Servlet Class Converted from UseBean.jspx

JSP Tutorials - Herong's Tutorial Examples

∟JavaBean Objects and "useBean" Action Elements

∟Servlet Class Converted from UseBean.jspx

This section describes the Servlet class converted from the UseBean.jspx JSP page. The converted Java Servlet class shows how 'useBean', 'setProperty' and 'getProperty' are converted.

If you are interested to see how Tomcat server converts "useBean", "setProperty" and "getProperty" action elements into Java statements before the final execution, open the Servlet class converted from UseBean.jspx at C:\local\tomcat\work\Catalina\localhost\ROOT\org\apache\jsp\UseBean_jspx.java

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/9.0.12
 * ...
 */
package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import herong.CacheBean;

public final class UseBean_jspx
    extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {

  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map<java.lang.String,java.lang.Long>
     _jspx_dependants;

  private javax.el.ExpressionFactory _el_expressionfactory;
  private org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long>
    getDependants() {
    return _jspx_dependants;
  }

  public void _jspInit() {
    ...
  }

  public void _jspDestroy() {
  }

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

    final javax.servlet.jsp.PageContext pageContext;
    javax.servlet.http.HttpSession session = null;
    final javax.servlet.ServletContext application;
    final javax.servlet.ServletConfig config;
    javax.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;
    javax.servlet.jsp.JspWriter _jspx_out = null;
    javax.servlet.jsp.PageContext _jspx_page_context = null;

    try {
      response.setContentType("text/html;charset=UTF-8");
      pageContext = _jspxFactory.getPageContext(
         this, request, response, null, true, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("<html>");
      out.write("<body>");

      CacheBean b = null;
      b = (CacheBean) _jspx_page_context.getAttribute("b",
         javax.servlet.jsp.PageContext.PAGE_SCOPE);
      if (b == null){
        b = new CacheBean();
        _jspx_page_context.setAttribute("b", b,
           javax.servlet.jsp.PageContext.PAGE_SCOPE);
      }

      org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(
         _jspx_page_context.findAttribute("b"), "text",
         "Hello world!", null, null, false);

      out.write("\n");
      out.write("Property from my JavaBean: \n");

      out.write(
         org.apache.jasper.runtime.JspRuntimeLibrary.toString(
(((CacheBean)_jspx_page_context.findAttribute("b")).getText())));

      out.write("<br/>");
      out.write("\n");
      out.write("Info from my JavaBean: \n");
      out.print(b.getInfo());
      out.write("</body>");
      out.write("</html>");
    } catch (java.lang.Throwable t) {
      ...
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

Note that:

The "page" directive element with "import" attribute was converted into a true Java "import" statement.
The "useBean" action element was converted into a block of code to load bean class, instantiate an object of that bean class, and put that object into the attribute collection in the page context object. The name of the attribute is set to the same as the object name.
The "setProperty" action element was converted into a call to introspecthelper() method.
The "getProperty" action element was converted into a call to a "get" method.
The "expression" element was translated into a call to "out.print()".