JSP and JSTL Tutorials - Tutorial Addendum - JavaServer Pages (JSP)

31 December 18:00

What is JSP?

JSP is a technology, not a language. It allows Web page authors to put activating data

into a Web certificate with Java statements anchored in appropriate HTML tags. The anchored Java

statements will be accomplished by the JSP enabled Web server, not by the Web browser.

JSP Page is a Web page, HTML document, with enbedded Java statements in a anatomy authentic by the

JSP specification. Actuality is a JSP page example, hello.jsp:

 

    <html><body>

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

    
</body></html>

Line 1 and 3 are accustomed HTML tags. But band 2 is a Java account anchored in appropriate HTML tag.

We understand how a accustomed Web page is served by a accustomed Web server:

Step 1: The Web browser sends a HTTP appeal to the Web server with the aisle name of

the Web page.

Step 2: The Web server picks up the Web page by afterward the defined aisle name.

Step 3: The Web server puts the agreeable of the Web page after any changes into

a HTTP response.

Step 4: The Web server sends the HTTP acknowledgment to the Web browser.

Here is how a JSP page is served by a JSP Web server:

Step 1: The Web browser sends a HTTP appeal to the Web server with the aisle name of

the JSP page.

Step 2: The Web server checks to see if there is a aggregate adaptation of the requested

JSP page. If no, it compiles the requested JSP page immediately.

Step 3: The Web server executes the aggregate adaptation of the requested JSP page, and

collects the achievement of the execution.

Step 4: The Web server puts the achievement of the beheading into a HTTP response.

Step 5: The Web server sends the HTTP acknowledgment to the Web browser.

There are two key processes complex in confined a JSP page:

Compilation: A JSP page haveto be aggregate into a Java Servlet class,


before it can be executed. The server can abridge a JSP page in real-time if the page


is requested for the first time, if the page is not pre-compiled.

Execution: If a JSP page is requested, its aggregate chic will be accomplished


on the server. The server will forward aback the achievement of the execution, not the agreeable


of the JSP page.

"Hello world!" Java Servlet Class

To accept added about the JSP accumulation process, let s use my hello.jsp again:

 

    <html><body>

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

    
</body></html>

Then save hello.jsp to localjakarta-tomcat-4.1.18webappsROOT,

and run IE with url: http://localhost:8080/hello.jsp.

You should see "Hello world!" in the IE window.

Now, if you attending at the directory: localjakarta-tomcat-4.1.18workstandalonelocalhost\_,

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 chic hello_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/html;charset=ISO-8859-1");

    
      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>

");

    
 out.println("Hello world!"); 

    
      out.write("

");

    
      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);

    
    }

    
  }

    
}