How do I get servlet request headers information?

By Wayan in Servlet 0 Comment 
package org.kodejava.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.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;

@WebServlet(urlPatterns = "/request-headers")
public class ServletRequestHeader extends HttpServlet implements Servlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();

        Enumeration<String> headerNames = request.getHeaderNames();
        while (headerNames.hasMoreElements()) {
            // Get request header name
            String name = headerNames.nextElement();

            // Get request header value
            String value = request.getHeader(name);
            writer.println("Header [" + name + "] = " + value + "<br/>");
        }

        writer.println("<br/>");

        headerNames = request.getHeaderNames();
        while (headerNames.hasMoreElements()) {
            String name = headerNames.nextElement();

            // Read request values, for header information that have multiple
            // values.
            Enumeration<String> values = request.getHeaders(name);
            while (values.hasMoreElements()) {
                String value = values.nextElement();
                writer.println("Header [" + name + "] = " + value + "<br/>");
            }
        }
        writer.close();
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Do Nothing!
    }
}

Maven dependencies

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

Maven Central

How do I get servlet request URL information?

By Wayan in Servlet 4 Comments

In the code example below we will extract information regarding the HTTP (Hypertext Transport Protocol) from the request object (HttpServletRequest). We will extract the protocol used (http / https), server name and its assigned port number. We will also read our application context path, servlet path, path info and the query string. If we combine all the previously mentioned information we will get something equals to the value returned by request.getRequestURL() method.

Let’s check the code snippet below to see what method of the HttpServletRequest class that we can call to get the information regarding the HTTP request object that we can collect.

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(urlPatterns = "/url-info")
public class ServletUrlInformation extends HttpServlet {

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

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Getting servlet request URL
        String url = request.getRequestURL().toString();

        // Getting servlet request query string.
        String queryString = request.getQueryString();

        // Getting request information without the hostname.
        String uri = request.getRequestURI();

        // Below we extract information about the request object path
        // information.
        String scheme = request.getScheme();
        String serverName = request.getServerName();
        int portNumber = request.getServerPort();
        String contextPath = request.getContextPath();
        String servletPath = request.getServletPath();
        String pathInfo = request.getPathInfo();
        String query = request.getQueryString();

        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        pw.print("Url: " + url + "<br/>");
        pw.print("Uri: " + uri + "<br/>");
        pw.print("Scheme: " + scheme + "<br/>");
        pw.print("Server Name: " + serverName + "<br/>");
        pw.print("Port: " + portNumber + "<br/>");
        pw.print("Context Path: " + contextPath + "<br/>");
        pw.print("Servlet Path: " + servletPath + "<br/>");
        pw.print("Path Info: " + pathInfo + "<br/>");
        pw.print("Query: " + query);
    }
}

When you access this servlet using the following url http://localhost:8080/url-info?x=1&y=1, you’ll get the following output in your browser:

Url: http://localhost:8080/url-info
Uri: /url-info
Scheme: http
Server Name: localhost
Port: 8080
Context Path:
Servlet Path: /url-info
Path Info: null
Query: x=1&y=1

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 directories recursively?

By Wayan in Core API, IO 0 Comment

The code below use File.mkdirs() method to create a collection of directories recursively. It will create a directory with all its necessary parent directories.

package org.kodejava.io;

import java.io.File;

public class CreateDirs {
    public static void main(String[] args) {
        // Define a deep directory structures and create all the
        // directories at once.
        String directories = "D:/kodejava/a/b/c/d/e/f/g/h/i";
        File file = new File(directories);

        // The mkdirs will create folder including any necessary
        // but nonexistence parent directories. This method returns
        // true if and only if the directory was created along with
        // all necessary parent directories.
        boolean created = file.mkdirs();
        System.out.println("Directories created? " + created);
    }
}

How do I compare string regardless of their case?

By Wayan in Basic, Core API 0 Comment

Here is an example of comparing two strings for equality without considering their case sensitivity. To do this we can use equalsIgnoreCase() method of the String class. Let’s see an example below:

package org.kodejava.basic;

public class EqualsIgnoreCase {
    public static void main(String[] args) {
        String uppercase = "ABCDEFGHI";
        String mixed = "aBCdEFghI";

        // To compare two string equality regarding it case use the
        // String.equalsIgnoreCase method.
        if (uppercase.equalsIgnoreCase(mixed)) {
            System.out.println("Uppercase and Mixed equals.");
        }
    }
}

How do I insert a string in the StringBuilder?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

public class StringBuilderInsert {
    public static void main(String[] args) {
        StringBuilder alphabets = new StringBuilder("abcdfghopqrstuvwxyz");
        System.out.println("alphabets = " + alphabets);

        //  |a|b|c|d|f|g|h|i|....
        //  0|1|2|3|4|5|6|7|8|...
        //
        // From the above sequence you can see that the index of the string is
        // started from 0, so when we insert a string in the fourth offset it
        // means it will be inserted after the "d" letter. There are other overload
        // version of this method that can be used to insert other type of data
        // such as char, int, long, float, double, Object, etc.
        alphabets.insert(4, "e");
        System.out.println("alphabets = " + alphabets);

        // Here we insert an array of characters to the StringBuilder.
        alphabets.insert(8, new char[] {'i', 'j', 'k', 'l', 'm', 'n'});
        System.out.println("alphabets = " + alphabets);
    }
}

The result of the code snippet above:

alphabets = abcdfghopqrstuvwxyz
alphabets = abcdefghopqrstuvwxyz
alphabets = abcdefghijklmnopqrstuvwxyz

How do I remove substring from StringBuilder?

By Wayan in Core API, Lang Package 0 Comment

This example demonstrate you how to use the StringBuilder delete(int start, int end) and deleteCharAt(int index) to remove a substring or a single character from a StringBuilder.

package org.kodejava.lang;

public class StringBuilderDelete {
    public static void main(String[] args) {
        StringBuilder lipsum = new StringBuilder("Lorem ipsum dolor sit " +
                "amet, consectetur adipisicing elit.");
        System.out.println("lipsum = " + lipsum);

        // We'll remove a substring from this StringBuilder starting from
        // the first character to the 28th character.
        lipsum.delete(0, 28);
        System.out.println("lipsum = " + lipsum);

        // Removes a char from the StringBuilder. In the example below we
        // remove the last character.
        lipsum.deleteCharAt(lipsum.length() - 1);
        System.out.println("lipsum = " + lipsum);
    }
}

The result of the code snippet above:

lipsum = Lorem ipsum dolor sit amet, consectetur adipisicing elit.
lipsum = consectetur adipisicing elit.
lipsum = consectetur adipisicing elit

How do I read servlet context initialization parameters?

By Wayan in Servlet 0 Comment 
package org.kodejava.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.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;

@WebServlet(urlPatterns = "/context-init-param")
public class ContextInitParameter extends HttpServlet implements Servlet {

    public ContextInitParameter() {
    }

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

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();

        // Get an instance of ServletContext
        ServletContext context = getServletContext();

        // To read context initialization parameter we can call context.getInitParameter() 
        // and pass the name of initialization parameter to be read. If the named
        // parameter does not exist the returned value will be null.
        //
        // In this example we read an initialization parameter called LOG.PATH
        String logPath = context.getInitParameter("LOG.PATH");
        writer.println("Log Path: " + logPath + "<br/>");

        // Reads all the name of servlet's initialization parameters. If the
        // servlet doesn't have any an empty enumeration will be returned.
        Enumeration<String> enumeration = context.getInitParameterNames();
        while (enumeration.hasMoreElements()) {
            String paramName = enumeration.nextElement();
            String paramValue = context.getInitParameter(paramName);

            writer.println("Context Init Param: [" + paramName + " = " + paramValue +
                    "]<br/>");
        }
    }
}

The context initialization parameter (context-param) look something like this in the web.xml file:

<web-app>
    ...
    <context-param>
        <param-name>locale</param-name>
        <param-value>id_ID</param-value>
    </context-param>
    <context-param>
        <param-name>LOG.PATH</param-name>
        <param-value>F:/Logs</param-value>
    </context-param>
    ...
</web-app>

Maven dependencies

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

Maven Central

How do I know session last access time?

By Wayan in Servlet 1 Comment 
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 javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

@WebServlet(name = "SessionLastAccessTime", urlPatterns = "/last-access-time")
public class SessionLastAccessTime extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession session = request.getSession();
        Date date = new Date(session.getLastAccessedTime());

        PrintWriter writer = response.getWriter();
        writer.println("Last accessed time: " + date);
    }

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

This servlet will return a result like:

Last accessed time: Mon Sep 27 06:43:03 CST 2021

Maven dependencies

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

Maven Central

How do I get a notification when session attribute was changed?

By Wayan in Servlet 0 Comment

Implementing the HttpSessionAttributeListener will make the servlet container inform you about session attribute changes. The notification is in a form of HttpSessionBindingEvent object. The getName() on this object tell the name of the attribute while the getValue() method tell about the value that was added, replaced or removed.

package org.kodejava.servlet;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener
public class SessionAttributeListener implements HttpSessionAttributeListener {

    @Override
    public void attributeAdded(HttpSessionBindingEvent event) {
        // This method is called when an attribute is added to a session.
        // The line below display session attribute name and its value.
        System.out.println("Session attribute added: ["
                + event.getName() + "] = [" + event.getValue() + "]");
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent event) {
        // This method is called when an attribute is removed from a session.
        System.out.println("Session attribute removed: ["
                + event.getName() + "] = [" + event.getValue() + "]");
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent event) {
        // This method is invoked when an attribute is replaced in a session.
        System.out.println("Session attribute replaced: ["
                + event.getName() + "] = [" + event.getValue() + "]");
    }
}

Maven dependencies

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

Maven Central

How do I capture session creation and removal events?

By Wayan in Servlet 0 Comment

The Servlet specification define an HttpSessionListener interface that can be implemented if we want to listen to session creation and removal events. The interface has two methods that we can implement, the sessionCreated(HttpSessionEvent event) and sessionDestroyed(HttpSessionEvent event) methods. To activate the listener we need to register it in the servlet container. To register the listener we can use the @WebListener annotation. Let’s see the full code snippet below.

package org.kodejava.servlet;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.util.Date;

@WebListener
public class MySessionListener implements HttpSessionListener {

    // Notification that a new session was created
    @Override
    public void sessionCreated(HttpSessionEvent event) {
        HttpSession session = event.getSession();

        System.out.println("New session created  : " + session.getId());
        System.out.println("Session creation time: " + new Date(session.getCreationTime()));
    }

    // Notification that a session was invalidated
    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        HttpSession session = event.getSession();

        System.out.println("Session destroyed  : " + session.getId());
    }
}

Maven dependencies

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

Maven Central