Of course! This is a fundamental concept in JSP (JavaServer Pages). Let's break down how to import Java classes and packages into a JSP file.
The core idea is that a JSP page is, behind the scenes, converted into a Java servlet. The <%@ page %> directive is how you give instructions to the JSP container (like Tomcat) about how to generate that underlying Java code.
The Primary Method: The page Directive
The standard and most common way to import a Java class or package is by using the page directive with the import attribute.
Syntax
<%@ page import="packageName.ClassName, anotherPackage.AnotherClass" %>
You can import multiple classes or packages by separating them with a comma.
Key Points:
- Placement: This directive should be placed at the top of your JSP file, usually before any HTML. It's good practice to put it right after the
<%@ page contentType... %>directive if you have one. - Semicolons: Notice there are no semicolons at the end of the import statement, unlike in Java.
- *`java.lang.
is Implicit:** You do **not** need to explicitly import classes from thejava.langpackage (e.g.,StringSystemObject`). They are automatically available. - *`java.util.
is NOT Implicit:** You must explicitly import classes fromjava.util(e.g.,ArrayListDateHashMap`).
Practical Examples
Let's look at some common use cases.
Example 1: Importing a Single Class
Imagine you have a simple utility class com.example.DateUtils.java.
DateUtils.java
package com.example;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DateUtils {
public static String getCurrentTimestamp() {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
return sdf.format(new Date());
}
}
index.jsp
Here's how you would import and use it in a JSP.
<%@ page import="com.example.DateUtils" %>
<%-- You can also import multiple classes on one line --%>
<%@ page import="java.util.List, java.util.ArrayList" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>JSP Import Example</title>
</head>
<body>
<h1>Welcome to JSP!</h1>
<p>The current server time is: <b><%= DateUtils.getCurrentTimestamp() %></b></p>
<hr>
<p>Here is an example of using an imported List:</p>
<%
List<String> names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
names.add("Charlie");
%>
<ul>
<% for(String name : names) { %>
<li><%= name %></li>
<% } %>
</ul>
</body>
</html>
Explanation:
<%@ page import="com.example.DateUtils" %>tells the JSP container to make theDateUtilsclass available in the generated servlet.<%= DateUtils.getCurrentTimestamp() %>is a JSP expression that calls the static method from our imported class.- Similarly,
ListandArrayListare imported so we can use them in the scriptlet (<% ... %>).
Example 2: Importing an Entire Package
If you plan to use multiple classes from the same package (like java.util), it's cleaner to import the whole package using an asterisk ().
products.jsp
<%@ page import="java.util.*" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>Product List</title>
</head>
<body>
<h2>Our Products</h2>
<%
// We can now use any class from java.util without importing them individually
Map<String, Double> products = new HashMap<>();
products.put("Laptop", 1200.50);
products.put("Mouse", 25.00);
products.put("Keyboard", 75.75);
%>
<table border="1">
<tr>
<th>Product</th>
<th>Price</th>
</tr>
<% for (Map.Entry<String, Double> entry : products.entrySet()) { %>
<tr>
<td><%= entry.getKey() %></td>
<td>$<%= entry.getValue() %></td>
</tr>
<% } %>
</table>
</body>
</html>
What About Other Imports?
You might see other directives like taglib or include, but for importing standard Java code, the page directive is the one you need.
<%@ taglib ... %>: Used to import custom tag libraries (like JSTL), not standard Java classes.<%@ include ... %>: Used to statically include the content of another file (HTML or JSP) at translation time. It doesn't import Java classes.
Summary Table
| Directive | Syntax | Purpose | Example |
|---|---|---|---|
page |
<%@ page import="..." %> |
Imports Java classes and packages for use in the JSP. | <%@ page import="java.util.List" %> |
taglib |
<%@ taglib uri="..." prefix="..." %> |
Imports a custom tag library for use in the JSP. | <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> |
include |
<%@ include file="..." %> |
Statically merges the content of another file into the current JSP. | <%@ include file="header.html" %> |
In short, whenever you need to use a Java class (like ArrayList, Date, or your own custom class) in a JSP, the first thing you should do is add an <%@ page import="..." %> directive at the top of the file.
