JSTL forEach tag

JSTL forEach tutorial shows how to use the forEach tag from the JSTL library.

JSTL

JavaServer Pages Standard Tag Library (JSTL) is a collection of useful JSP tags that provide the core functionality common to many JSP applications.

forEach tag

JSTL <c:forEach> tag is a basic iteration tag. It iterates over various Java collection types.

The <c:forEach> tag contains the following attributes:

forEach taglib declaration

The <c:forEach> tag belongs to the core JSTL tags.

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

To use the tag, we need to include this declaration.

JSTL Maven artifact

To use the JSTL library, we need the following Maven dependency:

<dependency>
    <groupId>jstl</groupId>
    <artifactId>jstl</artifactId>
    <version>1.2</version>
</dependency>

forEach tag example

The following JSP page contains the <c:forEach> tag. In addiction to <c:forEach> tag, we also use <c:out> for displaying variables.

index.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <c:forEach var="counter" begin="1" end="8">
            <c:out value="${counter}"/>
        </c:forEach>
    </body>
</html>

The example shows values 1..8 in the output.

forEach tag example II

The next JSP example reads parameters sent from a link.

index.html
<!DOCTYPE html>
<html>
    <head>
        <title>Start Page</title>
        <meta charset="UTF-8">
    </head>
    <body>
        
        <a href="target.jsp?name=Jane&age=23&occupation=accountant">Show page</a>
        
    </body>
</html>

The index.html page contains a link that sends three parameters to the target.jsp page.

target.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <c:forEach var="par" items="${param}">

            <c:out value="${par.key}"/>: <c:out value="${par.value}"/> <br>

        </c:forEach>
    </body>
</html>

The JSP page receives parameters in the implicit param object, which is a map.

<c:forEach var="par" items="${param}">

    <c:out value="${par.key}"/>: <c:out value="${par.value}"/> <br>

</c:forEach>

We go over the map and print the key/value pairs.

forEach tag example III

The HTML <select> is a control that provides a menu of options. With its multiple attribute, the user can select multiple values form the control.

index.html
<!DOCTYPE html>
<html>
    <head>
        <title>Languages</title>
        <meta charset="UTF-8">
    </head>
    <body>

        <form action="target.jsp">
            <div>Select languages:</div>

            <select name="languages" size="7" multiple="multiple">
                <option value='Ada'>Ada</option>
                <option value='C'>C</option>
                <option value='C++'>C++</option>
                <option value='Cobol'>Cobol</option>
                <option value='Eiffel'>Eiffel</option>
                <option value='Objective-C'>Objective-C</option>
                <option value='Java'>Java</option>
            </select>

            <button type="submit">Submit</button>

        </form>

    </body>
</html>

We create a <select> control that contains seven values. When we submit the form, the selected values are sent to the target.jsp file.

target.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Languages</title>
    </head>
    <body>
        <c:forEach items="${paramValues.languages}" var="lang">
            <c:out value="${lang}"/>
        </c:forEach>
    </body>
</html>

The valuues from the <select> control are available from the implicit paramValues object, which is a map. The key is the request parameter name (languages) and the values are in an array of strings.

<c:forEach items="${paramValues.languages}" var="lang">
    <c:out value="${lang}"/>
</c:forEach>

We go over the array and print its elements.

forEach tag example IV

The following example displays data in an HTML table.

index.html
<!DOCTYPE html>
<html>
    <head>
        <title>Start Page</title>
        <meta charset="UTF-8">
    </head>
    <body>
        <p>
            <a href="MyServlet">Show all cities</a>
        </p>
    </body>
</html>

In the index.html page we have a link that calls MyServlet. The servlet loads data with a service method and dispatches to the JSP page.

City.java
package com.zetcode.bean;

public class City {
    
    private Long id;
    private String name;
    private int population;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public City(Long id, String name, int population) {
        this.id = id;
        this.name = name;
        this.population = population;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPopulation() {
        return population;
    }

    public void setPopulation(int population) {
        this.population = population;
    }
}

This is the City class; it contains id, name, and population attributes.

MyServlet.java
package com.zetcode.web;

import com.zetcode.bean.City;
import com.zetcode.service.CityService;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "MyServlet", urlPatterns = {"/MyServlet"})
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=UTF-8");
        
        List<City> cities = CityService.getAllCities();
        
        request.setAttribute("cities", cities);
        
        request.getRequestDispatcher("showCities.jsp").forward(request, response);
    }
}

The servlet reads data with CityService.getAllCities(), sets the list object to the attributes with setAttribute(), and forwards to the showCities.jsp.

CityService.java
package com.zetcode.service;

import com.zetcode.bean.City;
import java.util.ArrayList;
import java.util.List;

public class CityService {
    
    public static List<City> getAllCities() {
    
       List<City> cities = new ArrayList<>();
        
        cities.add(new City(1L, "Bratislava", 432000));
        cities.add(new City(2L, "Budapest", 1759000));
        cities.add(new City(3L, "Prague", 1280000));
        cities.add(new City(4L, "Warsaw", 1748000));
        cities.add(new City(5L, "Los Angeles", 3971000));
        cities.add(new City(6L, "New York", 8550000));
        cities.add(new City(7L, "Edinburgh", 464000));
        cities.add(new City(8L, "Berlin", 3671000));
        
        return cities;
    }
}

The getAllCities() method returns a list of cities.

showCities.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Cities</title>
    </head>
    <body>
        <h2>Cities</h2>
        
        <table>
            <thead>
                <tr>
                    <th>Id</th>
                    <th>Name</th>
                    <th>Population</th>
                </tr>
            </thead>
            
            <tbody>
                <c:forEach items="${cities}" var="city">
                <tr>
                    <td>${city.id}</td>
                    <td>${city.name}</td>
                    <td>${city.population}</td>
                </tr>
                </c:forEach>   
            </tbody>
        </table>
    </body>
</html>

In the showCities.jsp, we display the cities in the HTML table with the <c:forEach> tag.

<td>${city.id}</td>
<td>${city.name}</td>
<td>${city.population}</td>

The attributes are read from the city object with the dot operator.

In this tutorial, we have covered the <c:forEach> tag from the JSTL library.

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