What is the difference between java direct or java bean in JSP?

Question

What is the difference if I use java code directly in JSP or use java bean in JSP?
Which class to use for receiving the passed parameter from html or java script? Any difference for java code and java bean in the way receiving the passed data?
How can I pass string from jsp to html or java script?

Answer 1

it's generally accepted as better design to separate presentation from logic. meaning, the java code in the jsp should be used to support displaying data, as oppsoed to implementing the application - like database access, etc.
when the logic is separated from the presentation, it allows you to reuse logic components within several jsp pages.
if you decide to change the presentation layer in the future (to support wap, for example) you don't need to rewrite your entire application, since the "guts" of the application is outside of the jsps.
it is also a good idea to separate your business logic from your data layer. adding a "buffer zone" between these layers helps in the same manner as in separating presentation from logic. if you're using flat files for storage now, upgrading to a database wouldn't require rewriting all your business logic, just the methods which write out the data to a file, for example.
once you feel comfortable with separating the various layers, check out the struts framework at http://jakarta.apache.org/
to answer your second question, to get parameters passed in from HTML forms, use ServletRequet's getParameter() method.
in tomcat:
<% String lastName = request.getParameter( "lastname" ); %>
to answer your third question: when displaying the HTML from withing a jsp, print out the string to a javascript variable or a hidden form element:
<% String firstName = "mike"; %>
<input type="hidden" name="firstname" value="<%= firstName %>">
<script language="javascript1.2">
var firstName = "<%= firstName %>";
</script>
this jsp results in the following html:
<input type="hidden" name="firstname" value="mike">
<script language="javascript1.2">
var firstName = "mike";
</script>