init-param and context-param

Question

What is the difference between  lt init-param gt  and  lt context-param gt

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What is the difference between  lt init-param gt  and  lt context-param gt       Single servlet versus multiple servlets   Other Answers give details  but here is the summary   A web app  that is  a    context     is made up of one or more servlets     lt init-param gt  defines a value available to a single specific servlet within a context   lt context-param gt  defines a value available to all the servlets within a context

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Consider the below definition in web xml   lt servlet gt       lt servlet-name gt HelloWorld lt  servlet-name gt       lt servlet-class gt TestServlet lt  servlet-class gt       lt init-param gt           lt param-name gt myprop lt  param-name gt           lt param-value gt value lt  param-value gt       lt  init-param gt   lt  servlet gt    You can see that init-param is defined inside a servlet element  This means it is only available to the servlet under declaration and not to other parts of the web application  If you want this parameter to be available to other parts of the application say a JSP this needs to be explicitly passed to the JSP  For instance passed as request setAttribute    This is highly inefficient and difficult to code    So if you want to get access to global values from anywhere within the application without explicitly passing those values  you need to use Context Init parameters   Consider the following definition in web xml    lt web-app gt         lt context-param gt              lt param-name gt myprop lt  param-name gt              lt param-value gt value lt  param-value gt         lt  context-param gt    lt  web-app gt    This context param is available to all parts of the web application and it can be retrieved from the Context object   For instance   getServletContext   getInitParameter    dbname       From a JSP  you can access the context parameter using the application implicit object   For example  application getAttribute    dbname

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lt context-param gt        lt param-name gt contextConfigLocation lt  param-name gt       lt param-value gt          classpath   META-INF PersistenceContext xml      lt  param-value gt   lt  context-param gt    I have initialized my PersistenceContext xml within  lt context-param gt  because all my servlets will be interacting with database in MVC framework   Howerver    lt servlet gt       lt servlet-name gt jersey-servlet lt  servlet-name gt       lt servlet-class gt com sun jersey spi spring container servlet SpringServlet lt  servlet-class gt       lt init-param gt           lt param-name gt contextConfigLocation lt  param-name gt           lt param-value gt              classpath ApplicationContext xml          lt  param-value gt       lt  init-param gt       lt init-param gt           lt param-name gt com sun jersey config property packages lt  param-name gt           lt param-value gt com organisation project rest lt  param-value gt       lt  init-param gt   lt  servlet gt    in the aforementioned code  I am configuring jersey and the ApplicationContext xml only to rest layer  For the same I am using  lt  init-param gt

User · Answer

lt init-param gt  and  lt context-param gt  are static parameters which are stored in web xml file  If you have any data which doesn t change frequently you can store it in one of them   If you want to store particular data which is confined to a particular servlet scope  then you can use  lt init-param gt   Anything you declare inside  lt init-param gt  is only accessible only for that particular servlet The init-param is declared inside the  lt servlet gt  tag    lt servlet gt        lt display-name gt HelloWorldServlet lt  display-name gt        lt servlet-name gt HelloWorldServlet lt  servlet-name gt        lt init-param gt            lt param-name gt Greetings lt  param-name gt            lt param-value gt Hello lt  param-value gt        lt  init-param gt   lt  servlet gt    and you can access those parameters in the servlet as follows   out println getInitParameter  Greetings       If you want to store data which is common for whole application and if it doesn t change frequently you can use  lt context-param gt  instead of servletContext setAttribute   method of the application context  For more information regarding usage of  lt context-param gt  VS ServletContext setAttribute   have a look at this question  context-param are declared under the tag web-app  You can declare and access the  lt context-param gt  as follows   lt web-app gt       lt context-param gt           lt param-name gt Country lt  param-name gt           lt param-value gt India lt  param-value gt       lt  context-param gt       lt context-param gt           lt param-name gt Age lt  param-name gt           lt param-value gt 24 lt  param-value gt       lt  context-param gt   lt  web-app gt    Usage in the application either in a JSP or Servlet  getServletContext   getInitParameter  Country    getServletContext   getInitParameter  Age

User · Answer

lt init-param gt  will be used if you want to initialize some parameter for a particular servlet  When request come to servlet first its init method will be called then doGet doPost whereas if you want to initialize some variable for whole application you will need to use  lt context-param gt    Every servlet will have access to the context variable

[java] init-param and context-param

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