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Mixing Scriptlets and HTML

 
  We have already seen how to use the "out" variable to generate HTML output from within a scriptlet.  For more complicated HTML, using the out variable all the time loses some of the advantages of JSP programming.  It is simpler to mix scriptlets and HTML.

Suppose you have to generate a table in HTML.  This is a common operation, and you may want to generate a table from a SQL table, or from the lines of a file.  But to keep our example simple, we will generate a table containing the numbers from 1 to N.  Not very useful, but it will show you the technique.

Here is the JSP fragment to do it:

<TABLE BORDER=2>
<%
    for ( int i = 0; i < n; i++ ) {
        %>
        <TR>
        <TD>Number</TD>
        <TD><%= i+1 %></TD>
        </TR>
        <%
    }
%>
</TABLE>
You would have to supply an int variable "n" before it will work, and then it will output a simple table with "n" rows.

The important things to notice are how the %> and <% characters appear in the middle of the "for" loop, to let you drop back into HTML and then to come back to the scriptlet.

The concepts are simple here -- as you can see, you can drop out of the scriptlets, write normal HTML, and get back into the scriptlet.  Any control expressions such as a "while" or a "for" loop or an "if" expression will control the HTML also.  If the HTML is inside a loop, it will be emitted once for each iteration of the loop.

Another example of mixing scriptlets and HTML is shown below -- here it is assumed that there is a boolean variable named "hello" available.  If you set it to true, you will see one output, if you set it to false, you will see another output.

<%
    if ( hello ) {
        %>
        <P>Hello, world
        <%
    } else {
        %>
        <P>Goodbye, world
        <%
    }
%>
It is a little difficult to keep track of all open braces and scriptlet start and ends, but with a little practice and some good formatting discipline, you will acquire competence in doing it.

Exercise:  Make the above examples work.  Write a JSP to output all the values returned by System.getProperties with "<BR>" embedded after each property name and value.  Do not output the "<BR>" using the "out" variable.
 

 

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