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attributes in servlet

Posted on 2014-03-30
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Hi,

I am reading about attributes in servlet.


http://www.javatpoint.com/attribute

I would like to know which attribute to use in which case. Is there is a harm if i use one attribute say application attribute in every case all the time.
Any example on using each of them(request/session/application attribute) and also
using

public Enumeration getInitParameterNames():Returns the names of the context's initialization parameters as an Enumeration of String objects.
public void removeAttribute(String name):Removes the attribute with the given name from the servlet context.

please advise
Any links resources ideas highly appreciated. Thanks in advance
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Question by:gudii9
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dpearson earned 2000 total points
ID: 39965389
Attributes are generally stored in either the servlet context (for global data or what it calls "application scope" data) or the session (for data relating to a specific user).

The decision about which to use depends on the type of data being stored.  For example, if you have a userID, that is part of the information for a specific user so it should go on the session (since that stores data for a particular user).  If it was stored in the servlet context (the global data) then you could only handle 1 user of the entire application - because there would be just one "userID" value stored globally.

Does that make sense?

initParameters are completely different.  They are constants defined in a file (the web.xml) file.  That's a useful place to store settings, e.g. the port number to use when accessing a database.

Doug
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by:gudii9
ID: 39973579
If it was stored in the servlet context (the global data) then you could only handle 1 user of the entire application - because there would be just one "userID" value stored globally.

can you please elaborate on this.

initParameters are completely different.  They are constants defined in a file (the web.xml) file.

i thought we get Global Attributes using ServletContext which are defined in initParameters . please advise
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by:dpearson
ID: 39974082
i thought we get Global Attributes using ServletContext which are defined in initParameters . please advise

Yes that's right - parameters or attributes in the servlet context are global.

can you please elaborate on this.
The servlet context is global - there is only one per application.  So it's the place to store global data e.g. you might have a link to the database in the servlet context because there's only one database used by the application.

The session is one per user - so it's usually the right place to store data about a user e.g. you might store the user id in the session.

Does that make sense?

Doug
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by:gudii9
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The servlet context is global - there is only one per application.  So it's the place to store global data e.g. you might have a link to the database in the servlet context because there's only one database used by the application.



ServletContext context=getServletContext();  
context.setAttribute("company","IBM");

we set as above right.

Init-param for a servlet done as below right
http://examples.javacodegeeks.com/enterprise-java/servlet/get-all-init-parameters-in-servlet/

10          <servlet>
11              <servlet-name>JCG Snippets Application</servlet-name>
12              <servlet-class>com.javacodegeeks.snippets.enterprise.GetAllInitParametersInServlet</servlet-class>
13              <init-param>
14                  <param-name>myparam1</param-name>
15                  <param-value>myvalue1</param-value>
16              </init-param>
17              <init-param>
18                  <param-name>myparam2</param-name>
19                  <param-value>myvalue2</param-value>
20              </init-param>
21          </servlet>
22       
23          <servlet-mapping>
24              <servlet-name>JCG Snippets Application</servlet-name>
25              <url-pattern>/jcgservlet</url-pattern>
26          </servlet-mapping>
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