How to truncate a string after n number of words?

By Wayan in Regex 1 Comment 
package org.kodejava.regex;

public class GetNumberOfWordsFromString {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog.";

        String one = truncateAfterWords(1, text);
        System.out.println("1 = " + one);

        String two = truncateAfterWords(2, text);
        System.out.println("2 = " + two);

        String four = truncateAfterWords(4, text);
        System.out.println("4 = " + four);

        String six = truncateAfterWords(6, text);
        System.out.println("6 = " + six);
    }

    /**
     * Truncate a string after n number of words.
     *
     * @param words number of words to truncate after.
     * @param text  the text.
     * @return truncated text.
     */
    public static String truncateAfterWords(int words, String text) {
        String regex = String.format("^((?:\\W*\\w+){%s}).*$", words);
        return text.replaceAll(regex, "$1");
    }
}

The result of the snippet:

1 = The
2 = The quick
4 = The quick brown fox
6 = The quick brown fox jumps over

How to get random key-value pair from Hashtable?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.example.util;

import java.util.Hashtable;
import java.util.Random;

public class HashtableGetRandom {
    public static void main(String[] args) {
        // Create a hashtable and put some key-value pair.
        Hashtable<String, String> colors = new Hashtable<>();
        colors.put("black", "#000");
        colors.put("red", "#f00");
        colors.put("green", "#0f0");
        colors.put("blue", "#00f");
        colors.put("white", "#fff");

        // Get a random entry from the hashtable.
        String[] keys = colors.keySet().toArray(new String[colors.size()]);
        String key = keys[new Random().nextInt(keys.length)];
        System.out.println(key + " = " + colors.get(key));
    }
}

How to monitor file or directory changes?

By Wayan in Core API, IO 2 Comments 
package org.kodejava.io;

import java.io.IOException;
import java.nio.file.*;

import static java.nio.file.StandardWatchEventKinds.*;

public class FileWatchDemo {
    public static void main(String[] args) {
        try {
            // Creates a instance of WatchService.
            WatchService watcher = FileSystems.getDefault().newWatchService();

            // Registers the logDir below with a watch service.
            Path logDir = Paths.get("F:/Temp/");
            logDir.register(watcher, ENTRY_CREATE, ENTRY_MODIFY, ENTRY_DELETE);

            // Monitor the logDir at listen for change notification.
            while (true) {
                WatchKey key = watcher.take();
                for (WatchEvent<?> event : key.pollEvents()) {
                    WatchEvent.Kind<?> kind = event.kind();

                    if (ENTRY_CREATE.equals(kind)) {
                        System.out.println("Entry was created on log dir.");
                    } else if (ENTRY_MODIFY.equals(kind)) {
                        System.out.println("Entry was modified on log dir.");
                    } else if (ENTRY_DELETE.equals(kind)) {
                        System.out.println("Entry was deleted from log dir.");
                    }
                }
                key.reset();
            }
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

To get the created, modified or deleted file you can see the following example: How to get the file name when using WatchService?.

How to get the file name when using WatchService?

By Wayan in Core API, IO 3 Comments 
package org.kodejava.io;

import java.io.IOException;
import java.nio.file.*;

import static java.nio.file.StandardWatchEventKinds.*;

public class WatchServiceGetFilename {
    public static void main(String[] args) {
        try {
            // Create a WatchService and register the logDir path with the
            // WatchService for ENTRY_CREATE.
            WatchService watcher = FileSystems.getDefault().newWatchService();
            Path logDir = Paths.get("F:/Temp");
            logDir.register(watcher, ENTRY_CREATE);

            while (true) {
                WatchKey key;
                try {
                    key = watcher.take();
                } catch (InterruptedException e) {
                    return;
                }

                for (WatchEvent<?> event : key.pollEvents()) {
                    if (event.kind() == ENTRY_CREATE) {
                        // Get the name of created file.
                        WatchEvent<Path> ev = cast(event);
                        Path filename = ev.context();

                        System.out.printf("A new file %s was created.%n",
                                filename.getFileName());
                    }
                }
                key.reset();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unchecked")
    private static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>) event;
    }
}

How to read file using Files.newBufferedReader?

By Wayan in Core API, IO 1 Comment

In the snippet below you’ll learn to open file for reading using Files.newBufferedReader() method in JDK 7. This method returns a java.io.BufferedReader which makes a backward compatibility with the old I/O system in Java.

To read a file you’ll need to provide a Path and the Charset to the newBufferedReader() method arguments.

package org.kodejava.io;

import java.io.BufferedReader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FilesNewBufferedReader {
    public static void main(String[] args) {
        Path logFile = Paths.get("app.log");
        try (BufferedReader reader =
                     Files.newBufferedReader(logFile, StandardCharsets.UTF_8)) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}