Archived: Java Class Converted by Tomcat 4.1.18

JSP Tutorials - Herong's Tutorial Examples

∟Archived: Java Class Converted by Tomcat 4.1.18

This section provides a tutorial example to show how Tomcat 4.1.18 converts a JSP page, hello.jsp, into a Java Servlet class source code, hello_jsp.java.

To see how Tomcat 4 converts a JSP page into a Java class and compiles it to a bytecode, let's open the hello.jsp JSP page again:

<html><body>
<% out.println("Hello world!"); %>
</body></html>

Then save hello.jsp to \local\jakarta-tomcat-4.1.18\webapps\ROOT, and run IE with url: http://localhost:8080/hello.jsp. You should see "Hello world!" in the IE window.

Now, if you look at the directory: \local\jakarta-tomcat-4.1.18\work\standalone\localhost\_, you will see a Java file: 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 {

  private static java.util.Vector _jspx_includes;

  public java.util.List getIncludes() {
    return _jspx_includes;
  }

  public void _jspService(HttpServletRequest request,
     HttpServletResponse response)
        throws java.io.IOException, ServletException {

    JspFactory _jspxFactory = null;
    javax.servlet.jsp.PageContext pageContext = null;
    HttpSession session = null;
    ServletContext application = null;
    ServletConfig config = null;
    JspWriter out = null;
    Object page = this;
    JspWriter _jspx_out = null;

    try {
      _jspxFactory = JspFactory.getDefaultFactory();
      response.setContentType("text/html;charset=ISO-8859-1");
      pageContext = _jspxFactory.getPageContext(
           this, request, response, null, true, 8192, true);
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("<html>");
      out.write("<body>\r\n");
 out.println("Hello world!");
      out.write("\r\n");
      out.write("</body>");
      out.write("</html>");
    } catch (Throwable t) {
      out = _jspx_out;
      if (out != null && out.getBufferSize() != 0)
        out.clearBuffer();
      if (pageContext != null) pageContext.handlePageException(t);
    } finally {
      if (_jspxFactory != null)
         _jspxFactory.releasePageContext(pageContext);
    }
  }
}

You will also see a Java bytecode file: hello_jsp.class.

What happened here was that Tomcat, the JSP Web server, has converted hello.jsp into hello_jsp.java, and compiled it to hello_jsp.class.

The Java file, hello_jsp.java, shows that:

hello_jsp is a sub class of org.apache.jasper.runtime.HttpJspBase, which is a sub class of javax.servlet.http.HttpServlet.
The important method in hello_jsp is _jspService() with two objects listed as parameters: one represents the Servlet request, and the other represents the Servlet response.
The static content of hello.jsp is converted into out.write() statements.
The embedded Java statement in hello.jsp is copied directly.