How do I generate UUID / GUID in Java?

By I Wayan Saryada in Core API, Util Package 0 Comment

UUID / GUID (Universally / Globally Unique Identifier) is frequently use in programming. Some of its usage are for creating random file names, session id in web application, transaction id and for record’s primary keys in database replacing the sequence or auto generated number.

To generate UUID in Java we can use the java.util.UUID class. This class was introduced in JDK 1.5. The UUID.randomUUID() method return a UUID object. To obtain the value of the random string generated we need to call the UUID.toString() method.

We can also get the version and the variant of the UUID using the version() method and variant() method respectively. Let’s see the code snippet below:

package org.kodejava.util;

import java.util.UUID;

public class RandomStringUUID {
    public static void main(String[] args) {
        // Creating a random UUID (Universally unique identifier).
        UUID uuid = UUID.randomUUID();
        String randomUUIDString = uuid.toString();

        System.out.println("Random UUID String = " + randomUUIDString);
        System.out.println("UUID version       = " + uuid.version());
        System.out.println("UUID variant       = " + uuid.variant());
    }
}

The result of our program is:

Random UUID String = 87a20cdd-25da-4dc2-b787-68054ec2c5ca
UUID version       = 4
UUID variant       = 2

How do I write and read object from HTTP Session?

By I Wayan Saryada in JSP 0 Comment

In this post you will learn how to write and read object from HTTP Session in JavaServer Page. The first example that we are looking at is using the classic JSP scriptlet, this is a very old way to work with JSP, but it is good for you to know a history. We write a JSP scriptlet inside the <% %> symbols. We can use the provided session object. To set an attribute in the session object we use the setAttribute(String name, Object value) method. In the example we create an attribute called loginDate and set the value to the current date.

To read a value from a session object we use the getAttribute(String name) method. This method return a type of Object, so we need to cast it to the original object. In this case we cast it to a java.util.Date. And then we print out the value read from the session object.

<%@ page import="java.util.Date" %>
<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>JSP - Session Write</title>
</head>
<body>
<%
// Creates a session attribute named login-date to store a java.util.Date.
session.setAttribute("loginDate", new Date());

// Read back the java.util.Date object from the session attribute.
Date loginDate = (Date) session.getAttribute("loginDate");
%>
Login Date: <%= loginDate %>
</body>
</html>

The second way that you can use to read values from session object is using the JSP Expression Language (EL). It looks like the following code snippet. You can use the sessionScope implicit object combined with the session attribute name. You can see two ways to use the sessionScope object below. The simplest one is to use the attribute name as the EL expression, and it will look smartly to find the value in the available scope.

<!DOCTYPE html>
<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>JSP - Session Read EL</title>
</head>
<body>
<p>Login Date: ${sessionScope.loginDate}</p>

<p>Login Date: ${sessionScope["loginDate"]}</p>

<p>Login Date: ${loginDate}</p>
</body>
</html>

How do I get the number of buttons on the mouse?

By I Wayan Saryada in AWT, Core API 0 Comment

MouseInfo provides methods for getting information about the mouse, such as mouse pointer location and the number of mouse buttons.

package org.kodejava.awt;

import java.awt.*;

public class MouseNumberOfButtons {
    public static void main(String[] args) {
        // Get the number of buttons on the mouse. On systems without a
        // mouse, returns -1. HeadlessException if
        // GraphicsEnvironment.isHeadless() returns true.
        int numberOfButtons = MouseInfo.getNumberOfButtons();
        System.out.println("Mouse Number Of Buttons = " + numberOfButtons);
    }
}

The output of the code snippet above:

Mouse Number Of Buttons = 5

How do I get the location of mouse pointer?

By I Wayan Saryada in AWT, Core API 5 Comments

MouseInfo provides methods for getting information about the mouse, such as mouse pointer location and the number of mouse buttons.

package org.kodejava.awt;

import java.awt.*;

public class MouseInfoDemo {
    public static void main(String[] args) {
        int i = 0;
        while (i < 10) {
            // Get the location of our mouse x and y coordinate using
            // the PointerInfo.getLocation() method which return an 
            // instance of Point.
            Point location = MouseInfo.getPointerInfo().getLocation();
            double x = location.getX();
            double y = location.getY();

            System.out.println("x = " + x);
            System.out.println("y = " + y);

            try {
                Thread.sleep(1000);
                i++;
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

How do I get the name of current executed method?

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

public class GetCurrentMethodName {
    public static void main(String[] args) {
        // Get the current executing method name
        String methodName =
                Thread.currentThread().getStackTrace()[1].getMethodName();
        System.out.println("methodName = " + methodName);

        GetCurrentMethodName obj = new GetCurrentMethodName();
        obj.executeAMethod();
    }

    private void executeAMethod() {
        // Get the current executing method name
        String methodName =
                Thread.currentThread().getStackTrace()[1].getMethodName();
        System.out.println("methodName = " + methodName);
    }
}

This program will print out the following string:

methodName = main
methodName = executeAMethod