Consideriamo una semplice jsp che stampa una stringa: hello.jsp
<%-- hello.jsp stampa il classico saluto --%>
<%! static private String str = "world!";%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head>
<title>Hello!</title>
</head>
<body>
<h1>Hello world!</h1>
<strong>Hello,<%= str.toUpperCase() %></strong>
</body>
</html>Supponiamo di memorizzare questa JSP nel context ROOT/.
La prima volta che viene questa JSP invocata tramite l'URL
http://localhost:8080/hello.jsp, Tomcat invoca il
compilatore Jasper che produce la servlet
equivalente ~tomcat/work/localhost/_/hello$jsp.java:
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import org.apache.jasper.runtime.*;
public class hello$jsp extends HttpJspBase {
static private String str = "world!";
public hello$jsp( ) { }
private static boolean _jspx_inited = false;
public final void _jspx_init()
throws org.apache.jasper.runtime.JspException { }
public void _jspService(HttpServletRequest request, HttpServletResponse response)
throws java.io.IOException, ServletException {
JspFactory _jspxFactory = null;
PageContext pageContext = null;
HttpSession session = null;
ServletContext application = null;
ServletConfig config = null;
JspWriter out = null;
Object page = this;
String _value = null;
try {
if (_jspx_inited == false) {
synchronized (this) {
if (_jspx_inited == false) {
_jspx_init();
_jspx_inited = true;
}
}
}
_jspxFactory = JspFactory.getDefaultFactory();
response.setContentType("text/html;charset=ISO-8859-1");
pageContext = _jspxFactory.getPageContext(this, request, response,
"", true, 8192, true);
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
out.write("\r\n\r\n<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\"\r\n\t \"http://www.w3.org/TR/REC-html40/loose.dtd\">\r\n\r\n<html>\r\n<head>\r\n <title>\r\n Esempio\r\n </title>\r\n</head>\r\n\r\n<body>\r\n <h1>Hello world!</h1>\r\n <strong>Hello, ");
out.print( str.toUpperCase() );
out.write("</strong>\r\n</body>\r\n</html>\r\n");
} catch (Throwable t) {
if (out != null && out.getBufferSize() != 0)
out.clearBuffer();
if (pageContext != null) pageContext.handlePageException(t);
} finally {
if (_jspxFactory != null) _jspxFactory.releasePageContext(pageContext);
}
}
}La servlet viene quindi eseguita dal servlet engine (Tomcat). Il risultato dell'esecuzione è il seguente file html:
<!DOCTYPE HTML
PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head>
<title>Hello!</title>
</head>
<body>
<h1>Hello world!</h1>
<strong>Hello, WORLD!</strong>
</body>
</html>