solution

pom.xml

@@ -59,5 +59,12 @@
             <artifactId>jakarta.xml.bind-api</artifactId>
             <version>3.0.1</version>
         </dependency>
+        <!-- https://mvnrepository.com/artifact/org.eclipse.persistence/org.eclipse.persistence.moxy -->
+		<dependency>
+		    <groupId>org.eclipse.persistence</groupId>
+		    <artifactId>org.eclipse.persistence.moxy</artifactId>
+		    <version>3.0.2</version>
+		</dependency>
+
 	</dependencies>
 </project>

src/main/java/cz/jezek/lab11/Match.java

@@ -3,6 +3,9 @@ package cz.jezek.lab11;
 import java.io.Serializable;
 import java.util.Objects;
 
+import jakarta.xml.bind.annotation.XmlAttribute;
+import jakarta.xml.bind.annotation.XmlElement;
+
 public class Match implements Serializable{
 
 	/**
@@ -10,10 +13,18 @@ public class Match implements Serializable{
 	 */
 	private static final long serialVersionUID = -7368303036334738923L;
 	
+	@XmlElement
 	private Oponents oponents;
+	
+	@XmlAttribute
 	private int player1Scorel;
+	
+	@XmlAttribute
 	private int player2Scorel;
 
+	public Match() {
+	}
+	
 	public Match(Player player1, int player1Scorel, Player player2, int player2Scorel) {
 		this.oponents = new Oponents(player1, player2);
 		this.player1Scorel = player1Scorel;

src/main/java/cz/jezek/lab11/Oponents.java

@@ -3,6 +3,8 @@ package cz.jezek.lab11;
 import java.io.Serializable;
 import java.util.Objects;
 
+import jakarta.xml.bind.annotation.XmlElement;
+
 public class Oponents implements Serializable{
 
 	/**
@@ -10,9 +12,15 @@ public class Oponents implements Serializable{
 	 */
 	private static final long serialVersionUID = 1L;
 	
+	@XmlElement
 	private Player player1;
+	
+	@XmlElement
 	private Player player2;
 
+	public Oponents() {
+	}
+	
 	public Oponents(Player player1, Player player2) {
 		super();
 		this.player1 = player1;

src/main/java/cz/jezek/lab11/Player.java

@@ -16,6 +16,9 @@ public class Player implements Serializable {
 				RandomGenerator.selectRandom(RandomGenerator.SURNAMES));
 	}
 
+	public Player() {
+	}
+	
 	public Player(String firstName, String lastName) {
 		super();
 		this.firstName = firstName;

src/main/java/cz/jezek/lab11/StreamMain.java

@@ -4,14 +4,21 @@ import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.ObjectInputStream;
 import java.io.OutputStream;
 import java.util.Comparator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
 import java.util.stream.Collectors;
 
+import org.eclipse.persistence.jaxb.MarshallerProperties;
+
 import jakarta.xml.bind.JAXBContext;
 import jakarta.xml.bind.JAXBException;
 import jakarta.xml.bind.Marshaller;
+import jakarta.xml.bind.Unmarshaller;
 
 public class StreamMain {
 
@@ -21,6 +28,11 @@ public class StreamMain {
     //printStatAboutTournament(tournament);
 
     saveTournament(tournament);
+    saveTournamentAsJSON(tournament);
+    
+    Tournament tournament2 = loadTournamentFromXML();
+    
+    System.out.println(tournament2);
   }
 
   public static void printStatAboutTournament(Tournament tournament) {
@@ -93,4 +105,51 @@ public class StreamMain {
 		e.printStackTrace();
 	}
   }
+  
+  
+  public static void saveTournamentAsJSON(Tournament tournament) {
+	  
+	    try  {
+	    	JAXBContext context = JAXBContext.newInstance(Tournament.class);
+	    	Marshaller marshaller = context.createMarshaller();
+	    	marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
+	    	marshaller.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
+	    	marshaller.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, true);
+	    	marshaller.marshal(tournament, System.out);
+	    	
+	    } catch (JAXBException exc) {
+	    	exc.printStackTrace();
+	    } 
+	  }
+ 
+
+  
+  public static Tournament loadTournamentFromXML() {
+	  
+	    try (InputStream is = new FileInputStream("tournament.xml")) {
+	    	JAXBContext context = JAXBContext.newInstance(Tournament.class);
+	    	Unmarshaller unmarshaller = context.createUnmarshaller();
+	    	Tournament result = (Tournament) unmarshaller.unmarshal(is);
+	    	Map<String,Player> tempPlayers = 
+	    			result.getPlayers().stream()
+	    			.collect(Collectors.toMap(p -> p.getLastName() + ";" + p.getFirstName(), 
+	    					                  p ->p ));
+	    	List<Match> tempMatches = new LinkedList<>(result.getMatches());
+	    	result.getMatches().clear();
+	    	for (Match m: tempMatches) {
+	    		String player1Key = m.getOponents().getPlayer1().getLastName() + ";" +  m.getOponents().getPlayer1().getFirstName();
+	    		String player2Key = m.getOponents().getPlayer2().getLastName() + ";" +  m.getOponents().getPlayer2().getFirstName();
+	    		result.getMatches().add(new Match(tempPlayers.get(player1Key), m.getPlayer1Scorel(), tempPlayers.get(player2Key), m.getPlayer2Scorel()));
+	    	}
+	    	
+	    } catch (JAXBException exc) {
+	    	exc.printStackTrace();
+	    } catch (FileNotFoundException e) {
+			e.printStackTrace();
+		} catch (IOException e) {
+			// TODO Auto-generated catch block
+			e.printStackTrace();
+		}
+	    return null;
+	  }
 }

src/main/java/cz/jezek/lab11/Tournament.java

@@ -24,7 +24,6 @@ public class Tournament implements Serializable{
   
   @XmlElement(name = "match")
   @XmlElementWrapper(name = "matches")
-  
   private List<Match> matches;
   
   @XmlAttribute

src/main/java/module-info.java

@@ -3,4 +3,5 @@ module cz.jezek.lab10 {
     exports cz.jezek.lab11;
     requires java.xml;
     requires jakarta.xml.bind;
+    requires org.eclipse.persistence.moxy;
 }
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