How do I load file from resource directory?

By Wayan in Core API, Lang Package 1 Comment

In the following code snippet we will learn how to load files from resource directory. Resource files can be in a form of image, audio, text, etc. Text resource file for example can be used to store application configurations, such as database configuration.

To load this resource file you can use a couple methods utilizing the java.lang.Class methods or the java.lang.ClassLoader methods. Both Class and ClassLoader provides getResource() and getResourceAsStream() methods to load resource file. The first method return a URL object while the second method return an InputStream.

When using the Class method, if the resource name started with “/” that identifies it is an absolute name. Absolute name means that it will load from the specified directory name or package name. While if it is not started with “/” then it is identified as a relative name. This means that it will look in the same package as the class that tries to load the resource.

App.class.getResource("database.conf");

The snippet will attempt to load the resource file from the same package as the App class. If the App class package is org.kodejava then the database.conf file must be located at /org/kodejava/. This is the relative resource name.

App.class.getResource("/org/kodejava/conf/database.conf"):

The snippet will attempt to load the resource file from the given package name. You should place the configuration file under /org/kodejava/conf/ to enable the application to load it. This is the absolute resource name.

Below is a snippet that use the Class method to load resources.

private void loadUsingClassMethod() throws IOException {
    System.out.println("LoadResourceFile.loadUsingClassMethod");
    Properties properties = new Properties();

    // Load resource relatively to the LoadResourceFile package.
    // This actually load resource from
    // "/org/kodejava/lang/database.conf".
    URL resource = getClass().getResource("database.conf");
    properties.load(new FileReader(Objects.requireNonNull(resource).getFile()));
    System.out.println("JDBC Driver: " + properties.get("jdbc.driver"));

    // Load resource using absolute name. This will read resource
    // from the root of the package. This will load "/database.conf".
    InputStream is = getClass().getResourceAsStream("/database.conf");
    properties.load(is);
    System.out.println("JDBC Driver: " + properties.get("jdbc.driver"));
}

When we use the ClassLoader method the resource name should not begins with a “/“. This method will not apply any absolute / relative transformation to the resource name like the Class method. Here a snippet of a method that use the ClassLoader method.

private void loadUsingClassLoaderMethod() throws IOException {
    System.out.println("LoadResourceFile.loadUsingClassLoaderMethod");
    Properties properties = new Properties();

    // When using the ClassLoader method, the resource name should
    // not be started with "/". This method will not apply any
    // absolute/relative transformation to the resource name.
    ClassLoader classLoader = getClass().getClassLoader();
    URL resource = classLoader.getResource("database.conf");
    properties.load(new FileReader(Objects.requireNonNull(resource).getFile()));
    System.out.println("JDBC URL: " + properties.get("jdbc.url"));

    InputStream is = classLoader.getResourceAsStream("database.conf");
    properties.load(is);
    System.out.println("JDBC URL: " + properties.get("jdbc.url"));
}

Below is the main program that calls the methods above.

package org.kodejava.lang;

import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Objects;
import java.util.Properties;

public class LoadResourceFile {
    public static void main(String[] args) throws Exception {
        LoadResourceFile demo = new LoadResourceFile();
        demo.loadUsingClassMethod();
        demo.loadUsingClassLoaderMethod();
    }
}

In the snippet above we load two difference resources. One contains Oracle database configuration and the other is MySQL database configuration.

/resources/org/kodejava/lang/database.conf

jdbc.driver=oracle.jdbc.driver.OracleDriver
jdbc.url=jdbc:oracle:thin:@localhost:1521:xe
jdbc.username=kodejava
jdbc.password=kodejava123

/resources/database.conf

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost/kodejava
jdbc.username=kodejava
jdbc.password=kodejava123

The result of this code snippet are:

LoadResourceFile.loadUsingClassMethod
JDBC Driver: oracle.jdbc.driver.OracleDriver
JDBC Driver: com.mysql.jdbc.Driver

LoadResourceFile.loadUsingClassLoaderMethod
JDBC URL: jdbc:mysql://localhost/kodejava
JDBC URL: jdbc:mysql://localhost/kodejava

How do I escape / display percent sign in printf statement?

By Wayan in Core API, Lang Package

You have a problem displaying the % sign when you want to print a number in percentage format using the printf() method. Because the % sign is use as a prefix of format specifiers, you need to escape it if you want to display the % sign as part of the output string.

To escape the percent sign (%) you need to write it twice, like %%. It will print out a single % sign as part of your printf() method output. Let see an example in the code snippet below:

package org.kodejava.lang;

public class EscapePercentSignExample {
    public static void main(String[] args) {
        String format = "The current bank interest rate is %6.2f%%.%n";
        System.out.printf(format, 10f);
    }
}

In the code snippet above we use the following format %6.2f%%.%n which can be explained as:

  • %6.2f format the number (10f) as six characters in width, right justified, with two places after decimal point. The f conversion character means it accept a float value.
  • %% will escape the % sign and print it as part of the output.
  • %n will print out a new line character.

When you execute the code, it will print:

The current bank interest rate is  10.00%.

How to split a string by a number of characters?

By Wayan in Core API, Lang Package 1 Comment

The following code snippet will show you how to split a string by numbers of characters. We create a method called splitToNChars() that takes two arguments. The first arguments is the string to be split and the second arguments is the split size.

This splitToNChars() method will split the string in a for loop. First we’ll create a List object that will store parts of the split string. Next we do a loop and get the substring for the defined size from the text and store it into the List. After the entire string is read we convert the List object into an array of String by using the List‘s toArray() method.

Let’s see the code snippet below:

package org.kodejava.lang;

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

public class SplitStringForEveryNChar {
    public static void main(String[] args) {
        String text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        System.out.println(Arrays.toString(splitToNChar(text, 3)));
        System.out.println(Arrays.toString(splitToNChar(text, 4)));
        System.out.println(Arrays.toString(splitToNChar(text, 5)));
    }

    /**
     * Split text into n number of characters.
     *
     * @param text the text to be split.
     * @param size the split size.
     * @return an array of the split text.
     */
    private static String[] splitToNChar(String text, int size) {
        List<String> parts = new ArrayList<>();

        int length = text.length();
        for (int i = 0; i < length; i += size) {
            parts.add(text.substring(i, Math.min(length, i + size)));
        }
        return parts.toArray(new String[0]);
    }
}

When run the code snippet will output:

[ABC, DEF, GHI, JKL, MNO, PQR, STU, VWX, YZ]
[ABCD, EFGH, IJKL, MNOP, QRST, UVWX, YZ]
[ABCDE, FGHIJ, KLMNO, PQRST, UVWXY, Z]

How do I split a string with multiple spaces?

By Wayan in Core API, Lang Package 3 Comments

This code snippet show you how to split string with multiple white-space characters. To split the string this way we use the "\s+" regular expression. The white-space characters include space, tab, line-feed, carriage-return, new line, form-feed.

Let’s see the code snippet below:

package org.kodejava.lang;

import java.util.Arrays;

public class SplitStringMultiSpaces {
    public static void main(String[] args) {
        String text = "04/11/2021    SHOES      RUNNING RED   99.9 USD";

        // Split the string using the \s+ regex to split multi spaces
        // line of text.
        String[] items = text.split("\\s+");
        System.out.println("Length = " + items.length);
        System.out.println("Items  = " + Arrays.toString(items));
    }
}

The result of the code snippet is:

Length = 6
Items  = [04/11/2021, SHOES, RUNNING, RED, 99.9, USD]

How do I create array of unique values from another array?

By Wayan in Core API, Lang Package 2 Comments

This code snippet show you how to create an array of unique numbers from another array of numbers.

package org.kodejava.lang;

import java.util.Arrays;

public class UniqueArray {
    /**
     * Return true if num appeared only once in the array.
     */
    public static boolean isUnique(int[] numbers, int num) {
        for (int number : numbers) {
            if (number == num) {
                return false;
            }
        }
        return true;
    }

    /**
     * Convert the given array to an array with unique values and
     * returns it.
     */
    public static int[] toUniqueArray(int[] numbers) {
        int[] temp = new int[numbers.length];
        // in case you have value of 0 in the array
        Arrays.fill(temp, -1);

        int counter = 0;
        for (int number : numbers) {
            if (isUnique(temp, number))
                temp[counter++] = number;
        }

        int[] uniqueArray = new int[counter];
        System.arraycopy(temp, 0, uniqueArray, 0, uniqueArray.length);
        return uniqueArray;
    }

    /**
     * Print given array
     */
    public static void printArray(int[] numbers) {
        for (int number : numbers) {
            System.out.print(number + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        int[] numbers = {1, 1, 2, 3, 4, 1, 4, 7, 9, 7};
        printArray(numbers);
        printArray(toUniqueArray(numbers));
    }
}

For other example to create unique array check the following example How do I remove duplicate element from array?.