How do I include a page fragment into JSP?

By I Wayan Saryada in JSP 2 Comments

In this example you can learn how to include a JSP fragment into another JSP page. This is a common practice when creating a web application where we usually have a navigation section, the main content and the footer of a web page. Using the include directive make it simpler to maintain the fragment of a web page, which mean that when we need to change for example the footer section we just need to alter the footer include file and all the page that includes it will get the benefit.

The page inclusion that using the include direction will occur at page translation time, it is when the JSP page is translated into a Servlet by JSP container. We can use any file extension name for the JSP fragment used by the include directive. In this example we use the .jspf extension which is short for JSP Fragment.

Here is an example of JSP with include directive.

<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>JSP - Include Directive</title>
</head>
<body>

<div id="header">
    <%@ include file="/include/common/header.jspf" %>
</div>

<div id="content">
    Main application content goes here!
</div>

<div id="footer">
    <%@ include file="/include/common/footer.jspf" %>
</div>

</body>
</html>

header.jspf fragment.

Header
<hr/>

footer.jspf fragment.

<hr/>
Footer

How do I define welcome files for web application?

By I Wayan Saryada in Servlet 0 Comment

The configuration below gives us example how to define a welcome-files to our web application. The welcome file is default file to be loaded by a servlet container when we access a URL without telling which page to load.

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>
</web-app>

How do I search collection elements?

By I Wayan Saryada in Core API, Util Package 0 Comment

This code example use the Collections.binarySearch() to search an specified object inside a specified collections. Prior to calling the binarySearch() method we need to sort the elements of the collection. If the object is not sorted according to their natural order the search result will be undefined.

package org.kodejava.util;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Collections;
import java.text.DateFormatSymbols;

public class CollectionSearch {
    public static void main(String[] args) {
        DateFormatSymbols dfs = new DateFormatSymbols();

        LinkedList<String> monthList =
                new LinkedList<>(Arrays.asList(dfs.getMonths()));

        // Sort the collection elements
        Collections.sort(monthList);
        System.out.println("Months = " + monthList);

        // Get the position of November inside the monthList. It returns a positive
        // value if the item found in the monthList.
        int index = Collections.binarySearch(monthList, "November");
        if (index > 0) {
            System.out.println("Found at index = " + index);
            System.out.println("Month = " + monthList.get(index));
        }
    }
}

The output of the code snippet above is below.

Months = [, April, August, December, February, January, July, June, March, May, November, October, September]
Found at index = 10
Month = November

How do I rotate elements of a collection?

By I Wayan Saryada in Core API, Util Package 0 Comment

This example demonstrate how to rotate the elements of a collection object. We can use the java.util.Collections class and call the rotate() method with the collection to rotate and the distance as the parameters.

package org.kodejava.util;

import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Arrays;

public class CollectionRotate {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();

        // Add some items into the collection
        for (int i = 0; i < 25; i++) {
            numbers.add(i);
        }

        // Print the collection items        
        System.out.println(Arrays.toString(numbers.toArray()));

        // Rotates the elements in the collection by the 10.
        Collections.rotate(numbers, 10);

        // Print the rotated collection items
        System.out.println(Arrays.toString(numbers.toArray()));
    }
}

Here is the program result:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]
[15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

How do I display file contents in hexadecimal?

By I Wayan Saryada in Core API, IO 0 Comment

In this program we read the file contents byte by byte and then print the value in hexadecimal format. As an alternative to read a single byte we can read the file contents into array of bytes at once to process the file faster.

package org.kodejava.io;

import java.io.FileInputStream;

public class HexDumpDemo {
    public static void main(String[] args) throws Exception {
        // Open the file using FileInputStream
        String fileName = "F:/Wayan/Kodejava/kodejava-example/data.txt";
        try (FileInputStream fis = new FileInputStream(fileName)) {
            // A variable to hold a single byte of the file data
            int i = 0;

            // A counter to print a new line every 16 bytes read.
            int count = 0;

            // Read till the end of the file and print the byte in hexadecimal
            // valueS.
            while ((i = fis.read()) != -1) {
                System.out.printf("%02X ", i);
                count++;

                if (count == 16) {
                    System.out.println();
                    count = 0;
                }
            }
        }
    }
}

And here are some result from the file read by the above program.

31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 
37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 
33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 
39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 
35 36 37 38 39 30 0A