The essential difference between scripts, declarations, and expressions in JSPs

<span id="Label3"></p><p><p><span style="font-size:18px"><span style="font-size:18px">Original Address:</span> <span style="font-size:18px">http://blog.csdn.net/csuliky/article/details/2444854</span></span></p></p><span style="font-size:18px"><span style="font-size:18px"> <span style="color:#ff0000">JSP scripting elements</span> </span></span><p><p><span style="font-size:18px">Using JSP scripting elements, You can embed Java code in a JSP page that will appear in the servlet generated by the current JSP Page.</span></p></p><p><p><span style="font-size:18px">enables JSPs to separate static content from dynamic Content. The script element package</span> <span style="font-size:18px">contains:</span></p></p><span style="font-size:18px"><span style="font-size:18px"> <span style="color:#ff0000">1. Expressions</span> </span></span><p><p><span style="font-size:18px">Expression: is the representation of the data, which the system calculates as a Value.</span></p></p><p><p><span style="font-size:18px">Syntax: <%= expression%></span></p></p><p><p><span style="font-size:18px">Example: <%=user.getname ()%></span></p></p><p><p><span style="font-size:18px">The essence of an expression: after converting a JSP page into a servlet, use out.print () to output the value of the Expression. If the return of User.getname ()</span></p></p><p><p><span style="font-size:18px">Return value is "liky", then in fact in the servlet will be converted to Out.print ("liky");</span></p></p><span style="font-size:18px"><span style="font-size:18px">So here are the two points to note:<br></span></span><p><p><span style="font-size:18px">1) If the expression is to invoke a method, then this method must have a return value instead of void, that is, void GetName ()</span></p></p><p><p><span style="font-size:18px">Method is not Callable.</span></p></p><p><p><span style="font-size:18px">2) there can be no semicolon after the method, for example <%=getname ();%> this is not allowed.</span></p></p><span style="font-size:18px"><span style="font-size:18px"> <span style="color:#ff0000">2. Scripts</span> </span></span><p><p><span style="font-size:18px">Script: is embedded in <%%> java code, here Java code and our general Java code is no different, so each statement</span></p></p><p><p><span style="font-size:18px">The same should be ";" The end, which is not the same as the expression</span></p></p><p><p><span style="font-size:18px">syntax:% code%></span></p></p><p><p><span style="font-size:18px">The nature of the script is to insert the code into the Servlet's service () method.</span></p></p><p><p><span style="font-size:18px">For example:</span></p></p><p><p><span style="font-size:18px"></span></p></p><pre code_snippet_id="1752590" snippet_file_name="blog_20160708_1_4183778" name="code" class="plain"><pre code_snippet_id="1752590" snippet_file_name="blog_20160708_1_4183778" name="code" class="plain"><% If (user! = Null) { %> Hello <B><%=user%></B> <% } Else { %> You haven ' t login! <% } %></pre></pre><p><p></p></p><p><p><span style="font-size:18px">Translated Into:</span></p></p><p><p><span style="font-size:18px"></span></p></p><pre code_snippet_id="1752590" snippet_file_name="blog_20160708_2_4151541" name="code" class="plain"><pre code_snippet_id="1752590" snippet_file_name="blog_20160708_2_4151541" name="code" class="plain">If (user! = Null) { out.println ("Hello <B>" + user + "</B>"); } else { out.println ("you haven ' t l ogin! "); }</pre></pre><p><p></p></p><span style="font-size:18px"><span style="font-size:18px"> <span style="color:#ff0000">3. Disclaimer</span> </span></span><span style="font-size:18px"><span style="font-size:18px">Declaration: is to allow the user to define variables, methods in the Servlet.<br></span></span><p><p><span style="font-size:18px">Syntax: <%! code%> for Example: <%! String getName () {return name;}%></span></p></p><p><p><span style="font-size:18px">The essence of the declaration is that the method of adding the declared variable to the servlet class (outside of any METHOD) is the servlet () Approach.</span></p></p><p><p><span style="font-size:18px"><br></span></p></p><span style="font-size:18px"><span style="font-size:18px">　<br></span></span><p><p>The essential difference between scripts, declarations, and expressions in JSPs</p></p></span>