Kode Java - Learn Java by Examples

Introduction to Apache Maven

By I Wayan Saryada in Maven, Tools Last modified: July 16, 2024 0 Comment

In this post you will learn about Apache Maven. What is Maven? In simple words, Maven is a tool that we can use to build and manage a Java based project. Compare to the older type of build tool such as Ant, which is also an Apache project, Maven gives developers a standard way to build projects, a clear definition of the projects consisted of, an easy way to publish project information and an easy management of the project libraries dependency.

In Maven, the project libraries (Jars) will be maintained in the Maven repository and can be shared among projects. We don’t need to include the Jars in the project’s source code, as what we usually do when using tool like Ant. And here are the main objectives of the Apache Maven project:

Making the build process easy.
Providing a uniform build system.
Providing quality project information.
Providing guidelines for best practices development.
Allowing transparent migration to a new features.

After you know a little about Maven, let’s continue to the next step, installing the Apache Maven.

Step 1. Downloading Apache Maven

Go to Apache Maven and from the Get Maven section on the left sidebar click Download link.
Download the appropriate installer for your platform. For example, I am downloading the .zip file. The latest version when this post is written is Maven 3.1.0 (apache-maven-3.1.0-bin.zip).
Extract the downloaded zip file. For example, I am extracting it into D:\Toolbox\apache-maven-3.1.0 directory.

Step 2. Configuring Environment Variables

After extracting Maven distribution you have to define M2_HOME environment variable. The value of this variable is the path to your Maven installation.
You can create environment variable using the following steps:
- Right click on My Computer.
- Select Properties menu.
- Select Advanced system settings.
- In the System Properties window select the Advanced tab and click the Environment Variables button.
- Add the variable in the System variables section.
- Click OK to proceed.
Add the %M2_HOME%\bin; into your PATH environment variable so that you can execute Maven command from any path inside your command prompt. This PATH variable can also be updated in the System variables section.
Open your command prompt and type echo %M2_HOME%. Pressing Enter and you should see the value of the variable printed on the console. For example:

D:\>echo %M2_HOME%
D:\Toolbox\apache-maven-3.1.0

To check if Maven also in your Path variable you can execute echo %PATH% in your command prompt. You should see the path to Maven binary in the Path variable.

D:\>echo %PATH%
D:\Toolbox\apache-maven-3.1.0\bin;C:\Program Files (x86)\Java\jdk1.7.0_13\bin;

Step 3. Running Maven

Now you have Maven installed and configured. Let’s run Maven for the first time.
To run Maven we use the mvn command.
For example to check the version of the Maven we run mvn -version
You will see the following output, more or less, it depends on the JDK version you have in your machine.

D:\>mvn -version
Apache Maven 3.1.0 (893ca28a1da9d5f51ac03827af98bb730128f9f2; 2013-06-28 10:15:32+0800)
Maven home: D:\Toolbox\apache-maven-3.1.0
Java version: 1.7.0_13, vendor: Oracle Corporation
Java home: C:Program Files (x86)\Java\jdk1.7.0_13\jre
Default locale: en_US, platform encoding: Cp1252
OS name: "windows 7", version: "6.1", arch: "x86", family: "windows"

Congratulations! You’ve installed Apache Maven successfully on your development machine. On the next post I will show you how to create a new project using Maven.

How do I create MySQL database programmatically in Java?

By I Wayan Saryada in JDBC Last modified: May 31, 2024 4 Comments

There are times that you might need to create a database or tables right after you run your program instead of manually creating it. In this example, I will show you how you can do this using JDBC and MySQL database. The first thing we need to do as usual when creating a JDBC program is to define a JDBC URL. One thing that you’ll notice here is that we don’t define the database name in the URL. So the URL will be like jdbc:mysql://localhost.

After defining the URL, we need to create a connection to the database. We issued the DriverManager.getConnection() method and pass the URL, username and password as the arguments. The next step is to create a PreparedStatement. When we call the preparedStatement() method we pass an SQL command to create the database, which is CREATE DATABASE IF NOT EXISTS demodb. This will create a new database if there is no database with demodb name exists in the database. Finally, call the PreparedStatement‘s execute() method

Now you can try for your self, start typing the following code snippet in your text editor or IDE, and execute it to create the database.

package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

public class CreateMySQLDatabaseExample {
    public static void main(String[] args) {
        // Defines the JDBC URL. As you can see, we are not specifying
        // the database name in the URL.
        String url = "jdbc:mysql://localhost";

        // Defines username and password to connect to database server.
        String username = "root";
        String password = "root";

        // SQL command to create a database in MySQL.
        String sql = "CREATE DATABASE IF NOT EXISTS demodb";

        try (Connection conn = DriverManager.getConnection(url, username, password);
             PreparedStatement stmt = conn.prepareStatement(sql)) {

            stmt.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

After you are executing the code snippet above you will find a new database named demodb created in your MySQL database server.

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Introduction to JetBrains IntelliJ IDEA Community Edition

By I Wayan Saryada in IntelliJ IDEA, Tools Last modified: June 11, 2023 0 Comment

In this post I will introduce to you the JetBrains IntelliJ IDEA, one the most powerful IDE (Integrated Development Environment) for Java development or other languages that run on the JVM such as Groovy and Scala. IntelliJ IDEA comes in two editions, the IntelliJJ IDEA Ultimate Edition and the IntelliJ IDEA Community Edition.

The IntelliJ IDEA Community Edition is an open source version of Intelli IDEA. That’s mean you can use it for free. If you work with standard Java, Groovy, Scala or mobile development using Android then the Community Edition can be your choice. If you work with in web or Java EE development then the Ultimate Edition is the way to go.

Here are some features that you will get when using the IntelliJ IDEA Community Edition:

An Intelligent code editor that has all the smarts for understanding Java, XML and Groovy code.
Refactorings, code inspections and intentions, super-fast navigation and search
Testing framework integration: JUnit and TestNG
Build tools support: Ant and Maven
Popular version control systems integration: CVS, Subversion and Git
Swing UI designer

After a bit of introduction, let’s begin the installation.

Step 1. Getting the Installation Distribution

Download the installation package of the IntelliJ IDEA Community Edition.
Click Download IntelliJ IDEA Community Edition to go the download page.
On the page you can see two editions, select the Community Edition. The current version available when this post was written is the version 12.1.4. You can also see that the download are available for Windows, Mac OS X and Linux. For this post I will download the Windows version. The download size for the Windows installer is around 130 MB.

Step 2. Install IntelliJ IDEA Community Edition

To begin, double-click the installer you’ve downloaded, for example ideaIC-12.1.4.exe.
You’ll be greeted with the following screen

intellij-idea-community-edition-setup-step-1

IntelliJ IDEA Setup Welcome Screen

Press the Next button to continue.
You’ll be asked the installation location. On Windows it will be defaulted to the C:\Program Files directory.
Press Next for a couple of times until the installation complete.
When you choose to run the IntelliJ IDEA for the first time you’ll get the following screen

Installation Complete Screen

Press OK button to start IntelliJ IDEA for the first time. You will be shown a splash screen right after you press the button and continued by the screen welcoming you to the IDE.

Welcome to IntelliJ IDEA

Step 3. Now you have the IntelliJ IDEA Community Edition installed in your machine. Let’s create your first program using IDEA.

From the Welcome Screen above click the Create New Project menu.
A New Project dialog window will be shown. In this dialog you can do:

Create a New Project Window Dialog

Enter the Project Type, choose Java Module.
Define the Project Name. We’ll just name it HelloWorld.
Choose the Project Location directory.
Select the JDK version you’ll be using.
Press the Next button followed by the Finish button to continue.

Step 4. IntelliJ IDEA Main Window, creating HelloWorld.java

Here is the Main Window of IntelliJ IDEA.

IntelliJ IDEA Community Edition

The bigger screenshot of the project explorer panel.

Project Explorer Window

Before we create a class let’s create a package.
Right-click the src folder, continued by selecting the New and Package menu.
Enter the package name, for instance org.kodejava.introduction
To create a class right click on the newly created package, select New and Java Class menu.
In the Create New Class dialog enter HelloWorld in the Name text field and choose Class from the Kind dropdown selection.
Type the following code in the editor.

package org.kodejava.introduction;

public class HelloWorld {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public static void main(String[] args) {
        HelloWorld hello = new HelloWorld();

        String name = "world";
        hello.setName(name);
        hello.sayHello();
    }

    private void sayHello() {
        System.out.println("Hello " + getName() + "!");
    }
}

Press Shift + F10 or click the green Run button to execute your code.
And we are done!

Other things you can do next is to learn more about the menu and the keyboard shortcuts that you can use while working with the IDE. One good place is to look at the Help, Tip of the Day menu.

That’s finishes our introduction to the IntelliJ IDEA Community Edition IDE. I hope you can continue your learning and this IDE will surely help you to understand Java better. Because it is not just a tool to write code, it will give you a lot of suggestion so that you can always improve your code quality.

How do I set up JAVA_HOME and Path variables in Windows?

By I Wayan Saryada in Basic, Core API Last modified: June 11, 2023 1 Comment

Setting up a JAVA_HOME and Path variables is the second thing you’ll need to do after installing a JDK (Java Development Kit). Although this is not required by Java itself, it is commonly use by other application. For instance then Apache Tomcat web application server and other application server will need it. Or we might need it if we want to compile or running our Java classes from the command prompt. It helps us to organize the default JDK and the execution path.

So here are the steps that we’ll need to do to configure the JAVA_HOME and Path variable on a Windows operating system.

Step 1. Finding the location of our JDK installation directory. If we already know where we have installed the JDK continue to the Step 2.

The JDK usually installed in the C:\Program Files\Java directory by default.
Under this directory we can find one or more versions of installed JDK, for examples I have jdk-14 and jdk-17. Just choose the default one we’re going to use.

Step 2. Setting JAVA_HOME variable

After we know the location of your JDK installation, we can copy the directory location from the Windows Explorer address bar.

Open Windows Explorer
Right-Click the Computer and select the Properties menu.
Click Advanced system settings and the System Properties windows will be shown.
Select the Advance tab.
Click the Environment Variables button.
A new Environment Variables window will be shown.
Under the System Variables, click the New button to create a new environment variable.
Enter the variable name as JAVA_HOME, all letters are in uppercase.
In the variable value enter the JDK installation path you’ve copy above.
Click OK.

Step 3. Setting the Path variable

After we’ve set the JAVA_HOME variable, now we can update the Path variable.

In the Environment Variables window, under the System Variables section find a variable named Path.
If we don’t have the Path variable we need to add one using the New button.
If we already have the Path variable we’ll need to update its value, click Edit button to update.
Add %JAVA_HOME%\bin; to the beginning of the Path variable value.
Press OK to when we are done.
Press another OK to close the Environment Variables window.

Step 4. Check to see if the settings work

Open your Windows Command Prompt.
Type java -version in the command line.
If everything was set correctly we’ll see the running version of your installed Java JDK.

As an example on my Windows Command Prompt I have something like:

D:\>java -version
java version "17" 2021-09-14 LTS
Java(TM) SE Runtime Environment (build 17+35-LTS-2724)
Java HotSpot(TM) 64-Bit Server VM (build 17+35-LTS-2724, mixed mode, sharing)

If you don’t see the correct output, for instance you get an error like “‘java’ is not recognized as an internal or external command, operable program or batch file.”, please retry the steps described above. Enjoy your new adventure with Java programming. Happy coding!

Using DigestUtils.sha1hex() method to generate SHA-1 digest

By I Wayan Saryada in Apache Commons, Commons Codec Last modified: October 4, 2023 1 Comment

In this example you’ll learn how to generate an SHA-1 digest using the Apache Commons Codec DigestUtils class. In the last two examples you’ve already seen how to generate the MD5 digest using the same library. Compared to the MD5 version the SHA-1 digest is known to be stronger to brute force attacks, but it is slower to generate. The SHA-1 produces a 160 bit (20 byte) message digest while the MD5 produces only a 128 bit message digest (16 byte).

In the code snippet below we demonstrate three different ways to use the DigestUtils.sha1Hex() method. In the first method in the example, the byteDigest(), we calculate the digest from an array of byte data. Followed by the second method, the inputStreamDigest() where we calculate the digest of an InputStream object. And on the last method we call the overload version of the sha1Hex() method to calculate the digest of a string.

Let’s see the full code snippet.

package org.kodejava.commons.codec;

import org.apache.commons.codec.digest.DigestUtils;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class SHAHashDemo {
    public static void main(String[] args) {
        SHAHashDemo demo = new SHAHashDemo();
        demo.byteDigest();
        demo.inputStreamDigest();
        demo.stringDigest();
    }

    /**
     * Calculates SHA-1 digest from byte array.
     */
    private void byteDigest() {
        System.out.println("SHAHashDemo.byteDigest");
        byte[] data = "The quick brown fox jumps over the lazy dog."
                .getBytes(StandardCharsets.UTF_8);
        String digest = DigestUtils.sha1Hex(data);
        System.out.println("Digest          = " + digest);
        System.out.println("Digest.length() = " + digest.length());
    }

    /**
     * Calculates SHA-1 digest of InputStream object.
     */
    private void inputStreamDigest() {
        System.out.println("SHAHashDemo.inputStreamDigest");
        String data = System.getProperty("user.dir") + "/data.txt";
        File file = new File(data);
        try (InputStream is = new FileInputStream(file)) {
            String digest = DigestUtils.sha1Hex(is);
            System.out.println("Digest          = " + digest);
            System.out.println("Digest.length() = " + digest.length());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * Calculate SHA-1 digest of a string / text.
     */
    private void stringDigest() {
        System.out.println("SHAHashDemo.stringDigest");
        String data = "This is just a simple data message for SHA digest demo.";
        String digest = DigestUtils.sha1Hex(data);
        System.out.println("Digest          = " + digest);
        System.out.println("Digest.length() = " + digest.length());
    }
}

When you run the code it will output the following result:

SHAHashDemo.byteDigest
Digest          = 408d94384216f890ff7a0c3528e8bed1e0b01621
Digest.length() = 40
SHAHashDemo.inputStreamDigest
Digest          = da39a3ee5e6b4b0d3255bfef95601890afd80709
Digest.length() = 40
SHAHashDemo.stringDigest
Digest          = 4290d13ca383c2159c442d75355d83e310a2ea15
Digest.length() = 40

Maven Dependencies

<dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
    <version>1.16.0</version>
</dependency>