How do I set the maximum age of a cookie?

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

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "CookieExpirationServlet", urlPatterns = "/cookie-expiration")
public class CookieExpirationServlet 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 {
        String username = request.getParameter("username");
        if (username != null) {
            Cookie cookie = new Cookie("username", username);

            // Set the cookie age to 600 seconds (10 minutes). Setting the age
            // to 0 will delete the cookie while giving it a negative value will
            // not store the cookie, and it will be deleted when the browser is
            // closed.
            cookie.setMaxAge(600);
            response.addCookie(cookie);
        }
    }
}

Maven dependencies

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

Maven Central

How do I know the class of an object?

By Wayan in Core API, Lang Package 0 Comment

For instance, you have a collection of objects in an List object, and you want to do some logic based on the object’s class. This can easily be done using the instanceof operator. The operator returns true if an object is an instance of a specified class, if not it will return false.

The instanceof operator is most likely used when implementing an equals(Object o) method of an object to check if the compared object is from the same class.

package org.kodejava.lang;

import java.util.ArrayList;
import java.util.List;

public class InstanceOfExample {
    public static void main(String[] args) {
        Person person = new Person("John");
        Animal animal = new Animal("Highland");
        Thing thing = new Thing("Red");
        String text = "hello";
        Integer number = 1000;

        List<Object> list = new ArrayList<>();
        list.add(person);
        list.add(animal);
        list.add(thing);
        list.add(text);
        list.add(number);

        for (Object o : list) {
            if (o instanceof Person) {
                System.out.println("My name is " + ((Person) o).getName());
            } else if (o instanceof Animal) {
                System.out.println("I live in " + ((Animal) o).getHabitat());
            } else if (o instanceof Thing) {
                System.out.println("My color is " + ((Thing) o).getColor());
            } else if (o instanceof String) {
                System.out.println("My text is " + o.toString());
            } else if (o instanceof Integer) {
                System.out.println("My value is " + ((Integer) o));
            }
        }
    }
}

class Person {
    private final String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class Animal {
    private final String habitat;

    public Animal(String habitat) {
        this.habitat = habitat;
    }

    public String getHabitat() {
        return habitat;
    }
}

class Thing {
    private final String color;

    public Thing(String color) {
        this.color = color;
    }

    public String getColor() {
        return color;
    }
}

The result of the code snippet above:

My name is John
I live in Highland
My color is Red
My text is hello
My value is 1000

How do I change an applet background color?

By Wayan in Applet, Core API 0 Comment

By default, the applet will usually have a grey background when displayed in a web browser. If you want to change it then you can call the setBackground(java.awt.Color) method and choose the color you want. Defining the background color in the init() method will change the color as soon as the applet initialized.

package org.kodejava.applet;

import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;

public class BackgroundColorApplet extends Applet {
    public void init() {
        // Here we change the default grey color background of an 
        // applet to yellow background.
        setBackground(Color.YELLOW);
    }

    public void paint(Graphics g) {
        g.setColor(Color.BLACK);
        g.drawString("Applet background example", 0, 50);
    }
}

Now we have the applet code ready. To enable the web browser to execute the applet create the following html page.

<!DOCTYPE html>
<html lang="en">
<head>
    <title>Applet Background Color</title>
</head>
<body>
<applet code="org.kodejava.applet.BackgroundColorApplet"
        height="150" width="350">
</applet>
</body>
</html>
** Deprecated: The Applet API is deprecated since JDK 9, no replacement.

How do I replace characters in string?

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

public class StringReplace {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog";
        System.out.println("Before: " + text);

        // The replace method replace all occurrences of character
        // 'o' with 'u' and returns a new string object.
        text = text.replace('o', 'u');
        System.out.println("After : " + text);
    }
}

The result of the code snippet:

Before: The quick brown fox jumps over the lazy dog
After : The quick bruwn fux jumps uver the lazy dug

How do I copy char array to string?

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

public class CharArrayCopyExample {
    public static void main(String[] args) {
        char[] data = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'};

        // Copy all value in the char array and create a new string out of it.
        String text = String.valueOf(data);
        System.out.println(text);

        // Copy a sub array from the char array and create a new string. The
        // following line will just copy 5 characters starting from array index
        // of 3. If the element copied is outside the array index an
        // IndexOutOfBoundsException will be thrown.
        text = String.copyValueOf(data, 3, 5);
        System.out.println(text);
    }
}

The result:

abcdefghij
defgh