Tomcat Interview Questions

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Tomcat Interview Questions – 1

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

  1. add a host entry in the server.xml file
      <Host appBase="www/appBase" name="www.myhostname.com"/>
  2. Create the the following file under conf/Catalina/www.myhostname.com/ROOT.xml
    <?xml version="1.0" encoding="UTF-8"?>
    <Context
        path="/"
        docBase="www/deploy/mywebapp.war"
        reloadable="true" antiJARLocking="true">
    </Context>

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

  3. 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. To add more sites just repeat and rinse, all webapps can share the same war file location and appbase

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();

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.

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" />

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 webinf/classes (or lib) directory. Normally, you would put custom realm and principal classes in the server directory because they depend on other classes there.

Here’s what you would like to do, but it throws ClassCastException:

MyPrincipal p = request.getUserPrincipal();
String emailAddress = p.getEmailAddress();

Here are 4 ways you might get around the classloader boundary:

  1. Reflection
    Principal p = request.getUserPrincipal();
    String emailAddress = p.getClass().getMethod("getEmailAddress", null).invoke(p, null);
  2. Move classes to a common classloader

    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.

  3. Common Interfaces
    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

  4. Serializing / Deserializing
    You might want to try serializing the response of ‘request.getUserPrincipal()’ and deserialize it to an instance of [webapp]MyPrincipal.

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.

How do I enable Server Side Includes (SSI)?

Two things have to be done for tomcat to aknowledge SSI scripts:

  1. Rename $CATALINA_BASE/server/lib/servlets-ssi.renametojar to $CATALINA_BASE/server/lib/servlets-ssi.jar.
  2. Uncomment the section of web.xml found in $CATALINA_BASE/conf/web.xml that deals with SSI. it looks like this when it is uncommented:
    <servlet>
            <servlet-name>ssi</servlet-name>
            <servlet-class>
              org.apache.catalina.ssi.SSIServlet
            </servlet-class>
            <init-param>
              <param-name>buffered</param-name>
              <param-value>1</param-value>
            </init-param>
            <init-param>
              <param-name>debug</param-name>
              <param-value>0</param-value>
            </init-param>
            <init-param>
              <param-name>expires</param-name>
              <param-value>666</param-value>
            </init-param>
            <init-param>
              <param-name>isVirtualWebappRelative</param-name>
              <param-value>0</param-value>
            </init-param>
            <load-on-startup>4</load-on-startup>
        </servlet>

How do I use DataSources with Tomcat?

When developing J2EE web applications, the task of database connection management can be daunting. Best practice involves using a J2EE DataSource to provide connection pooling, but configuring DataSources in web application servers and connecting your application to them is often a cumbersome process and poorly documented.

The usual procedure requires the application developer to set up a DataSource in the web application server, specifying the driver class, JDBC URL (connect string), username, password, and various pooling options. Then, the developer must reference the DataSource in his application’s web.xml configuration file, and then access it properly in his servlet or JSP. Particularly during
development, setting all of this up is tedious and error-prone.

With Tomcat 5.5, the process is vastly simplified. Tomcat allows you to configure DataSources for your J2EE web application in a context.xml file that is stored in your web application project. You don’t have to mess with configuring the DataSource separately in the Tomcat server.xml, or referencing it in your application’s web.xml file. Here’s how:

Install the JDBC Driver

Install the .jar file(s) containing the JDBC driver in Tomcat’s common/lib folder. You do not need to put them in your application’s WEB-INF/lib folder. When working with J2EE DataSources, the web application server manages connections for your application.

Create META-INF/context.xml

In the root of your web app directory structure, create a folder named META-INF (all caps). Inside that folder, create a file named context.xml that contains a Resource like this:

<?xml version="1.0" encoding="UTF-8"?>

<Context>

  <Resource name="jdbc/WallyDB" auth="Container"
            type="javax.sql.DataSource" username="wally" password="wally"
            driverClassName="com.microsoft.sqlserver.jdbc.SQLServerDriver"
            url="jdbc:sqlserver://localhost;DatabaseName=mytest;SelectMethod=cursor;"
            maxActive="8"
            />

</Context>

This example shows how to configure a DataSource for a SQL Server database named mytest located on the development machine. Simply edit the Resource name, driverClassName, username, password, and url to provide values appropriate for your JDBC driver.

Access the DataSource in Your Application

From a Servlet

Here’s how you might access the data in a servlet:

InitialContext ic = new InitialContext();
  DataSource ds = (DataSource) ic.lookup("java:comp/env/jdbc/WallyDB");
  Connection c = ds.getConnection();
  ...
  c.close();

Notice that, when doing the DataSource lookup, you must prefix the JNDI name of the resource with java:comp/env/

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About Krishna Srinivasan

He is Founder and Chief Editor of JavaBeat. He has more than 8+ years of experience on developing Web applications. He writes about Spring, DOJO, JSF, Hibernate and many other emerging technologies in this blog.

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