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