Difference b/w <context-param> and <init-param>

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

Now the question is, how doe开发者_JS百科s it differentiate <context-param> and <init-param>?

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");

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.