How do I know if a class object is an interface or a class?

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

public class CheckForInterface {
    public static void main(String[] args) {
        // Checking whether Cloneable is an interface or class
        Class<?> clazz = Cloneable.class;
        boolean isInterface = clazz.isInterface();
        System.out.println(clazz.getName() + " is an interface = " + isInterface);

        // Checking whether String is an interface or class
        clazz = String.class;
        isInterface = clazz.isInterface();
        System.out.println(clazz.getName() + " is an interface = " + isInterface);
    }
}

java.lang.Cloneable is an interface = true
java.lang.String is an interface = false

How do I get interfaces implemented by a class?

By Wayan in Core API, Lang Package 0 Comment

The getClass().getInterfaces() method return an array of Class that represents the interfaces implemented by an object.

package org.kodejava.lang;

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

public class ClassInterfaces {
    public static void main(String[] args) {
        // Get an instance of Date class
        Date date = Calendar.getInstance().getTime();

        // Get all interfaces implemented by the java.util.Date class and
        // print their names.
        Class<?>[] interfaces = date.getClass().getInterfaces();
        for (Class<?> i : interfaces) {
            System.out.printf("Interface of %s = %s%n", date.getClass().getName(), i.getName());
        }

        // For the primitive type the interface will be an empty array.
        interfaces = char.class.getInterfaces();
        for (Class<?> i : interfaces) {
            System.out.printf("Interface of %s = %s%n", char.class.getName(), i.getName());
        }
    }
}

The java.util.Date class implements the following interfaces:

Interface of java.util.Date = java.io.Serializable
Interface of java.util.Date = java.lang.Cloneable
Interface of java.util.Date = java.lang.Comparable

How do I get package name of a class?

By Wayan in Core API, Lang Package 0 Comment

To get the package name of a class we can use the getClass().getPackage() method of the inspected object.

package org.kodejava.lang;

import java.util.Date;

public class GetPackageName {
    public static void main(String[] args) {
        // Create an instance of Date class, and then obtain the class package
        // name.
        Date date = new Date();
        Package pack = date.getClass().getPackage();
        String packageName = pack.getName();
        System.out.println("Package Name = " + packageName);

        // Create an instance of our class and again get its package name
        GetPackageName object = new GetPackageName();
        packageName = object.getClass().getPackage().getName();
        System.out.println("Package Name = " + packageName);
    }
}

Our code printed the following output:

Package Name = java.util
Package Name = org.kodejava.lang

How do I get super class of an object?

By Wayan in Core API, Lang Package 0 Comment

To get the super class of an object we can call the object’s getClass() method. After getting the class type of the object we call the getSuperclass() method to get the superclass. Let’s see the code snippet below.

package org.kodejava.lang;

public class ObtainingSuperClass {
    public static void main(String[] args) {
        // Create an instance of String class
        Object object1 = new String("Hello");

        // Get String class super class
        Class<?> clazz1 = object1.getClass().getSuperclass();
        System.out.println("Super Class = " + clazz1);

        // Create an instance of StringIndexOutOfBoundsException class
        Object object2 = new StringIndexOutOfBoundsException("Error message");

        // Get StringIndexOutOfBoundsException class super class
        Class<?> clazz2 = object2.getClass().getSuperclass();
        System.out.println("Super Class = " + clazz2);
    }
}

The program above prints the following string:

Super Class = class java.lang.Object
Super Class = class java.lang.IndexOutOfBoundsException

How do I split up string using regular expression?

By Wayan in Regex 0 Comment

This code snippet uses the java.util.regex.Pattern.split() method to split-up input string separated by commas or whitespaces (spaces, tabs, new lines, carriage returns, form feeds).

package org.kodejava.regex;

import java.util.regex.Pattern;

public class RegexSplitExample {
    public static void main(String[] args) {
        // Pattern for finding commas, whitespaces (spaces, tabs, new lines,
        // carriage returns, form feeds).
        String pattern = "[,\\s]+";
        String colors = """
                Red,White, Blue   Green        Yellow,
                Orange Pink""";

        Pattern splitter = Pattern.compile(pattern);
        String[] results = splitter.split(colors);

        for (String color : results) {
            System.out.format("Color = \"%s\"%n", color);
        }
    }
}

The result of our code snippet is:

Color = "Red"
Color = "White"
Color = "Blue"
Color = "Green"
Color = "Yellow"
Color = "Orange"
Color = "Pink"

How do I get a list of stored procedure names?

By Wayan in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.sql.*;

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

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            DatabaseMetaData metadata = conn.getMetaData();
            ResultSet result = metadata.getProcedures("kodejava", "%", "%");

            System.out.println("Catalog - Schema - Name");
            while (result.next()) {
                System.out.println(result.getString("PROCEDURE_CAT") +
                        " - " + result.getString("PROCEDURE_SCHEM") +
                        " - " + result.getString("PROCEDURE_NAME"));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

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

Maven Central

How do I read CLOBs data from database?

By Wayan in JDBC 1 Comment 
package org.kodejava.jdbc;

import java.io.File;
import java.io.FileWriter;
import java.io.Reader;
import java.nio.charset.StandardCharsets;
import java.sql.*;

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

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            String sql = "SELECT book_id, data FROM book_excerpt";
            PreparedStatement stmt = conn.prepareStatement(sql);

            ResultSet resultSet = stmt.executeQuery();
            while (resultSet.next()) {
                long bookId = resultSet.getLong("book_id");
                // Get the character stream of our CLOB file
                Reader reader = resultSet.getCharacterStream("data");

                File file = new File(bookId + ".txt");
                try (FileWriter writer = new FileWriter(file, StandardCharsets.UTF_8)) {
                    char[] buffer = new char[1];
                    while (reader.read(buffer) > 0) {
                        writer.write(buffer);
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The structure of book_excerpt table.

CREATE TABLE `book_excerpt`
(
    `id`          bigint(20) unsigned NOT NULL AUTO_INCREMENT,
    `book_id`     bigint(20) unsigned NOT NULL,
    `description` varchar(255)        NOT NULL,
    `data`        longtext,
    PRIMARY KEY (`id`),
    CONSTRAINT `book_excerpt_ibfk_1` FOREIGN KEY (`book_id`) REFERENCES `book` (`id`)
) ENGINE = InnoDB;

Maven Dependencies

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

Maven Central

How do I store CLOBs data into database?

By Wayan in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.io.File;
import java.io.FileReader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

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

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            conn.setAutoCommit(false);

            String sql = "INSERT INTO book_excerpt " +
                         "(book_id, description, data) VALUES (?, ?, ?)";

            File data = new File("java-8-in-action.txt");
            try (PreparedStatement stmt = conn.prepareStatement(sql);
                 FileReader reader = new FileReader(data)) {

                stmt.setLong(1, 1L);
                stmt.setString(2, "Java 8 in Action");
                stmt.setCharacterStream(3, reader, (int) data.length());
                stmt.execute();

                conn.commit();
            } catch (Exception e) {
                conn.rollback();
                e.printStackTrace();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

The structure of book_excerpt table.

CREATE TABLE `book_excerpt`
(
    `id`          bigint(20) unsigned NOT NULL AUTO_INCREMENT,
    `book_id`     bigint(20) unsigned NOT NULL,
    `description` varchar(255)        NOT NULL,
    `data`        longtext,
    PRIMARY KEY (`id`),
    CONSTRAINT `book_excerpt_ibfk_1` FOREIGN KEY (`book_id`) REFERENCES `book` (`id`)
) ENGINE = InnoDB;

Maven Dependencies

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

Maven Central

How do I read BLOBs data from database?

By Wayan in JDBC 0 Comment

This example shows you how to read BLOBs data from database table.

package org.kodejava.jdbc;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;

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

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            String sql = "SELECT name, image FROM product_image";

            PreparedStatement stmt = conn.prepareStatement(sql);
            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                String name = rs.getString("name");

                File image = new File(name);
                try (FileOutputStream fos = new FileOutputStream(image)) {
                    byte[] buffer = new byte[1024];

                    // Get the binary stream of our BLOB data
                    InputStream is = rs.getBinaryStream("image");
                    while (is.read(buffer) > 0) {
                        fos.write(buffer);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Table structure of product_image

CREATE TABLE `product_image`
(
    `id`          bigint(20) unsigned NOT NULL AUTO_INCREMENT,
    `product_id`  bigint(20) unsigned NOT NULL,
    `name`        varchar(255)        NOT NULL,
    `description` varchar(255) DEFAULT NULL,
    `image`       blob,
    PRIMARY KEY (`id`),
    KEY `product_id` (`product_id`),
    CONSTRAINT `product_image_ibfk_1` FOREIGN KEY (`product_id`) REFERENCES `product` (`id`)
) ENGINE = InnoDB;

Maven Dependencies

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

Maven Central

How do I store BLOBs data into database?

By Wayan in JDBC 1 Comment

Database BLOBs (Binary Large Objects) can be used to store any data, such as images, audio, or video files, for instance. This example shows you how we use JDBC library to store image in our database. To send the binary information to the database, we can call the PreparedStatement.setBinaryStream() method and pass the appropriate input stream and its size.

package org.kodejava.jdbc;

import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

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

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            conn.setAutoCommit(false);

            String sql = "INSERT INTO product_image " +
                         "(product_id, name, description, image) VALUES (?, ?, ?, ?)";
            String image = "/uml-distilled-3rd-edition.jpg";

            try (PreparedStatement stmt = conn.prepareStatement(sql);
                 InputStream is = BlobDemo.class.getResourceAsStream(image)) {

                stmt.setLong(1, 1L);
                stmt.setString(2, "uml-distilled-3rd-edition.jpg");
                stmt.setString(3, "UML Distilled 3rd Edition");
                stmt.setBinaryStream(4, is);
                stmt.execute();

                conn.commit();
            } catch (Exception e) {
                conn.rollback();
                e.printStackTrace();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

The structure of product_image table.

CREATE TABLE `product_image`
(
    `id`          bigint(20) unsigned NOT NULL AUTO_INCREMENT,
    `product_id`  bigint(20) unsigned NOT NULL,
    `name`        varchar(255)        NOT NULL,
    `description` varchar(255) DEFAULT NULL,
    `image`       blob,
    PRIMARY KEY (`id`),
    KEY `product_id` (`product_id`),
    CONSTRAINT `product_image_ibfk_1` FOREIGN KEY (`product_id`) REFERENCES `product` (`id`)
) ENGINE = InnoDB;

Maven Dependencies

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

Maven Central