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

How do I read request parameter from servlet?

By Wayan in Servlet 0 Comment

When creating an application with Java servlet most of the time we will work with the request and response object. From the request object we can read the parameter submitted by the user’s browser either through an HTTP GET or POST method.

Basically what you need to know is when you try to get the passed parameter from inside the servlet you can call the request.getParameter(paramName) where the paramName is the name of parameter that you want to read from the servlet request object.

In this example I’ll show you how to read the parameter to process user action in a very simple login servlet. In this example we’ll create a login form, a JSP page that accept user input for a username and password.

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
<html lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Login Page</title>
</head>
<body>
<form id="loginForm" action="${pageContext.request.contextPath}/login" method="post">
    <label for="username">Username</label>
    <input id="username" type="text" name="username"/>
    <label for="password">Password</label>
    <input id="password" type="password" name="password"/>
    <input type="submit" value="Login"/>
</form>
</body>
</html>

In this form you’ll have to input box for a username and password. You also have a submit button for executing the login process. Now we have the form, let’s create the login servlet.

package org.kodejava.servlet;

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 java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "LoginServlet", urlPatterns = "/login")
public class LoginServlet extends HttpServlet implements Servlet {
    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response) throws IOException {
        doLogin(request, response);
    }

    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response) throws IOException {
        doLogin(request, response);
    }

    protected void doLogin(HttpServletRequest request,
                           HttpServletResponse response) throws IOException {
        // Here we read the parameters from servlet request
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        PrintWriter pw = response.getWriter();
        if (username != null && username.equals("administrator")
                && password != null && password.equals("secret")) {
            // authentication accepted!
            pw.println("Success!");
        } else {
            // authentication denied!
            pw.println("Denied!");
        }
        pw.close();
    }
}

Now you have everything, you can deploy the application on your servlet container, for example Apache Tomcat. Access your login page in the following address:

http://localhost:8080/login.jsp

You can also access the servlet directly from the following url:

http://localhost:8080/login

To pass the username and password information you can append the parameter like:

http://localhost:8080/login?username=administrator&password=secret

This will call the servlet and validate your login information.

Maven dependencies

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

Maven Central