requestScope and param both are types of map. requestScope contains request scoped attribute name as key and its value as a value in a map. Whereas, param contains form parameter name as key and its value as a value in a map.
A "parameter"(param) is a form field name/value pair passed from the HTML side of the world or other hand query string. Its value is a String.
An "attribute"(requestScope) is a Java object name/value pair passed only through the internal JavaServer processes. (I.e. it can come from a JSP or servlet but not an HTML page.) Its value is an Object.
You can't alter the request parameters, just read them. If you could there would be a setParameter() method. Parameters and attributes do not share a name space so a parameter named "foo" and an attribute keyed "foo" are distinct.
Hope This Helps
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