. They are static.

Ques 3. How do I use DataSources with Tomcat?

Ques 4. How will you load properties file?

• Use a ResourceBundle. See the Java docs for the specifics of how the ResourceBundle class works. Using this method, the properties file must go into the WEB-INF/classes directory or in a jar file contained in the WEB-INF/lib directory. 
  
• Another way is to use the method getResourceAsStream() from the ServletContext class. This allows you update the file without having to reload the webapp as required by the first method. Here is an example code snippet, without any error trapping: 

// Assuming you are in a Servlet extending HttpServlet
// This will look for a file called "/more/cowbell.properties" relative
// to your servlet Root Context
InputStream is = getServletContext().getResourceAsStream("/more/cowbell.properties");
Properties p = new Properties();
p.load(is);
is.close();

Ques 5. What is different between webserver and application server?

The basic difference between a web server and an
application server is Webserver can execute only web applications i,e servlets and JSPs and has only a single container known as Web container which is used to interpret/execute web
applications.
Application server can execute Enterprise application, i,e (servlets, jsps, and EJBs) it is having two containers
1. Web Container(for interpreting/executing servlets and jsps)
2. EJB container(for executing EJBs). it can perform operations like load balancing , transaction demarcation etc.

Ques 6. How do you create multiple virtual hosts?

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 7. Can I set Java system properties differently for each webapp?

No. If you can edit Tomcat's startup scripts, you can add "-D" options to Java. But there is no way to add such properties in web.xml or the webapp's context.

Ques 8. How do I configure Tomcat to work with IIS and NTLM?

Follow the standard instructions for when the isapi_redirector.dll

• Configure IIS to use "integrated windows security"
  
• In server.xml, make sure you disable tomcat authentication: 
  

<Connector port="8009" enableLookups="false" redirectPort="8443" protocol="AJP/1.3" tomcatAuthentication="false" />

Ques 9. How can I access members of a custom Realm or Principal?

When you create a custom subclass of RealmBase or GenericPrincipal and attempt to use those classes in your webapp code, you'll probably have problems with ClassCastException. This is because the instance returned by request.getUserPrincipal() is of a class loaded by the server's classloader, and you are trying to access it through you webapp's classloader. While the classes maybe otherwise exactly the same, different (sibling) classloaders makes them different classes.


This assumes you created a My Principal class, and put in Tomcat's server/classes (or lib) directory, as well as in your webapp's WEB-INF/classes (or lib) directory. Normally, you would put custom realm and principal classes in the server directory because they depend on other classes there.

Principal p = request.getUserPrincipal(); 

String emailAddress = p.getClass().getMethod("getEmailAddress", null).invoke(p, null);

You could put your custom classes in a classloader that is common to both the server and your webapp - e.g., either the "common" or bootstrap classloaders. To do this, however, you would also need to move the classes that your custom classes depend on up to the common classloader, and that seems like a bad idea, because there a many of them and they a core server classes. 

Rather than move the implementing custom classes up, you could define interfaces for your customs classes, and put the interfaces in the common directory. You're code would look like this: 

public interface MyPrincipalInterface extends java.security.Principal { 

public String getEmailAddress();

}

public class MyPrincipal implements MyPrincipalInterface { 

...

public String getEmailAddress() {

return emailAddress;

}

}

public class MyServlet implements Servlet { 

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws

ServletException, IOException {

MyPrincipalInterface p = (MyPrincipalInterface)request.getUserPrincipal();

String emailAddress = p.getEmailAddress();

...

}

Notice that this method gives you pretty much the webapp code you wanted in the first place

You might want to try serializing the response of 'request.getUserPrincipal()' and deserialize it to an instance of [webapp]MyPrincipal.

Ques 10. How do I override the default home page loaded by Tomcat?

After successfully installing Tomcat, you usually test it by loading http://localhost:8080 . The contents of that page are compiled into the index_jsp servlet. The page even warns against modifying the index.jsp files for this reason. Luckily, it is quite easy to override that page. Inside $TOMCAT_HOME/conf/web.xml there is a section called <welcome-file-list> and it looks like this:

<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
The default servlet attempts to load the index.* files in the order listed. You may easily override the index.jsp file by creating an index.html file at $TOMCAT_HOME/webapps/ROOT. It's somewhat common for that file to contain a new static home page or a redirect to a servlet's main page. A redirect would look like:

<html>

<head>
<meta http-equiv="refresh" content="0;URL=http://mydomain.com/some/path/to/servlet/homepage/">
</head>

<body>
</body>

</html>
This change takes effect immediately and does not require a restart of Tomcat.

Ques 11. How do I enable Server Side Includes (SSI)?

Ques 12. What is Jasper?

• Jasper is Tomcat's JSP Engine. Tomcat 5.x uses Jasper 2, which is an implementation of the Sun Microsystems's JavaServer Pages 2.0 specification.
• Jasper parses JSP files to compile them into Java code as servlets (that can be handled by Catalina).
• At runtime, Jasper is able to automatically detect JSP file changes and recompile them.

Ques 13. Explain the concepts of Tomcat Servlet Container.

• A servlet container is a specialized web server that supports servlet execution.
• It combines the basic functionality of a web server with certain Java/servlet specific optimizations and extensions (such as an integrated Java runtime environment, and the ability to automatically translate specific URLs into servlet requests).
• Individual servlets are registered with a servlet container, providing the container with information such as the functionality, the URL used for identification.
• The servlet container then initializes the servlet as necessary and delivers requests to the servlet as they arrive.
• Many containers can dynamically add and remove servlets from the system, allowing new servlets to quickly be deployed or removed without affecting other servlets running from the same container.
• Servlet containers are also referred to as web containers or web engines.

Ques 14. Question : How to communicate between two webservers in two diff systems?

By using plug module .

Ques 15. How web server handles multiple requests for same action class(Struts) concurrently?

Struts or any webserver makes new thread for each new request. so multiple request is served with new request object.

Ques 16. Suppose when we are starting startup.bat file of Tomcat server it is not started. DOS window appears for a Second only. What we need do?

Your set up might have been not done well.