Question: What are the lifecycle methods
of
Servlet?
Answer: The interface javax.servlet.Servlet, defines the three life-cycle methods. These are:
public void init(ServletConfig config) throws ServletException
public void service( ServletRequest req, ServletResponse res) throws ServletException, IOException
public void destroy()
The container manages the lifecycle of the Servlet. When a new request come to a Servlet, the container performs the following steps.
1. If an instance of the servlet does not exist, the web container
* Loads the servlet class.
* Creates an instance of the servlet class.
* Initializes the servlet instance by calling the init method. Initialization is covered in Initializing a Servlet.
2. The container invokes the service method, passing request and response objects.
3. To remove the servlet, container finalizes the servlet by calling the servlet's destroy method.
Answer: The interface javax.servlet.Servlet, defines the three life-cycle methods. These are:
public void init(ServletConfig config) throws ServletException
public void service( ServletRequest req, ServletResponse res) throws ServletException, IOException
public void destroy()
The container manages the lifecycle of the Servlet. When a new request come to a Servlet, the container performs the following steps.
1. If an instance of the servlet does not exist, the web container
* Loads the servlet class.
* Creates an instance of the servlet class.
* Initializes the servlet instance by calling the init method. Initialization is covered in Initializing a Servlet.
2. The container invokes the service method, passing request and response objects.
3. To remove the servlet, container finalizes the servlet by calling the servlet's destroy method.
Question: What are the type of protocols
supported by HttpServlet?
Answer: It extends the GenericServlet base class and provides an framework for handling the HTTP protocol. So, HttpServlet only supports HTTP and HTTPS protocol.
Question: What are the directory
Structure of
Web Application?Answer: It extends the GenericServlet base class and provides an framework for handling the HTTP protocol. So, HttpServlet only supports HTTP and HTTPS protocol.
Answer: Web component follows the standard directory structure defined in the J2EE specification.
Question: What is ServletContext?
Answer: ServletContext is an Interface that defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file. There is one context per "web application" per Java Virtual Machine. (A "web application" is a collection of servlets and content installed under a specific subset of the server's URL namespace such as
Answer: ServletContext is an Interface that defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file. There is one context per "web application" per Java Virtual Machine. (A "web application" is a collection of servlets and content installed under a specific subset of the server's URL namespace such as
/catalog and possibly
installed via
a .war file.)
Question: What is meant by
Pre-initialization of
Servlet?
Answer: When servlet container is loaded, all the servlets defined in the web.xml file does not initialized by default. But the container receives the request it loads the servlet. But in some cases if you want your servlet to be initialized when context is loaded, you have to use a concept called pre-initialization of Servlet. In case of Pre-initialization, the servlet is loaded when context is loaded. You can specify <load-on-startup>1</load-on-startup>
in between the <servlet></servlet> tag.
Answer: When servlet container is loaded, all the servlets defined in the web.xml file does not initialized by default. But the container receives the request it loads the servlet. But in some cases if you want your servlet to be initialized when context is loaded, you have to use a concept called pre-initialization of Servlet. In case of Pre-initialization, the servlet is loaded when context is loaded. You can specify <load-on-startup>1</load-on-startup>
in between the <servlet></servlet> tag.
Question: What mechanisms are used by a
Servlet Container to maintain session information?
Answer: Servlet Container uses Cookies, URL rewriting, and HTTPS protocol information to maintain the session.
Answer: Servlet Container uses Cookies, URL rewriting, and HTTPS protocol information to maintain the session.
Question: What do you understand by
servlet
mapping?
Answer: Servlet mapping defines an association between a URL pattern and a servlet. You can use one servlet to process a number of url pattern (request pattern). For example in case of Struts *.do url patterns are processed by Struts Controller Servlet.
Answer: Servlet mapping defines an association between a URL pattern and a servlet. You can use one servlet to process a number of url pattern (request pattern). For example in case of Struts *.do url patterns are processed by Struts Controller Servlet.
Question: What must be implemented by
all
Servlets?
Answer: The Servlet Interface must be implemented by all servlets.
Answer: The Servlet Interface must be implemented by all servlets.
Question: What are the differences
between
Servlet and Applet?
Answer: Servlets are server side components that runs on the Servlet container. Applets are client side components and runs on the web browsers. Servlets have no GUI interface.
Answer: Servlets are server side components that runs on the Servlet container. Applets are client side components and runs on the web browsers. Servlets have no GUI interface.
Question: What are the uses of
Servlets?
Answer: * Servlets are used to process the client request.
* A Servlet can handle multiple request concurrently and be used to develop high performance system
* A Servlet can be used to load balance among serveral servers, as Servlet can easily forward request.
Question:
What
are the objects that are received when a servlets accepts call from
client? Answer: * Servlets are used to process the client request.
* A Servlet can handle multiple request concurrently and be used to develop high performance system
* A Servlet can be used to load balance among serveral servers, as Servlet can easily forward request.
Answer: The objects are ServeltRequest and ServletResponse . The ServeltRequest encapsulates the communication from the client to the
server. While ServletResponse encapsulates the communication from the Servlet back to the client.
What is Servlet?
A servlet is a Java technology-based Web component, managed by a container called servlet container or servlet engine, that generates dynamic content and interacts with web clients via a request\/response paradigm.
A servlet is a Java technology-based Web component, managed by a container called servlet container or servlet engine, that generates dynamic content and interacts with web clients via a request\/response paradigm.
Why is Servlet so
popular?
Because servlets are platform-independent Java classes that are compiled to platform-neutral byte code that can be loaded dynamically into and run by a Java technology-enabled Web server.
Because servlets are platform-independent Java classes that are compiled to platform-neutral byte code that can be loaded dynamically into and run by a Java technology-enabled Web server.
What is servlet container?
The servlet container is a part of a Web server or application server that provides the network services over which requests and responses are sent, decodes MIME-based requests, and formats MIME-based responses. A servlet container also contains and manages servlets through their lifecycle.
The servlet container is a part of a Web server or application server that provides the network services over which requests and responses are sent, decodes MIME-based requests, and formats MIME-based responses. A servlet container also contains and manages servlets through their lifecycle.
When a client request
is sent to the servlet container,
how does the container choose which servlet to invoke?
The servlet container determines which servlet to invoke based on the configuration of its servlets, and calls it with objects representing the request and response.
The servlet container determines which servlet to invoke based on the configuration of its servlets, and calls it with objects representing the request and response.
If a servlet is not
properly initialized, what exception
may be thrown?
During initialization or service of a request, the servlet instance can throw an UnavailableException or a ServletException.
During initialization or service of a request, the servlet instance can throw an UnavailableException or a ServletException.
Given the request path
below, which are context path,
servlet path and path info?
/bookstore/education/index.html
context path: /bookstore
servlet path: /education
path info: /index.html
/bookstore/education/index.html
context path: /bookstore
servlet path: /education
path info: /index.html
What is filter? Can
filter be used as request or
response?
A filter is a reusable piece of code that can transform the content of HTTP requests,responses, and header information. Filters do not generally create a response or respond to a request as servlets do, rather they modify or adapt the requests for a resource, and modify or adapt responses from a resource.
A filter is a reusable piece of code that can transform the content of HTTP requests,responses, and header information. Filters do not generally create a response or respond to a request as servlets do, rather they modify or adapt the requests for a resource, and modify or adapt responses from a resource.
When using servlets to
build the HTML, you build a
DOCTYPE line, why do you do that?
I
know all major browsers ignore it even though the HTML
3.2 and 4.0 specifications require it. But building a
DOCTYPE line tells HTML validators which version of HTML
you are using so they know which specification to check
your document against. These validators are valuable
debugging services, helping you catch HTML syntax
errors.
What is new in ServletRequest interface ? (Servlet 2.4)
The following methods have been added to ServletRequest 2.4 version:
public int getRemotePort()
public java.lang.String getLocalName()
public java.lang.String getLocalAddr()
public int getLocalPort()
The following methods have been added to ServletRequest 2.4 version:
public int getRemotePort()
public java.lang.String getLocalName()
public java.lang.String getLocalAddr()
public int getLocalPort()
Request parameter
How to find whether a parameter exists
in the request object?
1.boolean hasFoo = !(request.getParameter("foo") == null || request.getParameter("foo").equals(""));
2. boolean hasParameter = request.getParameterMap().contains(theParameter);
(which works in Servlet 2.3+)
1.boolean hasFoo = !(request.getParameter("foo") == null || request.getParameter("foo").equals(""));
2. boolean hasParameter = request.getParameterMap().contains(theParameter);
(which works in Servlet 2.3+)
How can I send
user authentication information while
making URL Connection?
You'll want to use HttpURLConnection.setRequestProperty and set all the appropriate headers to HTTP authorization.
You'll want to use HttpURLConnection.setRequestProperty and set all the appropriate headers to HTTP authorization.
Can we use the
constructor, instead of init(), to
initialize servlet?
Yes , of course you can use the constructor instead of init(). There's nothing to stop you. But you shouldn't. The original reason for init() was that ancient versions of Java couldn't dynamically invoke constructors with arguments, so there was no way to give the constructur a ServletConfig. That no longer applies, but servlet containers still will only call your no-arg constructor. So you won't have access to a ServletConfig or ServletContext.
Yes , of course you can use the constructor instead of init(). There's nothing to stop you. But you shouldn't. The original reason for init() was that ancient versions of Java couldn't dynamically invoke constructors with arguments, so there was no way to give the constructur a ServletConfig. That no longer applies, but servlet containers still will only call your no-arg constructor. So you won't have access to a ServletConfig or ServletContext.
How can a servlet
refresh automatically if some new data
has entered the database?
You can use a client-side Refresh or Server Push
You can use a client-side Refresh or Server Push
What mechanisms are used by a
Servlet Container to
maintain session information?
Cookies, URL rewriting, and HTTPS protocol information are used to maintain session information
Cookies, URL rewriting, and HTTPS protocol information are used to maintain session information
Difference between GET
and POST
In GET your entire form submission can be encapsulated in one URL, like a hyperlink. query length is limited to 260 characters, not secure, faster, quick and easy.
In POST Your name/value pairs inside the body of the HTTP request, which makes for a cleaner URL and imposes no size limitations on the form's output. It is used to send a chunk of data to the server to be processed, more versatile, most secure.
In GET your entire form submission can be encapsulated in one URL, like a hyperlink. query length is limited to 260 characters, not secure, faster, quick and easy.
In POST Your name/value pairs inside the body of the HTTP request, which makes for a cleaner URL and imposes no size limitations on the form's output. It is used to send a chunk of data to the server to be processed, more versatile, most secure.
What is session?
The session is an object used by a servlet to track a user's interaction with a Web application across multiple HTTP requests.
The session is an object used by a servlet to track a user's interaction with a Web application across multiple HTTP requests.
What is servlet
mapping?
The servlet mapping defines an association between a URL pattern and a servlet. The mapping is used to map requests to servlets.
The servlet mapping defines an association between a URL pattern and a servlet. The mapping is used to map requests to servlets.
What is servlet context
?
The servlet context is an object that contains a servlet's view of the Web application within which the servlet is running. Using the context, a servlet can log events, obtain URL references to resources, and set and store attributes that other servlets in the context can use. (answer supplied by Sun's tutorial).
The servlet context is an object that contains a servlet's view of the Web application within which the servlet is running. Using the context, a servlet can log events, obtain URL references to resources, and set and store attributes that other servlets in the context can use. (answer supplied by Sun's tutorial).
Which interface
must be implemented by all servlets?
Servlet interface.
Servlet interface.
Explain the life cycle
of Servlet.
Loaded(by
the container for first request or on start up
if config file suggests load-on-startup), initialized(
using init()), service(service() or doGet() or doPost()..),
destroy(destroy()) and unloaded.
When is the servlet
instance created in the life cycle
of servlet? What is the importance of configuring a
servlet?
An instance of servlet is created when the servlet is loaded for the first time in the container. Init() method is used to configure this servlet instance. This method is called only once in the life time of a servlet, hence it makes sense to write all those configuration details about a servlet which are required for the whole life of a servlet in this method.
An instance of servlet is created when the servlet is loaded for the first time in the container. Init() method is used to configure this servlet instance. This method is called only once in the life time of a servlet, hence it makes sense to write all those configuration details about a servlet which are required for the whole life of a servlet in this method.
Why don't we write a
constructor in a servlet?
Container writes a no argument constructor for our servlet.
Container writes a no argument constructor for our servlet.
When we don't write any
constructor for the servlet, how
does container create an instance of servlet?
Container creates instance of servlet by calling Class.forName(className).newInstance().
Container creates instance of servlet by calling Class.forName(className).newInstance().
Once the destroy()
method is called by the container,
will the servlet be immediately destroyed? What happens
to the tasks(threads) that the servlet might be
executing at that time?
Yes, but Before calling the destroy() method, the servlet container waits for the remaining threads that are executing the servlet’s service() method to finish.
Yes, but Before calling the destroy() method, the servlet container waits for the remaining threads that are executing the servlet’s service() method to finish.
What is the
difference between callling a
RequestDispatcher using ServletRequest and
ServletContext?
We can give relative URL when we use ServletRequest and not while using ServletContext.
We can give relative URL when we use ServletRequest and not while using ServletContext.
Why is it that we can't
give relative URL's when using
ServletContext.getRequestDispatcher() when we can use
the same while calling
ServletRequest.getRequestDispatcher()?
Since ServletRequest has the current request path to evaluae the relative path while ServletContext does not.
Since ServletRequest has the current request path to evaluae the relative path while ServletContext does not.
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