How do I execute stored procedure?

By Wayan in JDBC 0 Comment

Stored-procedure are user-generated functions or procedures that, once created in the database, it can be called by the client applications, such as Java application. In this example we’ll demonstrate how to use the JDBC java.sql.CallableStatement to call a stored procedure. The store procedure in this example is just for selecting records from the products table.

package org.kodejava.jdbc;

import java.sql.*;

public class CallableStatementDemo {
    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 connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Create a CallableStatement to execute the GetAllProducts() 
            // procedure.
            CallableStatement stmt =
                    connection.prepareCall("{CALL Get_All_Products()}");

            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                System.out.println(rs.getLong("id") + "\t"
                        + rs.getString("code") + "\t"
                        + rs.getString("name") + "\t"
                        + rs.getDouble("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Below is the stored procedure definition that was executed in the code above.

DELIMITER ;;
CREATE PROCEDURE `Get_All_Products`()
BEGIN
    SELECT * FROM product;
END;;
DELIMITER ;

When running the code snippet, the result will be something like this:

1   P0000001    UML Distilled 3rd Edition   25.0
3   P0000003    PHP Programming 20.0
4   P0000004    Longman Active Study Dictionary 40.0
5   P0000005    Ruby on Rails   24.0
6   P0000006    Championship Manager    0.0
7   P0000007    Transport Tycoon Deluxe 0.0
8   P0000008    Roller Coaster Tycoon 3 0.0
9   P0000009    Pro Evolution Soccer    0.0
10  P0000010    Data Structures, Algorithms 50.99

Maven Dependencies

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

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How do I sort items in a Set?

By Wayan in Core API, Util Package 0 Comment

The trick to sort a java.util.Set is to use the implementation of a java.util.SortedSet such as the java.util.TreeSet class. The example below shows you the result of using the java.util.TreeSet class, in which the items in it will be sorted based on the element’s natural order.

package org.kodejava.util;

import java.util.Set;
import java.util.TreeSet;

public class TreeSetDemo {
    public static void main(String[] args) {
        // The TreeSet class is an implementation of a SortedSet, this means
        // that when you are using the TreeSet to store you data collections
        // you'll get the items ordered base on its elements natural order.
        Set<String> set = new TreeSet<>();

        // In the example below we add some letters to the TreeSet, this mean
        // that the alphabets will be ordered based on the alphabet order
        // which is from A to Z.
        set.add("Z");
        set.add("A");
        set.add("F");
        set.add("B");
        set.add("H");
        set.add("X");
        set.add("N");

        for (String item : set) {
            System.out.print(item + " ");
        }
    }
}

This demo prints:

A B F H N X Z

How do I create a string search and replace using regex?

By Wayan in Regex 0 Comment

In this example you’ll see how we can create a small search and replace program using the regular expression classes in Java. The code below will replace all the brown words to red.

package org.kodejava.regex;

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class StringReplace {
    public static void main(String[] args) {
        String source = "The quick brown fox jumps over the brown lazy dog.";
        String find = "brown";
        String replace = "red";

        // Compiles the given regular expression into a pattern.
        Pattern pattern = Pattern.compile(find);

        // Creates a matcher that will match the given input against the
        // pattern.
        Matcher matcher = pattern.matcher(source);

        // Replaces every subsequence of the input sequence that matches
        // the pattern with the given replacement string.
        String output = matcher.replaceAll(replace);

        System.out.println("Source = " + source);
        System.out.println("Output = " + output);
    }
}

The result of the code snippet is:

Source = The quick brown fox jumps over the brown lazy dog.
Output = The quick red fox jumps over the red lazy dog.

How do I do regular expression in Java?

By Wayan in Regex 0 Comment

This example demonstrates how we do regular expression in Java. The regular expression classes is in the java.uti.regex package. The main class including the java.util.regex.Pattern class and the java.util.regex.Matcher class.

In this example we are only testing to match a string literal if it is exists in the following sentence, we are searching the word “lazy”.

package org.kodejava.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexDemo {
    public static void main(String[] args) {
        /*
         * To create a Pattern instance we must call the static method
         * called compile() in the Pattern class. Pattern object is
         * the compiled representation of a regular expression.
         */
        Pattern pattern = Pattern.compile("lazy");

        /*
         * The Matcher class also doesn't have the public constructor
         * so to create a matcher call the Pattern's class matcher()
         * method. The Matcher object itself is the engine that match
         * the input string against the provided pattern.
         */
        String input = "The quick brown fox jumps over the lazy dog";
        Matcher matcher = pattern.matcher(input);

        while (matcher.find()) {
            System.out.format("Text \"%s\" found at %d to %d.%n",
                    matcher.group(), matcher.start(), matcher.end());
        }
    }
}

The output of the code snippet above is:

Text "lazy" found at 35 to 39.

Java Programming Keywords Summary

By Wayan in Basic, Core API 0 Comment

Here are the summary of the available keywords in the Java programming language. Keywords are reserved words that already taken and internally used by Java, so we cannot create variables and name it using this keyword.

Keyword Meaning
abstract an abstract class or method
assert used to locate internal program errors
boolean the Boolean type
break breaks out of a switch or loop
byte the 8-bit integer type
case a case of a switch
catch the clause of a try block catching an exception
char the Unicode character type
class defines a class type
const not used
continue continues at the end of a loop
default the default clause of a switch
do the top of a do/while loop
double the double-precision floating-number type
Keyword Meaning
else the else clause of an if statement
enum define an enum type
extends defines the parent class of a class
final a constant, or a class or method that cannot be overridden
finally the part of a try block that is always executed
float the single-precision floating-point type
for a loop type
goto not used
if a conditional statement
implements defines the interface(s) that a class implements
import imports a package
instanceof tests if an object is an instance of a class
int the 32-bit integer type
interface an abstract type with methods that a class can implement
long the 64-bit long integer type
Keyword Meaning
native a method implemented by the host system
new allocates a new object or array
null a null reference
package a package of classes
private a feature that is accessible only by methods of this class
protected a feature that is accessible only by methods of this class, its children, and other classes in the same package
public a feature that is accessible by methods of all classes
return returns from a method
short the 16-bit integer type
static a feature that is unique to its class, not to objects of its class
strictfp Use strict rules for floating-point computations
super the superclass object or constructor
switch a selection statement
synchronized a method or code block that is atomic to a thread
this the implicit argument of a method, or a constructor of this class
Keyword Meaning
throw throws an exception
throws the exceptions that a method can throw
transient marks data that should not be persistent
try a block of code that traps exceptions
void denotes a method that returns no value
volatile ensures that a field is coherently accessed by multiple threads
while a while loop type

How do I read an XML document using JDOM?

By Wayan in JDOM 0 Comment

This example provide a small code snippet on how to use JDOM to parse an XML document, iterates each of the element and read the element or attributes values. To play with this example you have to have the JDOM library. You can download it from JDOM website.

package org.kodejava.jdom;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.input.SAXBuilder;

import java.io.ByteArrayInputStream;
import java.nio.charset.StandardCharsets;
import java.util.List;

public class ReadXmlDocument {
    public static void main(String[] args) {
        // Our imaginary xml file to be processed in this example.
        String data = """
                <root>
                    <row>
                        <column name="username" length="16">admin</column>
                        <column name="password" length="128">secret</column>
                    </row>
                    <row>
                        <column name="username" length="16">jdoe</column>
                        <column name="password" length="128">password</column>
                    </row>
                </root>""";

        // Create an instance of SAXBuilder
        SAXBuilder builder = new SAXBuilder();
        try {
            // Tell the SAXBuilder to build the Document object from the
            // InputStream supplied.
            Document document = builder.build(
                    new ByteArrayInputStream(data.getBytes(StandardCharsets.UTF_8)));

            // Get our xml document root element which equals to the
            // <root> tag in the xml document.
            Element root = document.getRootElement();

            // Get all the children named with <row> in the document.
            // The method return the children as a java.util.List
            // object.
            List<Element> rows = root.getChildren("row");
            for (Element row : rows) {
                // Convert each row to an Element object and get its
                // children which will return a collection of <column>
                // elements. When we have to column row we can read
                // the attribute value (name, length) as defined above
                // and also read its value (between the <column></column>
                // tag) by calling the getText() method.
                //
                // The getAttribute() method also provide a handy method
                // if we want to convert the attribute value to a correct
                // org.kodejava.data type, in the example we read the length attribute
                // value as an integer.
                List<Element> columns = row.getChildren("column");
                for (Element column : columns) {
                    String name = column.getAttribute("name").getValue();
                    String value = column.getText();
                    int length = column.getAttribute("length").getIntValue();

                    System.out.println("name = " + name);
                    System.out.println("value = " + value);
                    System.out.println("length = " + length);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>org.jdom</groupId>
    <artifactId>jdom2</artifactId>
    <version>2.0.6.1</version>
</dependency>

Maven Central

How do I sort items of an ArrayList?

By Wayan in Core API, Util Package 0 Comment

This example shows you how we can sort items of an ArrayList using the Collections.sort() method. Beside accepting the list object to be sorted we can also pass a Comparator implementation to define the sorting behaviour such as sorting in descending or ascending order.

package org.kodejava.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ArrayListSortExample {
    public static void main(String[] args) {
        /*
         * Create a collections of colours
         */
        List<String> colours = new ArrayList<>();
        colours.add("red");
        colours.add("green");
        colours.add("blue");
        colours.add("yellow");
        colours.add("cyan");
        colours.add("white");
        colours.add("black");

        /*
         * We can sort items of a list using the Collections.sort() method.
         * We can also reverse the order of the sorting by passing the
         * Collections.reverseOrder() comparator.
         */
        Collections.sort(colours);
        System.out.println(Arrays.toString(colours.toArray()));

        colours.sort(Collections.reverseOrder());
        System.out.println(Arrays.toString(colours.toArray()));
    }
}

The code will output:

[black, blue, cyan, green, red, white, yellow]
[yellow, white, red, green, cyan, blue, black]

How do I sort array values in case-insensitive order?

By Wayan in Core API, Util Package 1 Comment

By default, when sorting an arrays the value will be ordered in case-sensitive order. This example show you how to order it in case-insensitive order.

package org.kodejava.util;

import java.util.Arrays;

public class SortArrayCaseSensitivity {
    public static void main(String[] args) {
        String[] teams = new String[5];
        teams[0] = "Manchester United";
        teams[1] = "chelsea";
        teams[2] = "Arsenal";
        teams[3] = "liverpool";
        teams[4] = "EVERTON";

        // Sort array, by default it will be sorted in case-sensitive order.
        // [Arsenal, EVERTON, Manchester United, chelsea, liverpool]
        Arrays.sort(teams);
        System.out.println("Case sensitive  : " + Arrays.toString(teams));

        // Sort array in case-insensitive order
        // [Arsenal, chelsea, EVERTON, liverpool, Manchester United]
        Arrays.sort(teams, String.CASE_INSENSITIVE_ORDER);
        System.out.println("Case insensitive: " + Arrays.toString(teams));
    }
}

The result of the code snippet above:

Case sensitive  : [Arsenal, EVERTON, Manchester United, chelsea, liverpool]
Case insensitive: [Arsenal, chelsea, EVERTON, liverpool, Manchester United]

How do I sort array values in descending order?

By Wayan in Core API, Util Package 0 Comment

Here you will find an example on how to sort the values of an array in ascending or descending order.

package org.kodejava.util;

import java.util.Arrays;
import java.util.Collections;

public class SortArrayWithOrder {
    public static void main(String[] args) {
        Integer[] points = new Integer[5];
        points[0] = 94;
        points[1] = 53;
        points[2] = 70;
        points[3] = 44;
        points[4] = 64;
        System.out.println("Original  : " + Arrays.toString(points));

        // Sort the points array, the default order is in ascending order.
        // [44, 53, 64, 70, 94]
        Arrays.sort(points);
        System.out.println("Ascending : " + Arrays.toString(points));

        // Sort the points array in descending order.
        // [94, 70, 64, 53, 44]
        Arrays.sort(points, Collections.reverseOrder());
        System.out.println("Descending: " + Arrays.toString(points));
    }
}

The result of the code snippet above are:

Original  : [94, 53, 70, 44, 64]
Ascending : [44, 53, 64, 70, 94]
Descending: [94, 70, 64, 53, 44]

How do I limit Hibernate query result?

By Wayan in Hibernate 0 Comment

In the example below you’ll see how to limit the number of records returned by hibernate queries. Limiting the query result is usually use for creating pagination, where we can navigate from page to page of data in our application but only a few of them are read from the database.

In hibernate Query object we need to specify the first result and max results by calling the setFirstResult() and setMaxResults() methods to limit the query results.

package org.kodejava.hibernate.service;

import org.hibernate.Session;
import org.hibernate.query.Query;
import org.kodejava.hibernate.SessionFactoryHelper;
import org.kodejava.hibernate.model.Label;

import java.util.List;

public class LabelService {
    public List<Label> getLabels(int pageNumber, int pageSize) {
        Session session =
                SessionFactoryHelper.getSessionFactory().getCurrentSession();
        session.beginTransaction();

        Query<Label> query = session.createQuery("from Label", Label.class);

        // Set the first record position and the max number of record to be
        // read. The setFirstResult() tell hibernate from which row the data
        // should be read. In the example if we have pages of 10 records,
        // passing the page number 2 will read 10 records from the 20th row
        // in the selected records.
        query.setFirstResult((pageNumber - 1) * pageSize);
        query.setMaxResults(pageSize);

        List<Label> labels = query.list();
        session.getTransaction().commit();
        return labels;
    }
}

package org.kodejava.hibernate;

import org.kodejava.hibernate.model.Label;
import org.kodejava.hibernate.service.LabelService;

import java.util.List;

public class LimitDemo {
    public static void main(String[] args) {
        LabelService service = new LabelService();

        List<Label> labels = service.getLabels(1, 10);
        for (Label label : labels) {
            System.out.println("Label = " + label);
        }
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>5.6.9.Final</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.0.33</version>
    </dependency>
</dependencies>

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