Servlet Basic Notes

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Difference between ServletConfig and ServletContext

ServletConfig

Signature: public interface ServletConfig

ServletConfig is implemented by the servlet containerto initialize a single servlet using init(). That is, you can pass initialization parameters to the servlet using the web.xml deployment descriptor. For understanding, this is similar to a constructor in a java class.

Example code:
<servlet>
<servlet-name>ServletConfigTest</servlet-name>
<servlet-class>com.javapapers.ServletConfigTest</servlet-class>
<init-param>
<param-name>topic</param-name>
<param-value>Difference between ServletConfig and ServletContext</param-value>
</init-param>
</servlet>

ServletContext


Signature: public interface ServletContext

ServletContext is implemented by the servlet container for all servlet to communicate with its servlet container, for example, to get the MIME type of a file, to get dispatch requests, or to write to a log file. That is to get detail about its execution environment. 

It is applicable only within a single Java Virtual Machine. If a web applicationa is distributed between multiple JVM this will not work. For understanding, this is like a application global variable mechanism for a single web application deployed in only one JVM.

The ServletContext object is contained within the ServletConfig object. That is, the ServletContext can be accessed using the ServletConfig object within a servlet. You can specify param-value pairs for ServletContext object in <context-param> tags in web.xml file.

 Example code:

<context-param>
<param-name>globalVariable</param-name>
<param-value>javapapers.com</param-value>
</context-param>