差异b / w <context-param>和<init-param>

Question

DD elements <context-param> and <init-param> both can be retrieved by the getInitParameter() method, in the servlet code.

Now the question is, how does it differentiate <context-param> and <init-param> ?

Answer 1

Servlet init parameters are for a single servlet only. Nothing outside that servlet can access that. It is declared inside the <servlet> tag of Deployment Descriptor, on the other hand context init parameter is for the entire web application. Any servlet or JSP in that web application can access context init parameter . Context parameters are declared in a tag <context-param> directly inside the <web-app> tag.

The methods for accessing context init parameter is

getServletContext().getInitParameter("name"); 

whereas the method for accessing servlet init parameter is

getServletConfig().getInitParameter("name");

Answer 2

As explained by Adeel Ansari, here , it depends on what object are you invoking the method getInitParameter() in the servlet code.

All servlets extends from and hence are instance of GenericServlet .

.

DD elements <context-param> can be retrieved by:

ServletContext context = this.getServletContext();
String paramValue = context.getInitParamter("paramName");

.

DD elements <init-param> both can be retrieved by:

ServletConfig config = this.getServletConfig();
String paramValue = config.getInitParamter("paramName");

Also note that since GenericServlet class implements ServletConfig interface, your servlet class is also ServletConfig (implies this = this.getServletConfig() ). Hence you can also get DD elements <init-param> directly by:

String paramValue = this.getInitParamter("paramName");

.

You can try this by having same param-name in both DD elements with different values and then print it in your servlet.