How do I iterate each character of a string?

By Wayan in Core API, Text Package 0 Comment

The following example show you how to iterate each character of a string using the java.text.CharacterIterator and java.text.StringCharacterIterator to count the number of vowels and consonants in the string.

package org.kodejava.text;

import java.text.CharacterIterator;
import java.text.StringCharacterIterator;

public class StringCharacterIteratorExample {
    private static final String text =
        "The quick brown fox jumps over the lazy dog";

    public static void main(String[] args) {
        CharacterIterator it = new StringCharacterIterator(text);

        int vowels = 0;
        int consonants = 0;

        // Iterates character sets from the beginning to the last character
        for (char ch = it.first(); ch != CharacterIterator.DONE; ch = it.next()) {
            if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
                vowels = vowels + 1;
            } else if (ch != ' ') {
                consonants = consonants + 1;
            }
        }

        System.out.println("Number of vowels: " + vowels);
        System.out.println("Number of consonants: " + consonants);
    }
}

The output of the code snippet above:

Number of vowels: 11
Number of consonants: 24

How do I disable auto-commit mode in JDBC?

By Wayan in JDBC 0 Comment

The code snippet below shows you how to disable auto-commit operation when executing JDBC commands or queries.

package org.kodejava.jdbc;

import java.sql.*;

public class AutoCommitSettingExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        // DO: Get a connection to database, we need to obtain the
        // database connection prior to executing any JDBC commands
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Disable the auto-commit operation. By default, every statement
            // executed against database in JDBC is in auto-commit mode. To
            // disable auto-commit set it to false
            connection.setAutoCommit(false);

            // DO: Execute some other database operation here
            String sql = "DELETE FROM book WHERE id = ?";
            try (PreparedStatement statement = connection.prepareStatement(sql)) {
                statement.setLong(1, 1L);
                statement.executeUpdate();

                // Finally we must call the commit method explicitly to finish
                // all database manipulation operation
                connection.commit();
            } catch (SQLException e) {
                // When some exception occurs rollback the transaction.
                connection.rollback();
                throw e;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central

How do I read text file in Servlet?

By Wayan in Servlet 5 Comments

This example show you how to read a text file in a servlet. Using the ServletContext.getResourceAsStream() method will enable you to read a file whether the web application is deployed in an exploded format or in a war file archive.

The following servlet read the configuration.properties file from the /WEB-INF directory in our web application. The configuration.properties file is just a regular text file with the following contents.

app.appname=Servlet Examples
app.version=1.0
app.copyright=2021

Here is our ReadTextFileServlet servlet class.

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.*;

@WebServlet(name = "ReadTextFileServlet", urlPatterns = "/read-text-file")
public class ReadTextFileServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html");

        // We are going to read a file called configuration.properties. This
        // file is placed under the WEB-INF directory.
        String filename = "/WEB-INF/configuration.properties";

        ServletContext context = getServletContext();

        // First get the file InputStream using ServletContext.getResourceAsStream()
        // method.
        InputStream is = context.getResourceAsStream(filename);
        if (is != null) {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader reader = new BufferedReader(isr);
            PrintWriter writer = response.getWriter();
            String text;

            // We read the file line by line and later will be displayed on the
            // browser page.
            while ((text = reader.readLine()) != null) {
                writer.println(text + "</br>");
            }
        }
    }
}

To access the servlet you can type http://localhost:8080/read-text-file in your browser URL address bar.

Maven dependencies

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

Maven Central

How do I create a scheduled task using timer?

By Wayan in Core API, Util Package 0 Comment

This example show you how to create a simple class for scheduling a task using Timer and TimerTask class.

package org.kodejava.util;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class TimerExample extends TimerTask {
    private final DateFormat formatter = new SimpleDateFormat("hh:mm:ss a");

    public static void main(String[] args) {
        // Create an instance of TimerTask implementor.
        TimerTask task = new TimerExample();

        // Create a new timer to schedule the TimerExample instance at a
        // periodic time every 5000 milliseconds (5 seconds) and start it
        // immediately
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(task, new Date(), 5000);
    }

    /**
     * This method is the implementation of a contract defined in the 
     * TimerTask class. This in the entry point of the task execution.
     */
    public void run() {
        // To make the example simple we just print the current time.
        System.out.println(formatter.format(new Date()));
    }
}

Here is the result printed by the code snippet above:

09:53:28 AM
09:53:33 AM
09:53:38 AM
09:53:43 AM
09:53:48 AM

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

How do I get the last date of a month?

By Wayan in Core API, Util Package 0 Comment

You want to know what is the last date for a current month. The code below show you how to get it.

package org.kodejava.util;

import java.util.Calendar;

public class LastDateOfMonth {
    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);

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

Here is the result of the code snippet:

Date     : Fri Sep 24 06:42:18 CST 2021
Last Date: 30