JSP and JSTL Tutorials - Tutorial Addendum - Using JavaBean Classes

31 December 18:00

(Continued from antecedent part...)

It s actual absorbing to see the Servlet chic translated from UseBean.jsp:

 

    package org.apache.jsp;

    
import javax. Servlet .*;

    
import javax. Servlet .http.*;

    
import javax. Servlet .jsp.*;

    
import org.apache.jasper.runtime.*;

    
import CacheBean;

    
public chic UseBean_jsp extends HttpJspBase {

    
  clandestine changeless java.util.Vector _jspx_includes;

    
  accessible java.util.List getIncludes() {

    
    acknowledgment _jspx_includes;

    
  }

    
  accessible abandoned _jspService(HttpServletRequest request, 

    
        HttpServletResponse response)

    
        throws java.io.IOException, ServletException {

    
    JspFactory _jspxFactory = null;

    
    javax. Servlet .jsp.PageContext pageContext = null;

    
    HttpSession   affair   = null;

    
    ServletContext appliance = null;

    
    ServletConfig config = null;

    
    JspWriter out = null;

    
    Item page = this;

    
    JspWriter _jspx_out = null;

    
    try {

    
      _jspxFactory = JspFactory.getDefaultFactory();

    
      response.setContentType("text/xml;charset=UTF-8");

    
      pageContext = _jspxFactory.getPageContext(this, request, response,

    
      			null, true, 8192, true);

    
      appliance = pageContext.getServletContext();

    
      config = pageContext.getServletConfig();

    
       affair  = pageContext.getSession();

    
      out = pageContext.getOut();

    
      _jspx_out = out;

    
      out.write("<html>");

    
      out.write("<body>");

    
      CacheBean b = null;

    
      synchronized (pageContext) {

    
        b = (CacheBean) pageContext.getAttribute("b", 

    
             PageContext.PAGE_SCOPE);

    
        if (b == null){

    
          try {

    
            b = (CacheBean) java.beans.Beans.instantiate(

    
                this.getClass().getClassLoader(), "CacheBean");

    
          } bolt (ClassNotFoundException exc) {

    
            bandy new InstantiationException(exc.getMessage());

    
          } bolt (Exception exc) {

    
            bandy new ServletException("Cannot make bean of chic " 

    
               + "CacheBean", exc);

    
          }

    
          pageContext.setAttribute("b", b, PageContext.PAGE_SCOPE);

    
        }

    
      }

    
      JspRuntimeLibrary.introspecthelper(pageContext.findAttribute("b"),

    
         "text", "Hello world!",null, null, false);

    
      out.write("

Property from my Bean: ");

    
      out.print(JspRuntimeLibrary.toString(((

    
         (CacheBean)pageContext.findAttribute("b")).getText())));

    
      out.write("<br/>");

    
      out.write("

Info from my Bean: ");

    
      out.print(b.getInfo());

    
      out.write("</body>");

    
      out.write("</html>");

    
    } bolt (Throwable t) {

    
      out = _jspx_out;

    
      if (out != absent && out.getBufferSize() != 0)

    
        out.clearBuffer();

    
      if (pageContext != null) pageContext.handlePageException(t);

    
    } assuredly {

    
      if (_jspxFactory != null) 

    
          _jspxFactory.releasePageContext(pageContext);

    
    }

    
  }

    
}

Note that:

The "page" charge aspect with "import" aspect was translated into a true

"import" Java statement.

The "useBean" activity aspect was translated into a block of cipher to amount bean


class, instantiate an item of that bean class, and put that item into the


attribute accumulating in the page ambience object. The name of the attribut is set


to the aforementioned as the item name.

The "setProperty" activity aspect was translated into a alarm to introspecthelper()

method.

The "getProperty" activity aspect was translated into a alarm to a "get" method.

The "expression" aspect was translated into a alarm to "out.print()".

Compilation Errors with Bobcat 4.1.18 and JDK 1.4.1

If you are using JDK 1.4.1 and aggravating to run the aloft example, you will get the

following accumulation error:

 

    org.apache.jasper.JasperException: Clumsy to abridge chic for JSP

    
An absurdity occurred at line: 8 in the jsp file: /UseBean.jsp

    
Generated  Servlet  error:

    
    [javac] Accumulation 1 antecedent file

    
C:localjakarta-tomcat-4.1.18workStandalonelocalhost

    
   \_UseBean_jsp.java:7:  .  expected

    
import CacheBean;

This is because JDK 1.4.1 does not acquiesce acceptation account to be acclimated on classes

in bearding bales any more. For added detail information, amuse see area

"Tomcat 4.1.18 with JDK 1.4.1" in this book.

Setting and Accepting JavaBeans Properties

As you can see from antecedent sections, a JavaBean is just a approved Java obect.

Once a JavaBean is created in a JSP, you can use JSP setProperty and getProperty

action elements to set and retrieve ethics of its properties. To abutment these

action elements, a JavaBean chic haveto apparatus set and get methods based on some

rules.

(Continued on next part...)

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