How to implement the hashCode and equals method using Apache Commons?

package org.kodejava.commons.lang;

public class ObjectHashCodeDemo {

    public static void main(String[] args) {
        Book book1 = new Book(1L, "Spring Boot in Action", "Craig Walls");
        Book book2 = new Book(2L, "Docker in Action", "Jeff Nickoloff");
        Book book3 = book1;

        System.out.println("book1.hashCode() = " + book1.hashCode());
        System.out.println("book2.hashCode() = " + book2.hashCode());
        System.out.println("book3.hashCode() = " + book3.hashCode());
    }
}
package org.kodejava.commons.lang;

import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;

import java.io.Serializable;

public class Book implements Serializable {
    private Long id;
    private String title;
    private String author;

    public Book(Long id, String title, String author) {
        this.id = id;
        this.title = title;
        this.author = author;
    }

    //~ Implements getters and setters here.

    public boolean equals(Object o) {
        if (o == this) {
            return true;
        }

        if (!(o instanceof Book)) {
            return false;
        }

        Book that = (Book) o;
        return new EqualsBuilder()
            .append(this.id, that.id)
            .append(this.title, that.title)
            .append(this.author, that.author)
            .isEquals();

        // You can also use reflection of the EqualsBuilder class.
        // return EqualsBuilder.reflectionEquals(this, that);
    }

    public int hashCode() {
        return new HashCodeBuilder()
            .append(id)
            .append(title)
            .append(author)
            .toHashCode();

        // Or even use the simplest method using reflection below.
        // return HashCodeBuilder.reflectionHashCode(this);
    }
}

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.13.0</version>
</dependency>

Maven Central

How do I checks if two dates are on the same day?

In this example, you will learn how to find out if two defined date objects are on the same day. It means that we are only interested in the date information and ignoring the time information of these date objects. We will be using an API provided by the Apache Commons Lang library. So here is the code snippet:

package org.kodejava.commons.lang;

import org.apache.commons.lang3.time.DateUtils;

import java.util.Calendar;
import java.util.Date;

public class CheckSameDay {
    public static void main(String[] args) {
        Date date1 = new Date();
        Date date2 = new Date();

        // Checks to see if the dates is on the same day.
        if (DateUtils.isSameDay(date1, date2)) {
            System.out.printf("%1$te/%1$tm/%1$tY and %2$te/%2$tm/%2$tY " +
                    "is on the same day.%n", date1, date2);
        }

        Calendar cal1 = Calendar.getInstance();
        Calendar cal2 = Calendar.getInstance();

        // Checks to see if the calendars is on the same day.
        if (DateUtils.isSameDay(cal1, cal2)) {
            System.out.printf("%1$te/%1$tm/%1$tY and %2$te/%2$tm/%2$tY " +
                    "is on the same day.%n", cal1, cal2);
        }

        cal2.add(Calendar.DAY_OF_MONTH, 10);
        if (!DateUtils.isSameDay(cal1, cal2)) {
            System.out.printf("%1$te/%1$tm/%1$tY and %2$te/%2$tm/%2$tY " +
                    "is not on the same day.", cal1, cal2);
        }
    }
}

The example results produced by this snippet are:

31/10/2021 and 31/10/2021 is on the same day.
31/10/2021 and 31/10/2021 is on the same day.
31/10/2021 and 10/11/2021 is not on the same day.

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.13.0</version>
</dependency>

Maven Central

How do I create a java.io.File object from URL?

The code snippet below uses the FileUtils.toFile(URL) method that can be found in the Apache Commons IO library to convert a URL into a File. The url protocol should be file or else null will be returned.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.Objects;

public class URLToFileObject {
    public static void main(String[] args) throws Exception {
        // FileUtils.toFile(URL url) convert from URL the File.
        String data = FileUtils.readFileToString(Objects.requireNonNull(
                        FileUtils.toFile(URLToFileObject.class.getResource("/data.txt"))),
                StandardCharsets.UTF_8);
        System.out.println("data = " + data);

        // Creates a URL with file protocol and convert it into a File object.
        File file = FileUtils.toFile(new URL("file:///D:/demo.txt"));
        data = FileUtils.readFileToString(file, StandardCharsets.UTF_8);
        System.out.println("data = " + data);
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

Maven Central

How do I create a BasicDataSource object?

This example demonstrates how to use the BasicDataSource class of Apache Commons DBCP to create a basic requirements for database connection. The configuration of the data source can be defined using some property method provided by this class. The basic properties are the driver classname, connection url, username and password.

After the datasource ready we can obtain a connection by calling the getConnection() method of the datasource. This method might throw an SQLException when error occurs.

package org.kodejava.commons.dbcp;

import org.apache.commons.dbcp2.BasicDataSource;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class BasicDataSourceExample {
    public static void main(String[] args) {
        // Creates a BasicDataSource and defines its properties
        // including the driver class name, JDBC url, username
        // and password.
        try (BasicDataSource dataSource = new BasicDataSource()) {
            dataSource.setUrl("jdbc:mysql://localhost/kodejava");
            dataSource.setUsername("kodejava");
            dataSource.setPassword("s3cr*t");

            // Get a connection from the data source and do a
            // database query with the obtained connection.
            try (Connection conn = dataSource.getConnection();
                 PreparedStatement stmt = conn.prepareStatement("SELECT * FROM author")) {
                ResultSet rs = stmt.executeQuery();
                while (rs.next()) {
                    System.out.println("Author name: " + rs.getString("author_name"));
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

We can simplify the code above so that we don’t have to close the PreparedStatement and Connection manually like we did in the finally block in the code snippet. We can use try-with-resources to automatically close resources. An example can be seen in the following example: How to automatically close resources in JDBC?.

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-dbcp2</artifactId>
        <version>2.10.0</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.1.0</version>
    </dependency>
</dependencies>

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How do I create a database connection pool?

This example shows you how to create a connection pool implementation using the Apache Commons DBCP library.

package org.kodejava.commons.dbcp;

import org.apache.commons.dbcp2.*;
import org.apache.commons.pool2.impl.GenericObjectPool;
import org.apache.commons.pool2.impl.GenericObjectPoolConfig;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class ConnectionPoolExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    private GenericObjectPool<PoolableConnection> connectionPool = null;

    public static void main(String[] args) throws Exception {
        ConnectionPoolExample demo = new ConnectionPoolExample();
        DataSource dataSource = demo.setUp();
        demo.printStatus();

        try (Connection conn = dataSource.getConnection();
             PreparedStatement stmt = conn.prepareStatement("SELECT * FROM author")) {
            demo.printStatus();

            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                System.out.println("Author name: " + rs.getString("author_name"));
            }
        }

        demo.printStatus();
    }

    public DataSource setUp() {
        // Creates a connection factory object, which will be used by
        // the pool to create the connection object. We pass the
        // JDBC url info, username and password.
        ConnectionFactory cf = new DriverManagerConnectionFactory(
                ConnectionPoolExample.URL,
                ConnectionPoolExample.USERNAME,
                ConnectionPoolExample.PASSWORD);

        // Creates a PoolableConnectionFactory that will wrap the
        // connection object created by the ConnectionFactory to add
        // object pooling functionality.
        PoolableConnectionFactory pcf = new PoolableConnectionFactory(cf, null);
        pcf.setValidationQuery("SELECT 1");

        // Creates an instance of GenericObjectPool that holds our
        // pool of connection objects.
        GenericObjectPoolConfig<PoolableConnection> config = new GenericObjectPoolConfig<>();
        config.setTestOnBorrow(true);
        config.setMaxTotal(10);
        connectionPool = new GenericObjectPool<>(pcf, config);
        pcf.setPool(connectionPool);

        return new PoolingDataSource<>(connectionPool);
    }

    private GenericObjectPool<PoolableConnection> getConnectionPool() {
        return connectionPool;
    }

    /**
     * Prints connection pool status.
     */
    private void printStatus() {
        System.out.println("Max   : " + getConnectionPool().getNumActive() + "; " +
                "Active: " + getConnectionPool().getNumActive() + "; " +
                "Idle  : " + getConnectionPool().getNumIdle());
    }
}

The code shows the following status as output example:

Max   : 0; Active: 0; Idle  : 0
Max   : 1; Active: 1; Idle  : 0
Author name: Raoul-Gabriel Urma
Author name: Mario Fusco
Author name: Alan Mycroft
Max   : 0; Active: 0; Idle  : 1

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-dbcp2</artifactId>
        <version>2.10.0</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.1.0</version>
    </dependency>
</dependencies>

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