[BAEL-15998] - Move articles out of core-java-io part 1

core-java-modules/core-java-nio-2/src/main/java/com/baeldung/selector/EchoClient.java

@@ -0,0 +1,50 @@
+package com.baeldung.selector;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.channels.SocketChannel;
+
+public class EchoClient {
+    private static SocketChannel client;
+    private static ByteBuffer buffer;
+    private static EchoClient instance;
+
+    public static EchoClient start() {
+        if (instance == null)
+            instance = new EchoClient();
+
+        return instance;
+    }
+
+    public static void stop() throws IOException {
+        client.close();
+        buffer = null;
+    }
+
+    private EchoClient() {
+        try {
+            client = SocketChannel.open(new InetSocketAddress("localhost", 5454));
+            buffer = ByteBuffer.allocate(256);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public String sendMessage(String msg) {
+        buffer = ByteBuffer.wrap(msg.getBytes());
+        String response = null;
+        try {
+            client.write(buffer);
+            buffer.clear();
+            client.read(buffer);
+            response = new String(buffer.array()).trim();
+            System.out.println("response=" + response);
+            buffer.clear();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return response;
+
+    }
+}

core-java-modules/core-java-nio-2/src/main/java/com/baeldung/selector/EchoServer.java

@@ -0,0 +1,75 @@
+package com.baeldung.selector;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.channels.SelectionKey;
+import java.nio.channels.Selector;
+import java.nio.channels.ServerSocketChannel;
+import java.nio.channels.SocketChannel;
+import java.util.Iterator;
+import java.util.Set;
+
+public class EchoServer {
+
+    private static final String POISON_PILL = "POISON_PILL";
+
+    public static void main(String[] args) throws IOException {
+        Selector selector = Selector.open();
+        ServerSocketChannel serverSocket = ServerSocketChannel.open();
+        serverSocket.bind(new InetSocketAddress("localhost", 5454));
+        serverSocket.configureBlocking(false);
+        serverSocket.register(selector, SelectionKey.OP_ACCEPT);
+        ByteBuffer buffer = ByteBuffer.allocate(256);
+
+        while (true) {
+            selector.select();
+            Set<SelectionKey> selectedKeys = selector.selectedKeys();
+            Iterator<SelectionKey> iter = selectedKeys.iterator();
+            while (iter.hasNext()) {
+
+                SelectionKey key = iter.next();
+
+                if (key.isAcceptable()) {
+                    register(selector, serverSocket);
+                }
+
+                if (key.isReadable()) {
+                    answerWithEcho(buffer, key);
+                }
+                iter.remove();
+            }
+        }
+    }
+
+    private static void answerWithEcho(ByteBuffer buffer, SelectionKey key) throws IOException {
+        SocketChannel client = (SocketChannel) key.channel();
+        client.read(buffer);
+        if (new String(buffer.array()).trim().equals(POISON_PILL)) {
+            client.close();
+            System.out.println("Not accepting client messages anymore");
+        }
+
+        buffer.flip();
+        client.write(buffer);
+        buffer.clear();
+    }
+
+    private static void register(Selector selector, ServerSocketChannel serverSocket) throws IOException {
+        SocketChannel client = serverSocket.accept();
+        client.configureBlocking(false);
+        client.register(selector, SelectionKey.OP_READ);
+    }
+
+    public static Process start() throws IOException, InterruptedException {
+        String javaHome = System.getProperty("java.home");
+        String javaBin = javaHome + File.separator + "bin" + File.separator + "java";
+        String classpath = System.getProperty("java.class.path");
+        String className = EchoServer.class.getCanonicalName();
+
+        ProcessBuilder builder = new ProcessBuilder(javaBin, "-cp", classpath, className);
+
+        return builder.start();
+    }
+}

core-java-modules/core-java-nio-2/src/main/java/com/baeldung/symlink/SymLinkExample.java

@@ -0,0 +1,56 @@
+package com.baeldung.symlink;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.DirectoryStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.IntStream;
+
+import static java.nio.file.StandardOpenOption.CREATE;
+import static java.nio.file.StandardOpenOption.TRUNCATE_EXISTING;
+
+public class SymLinkExample {
+
+    public void createSymbolicLink(Path link, Path target) throws IOException {
+        if (Files.exists(link)) {
+            Files.delete(link);
+        }
+        Files.createSymbolicLink(link, target);
+    }
+
+    public void createHardLink(Path link, Path target) throws IOException {
+        if (Files.exists(link)) {
+            Files.delete(link);
+        }
+        Files.createLink(link, target);
+    }
+
+    public Path createTextFile() throws IOException {
+        byte[] content = IntStream.range(0, 10000)
+            .mapToObj(i -> i + System.lineSeparator())
+            .reduce("", String::concat)
+            .getBytes(StandardCharsets.UTF_8);
+        Path filePath = Paths.get(".", "target_link.txt");
+        Files.write(filePath, content, CREATE, TRUNCATE_EXISTING);
+        return filePath;
+    }
+
+    public void printLinkFiles(Path path) throws IOException {
+        try (DirectoryStream<Path> stream = Files.newDirectoryStream(path)) {
+            for (Path file : stream) {
+                if (Files.isDirectory(file)) {
+                    printLinkFiles(file);
+                } else if (Files.isSymbolicLink(file)) {
+                    System.out.format("File link '%s' with target '%s'%n", file, Files.readSymbolicLink(file));
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        new SymLinkExample().printLinkFiles(Paths.get("."));
+    }
+
+}

core-java-modules/core-java-nio-2/src/main/java/com/baeldung/watcher/DirectoryWatcherExample.java

@@ -0,0 +1,23 @@
+package com.baeldung.watcher;
+
+import java.io.IOException;
+import java.nio.file.*;
+
+public class DirectoryWatcherExample {
+
+    public static void main(String[] args) throws IOException, InterruptedException {
+        WatchService watchService = FileSystems.getDefault().newWatchService();
+        Path path = Paths.get(System.getProperty("user.home"));
+        path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);
+        WatchKey key;
+        while ((key = watchService.take()) != null) {
+            for (WatchEvent<?> event : key.pollEvents()) {
+                System.out.println("Event kind:" + event.kind() + ". File affected: " + event.context() + ".");
+            }
+            key.reset();
+        }
+
+        watchService.close();
+    }
+
+}