JSP

• JSP (JavaServer Pages)
• Allows Java within HTML pages
• JSP tags are processed on a web server; the resulting HTML is sent to the client
• The usage of JSP tags is comparable to the usage of PHP or ASP tags

• An extension of Java Servlets
• Tomcat supports JSP and Java Servlets

JSP tags

<%  java-expressions %>                          Scriptlet
<%= single-java-expression-to-output %>          Expression
<%! java-declaration-expressions %>              Declaration

<%@ [page, include, taglib] jsp-directive %>     Directive

    <%@ page import="java.sql.*" %>
    <%@ include file="filename.jsp" %>

    <%@ page language="java" %>

Input / output

• out.println sends output to the browser
• System.out.println sends output to the server log

Comments

<%-- Comment --%>

Hello, world

<%= "Hello, World!" %>

JSP tag libraries

• JSP Tag Extension API
• Allows developers to define and implement a set of custom JSP tags
  
• A Java class that implements one of the Tag interfaces is written for each custom tag
  
• An XML file (.tld) defines the custom tags and the Java classes that implement the tags

<%@ taglib uri="taglib.tld" prefix="prefix" %>
<prefix:tag> ... </prefix:tag>

public class MyTag extends TagSupport {
    // Constructor
    public MyTag() { ... }

    // Release instance variables
    public void release() { ... }

    // Called for the start tag
    public int doStartTag() { ... }

    // Called at the end tag   
    public int doEndTag() { ... }
}