How do I sort a java.util.Enumeration?

By I Wayan Saryada in Core API, Util Package 1 Comment

In this code snippet you will see how to sort the content of an Enumeration object. We start by creating a random numbers and stored it in a Vector. We use these numbers and create a Enumeration object by calling Vector‘s elements() method. We convert it to java.util.List and then sort the content of the List using Collections.sort() method. Here is the complete code snippet.

package org.kodejava.util;

import java.util.*;

public class EnumerationSort {
    public static void main(String[] args) {
        // Creates random data for sorting source. Will use java.util.Vector
        // to store the random integer generated.
        Random random = new Random();
        Vector<Integer> data = new Vector<>();
        for (int i = 0; i < 10; i++) {
            data.add(Math.abs(random.nextInt()));
        }

        // Get the enumeration from the vector object and convert it into
        // a java.util.List. Finally, we sort the list using
        // Collections.sort() method.
        Enumeration<Integer> enumeration = data.elements();
        List<Integer> list = Collections.list(enumeration);
        Collections.sort(list);

        // Prints out all generated number after sorted.
        for (Integer number : list) {
            System.out.println("Number = " + number);
        }
    }
}

An example result of the code above is:

Number = 20742427
Number = 163885840
Number = 204704456
Number = 560032429
Number = 601762809
Number = 1300593322
Number = 1371678147
Number = 1786580321
Number = 1786731301
Number = 1856215303

How do I insert a new record into a database using JdbcTemplate?

By I Wayan Saryada in Spring JDBC 3 Comments

The following example show you how to use the Spring’s JdbcTemplate class to insert a record into database.

package org.kodejava.spring.jdbc;

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import javax.sql.DataSource;
import java.sql.Types;
import java.util.Date;

public class InsertDemo {
    private static final String INSERT_QUERY = """
            INSERT INTO record (title, release_date, artist_id, label_id, created)
            VALUES (?, ?, ?, ?, ?)
            """;

    private final DataSource dataSource;

    public InsertDemo(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    public static DriverManagerDataSource getDataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setUrl("jdbc:mysql://localhost/musicdb");
        dataSource.setUsername("root");
        dataSource.setPassword("");
        return dataSource;
    }

    public static void main(String[] args) {
        InsertDemo demo = new InsertDemo(getDataSource());
        demo.saveRecord("Rock Beatles", new Date(), 1, 1);
    }

    public void saveRecord(String title, Date releaseDate, Integer artistId, Integer labelId) {
        // Creates an instance of JdbcTemplate and passes a connection
        // to the database.
        JdbcTemplate template = new JdbcTemplate(this.dataSource);

        // Defines the query arguments and the corresponding SQL types
        // of the arguments.
        Object[] params = new Object[]{
                title, releaseDate, artistId, labelId, new Date()
        };
        int[] types = new int[]{
                Types.VARCHAR,
                Types.DATE,
                Types.INTEGER,
                Types.INTEGER,
                Types.DATE
        };

        // Calls JdbcTemplate.update() methods to create a new data
        // in the records table. The update method in general will
        // return number of row / rows processed by the executed query
        int row = template.update(INSERT_QUERY, params, types);
        System.out.println(row + " row inserted.");
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>6.1.10</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.4.0</version>
    </dependency>
</dependencies>

Maven Central Maven Central

How do I create a Data Source object for JdbcTemplate?

By I Wayan Saryada in Spring JDBC 2 Comments

In this example you will learn how to create and configure a DriverManagerDataSource object that will be used by the JdbcTemplate object. There are some information required when creating a DataSource including the JDBC driver class, the JDBC Url of the target database, the username and password for connecting to database server.

package org.kodejava.spring.jdbc;

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import javax.sql.DataSource;
import java.util.List;
import java.util.Map;

public class DataSourceDemo {
    public static final String DRIVER = "com.mysql.cj.jdbc.Driver";
    public static final String JDBC_URL = "jdbc:mysql://localhost/musicdb";
    public static final String USERNAME = "root";
    public static final String PASSWORD = "";

    public static void main(String[] args) {
        // Creates an instance of DriverManagerDataSource and pass
        // it to the JdbcTemplate.
        DataSource source = getDataSource();
        JdbcTemplate template = new JdbcTemplate(source);

        // After creating a template with a data source inject we
        // can do a database manipulation such as the CRUD operation.
        System.out.println("DataSource = " + template.getDataSource());
        List<Map<String, Object>> records = template.queryForList("SELECT * FROM record");
        for (Map<String, Object> record : records) {
            System.out.println("Records = " + record);
        }
    }

    /**
     * Returns a DataSource object for connection to the database.
     *
     * @return a DataSource.
     */
    private static DataSource getDataSource() {
        // Creates a new instance of DriverManagerDataSource and sets
        // the required parameters such as the Jdbc Driver class,
        // Jdbc URL, database username and password.
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(DataSourceDemo.DRIVER);
        dataSource.setUrl(DataSourceDemo.JDBC_URL);
        dataSource.setUsername(DataSourceDemo.USERNAME);
        dataSource.setPassword(DataSourceDemo.PASSWORD);
        return dataSource;
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>6.1.10</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.4.0</version>
    </dependency>
</dependencies>

Maven Central Maven Central

How do I read a file into byte array using Apache Commons IO?

By I Wayan Saryada in Apache Commons, Commons IO 0 Comment

The following example shows you how to read file contents into byte array. We use the IOUtils class of the Apache Commons IO library.

package org.kodejava.commons.io;

import org.apache.commons.io.IOUtils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class FileToByteArray {
    public static void main(String[] args) {
        File file = new File("README.md");
        try {
            InputStream is = new FileInputStream(file);
            byte[] bytes = IOUtils.toByteArray(is);

            System.out.println("Byte array size: " + bytes.length);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central

How do I create JTree with different icons for each node?

By I Wayan Saryada in Swing 10 Comments

The example below demonstrates you how to create a JTree that have a different icons for each node of the tree.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreeCellRenderer;
import java.awt.*;
import java.net.URL;

public class JTreeDifferentNodeIcon extends JFrame {
    public JTreeDifferentNodeIcon() throws HeadlessException {
        initializeUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(
                () -> new JTreeDifferentNodeIcon().setVisible(true));
    }

    private void initializeUI() {
        setSize(200, 400);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Countries");
        DefaultMutableTreeNode asia = new DefaultMutableTreeNode("Asia");
        Country[] countries = new Country[]{
                new Country("India", "/flags/in.png"),
                new Country("Singapore", "/flags/sg.png"),
                new Country("Indonesia", "/flags/id.png"),
                new Country("Vietnam", "/flags/vn.png"),
        };

        for (Country country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            asia.add(node);
        }

        DefaultMutableTreeNode northAmerica = new DefaultMutableTreeNode("North America");
        countries = new Country[]{
                new Country("United States", "/flags/us.png"),
                new Country("Canada", "/flags/ca.png")
        };

        for (Country country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            northAmerica.add(node);
        }

        DefaultMutableTreeNode southAmerica = new DefaultMutableTreeNode("South America");
        countries = new Country[]{
                new Country("Brazil", "/flags/br.png"),
                new Country("Argentina", "/flags/ar.png"),
                new Country("Uruguay", "/flags/uy.png")
        };
        for (Country country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            southAmerica.add(node);
        }

        DefaultMutableTreeNode europe = new DefaultMutableTreeNode("Europe");
        countries = new Country[]{
                new Country("United Kingdom", "/flags/gb.png"),
                new Country("Germany", "/flags/de.png"),
                new Country("Spain", "/flags/es.png"),
                new Country("France", "/flags/fr.png"),
                new Country("Italy", "/flags/it.png")
        };
        for (Country country : countries) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(country);
            europe.add(node);
        }

        root.add(asia);
        root.add(northAmerica);
        root.add(southAmerica);
        root.add(europe);

        final JTree tree = new JTree(root);
        tree.setCellRenderer(new CountryTreeCellRenderer());
        tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);
        tree.addTreeSelectionListener(e -> {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) tree.getLastSelectedPathComponent();
            if (node == null) {
                return;
            }

            Object nodeInfo = node.getUserObject();
            if (node.isLeaf()) {
                Country country = (Country) nodeInfo;
                System.out.println("country = " + country.getName());
            }
        });

        JScrollPane pane = new JScrollPane(tree);
        pane.setPreferredSize(new Dimension(200, 400));

        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(pane, BorderLayout.CENTER);
    }

    static class CountryTreeCellRenderer implements TreeCellRenderer {
        private final JLabel label;

        CountryTreeCellRenderer() {
            label = new JLabel();
        }

        public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded,
                                                      boolean leaf, int row, boolean hasFocus) {
            Object userObject = ((DefaultMutableTreeNode) value).getUserObject();
            if (userObject instanceof Country country) {
                URL imageUrl = getClass().getResource(country.getFlagIcon());
                if (imageUrl != null) {
                    label.setIcon(new ImageIcon(imageUrl));
                }
                label.setText(country.getName());
            } else {
                label.setIcon(null);
                label.setText(value.toString());
            }
            return label;
        }
    }

    static class Country {
        private String name;
        private String flagIcon;

        Country(String name, String flagIcon) {
            this.name = name;
            this.flagIcon = flagIcon;
        }

        public String getName() {
            return name;
        }

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

        public String getFlagIcon() {
            return flagIcon;
        }

        public void setFlagIcon(String flagIcon) {
            this.flagIcon = flagIcon;
        }
    }
}

Here is the result of our program above:

JTree Nodes With Icons

JTree Nodes With Icons

Flag icons by FamFamFam Flag Icons.