How do I convert day-of-the-year to date?

By Wayan in Core API, Util Package 4 Comments

In the following example we want to get the date of the specified day-of-the-year. We can define a calendar for a specific day of the year by setting the java.util.Calendar object DAY_OF_YEAR field using the set() method. The method take the field to be set and a value.

package org.kodejava.util;

import java.util.Calendar;

public class DayOfYearToDate {
    public static void main(String[] args) {
        // In the example we want to get the date value of the specified
        // day of the year. Using the calendar object we can define our
        // calendar for a specific day of the year.
        int dayOfYear = 112;
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_YEAR, dayOfYear);
        System.out.println("Day " + dayOfYear + " of the current year = "
                + calendar.getTime());

        // If you want to get the date for a specific day of year and for
        // a specific year, you can also pass the year information to the
        // calendar object.
        int year = 2020;
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.DAY_OF_YEAR, dayOfYear);
        System.out.println("Day " + dayOfYear + " in year " + year
                + " = " + calendar.getTime());
    }
}

And here is an example result of the code above:

Day 112 of the current year = Thu Apr 22 06:34:14 CST 2021
Day 112 in year 2020 = Tue Apr 21 06:34:14 CST 2020

How do I use JNDI to get database connection or data source?

By Wayan in Core API, JNDI 0 Comment 
package org.kodejava.jndi;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.servlet.Servlet;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

@WebServlet(name = "JNDITestServlet", urlPatterns = "/jndi-datasource-test")
public class JNDITestServlet extends HttpServlet implements Servlet {

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

        // This implementation of doGet method show us an example to use
        // conn obtained in the getConnection() method.
        DateFormat format = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");

        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();

        try (Connection connection = getConnection()) {
            // A query to get current date time from Oracle database
            String sql = "select current_timestamp() as SYSDATE";
            PreparedStatement statement = connection.prepareStatement(sql);
            ResultSet rs = statement.executeQuery();
            while (rs.next()) {
                Date date = rs.getTimestamp("SYSDATE");
                writer.println("The current date is " + format.format(date));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    /**
     * Get a database connection from the registered data source in the
     * servlet container. To registered the JNDI data source you should
     * refer to your servlet container documentation.
     *
     * @return a database connection
     */
    private Connection getConnection() {
        Connection connection = null;
        try {
            InitialContext initialContext = new InitialContext();
            Context context = (Context) initialContext.lookup("java:/comp/env");
            DataSource dataSource = (DataSource) context.lookup("jdbc/DataSource");
            connection = dataSource.getConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return connection;
    }
}

Configure the JNDI DataSource in Tomcat conf/context.xml configuration file. And don’t forget to copy the JDBC driver library to Tomcat’s lib directory.

<?xml version="1.0" encoding="UTF-8"?>
<Context>
    ...
    <Resource name="jdbc/DataSource" auth="Container" type="javax.sql.DataSource"
               maxTotal="100" maxIdle="30" maxWaitMillis="10000"
               username="root" password="" driverClassName="com.mysql.cj.jdbc.Driver"
               url="jdbc:mysql://localhost:3306/kodejava"/>
    ...
</Context>

Maven dependencies

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

Maven Central

How can I get current working directory?

By Wayan in Core API, IO 0 Comment

A system properties named user.dir can be used if you want to find the current working directory of your Java program.

package org.kodejava.io;

public class CurrentDirectoryExample {
    public static void main(String[] args) {
        // System property key to get current working directory.
        String USER_DIR_KEY = "user.dir";
        String currentDir = System.getProperty(USER_DIR_KEY);

        System.out.println("Working Directory: " + currentDir);
    }
}

Result example:

Working Directory: F:\Wayan\Kodejava\kodejava-example

How do I check if parameter is exists in servlet request?

By Wayan in Servlet 0 Comment

ServletRequest or HttpServletRequest object has a map object that maps parameter name and its value. By accessing this map we can check if a parameter was passed in servlet request. Let’s see the example below.

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;

@WebServlet(name = "ParameterCheck", urlPatterns = "/parameter-check")
public class ParameterCheck extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        // Check if username parameter exists
        if (req.getParameterMap().containsKey("username")) {
            String username = req.getParameter("username");
            System.out.println("username = " + username);
        }

        // Check if password parameter exists
        if (req.getParameterMap().containsKey("password")) {
            String password = req.getParameter("password");
            System.out.println("password = " + password);
        }
    }
}

Maven dependencies

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

Maven Central

How do I get parameter names from servlet request?

By Wayan in Servlet 0 Comment

This example show you how to obtain parameter name from servlet request. By calling request.getParameterNames() you will get an Enumeration object by iterating this object you can get the parameter names.

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;
import java.util.Enumeration;

@WebServlet(name = "ParameterName", urlPatterns = "/parameter-names")
public class ParameterName extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        PrintWriter pw = response.getWriter();

        // Let's obtains parameters name here!
        Enumeration<String> enumeration = request.getParameterNames();
        while (enumeration.hasMoreElements()) {
            String parameterName = enumeration.nextElement();
            pw.println("Parameter = " + parameterName);
        }
        pw.close();
    }
}

When you call the servlet and pass some parameters you get the parameter name echoed on the web browser.

http://localhost:8080/parameter-names?txid=001&item=10&price=1000

Parameter = txid
Parameter = item
Parameter = price

Maven dependencies

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

Maven Central