Closes unclosed streams in message example

The streams used to read and write the message object in the example
4 were not closed. This commit fixes this error.

pom.xml

@@ -7,7 +7,7 @@
 
 	<groupId>es.uvigo.esei.dai</groupId>
 	<artifactId>sockets</artifactId>
-	<version>1.0.0</version>
+	<version>1.0.1</version>
 
 	<name>Ejemplos de DAI - Sockets</name>
 	<inceptionYear>2014</inceptionYear>

src/main/java/es/uvigo/esei/dai/sockets/example4/MessageReceiver.java

@@ -37,10 +37,10 @@ public class MessageReceiver {
 
         socket.receive(packet);
 
-        try {
+        try (
           final ByteArrayInputStream input = new ByteArrayInputStream(buffer);
-          final ObjectInputStream dataInput = new ObjectInputStream(input);
-
+          final ObjectInputStream dataInput = new ObjectInputStream(input)
+        ) {
           final Message message = (Message) dataInput.readObject();
 
           System.out.println("SUBJECT: " + message.getSubject());

src/main/java/es/uvigo/esei/dai/sockets/example4/MessageSender.java

@@ -32,19 +32,21 @@ import java.util.Date;
 public class MessageSender {
   public static void main(String[] args) {
     try (DatagramSocket socket = new DatagramSocket()) {
-      final ByteArrayOutputStream output = new ByteArrayOutputStream(60000);
-      final ObjectOutputStream dataOutput = new ObjectOutputStream(output);
-
-      final Message message = new Message("Time", "Current time: " + new Date());
-      System.out.println("SUBJECT: " + message.getSubject());
-      System.out.println("MESSAGE: " + message.getMessage());
-      dataOutput.writeObject(message);
-
-      final DatagramPacket packet = new DatagramPacket(
-        output.toByteArray(), output.size(), InetAddress.getLocalHost(), 1234
-      );
-
-      socket.send(packet);
+      try (
+        final ByteArrayOutputStream output = new ByteArrayOutputStream(1500);
+        final ObjectOutputStream dataOutput = new ObjectOutputStream(output)
+      ) {
+        final Message message = new Message("Time", "Current time: " + new Date());
+        System.out.println("SUBJECT: " + message.getSubject());
+        System.out.println("MESSAGE: " + message.getMessage());
+        dataOutput.writeObject(message);
+  
+        final DatagramPacket packet = new DatagramPacket(
+          output.toByteArray(), output.size(), InetAddress.getLocalHost(), 60000
+        );
+  
+        socket.send(packet);
+      }
     } catch (final IOException e) {
       System.out.print("Connection error: ");
       System.out.println(e.getMessage());