feature: convert models to Java records and modernize the topic service layer

src/main/java/hello/controller/TopicController.java

@@ -3,6 +3,7 @@
 import hello.model.Topic;
 import hello.service.TopicService;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
 
 import java.util.List;
@@ -29,8 +30,10 @@ public List<Topic> getAllTopics() {
      * @return
      */
     @RequestMapping("/topic/{id}")
-    public Topic getTopicWithID(@PathVariable String id) {
-        return topicService.getTopicWithId(id);
+    public ResponseEntity<Topic> getTopicWithID(@PathVariable String id) {
+        return topicService.getTopicWithId(id)
+                .map(ResponseEntity::ok)
+                .orElseGet(() -> ResponseEntity.notFound().build());
     }
 
     /**

src/main/java/hello/declaration/CustomPredicate.java

@@ -4,6 +4,7 @@
  * Use as a Functional Interface
  * @param <T>
  */
+@FunctionalInterface
 public  interface  CustomPredicate <T>{
     boolean test(T t);
 }

src/main/java/hello/model/Customer.java

@@ -1,45 +1,4 @@
 package hello.model;
 
-public class Customer {
-    private long id;
-    private String firstName, lastName;
-
-    @Override
-    public String toString() {
-        return "Customer{" +
-                "id=" + id +
-                ", firstName='" + firstName + '\'' +
-                ", lastName='" + lastName + '\'' +
-                '}';
-    }
-
-    public Customer(long id, String firstName, String lastName) {
-        this.id = id;
-        this.firstName = firstName;
-        this.lastName = lastName;
-    }
-
-    public long getId() {
-        return id;
-    }
-
-    public void setId(long id) {
-        this.id = id;
-    }
-
-    public String getFirstName() {
-        return firstName;
-    }
-
-    public void setFirstName(String firstName) {
-        this.firstName = firstName;
-    }
-
-    public String getLastName() {
-        return lastName;
-    }
-
-    public void setLastName(String lastName) {
-        this.lastName = lastName;
-    }
+public record Customer(long id, String firstName, String lastName) {
 }

src/main/java/hello/model/Greeting.java

@@ -1,21 +1,4 @@
 package hello.model;
 
-public class Greeting {
-    private final long id;
-    private final String content;
-
-    public Greeting(long id, String content) {
-        this.id = id;
-        this.content = content;
-    }
-
-
-    public long getId() {
-
-        return id;
-    }
-
-    public String getContent() {
-        return content;
-    }
+public record Greeting(long id, String content) {
 }

src/main/java/hello/model/Quote.java

@@ -1,34 +1,4 @@
 package hello.model;
 
-public class Quote {
-    private String type;
-    private Value value;
-
-    @Override
-    public String toString() {
-        return "Quote{" +
-                "type='" + type + '\'' +
-                ", value=" + value +
-                '}';
-    }
-
-    public String getType() {
-        return type;
-    }
-
-    public void setType(String type) {
-        this.type = type;
-    }
-
-    public Value getValue() {
-        return value;
-    }
-
-    public void setValue(Value value) {
-        this.value = value;
-    }
-
-    public Quote() {
-
-    }
+public record Quote(String type, Value value) {
 }

src/main/java/hello/model/Topic.java

@@ -1,43 +1,4 @@
 package hello.model;
 
-
-public class Topic {
-    private String id;
-    private String subjectName;
-    private String subjectDescription;
-
-    public Topic() {
-    }
-
-    public String getId() {
-        return id;
-    }
-
-    public void setId(String id) {
-        this.id = id;
-    }
-
-    public String getSubjectName() {
-        return subjectName;
-    }
-
-    public void setSubjectName(String subjectName) {
-        this.subjectName = subjectName;
-    }
-
-    public String getSubjectDescription() {
-        return subjectDescription;
-    }
-
-    public void setSubjectDescription(String subjectDescription) {
-        this.subjectDescription = subjectDescription;
-    }
-
-    public Topic(String id, String subjectName, String subjectDescription) {
-        super();
-        this.id = id;
-        this.subjectName = subjectName;
-        this.subjectDescription = subjectDescription;
-    }
-
+public record Topic(String id, String subjectName, String subjectDescription) {
 }

src/main/java/hello/model/Value.java

@@ -1,33 +1,4 @@
 package hello.model;
 
-public class Value {
-    private Long id;
-    private String quote;
-
-    public Value() {
-    }
-
-    @Override
-    public String toString() {
-        return "Value{" +
-                "id=" + id +
-                ", quote='" + quote + '\'' +
-                '}';
-    }
-
-    public Long getId() {
-        return id;
-    }
-
-    public void setId(Long id) {
-        this.id = id;
-    }
-
-    public String getQuote() {
-        return quote;
-    }
-
-    public void setQuote(String quote) {
-        this.quote = quote;
-    }
+public record Value(Long id, String quote) {
 }

src/main/java/hello/service/TopicService.java

@@ -35,8 +35,8 @@ public List<Topic> getAllTopics() {
      * @param id
      * @return
      */
-    public Topic getTopicWithId(String id) {
-        return topics.stream().filter(topic -> topic.getId().equals(id)).findFirst().get();
+    public Optional<Topic> getTopicWithId(String id) {
+        return topics.stream().filter(topic -> topic.id().equals(id)).findFirst();
     }
 
     public void addTopic(Topic topic) {
@@ -50,7 +50,7 @@ public void addTopic(Topic topic) {
      * @param topic
      */
     public void updateTopic(String id, Topic topic) {
-        OptionalInt indexOfElement = IntStream.range(0, topics.size()).filter(index -> id.equals(topics.get(index).getId())).findFirst();
+        OptionalInt indexOfElement = IntStream.range(0, topics.size()).filter(index -> id.equals(topics.get(index).id())).findFirst();
         if (indexOfElement.isPresent()) topics.set(indexOfElement.getAsInt(), topic);
     }
 
@@ -60,7 +60,7 @@ public void updateTopic(String id, Topic topic) {
      * @param id
      */
     public void deleteTopic(String id) {
-        topics.removeIf(topic -> topic.getId().equals(id));
+        topics.removeIf(topic -> topic.id().equals(id));
     }
 
     /**
@@ -70,7 +70,7 @@ public void deleteTopic(String id) {
      * @return
      */
     public List<Topic> filterMinimumLengthForId(Integer minLength) {
-        return printTopicsWithPredicate(topics, topic -> topic.getId().length() > minLength);
+        return printTopicsWithPredicate(topics, topic -> topic.id().length() > minLength);
     }
 
 
@@ -96,7 +96,7 @@ private static List<Topic> printTopicsWithPredicate(List<Topic> topicList, Custo
      * @return
      */
     public List<Topic> sortTopicsWithID() {
-        topics.sort(Comparator.comparing(Topic::getId));
+        topics.sort(Comparator.comparing(Topic::id));
         return topics;
     }
 
@@ -107,7 +107,7 @@ public List<Topic> sortTopicsWithID() {
      * @return
      */
     public String returnAllTopicIDWithStringSlicing() {
-        List<String> topicIds = topics.stream().map(topic -> topic.getId()).collect(Collectors.toList());
+        List<String> topicIds = topics.stream().map(Topic::id).toList();
         return String.join(":", topicIds);
     }
 
@@ -147,13 +147,11 @@ public String splitAllIdWithColonSelectIDWithJavaKeywordThenSortThenJoin(String
      */
     public String findIdHavingCharacter() {
         Pattern pattern = Pattern.compile(".*g.*");
-        Object[] topicIdObjectList = topics.stream().map(topic -> topic.getId()).collect(Collectors.toList()).toArray();
-
-        String[] topicIdList = Arrays.stream(topicIdObjectList).toArray(String[]::new);
+        String[] topicIdList = topics.stream().map(Topic::id).toArray(String[]::new);
 
         return Stream.of(topicIdList)
                 .filter(pattern.asPredicate())
-                .collect(Collectors.toList())
+                .toList()
                 .toString();
     }