SCWCD : The servlet model CHAP : 2

1
The Servlet Model
Helmi ben abdallah @rchitect JEE

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THE FOLLOWING SUN CERTIFIED WEB COMPONENT DEVELOPER FOR
J2EE PLATFORM EXAM OBJECTIVES COVERED IN THIS CHAPTER:
• 1.1 For each of the HTTP
methods,GET,POST, andPUT,
identifythe corresponding method in
the HttpServletclass.
• 1.3 For each of the following
operations, identify the interfaceand
method name that should be used:
> Retrieve HTML form parameters from the
request
> Retrieve a servlet initialization parameter
> Retrieve HTTP request header information
> Set an HTTP response header
> set the content type of the response
> Acquire a text stream for the response
> Acquire a binary stream for the response
> Redirect an HTTP request to another URL
1.4 Identify the interface and method to
access values and resources and to
set object attributes within the
following three web scopes:
Request
Session
Context
1.5 Given a life-cycle method: init,service
, or destroy, identify correct
statements bout its purpose or about
how and when it is invoked.
1.6 Use a RequestDispatcher to include
or forward to a web resource.

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• The Servlet model is designed to allow small reusable server
programs the ability to process a variety of requests from a
client and then return a response efficiently.
• Depending on the HTTP request sent to the client, a specific
servlet method will be assigned to handle the response.
• Remember, a request is an object containing the client’s intent,
header information, and possible parameters.

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doXXX (…)
• Method Signature :
protected void doXXX(HttpServletRequest req ,HttpServletResponse res)
throws ServletException, IOException.
• The return value is void because the response is sent by the container.
• A request and response object are provided via the parameters.
• both the ServletException and IOException are thrown in the event of
transmission or streaming errors.

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Parameters
• By using the parameters passed in, you can access and
create the necessary information to complete the
requested task.
• HttpServletRequest req provides you a handle to the
original request. By using this object, you get HTML
parameters, header data, the method type, and date
information.
• HttpServletResponse resp provides you a handle to
construct a response.
• Remember, a response is an object that often contains
header information and a possible body for the client to
display.

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Error Handler :The following list identifies the
potential problems that can take place:
• If a content header cannot be handled, the container should
issue an error message (HTTP 501 - Not Implemented) and
discard the request. 5xx error codes are usually reserved for
server errors, and 3xx and 4xx error codes are reserved for
application or container errors.
• If the request sent is incorrectly formatted, the doXXX(…)
method will ignore any logic included in the method and simply
return an HTTP 400 - Bad Request error message.
• If an input or output error is detected when the servlet handles
the HTTP request, a java.io.IOException is thrown.
• If the HTTP request cannot be processed, a ServletException is
thrown.

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doGet (…) : The GET method should be based
on the following components:
• Safe This implies that the user cannot be held
accountable for any side effects. For example, querying
data has no side effects, whereas changing data does.
• Idempotent This means that the request can be safely
repeated. Again, making a query is both safe and
idempotent; buying a product online is not safe or
idempotent.

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• A doGet(…) method is generally coded by using the
following steps:
• 1. Reads the request data
• 2. Writes the response headers
• 3. Gets the response’s writer or output stream object
• 4. Writes the response data

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Good practices
• set the content type of the response to identify its format. For
example, you could set it to text/html if the response output is
written by using HTML tags, or text/plain if it’s just simple text
strings. This is especially important when using a PrintWriter
object to return a response.
• The number of connections established will depend upon default
content length of the header, and size of the content to be
traversed from web server to the client.
> response.setContentLength(int contentSize);

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1. Use StringBuffer rather than using + operator when you
concatenate multiple strings
2. Use print() method instead of println() method
3. Use ServletOutputStream instead of PrintWriter
4. Initialize the PrintWriter with proper size
5. Flush the data partly
6. Minimize the amount of code in the synchronized block
7. Set the content length

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doPost (…)
when to use a POST request, which calls the
doPost(…).
The code for this signature is written as follows
protected void doPost(HttpServletRequest req,
HttpServletResponse res)
throws ServletException, IOException

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doPut (…)
The following is how the code for doPut(…) should be written:
protected void doPut(HttpServletRequest req,

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doHead (…)
The following shows how to define a doHead(…) method:
protected void doHead(HttpServletRequest req,

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doDelete (…)
The method signature for doDelete(…) is as follows:
protected void doDelete(HttpServletRequest req,

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doOptions (…)
The method signature for the doOptions(…) method is as follows:
protected void doOptions(HttpServletRequest req, HttpServletResponse
res) throws ServletException, IOException
Let’s say your servlet overrides the doGet(…) and doPost(…) methods.
An OPTIONS request will return the following header:
HTTP/1.0 200 OK
Allow: GET, HEAD, POST, TRACE, OPTIONS
Servlet-Engine: Tomcat Web Server/3.2.3
(JSP 1.1; Servlet 2.2; Java 1.3; Windows 2000 5.0 x86;
java.vendor=Sun Microsystems Inc.)

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• Now, you might be asking yourself why all those
methods are available if you’ve overridden only the
doGet(…) and doPost(…) methods.
• The reason is that if you override the doGet method,
by default, you also inherit the HEAD and TRACE
methods.
• You don’t have to override the doHead(…) and
doTrace(…) methods, and the default execution will
be performed.

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doTrace (…)
The server indirectly calls the doTrace(…) method when a
TRACE request is sent.
A TRACE request is used to return the headers sent with
the request to the client. It is usually used to help debug
the servlet.
The method signature for the doTrace(…) method is as
follows:
protected void doTrace(HttpServletRequest req,
Httpservletresponse
res) throws ServletException, IOException

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ServletRequest and ServletResponse
Interface

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Parameters
• The ServletRequest object gives you access to data
often used to initialize a servlet. These methods are
as follows:
• String getParameter(String name)
• Enumeration getParameterNames()
• String[] getParameterValues(String name)

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<HTML> <BODY>
<FORM ACTION=’/servlet/GetData’ METHOD=’GET’>
<P>Name: <INPUT TYPE=’TEXT’ SIZE=’25’ name=’firstName’>
<P>Destination:
<SELECT NAME=’location’></P>
<OPTION VALUE=’California’>California
<OPTION VALUE=’Washington’>Washington
<OPTION VALUE=’New York’>New York
<OPTION VALUE=’Florida’>Florida
</SELECT> </P>
<P><INPUT TYPE=’submit’ VALUE=’GO!’></P>
</FORM>
</BODY></HTML>

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public class GetData extends HttpServlet {
protected void doGet(HttpServletRequest req,
throws ServletException, IOException {
String enteredName = req.getParameter("firstName");
Enumeration ctrlNames = req.getParameterNames();
String[] states = req.getParameterValues("location");
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<HTML>");
out.println("<BODY>");
out.println("<P>Name entered: " + enteredName +
"</P>");
out.println("<P>Control Names are: <BR>");
while(ctrlNames.hasMoreElements()) {
out.println((String)ctrlNames.nextElement() +
"<BR>");
}
out.println("</P><P>The values
selected are: ");
for (int i=0; i<states.length;i++) {
out.println(states[i] + "<BR>");
}
out.println("</P></BODY>");
out.println("</HTML>");
out.close();

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ServletResponse
• void setContentType(String type) :Before sending response
information, you must notify the receiving application of the
content type so it knows how to handle the response data.
• OutputStream getOutputStream() :This method provides a
binary stream that enables you to transfer the data by using
bytes.
• PrintWriter getWriter() : transfer the data in character or
Unicode format. A PrintWriter stream is used to write text.

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Attributes
• Object getAttribute(String name)
• Enumeration getAttributeNames()
• void setAttribute(String key, Object value)
• Setting the attribute is similar to adding a value to a
java.util.Map object. You define the key, a String, and
then the associated object.

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In an attempt to ensure a standard among vendors, the
specification requires each container to predefine six
attribute values when a request is generated.
If you intend to forward the request to another servlet, you might want to change the value
associated with a particular attribute. By using the setAttribute(…), you can accomplish this
task by passing in the request attribute name and the new value.

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Internationalization
• the ServletRequest class is also used to acquire the originating
locale of a servlet.
• The following two methods become useful for such a scenario:
> Locale getLocale()
> Enumeration getLocales()
• Another option is to set the locale through the
ServletResponse object.Syntactically, the method is as
follows:
• void setLocale(java.util.Locale loc)

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Data Encoding
• A ServletRequest object enables data encoding to help with
this type of situation.
• To read a request coming from a website that uses a different
encoding mechanism requires that you change the character
encoding value to a standard understood by the receiving
system.
> void setCharacterEncoding(String env)
> String getCharacterEncoding()
• The setCharacterEncoding(…) method overrides the assigned encoding
value to enable the servlet to read parameters or input from the request.
• The method does throw a runtime exception called
java.io.UnsupportedEncodingException if the encoding mechanism is not
valid

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• GET /Register/index.html HTTP/1.0
• Date: Fri, 26 Oct 2001 17:12:10 GMT
• User-Agent: Mozilla/4.75[en](Windows NT 5.0; U)
• Accept: image/gif, image/x-xbitmap, image/jpeg, */*
• Host: educationaledge.net
• Accept-Encoding: gzip, deflate
• Accept-Language: en-us
• Connection: keep-alive

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public class HeaderServlet extends HttpServlet {
protected void service(HttpServletRequest req,
HttpServletResponse resp)
String acceptValue = req.getHeader("Accept");
Enumeration allValues = req.getHeaders("Accept");
Enumeration headerNames = req.getHeaderNames();
int numbericValue = req.getIntHeader("Max-Forwards");
long dateValue = req.getDateHeader("Date");
String method = req.getMethod();
super.service(req, resp);
}

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getHeaderNames() returns all headers:
• Date
• User-Agent
• Accept
• Host
• Accept-Encoding
• Accept-Language
• Connection
getIntHeader(“Max-Forwards”) returns -1
getDateHeader(“Date”) returns date in milliseconds since 1/1/70
getMethod() returns GET

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protected void doGet(HttpServletRequest req,
response.setContentType("text/html");
res.setHeader("Server", "The SuperDooper Server/1.0")
res.setIntHeader("Content-length", 1029)
res.setDateHeader("Last-modified", 1003947922649);
res.sendRedirect("http://otherserver.com:8090/index.html");
…}
HTTP/1.0 200 OK
Date: Sat Oct 17 12:14:15 PDT 2001
Server: The SuperDooper Server/1.0
MIME-version: 1.0
Content-Type: text/html
Last-Modified: Wed Oct 24 11:27:15 PDT 2001
Content-Length: 1029

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Path Elements
• When a client attempts to locate a servlet, it searches
through a specific path to reach its destination. The path
itself, or the request URI, is generally
• composed of three important sections:
• Request URI = contextPath + servletPath + pathInfo

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Context Path
• For each web application, there is one context.
• All servlet classes within that web application will share
that one context. Here is the method signature:
• public String getContextPath()
• The rules for the context path are as follows:
> The path begins with a forward slash (/) but does not end with a
forward slash (/).
> The path is an empty string, “”, if the context is at the base of
the web server’s URL namespace.

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Servlet Path
• The servlet path identifies the mapped directory name
associated to the actual servlet. Usually this consists of
either the mapped servlet name or a mapped path to the
servlet, but nothing more.
• Here is the method signature:
• public String getServletPath()
• The rules for the servlet path are as follows:
> The path is an empty string if url-pattern matches a /* pattern.
> The path begins with a forward slash (/) in all other cases.

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Path Info
• The path info consists of extra path information between
the servlet path and the query string.
• public String getPathInfo()
• The rule for the path info is as follows:
> If path information does not exist, the method returns a null.

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assuming the context is defined as:
/games.

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Path Translations
• If the developer is interested in accessing file system path
information,they can do so through the ServletContext by
using the following method:
• String getRealPath(String path)
• The getRealPath(…) takes in a virtual path value and returns
its absolute file path on the server. If for example, you passed
in index.html, the return string would represent the entire URL,
such as c:Javajakartatomcat-4.0webappstestindex.html.
• The format of the URL is dependent on the platform. If a
Unix server ran the request, it would format the root and
slashes differently.

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• The other method used to translate virtual paths is
available in the HttpServletRequest class:
• String getPathTranslated()
• This method takes the path info of the request and
computes its real path.
• If there is no additional information between the servlet
path and the query string, the method returns a null.

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Cookies
• A cookie is a small data object sent to the browser by the
servlet. It is made up of a name, a single value, and optional
descriptive attributes, such as a version number and path
information.
• When the user opts to accept the cookie, the browser
typically saves the object and then nds the name and value
of each cookie during each request.
• This technique is used to help manage servlet sessions.

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• the developer can then extract the desired cookie attributes.
Cookie[] getCookies()
• This method returns an array of all the Cookie objects
contained within the request.
• If the developer were then interested in sending a cookie to
the browser, they could do so by calling the addCookie(…)
method of the HttpServletResponse interface.

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• An HttpSession object is created when a client makes its first
request to an application. It provides a way to identify and
store information about the user for an extended period of
time.
• While a request and its attributes will cease to exist after its
response is sent, a session, once created, will continue to
exist until it either is manually terminated or times out.

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There are several methods that provide
information or control over the life span
of an HttpSession object
• public long getLastAccessedTime() : The getLastAccessedTime() method returns the
number of milliseconds since the birth of Unix, January 1, 1970
• public int getMaxInactiveInterval() : To get the number of seconds the container will allow
between requests to keep the session active
• public void setMaxInactiveInterval(int seconds)
• public boolean isNew() : It returns a true value if the client does not know about the session
or has not joined it yet. Joining a session means the client returns session tracking information
sent by the server. If the client, however, refuses to join a session, then a new session is
created for each request. This usually occurs when the web container uses only cookies for
session tracking and the client refuses to accept cookies.
• public void invalidate() : manually terminate a session. It first unbinds all associated
• attribute objects and then prepares the session for garbage collection.

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The methods associated to a session’s
attributes are as follows:
• public void setAttribute(String name, Object value)
• public Object getAttribute(String name)
• public Enumeration getAttributeNames()
• public void removeAttribute(String name)
• public String getId() :This method returns a string
containing the unique identifier assigned to the particular
session. One way to use the session ID is for storage of
session information to a persistent data source. This is most
useful when the session is transferred from one web
container to another.

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The Servlet Life Cycle
the container determines:
• When a servlet is loaded and instantiated.
• How to directly handle client requests or dispatch them to
another resource.
• When to take a servlet out of service.

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Loading and Instantiating
• A servlet can be instantiated when the container starts or when
the container receives a request that needs to be serviced.
• Before instantiation, the container locates all the needed
classes for the servlet and uses the standard ClassLoader to
load the servlet class itself.
• There are no restrictions on where the files can be loaded a
local or remote file system or another network altogether is
acceptable.
• The servlet is instantiated, and its default constructor is read.
There is no reason to include a non-default constructor within a
servlet,because it would never get called.

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• After the constructor is read, the container creates an object
called the ServletConfig. It contains name/value parameters
defined from within a file .
• The ServletConfig object is passed to the Servlet interface
method called:
public void init(ServletConfig config) throws
ServletException
• When this method is called, it actually causes the Servlet’s
implementing class, GenericServlet, to invoke its version of the
method.
• it is important that the GenericServlet’s init(ServletConfig
config) method be processed before any other servlet method
is called.

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<web-app>
<servlet>
<servlet-name>CalendarServlet</servlet-name>
<servlet-class>CalendarServlet</servlet-class>
<init-param>
<param-name>Year</param-name>
<param-value>2001</param-value>
</init-param>
<init-param>
<param-name>taxrate</param-name>
<param-value>.0725</param-value>
</init-param>
</servlet>
</web-app>
public class CalendarServlet
extends HttpServlet {
int year;
double rate;
public void init() throws
ServletException {
ServletConfig config =
getServletConfig();
String yearParam =
config.getInitParameter(“Year”);
year =
Integer.parseInt(yearParam);
String rateParam =
config.getInitParameter(“taxrate”);
rate = Float.parseFloat(rateParam);

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An additional benefit to the ServletConfig object is that it
grants you access to the following information:
• ServletContext By using the getServletContext() method, you can get
a handle to this object, which provides the servlet with the means to
communicate with the container. For example, by using the
ServletContext, the servlet can ask the container to get the MIME type of
a file by using the method getMimeType(String file), dispatch requests by
using the method getRequestDispatcher(String path), or write to a log file
by using the method log(String msg).
• Servlet name By using the getServletName() method, you receive the
name of the servlet instance. It is provided by either the deployment
descriptor or its default class name.

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The ServletConfig object is available to the servlet after the init()
method is called. However, several problems can occur
• The first scenario occurs when the init() method throws a ServletException. This usually
happens if there is an initialization failure—for example, if the container fails to find the
initialization parameters. Failure to initialize would cause the servlet to be released from
the container.
• Another exception that can be thrown is an UnavailableException, which is a subclass of
ServletException. This usually happens when you are looking to see whether a service is
accessible—and it’s not. If this particular exception is thrown, the container must wait a
minimal time period before attempting to create and initialize a new instance of the
servlet. There is no need to wait if a ServletException is thrown.
• The final situation occurs when the init() method does not return in a specified time
period defined by the web server. If no problems occur, the servlet is ready for the next
phase of its life cycle: service(…).
The init() method must complete successfully before the servlet can begin to receive
requests

70
Request Dispatching
• RequestDispatcher getRequestDispatcher(String path)
• The argument to the getRequestDispatcher method is a string
that describes the relative or absolute path of the ServletContext
for which you are forwarding the request basically it’s the
receiving servlet’s URI or URL.
• As a reminder, the ServletContext is the object used to
communicate with the container.

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Because there is only one context per web application, there are some rules
about where a request can be dispatched:
• The relative path cannot extend outside the current servlet context. To do
so, you must use the getContext() method. It returns the absolute URL to
the context requested.
• A servlet cannot dispatch a request to a context on another server.
The semantics of the path are as follows:
• If the path begins with a forward slash (/), it is considered relative to the
current context.
• If the path contains a query string, the name/value pairs will be added to
the receiving servlet’s parameter list.
getNamedDispatcher(String) : enables the developer to get the
RequestDispatcher for a resource by specifying its name rather than
path. The name can be accessed in several ways: it can be hard-
coded, in the DTD, or as an attribute of the request

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public class ServletOne extends HttpServlet {
public void doGet(HttpServletRequest req,
String uri = “/servlet/ServletTwo”;
RequestDispatcher reqDis1 = req.getRequestDispatcher(uri);
String name = “ServletTwo”;
RequestDispatcher reqDis2 =
getServletContext().getNamedDispatcher(name);
String query = “/servlet/ServletTwo?name=Roney”;
RequestDispatcher reqDis3 =
req.getRequestDispatcher(query);
}}
The first two examples should return the same
dispatcher. The third example simply shows how a
query string can be attached to the URI. In order for
these parameters to be sent with the request

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include (…)
public void doGet(HttpServletRequest req, HttpServletResponse res)
res.setContentType(“text/html”);
out.println(“<HTML><TITLE>Welcome to the Magic Show
</TITLE></HTML>”);
out.println(“<BODY>”);
out.println(“Watch the video stream below: “);
RequestDispatcher disp =
req.getRequestDispatcher(“/servlet/MagicVideo?video=1”);
disp.include(req, res);
out.println(“Tune in daily for a new trick”);
out.println(“</BODY></HTML>”);
}

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• The target servlet cannot change the response status code or set
headers any attempt to make a change is ignored.
• The target can, however, process the request because it does
gain access to the request object, via the getAttribute(…) method.
• Here are the attributes that a target servlet can access when
invoked through an include(…):
> request_uri
> context_path
> servlet_path
> path_info
> query_string
Unfortunately, these variables are assigned values only if you access the target servlet by
using the request object’s getRequestDispatcher(…) method.
The getNamedDispatcher(…) method leaves these values unset.

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forward (…)
• The forward(…) method is used to forward a request to another
servlet.
• The originating servlet can perform some preliminary functions
on the request and have another servlet generate the
response.
• The act of having another servlet perform the task is invisible
to the client.
public void forward(ServletRequest req, ServletResponse res)

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Here is an example servlet that calls
another servlet to generate a
public class PassMessageServlet extends HttpServlet {
req.setAttribute("message", "Life is good");
RequestDispatcher disp=
req.getRequestDispatcher("/servlet/Test");
disp.forward(req, res);
}
}

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public class Test extends HttpServlet {
String theMessage =
(String)req.getAttribute("message");
res.setContentType("text/html");
out.println("<BODY>" + theMessage
+ "</BODY></HTML>");
out.close(); }

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The rules associated to a forward(…) call are
as follows:
• The forward(…) method can be called only if output has not
been committed to the client; otherwise, an
IllegalStateException is thrown.
• The calling servlet can set headers and set status code
information. But it must send the same request and response
objects to the target.
• If the response buffer contains data that has not been
committed, a call to forward(…) will clear the buffer before
calling the service(…) method of the target servlet.
• The target servlet must send and commit its response before
the forward(…) method can return.

79
End of Service
• The longevity of a servlet’s life is not defined.
• When the time comes to remove a servlet from service, the container calls
the Servlet interface’s destroy() method. Here is the method signature:
public void destroy()
• This method is used to release all resources, such as threads or
connections, and save any persistent data.
• before the destroy() method can be called, the container must wait for all
threads running in the service(…) method to complete or time out.
• After a servlet is destroyed, and its destroy() method has been called, the
servlet is ready for garbage collection. Consequently, the container cannot
send any requests to that servlet. It would need to create a new instance.

81
Which of the following statements is false? (Choose all that
apply.)
A. The doHead(…) method in HttpServlet will execute
the doGet method if the doHead(…) method has not been
overridden by the programmer.
B. There is no doHead(…) method for a HEAD request.
C. A GET request invokes the doHead(…) method and
then the doGet(…) method.
D. A HEAD request will return only the headers as a
response.

82
• B, C. There is a doHead(…) method defined by the
servlet spec. In 2.3, it is a protected method, which
means you can include the method in your servlet code if
you extend HttpServlet. This would result in a call to your
servlet’s doHead(…) method. The third option is false
because a GET request does not invoke the doHead(…)
method; itinvokes the doGet(…) method instead.

83
Which of the following options best defines the full signature
name for the servlet method associated with a POST request?
(Choose all that apply.)
A. protected void doPost(HttpServletRequest req,
HttpServletResponse res) throws IOException,ServletException
B. public void doPost(HttpServletRequest
req,HttpServletResponse res) throws IOException
C. public void doPost(ServletRequest req,ServletResponse
res) throws IOException,ServletException
D. private void doPost(HttpServletRequest
req,HttpServletResponse res) throws IOException,
ServletException

84
• A, B. The doPost(…) method is defined in the HttpServlet
class with a protected access modifier. When overriding a
method, you can change the modifier to one that is more
public. That eliminates the last option. The third option fails
because the parameters passed are HttpServletRequest and
HttpServletResponse.
• Finally, the first two answers are correct because you can
override a method and throw fewer exceptions than that of
your parent, or you could match the signature exactly.

85
Which HttpServlet method should be used to publish a
resource on the server?
A. doGet(…)
B. doOptions(…)
C. doPost(…)
D. doPut(…)

86
• D. A PUT request is used to publish resources at a
location on the server. This method calls its
corresponding doPut(…) method in the servlet to help
perform this task.

87
Which of the following is false?
A. doGet(…) is for handling HTTP GET requests.
B. doPost(…) is for handling HTTP POST requests.
C. doPut(…) is for handling HTTP PUT requests.
D. doHead(…) is for handling HTTP HEAD requests.
E. None of the above.

88
• E. As per the servlet spec 2.3, all methods described
handle the HTTP request methods defined.
Consequently, the answer is “None of the above.

89
What is the method declaration for the method used in the
HttpServlet class that handles the HTTP POST request?
A. doPost(ServletRequest req, ServletResponse res)
B. servicePost()
C. doPost(HttpServletRequest req,HttpServletResponse res)
D. service(HttpServletRequest req,HttpServletResponse res)

90
• C. The doPost(…) method is called when an HTTP POST
is submitted.
• The two arguments passed in are an HttpServletRequest
• And HttpServletResponse.

91
Given the following request, what result would you expect from the subsequent
method call?
GET /Register/index.html HTTP/1.0
Date: Fri, 26 Oct 2001 17:12:10 GMT
User-Agent: Mozilla/4.75[en](Windows NT 5.0; U)
Accept: image/gif, image/x-xbitmap, image/jpeg, */*
Host: educationaledge.net
Accept-Encoding: gzip, deflate
------------------------req.getHeader(“Accept”);
A. A string representing image/gif, image/x-xbitmap,image/jpeg, */*
B. A string array representing image/gif, image/x-xbitmap,image/jpeg, */*
C. A string representing image/gif
D. A string representing */*

92
• A. The getHeader() method returns a string
representation of the
• entire value. Consequently, all values are grouped into
one string
• object. The method getHeaders() parses the values and
returns them
• in an array.

93
Given a call to the following method, what response would
you expect?
request.getDateHeader(“User-Agent”);
A. An IOException is thrown.
B. A DateFormatException is thrown.
C. An IllegalArgumentException is thrown.
D. A -1 is returned.

94
• C. If the header value cannot be converted to a date, then
an
• IllegalArgumentException is thrown.

95
Which interface gives you access to the
getParameterNames() method? (Choose all that apply.)
A. ServletRequest
B. ServletResponse
C. HttpServletRequest
D. HttpServletResponse

96
• A, C. Because the HttpServletRequest interface extends
• ServletRequest, it too has access to the
getParameterNames()
• method.

97
Which of the following methods must be both safe and
idempotent? (Choose all that apply.)
A. doGet
B. doHead
C. doPut
D. doPost

98
• A, B. Both the doGet(…) and doHead(…) methods should
be written to be safe, meaning the user should not be
held accountable if the request is processed. They should
also be idempotent, which means no negative side effects
should occur if the request is processed multiple times.

99
Given the following code snippet, what output would you
expect?Calling servlet:
public void doGet(HttpServletRequest req, HttpServletResponse res)
res.setContentType("text/html"); PrintWriter out = res.getWriter();
out.println("<BODY>Will you see the source?");
out.println("</BODY></HTML>");
RequestDispatcher disp= req.getRequestDispatcher("/servlet/Test");
disp.forward(req, res); out.close();}
Target servlet:
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws
ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<HTML><TITLE>The Test</TITLE>");
out.println("<BODY>Will you see the target?");
out.println("</BODY></HTML>");
out.close();
A. “Will you see the source?”
B. “Will you see the target?”
C. An IllegalStateException is thrown.
D. Nothing appears; the thread hangs.
E. Both “Will you see the source?” and
“Will you see the target?” will appear.

100
• B. A forward(…) is used to forward responsibility to
complete the response to another servlet. If the calling
servlet adds data to the response buffer, the target servlet
erases that information. Consequently, you see the output
from the target response stream only.

101
Which of the following statements is true?
A. If the target servlet does not commit or send its
response, the calling servlet can still continue processing
logic after the forward(…) call.
B. Control does not return to the originating servlet
after a forward(…) call is made.
C. A forward(…) call will not continue to process until
the target servlet commits or sends its response.
D. None of the above.

102
• C
• A forward(…) call is a blocking method. This means the
target
• servlet must commit or send its response before control
can be returned
• to the forwarding servlet.

103
Which of the following methods will enable you to get one or
more values set by a request object? (Choose all that
apply.)
A. getParameter(String name)
B. getAttribute(String name)
C. getAttributes()
D. getAllAttributes()
E. getAllParamters()

104
• B, C. The first option fails because getParameter(String
name) returns only a value associated to the parameter
name passed. The getAttribute(…) method takes in a key
string and returns a single value set by a request using
the setAttribute(…) method. To retrieve all attributes in an
enumeration, simply call getAttributes().

105
Given the following request URI, which option best
describes the context path?
/cars/sportsCars/index.html
A. /cars
B. /cars/sportsCars
C. /sportsCars
D. Not enough information to determine the answer

106
• D. The context path defines the path of the context for
which the servlet resides. If the context is defined to be at
the base of the web server’s URL namespace, then the
context is an empty string. If that is the case, then
/cars/sportsCars represents the servlet path, and the
• context path is blank. If that is not the case, then /cars is
the context path. Because you don’t know where the
context was defined, you have no choice but to select the
last option.

107
Given the following request URI, where the context path is
defined as /furniture and the servlet is called Search, which
option best describes the result returned from the
getPathInfo() method?
/furniture/tables/Search?type=kitchen
A. “”—empty string
B. /Search
C. /Search?type = kitchen
D. null

108
• D. The path info returned is the data between the servlet
path and query string. Because the servlet is called
Search and the query string begins immediately after, the
method getPathInfo() returns null.

109
The ServletContext object can be directly accessed from
which of the following objects? (Choose all that apply.)
A. HttpServlet
B. ServletRequest
C. ServletConfig
D. ServletResponse

110
• A, C. The ServletConfig interface has a method called
• getServletContext() that returns a handle to the
ServletContext object. You can obtain a handle to this
object through the HttpServlet class as well. Its parent
class, GenericServlet, also has the same method defined,
getServletContext().

SCWCD : The servlet model CHAP : 2

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