Tech-Notes

Java SE
Java EE servelets, web projects
Java ME

package myproject;
public class MyServlet extends HttpServlet{
  public void service(HttpServletRequest req,HttpServletResponse res){
    int i = Integer.parseInt(req.getParameter("i"));
    int j = Integer.parseInt(req.getParameter("j"));
    int k = i + j;
    PrintWriter out = res.getWriter();
    out.println(k);
  }
}

<xml>
<web-app>
 <display-name>myproject</display-name>
 <servlet>
 	<servlet-name>add</servlet-name>
 	<servlet-class>myproject.AddServelet</servlet-class>
 </servlet>
 <servlet-mapping>
 	<servlet-name>add</servlet-name>
 	<url-pattern>/add</url-pattern>
 </servlet-mapping>
</web-app>

service() - handle both get post
doGet() - handle get method
doPost() - handle post method

Call servlet from another servlet:

    req.setAttribute("a","3");   //use res.getAttribute("a"); in another servlet
    RequestDispatcher rd = req.getRequestDispatcher("anotherServeletName"); 
    rd.forward(req,res); 

Redirect:

req.setAttribute("a","3");   //use res.getAttribute("a"); in another servlet 
req.sendRedirect("servletName");  // in browser url get changed

Session:

HttpSession session = res.getSession();
session.setAttribute("K","3");
session.setAttribute("k");
session.removeAttribute("k");

Cookies

Cookie cookie = new Cookie("k",k);
res.addCookie(cookie);
Cookie cookie[] = res.getCookies();

ServletContext

<context-param>
  <param-name>username</param-name>
  <param-value>muthu</param-value>
</context-param>  

ServletContext ctx = getServletContext();
String username = ctx.getInitParameter("username");

ServletConfig

<servlet>
  <servlet-name>add</servlet-name>
  <servlet-class>com.AddServlet</servlet-class>
  <init-param>
    <param-name>username<param-name>
    <param-value>muthu<param-value>
  </init-param>
</servlet>
ServletConfig ctx = getServletConfig();
String username = ctx.getInitParameter("username");

Annotations : @WebServlet(“/url”)

---

JSP:

<%!  %> jsp declaration // int a =0;
<%   %> jsp scriplet    // a= c+ d; 
<%=  %> jsp expression  // equals to out.println();
<%@  %> jsp directive   // <%@ page import= "      .*"%> // to import class or package
                           <%@ include file= "" %>
                           <%@ taglib uri="url" prefix="fx" %>    <fx:h1>

Attributes for @page:
language=”any scripting lang”
extends=”className”
import=”importList”
session=”true|false”
autoFlush=”true|false”
contentType=”ctinfo”
errorPage=”error_url” //for exception handling
isErrorPage=”true|false” <%exception >
info=”information”
isELIgnored=”true|false”
isThreadSafe=”true|false”

Implicit objects available in jsp:
request (HttpServletRequest)
response (HttpServletResponse)
pageContext (PageContext)
out (JspWriter) - PrintWriter object
session - HttpSession
application - (ServletContext)
config - (ServletConfig)

---

JSTL - Java standard tag libray:\

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> 
<c:out value="hello world"/>
<c:out value="${attributeName}"/>
${attributeName}     //call the jsp via requestDispatcher & setattribute

JSTL Sql tags:

<sql:setDataSource var="db" driver="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3307/mysql" user="root" password=""/>
<sql:query var="rs" dataSource="${db}">select * from user_details</sql:query>
<c:foreach items="${rs.rows}" var="obj">
  <c:out value="${obj.name}"></c:out>
</c:foreach>

JSTL function tags:

<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %> 
${fn:length(str)}
${fn:split(str,",")}
${fn:indexOf(str,"world")}
${fn:contains(str,"world")}