How do I share object or data between users in web application?

By Wayan in Servlet 0 Comment

In a web application there are different type of scope where we can store object or data. There are a page, request, session and application scope.

To share data between users of the web application we can put a shared object in application scope which can be done by calling setAttribute() method of the ServletContext. By this way data can then be accessing by other users by calling the getAttribute() method of the ServletContext.

Let’s see the example code in a simple servlet.

package org.kodejava.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "SharedObjectServlet", urlPatterns = "/shared-object")
public class ApplicationContextScopeAttribute extends HttpServlet {

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

        ServletContext context = this.getServletContext();
        context.setAttribute("HELLO.WORLD", "Hello World 123");
    }
}

And here is what we code in the JSP page to access it.

<%= request.getServletContext().getAttribute("HELLO.WORLD") %>

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I format a date-time value?

By Wayan in Core API, Text Package 0 Comment

In the DateFormat class there are some predefined constants that we can use to format a date time value. Here is an example of it.

package org.kodejava.text;

import java.text.DateFormat;
import java.util.Date;

public class DefaultDateFormatExample {
    public static void main(String[] args) {
        Date date = new Date();

        // Format date in a short format
        String today = DateFormat.getDateTimeInstance(DateFormat.SHORT,
                DateFormat.SHORT).format(date);
        System.out.println("Today " + today);

        // Format date in a medium format
        today = DateFormat.getDateTimeInstance(DateFormat.MEDIUM,
                DateFormat.MEDIUM).format(date);
        System.out.println("Today " + today);

        // Format date in a long format
        today = DateFormat.getDateTimeInstance(DateFormat.LONG,
                DateFormat.LONG).format(date);
        System.out.println("Today " + today);
    }
}

And you’ll see the result as follows:

Today 9/24/21 9:40 AM
Today Sep 24, 2021 9:40:28 AM
Today September 24, 2021 9:40:28 AM CST

How do I format a date into dd/MM/yyyy?

By Wayan in Core API, Text Package 11 Comments

Formatting how data should be displayed on the screen is a common requirement when creating a program or application. Displaying information in a good and concise format can be an added values to the users of the application. In the following code snippet we will learn how to format a date into a certain display format.

For these purposes we can utilize the DateFormat and SimpleDateFormat classes from the java.text package. We can easily format a date in our program by creating an instance of SimpleDateFormat class and specify to format pattern. Calling the DateFormat.format(Date date) method will format a date into a date-time string.

You can see the details about date and time patters in the following link: Date and Time Patterns. Now, let’s see an example as shown in the code snippet below.

package org.kodejava.text;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateFormatExample {
    public static void main(String[] args) {
        Date date = Calendar.getInstance().getTime();

        // Display a date in day, month, year format
        DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
        String today = formatter.format(date);
        System.out.println("Today : " + today);

        // Display date with day name in a short format
        formatter = new SimpleDateFormat("EEE, dd/MM/yyyy");
        today = formatter.format(date);
        System.out.println("Today : " + today);

        // Display date with a short day and month name
        formatter = new SimpleDateFormat("EEE, dd MMM yyyy");
        today = formatter.format(date);
        System.out.println("Today : " + today);

        // Formatting date with full day and month name and show time up to
        // milliseconds with AM/PM
        formatter = new SimpleDateFormat("EEEE, dd MMMM yyyy, hh:mm:ss.SSS a");
        today = formatter.format(date);
        System.out.println("Today : " + today);
    }
}

Let’s view what we got on the console:

Today : 24/09/2021
Today : Fri, 24/09/2021
Today : Fri, 24 Sep 2021
Today : Friday, 24 September 2021, 09:36:32.724 AM

How do I get my web application real path?

By Wayan in Servlet 3 Comments

This code helps you to get the physical path where your web application is deployed on the server. It may be useful, so you can for instance read or write files on the server. Please be aware that this method will only work when your web application is deployed in an exploded way, if it was deployed in a war format the getRealPath() method just return null.

package org.kodejava.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "RealPathServlet", urlPatterns = "/real-path")
public class GetWebApplicationPathServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String path = getServletContext().getRealPath("/");
        PrintWriter writer = response.getWriter();
        writer.println("Application path: " + path);
    }
}

If you tried access the servlet you’ll get an output like:

Application path: F:\Wayan\Kodejava\kodejava-example\kodejava-servlet\target\kodejava-servlet\

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I get the last day of a month?

By Wayan in Core API, Util Package 2 Comments 
package org.kodejava.util;

import java.text.DateFormatSymbols;
import java.util.Calendar;

public class LastDayOfMonth {
    public static void main(String[] args) {
        // Get a calendar instance
        Calendar calendar = Calendar.getInstance();

        // Get the last date of the current month. To get the last date for a
        // specific month you can set the calendar month using calendar object
        // calendar.set(Calendar.MONTH, theMonth) method.
        int lastDate = calendar.getActualMaximum(Calendar.DATE);

        // Set the calendar date to the last date of the month so then we can
        // get the last day of the month
        calendar.set(Calendar.DATE, lastDate);
        int lastDay = calendar.get(Calendar.DAY_OF_WEEK);

        // Print the current date and the last date of the month
        System.out.println("Last Date: " + calendar.getTime());

        // The lastDay will be in a value from 1 to 7 where 1 = Sunday and 7 =
        // Saturday. The first day of the week is based on the locale.
        System.out.println("Last Day : " + lastDay);

        // Get weekday name
        DateFormatSymbols dfs = new DateFormatSymbols();
        System.out.println("Last Day : " + dfs.getWeekdays()[lastDay]);
    }
}

Here is the output of the code snippet above:

Last Date: Thu Sep 30 06:44:05 CST 2021
Last Day : 5
Last Day : Thursday