Finishing the Project: Java Web Development in Eclipse and Tomcat - What just happened?
(Page 4 of 4 )
You must be wondering what happened. How can Welcome aboard <%=username%> dynamically become Welcome aboard user? How are the user name and password entered in the login.html page being carried over to welcome.jsp? This brings us to another important Java web component called Servlet.
First, the parameters entered in the form fields are carried over from login.html to welcome.jsp by the request object.
Secondly, let's navigate from file explore to:
C:JavaWebDev_Tutorials_Workspace.metadata.plugins
org.eclipse.wst.server.
coretmp0workCatalinalocalhostJavaWebDev_Tutorial_1orgapachejsp
(Catalina is another name for version 5 Tomcat)
You'll find welcome_jsp.java and welcome_jsp.class, which are compiled from Java. Those two files are created and managed by the Eclipse environment.
Let's import welcome_jsp.java into Eclipse IDE to see the details.
First, highlight the Java Resources folder, then from the content menu, select import -> File System.
Then browse into the directory above.
Click Finish, and the Java code shows on the Eclipse content panel. Below is the full text; you can instantly recognize that the red portion is from welcome.jsp
<% Œ
String secreteUser = "user";
String secretePass = "pass";
String username = request.getParameter("username"); Ž
String password = request.getParameter("password");
%>
<%if(!(username.equals(secreteUser) || password.equals(secretePass))) {%>
Wrong username / password
<%} else {%>
Welcome aboard <%=username%>!
<%}%> '
Now you have figured out the relationship between JSP and Servlet! Let's go a step further to prove that JSP actually is the text form of the Servlet class.
package org.apache.jsp;
import Javax.servlet.*;
import Javax.servlet.http.*;
import Javax.servlet.jsp.*;
public final class welcome_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
private static Java.util.Vector _jspx_dependants;
public Java.util.List getDependants() {
return _jspx_dependants;
}
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;
JspWriter _jspx_out = null;
PageContext _jspx_page_context = null;
try {
_jspxFactory = JspFactory.getDefaultFactory();
response.setContentType("text/html");
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>n");
out.write("<head>rn");
out.write("n");
out.write("<title>Welcome page</title>n");
out.write("</head>n");
out.write("<body>rn");
out.write("<pre>n");
String secreteUser = "user";
String secretePass = "pass";
String username = request.getParameter("username");
String password = request.getParameter("password");
out.write('r');
out.write('n');
if(!(username.equals(secreteUser) || password.equals(secretePass))) {
out.write("rn");
out.write("Wrong username / passwordrn");
} else {
out.write("rn");
out.write("Welcome aboard ");
out.print(username);
out.write(" !rn");
}
out.write("rn");
out.write("</pre>n");
out.write("</body>n");
out.write("</html>");
} catch (Throwable t) {
if (!(t instanceof SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
out.clearBuffer();
if (_jspx_page_context != null)
_jspx_page_context.handlePageException(t);
}
} finally {
if (_jspxFactory != null)
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
Now let's do a little more work to prove that JSP actually is a Servlet. Modify login.html's form part
<form action="welcome.jsp" method="post">
To
<form action="welcome_jsp" method="post">
Next, expand WebContent -> WEB-INF, and Click web.xml. This is the web application configuration file. Modify the content to the following:
<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<display-name>JavaWebDev_Tutorial_1</display-name>
<servlet>
<description></description>
<display-name>welcome_jsp</display-name>
<servlet-name>welcome_jsp</servlet-name>
<servlet-class>org.apache.jsp.welcome_jsp</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>welcome_jsp</servlet-name>
<url-pattern>/welcome_jsp</url-pattern>
</servlet-mapping>
</web-app>
The web.xml defines the Servlet we just imported from and the servlet-mapping's url-pattern pointed to the org.apache.jsp.welcome_jsp.welcome_jsp servlet with the short name welcome_jsp corresponding to login.htm action part here:
<form action="welcome_jsp" method="post">
If you run the application again, you'll get the same result.
To explain it further, the welcome_jsp actually extends org.apache.jasper.runtime.HttpJspBase
public final class welcome_jsp extends org.apache.jasper.runtime.HttpJspBase
Here is the class hierarchy:
(http://tomcat.apache.org/tomcat-4.1-
doc/jasper/docs/api/org/apache/jasper/runtime/HttpJspBase.html)
java.lang.Object
javax.servlet.GenericServlet
javax.servlet.http.HttpServlet
org.apache.jasper.runtime.HttpJspBase
So the welcome_jsp is indeed a Servlet and it's generated from welcome.jsp by the Eclipse environment.
Summary
In this short tutorial, we introduced the Integrated Java Web Development environment with Eclipse and how to develop, test, and configure a web application. We are ready to move to the next in upcoming articles.
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