JSP Tags

As in other languages, there are a few main tags in JSP. 

 

Scriptlet tag

A scriptlet tag is used to execute java source code in JSP.

<!-- Scriptlet Tag -->
<%
	// Basic variables 
int i = 30;
double d = 3.14;
char c1 = 'A';
char c2 = '자';
boolean b1 = true;
boolean b2 = false;

// Reference variables
// 1. Class
String str1 = "JSP";
String str2 = new String("JSP");

// 2. Array 
String[] str = { "Java", "JSP", "Oracle", "HTML", "Python" };

for (int j = 0; j < str.length; j++) {
	out.println(str[j] + "\t"); // println doesn't have a function of printing out in a new line.
}

out.println("<br>");
%>

<%
	for (String s : str) {
%>
<%=s%>
<br>
<%
	}
%>

<%
	// 3. Interface : List
List list = new ArrayList(); // Upcasting 
// You need to import with the page tag.
list.add(50);
list.add(50.33);
list.add('A');
list.add(true);
list.add("JSP");

for (int j = 0; j < list.size(); j++){
	 out.println(list.get(j)+"\t");
}
%>
<br>

Declaration tag

It is used to declare fields and methods.

The code written inside the JSP declaration tag is placed outside the service() method of the auto-generated Servlet.

<!-- Declaration tag -->
<!-- To declare methods -->
<%!
public int add(int a, int b){
	int c =  a + b;
	return c;
}

public int subtract(int a, int b){
	int c = a - b;
	return c;
}

public int multiply(int a, int b){
	int c = a * b;
	return c;
}

%>
<%
int result1 = add(3, 9); // To call add method
int result2 = subtract(3, 9); // To call add method
int result3 = multiply(3, 9); // To call add method
%>

3 + 9 = <%=result1 %> <br>
3 - 9 = <%=result2 %> <br>
10 * 25 = <%=result3 %> <br>
10 * 25 = <%=multiply(10, 25) %> <br>

 

Wait, what is the Servlet?

According to Oracle,  "A servlet is a Java programming language class that is used to extend the capabilities of servers that host applications accessed by means of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers. For such applications, Java Servlet technology defines HTTP-specific servlet classes."

 

The main difference between Servlet and JSP is that Servlet is java based, whereas JSP is HTML based. 

Let's get back to the tags then. 

 

Expression tag

It is to the output stream of the response.

<!-- Expression Tag -->
Print out :
<%="Print Success"%>
<br>
Result :
<%=1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10%>
<br>
i =
<%=i%>
<br>
d =
<%=d%>
<br>
c1 =
<%=c1%>
<br>
c2 =
<%=c2%>
<br>
b1 =
<%=b1%>
<br>
b2 =
<%=b2%>
<br>
str1 =
<%=str1%>
<br>
str2 =
<%=str2%>
<br>

Directive tag

Directive tag gives special instruction to Web Container at page translation time. There are three types of directive tags : page, include and taglib.

 

Page tag, is what you always see on the top of every JSP file, also to import, we use the page tags.

<%@ page language="java" contentType="text/html; charset=EUC-KR"
	pageEncoding="EUC-KR"%>
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>

<!-- To import all in java.util package, you can use this code below -->
<%@ page import= "java.util.*" %>

We will study more about import in the next post.

Directive tag	Description
<%@ page ... %>	defines page dependent properties such as language, session, errorPage etc.
<%@ include ... %>	defines file to be included.
<%@ taglib ... %>	declares tag library used in the page

Action tag

Action tags are used to control the flow between pages and to use Java Bean. The JSP action tags are given below.

Action tag	Description
jsp:forward	forwards the request and response to another resource.
jsp:include	includes another resource.
jsp:useBean	creates or locates bean object.
jsp:setProperty	sets the value of property in bean object.
jsp:getProperty	prints the value of property of the bean.
jsp:plugin	embeds another components such as applet.
jsp:param	sets the parameter value. It is used in forward and include mostly.
jsp:fallback	can be used to print the message if plugin is working. It is used in jsp:plugin.