Refactor codebase for Clean Code principles: eliminate duplication, improve clarity

src/main/java/io/spring/Util.java

@@ -1,7 +1,13 @@
 package io.spring;
 
 public class Util {
-  public static boolean isEmpty(String value) {
+  public static boolean isNullOrEmpty(String value) {
     return value == null || value.isEmpty();
   }
+
+  /** @deprecated Use {@link #isNullOrEmpty(String)} instead */
+  @Deprecated
+  public static boolean isEmpty(String value) {
+    return isNullOrEmpty(value);
+  }
 }

src/main/java/io/spring/api/ArticleApi.java

@@ -79,10 +79,8 @@ public ResponseEntity deleteArticle(
   }
 
   private Map<String, Object> articleResponse(ArticleData articleData) {
-    return new HashMap<String, Object>() {
-      {
-        put("article", articleData);
-      }
-    };
+    Map<String, Object> response = new HashMap<>();
+    response.put("article", articleData);
+    return response;
   }
 }

src/main/java/io/spring/api/ArticlesApi.java

@@ -7,6 +7,7 @@
 import io.spring.core.article.Article;
 import io.spring.core.user.User;
 import java.util.HashMap;
+import java.util.Map;
 import javax.validation.Valid;
 import lombok.AllArgsConstructor;
 import org.springframework.http.ResponseEntity;
@@ -29,12 +30,9 @@ public class ArticlesApi {
   public ResponseEntity createArticle(
       @Valid @RequestBody NewArticleParam newArticleParam, @AuthenticationPrincipal User user) {
     Article article = articleCommandService.createArticle(newArticleParam, user);
-    return ResponseEntity.ok(
-        new HashMap<String, Object>() {
-          {
-            put("article", articleQueryService.findById(article.getId(), user).get());
-          }
-        });
+    Map<String, Object> response = new HashMap<>();
+    response.put("article", articleQueryService.findById(article.getId(), user).get());
+    return ResponseEntity.ok(response);
   }
 
   @GetMapping(path = "feed")

src/main/java/io/spring/api/CommentsApi.java

@@ -56,12 +56,9 @@ public ResponseEntity getComments(
     Article article =
         articleRepository.findBySlug(slug).orElseThrow(ResourceNotFoundException::new);
     List<CommentData> comments = commentQueryService.findByArticleId(article.getId(), user);
-    return ResponseEntity.ok(
-        new HashMap<String, Object>() {
-          {
-            put("comments", comments);
-          }
-        });
+    Map<String, Object> response = new HashMap<>();
+    response.put("comments", comments);
+    return ResponseEntity.ok(response);
   }
 
   @RequestMapping(path = "{id}", method = RequestMethod.DELETE)
@@ -85,11 +82,9 @@ public ResponseEntity deleteComment(
   }
 
   private Map<String, Object> commentResponse(CommentData commentData) {
-    return new HashMap<String, Object>() {
-      {
-        put("comment", commentData);
-      }
-    };
+    Map<String, Object> response = new HashMap<>();
+    response.put("comment", commentData);
+    return response;
   }
 }
 

src/main/java/io/spring/api/CurrentUserApi.java

@@ -33,8 +33,8 @@ public ResponseEntity currentUser(
       @AuthenticationPrincipal User currentUser,
       @RequestHeader(value = "Authorization") String authorization) {
     UserData userData = userQueryService.findById(currentUser.getId()).get();
-    return ResponseEntity.ok(
-        userResponse(new UserWithToken(userData, authorization.split(" ")[1])));
+    String token = io.spring.api.security.AuthorizationHeaderParser.extractTokenOrThrow(authorization);
+    return ResponseEntity.ok(userResponse(new UserWithToken(userData, token)));
   }
 
   @PutMapping
@@ -45,14 +45,13 @@ public ResponseEntity updateProfile(
 
     userService.updateUser(new UpdateUserCommand(currentUser, updateUserParam));
     UserData userData = userQueryService.findById(currentUser.getId()).get();
-    return ResponseEntity.ok(userResponse(new UserWithToken(userData, token.split(" ")[1])));
+    String extractedToken = io.spring.api.security.AuthorizationHeaderParser.extractTokenOrThrow(token);
+    return ResponseEntity.ok(userResponse(new UserWithToken(userData, extractedToken)));
   }
 
   private Map<String, Object> userResponse(UserWithToken userWithToken) {
-    return new HashMap<String, Object>() {
-      {
-        put("user", userWithToken);
-      }
-    };
+    Map<String, Object> response = new HashMap<>();
+    response.put("user", userWithToken);
+    return response;
   }
 }

src/main/java/io/spring/api/UsersApi.java

@@ -58,11 +58,9 @@ public ResponseEntity userLogin(@Valid @RequestBody LoginParam loginParam) {
   }
 
   private Map<String, Object> userResponse(UserWithToken userWithToken) {
-    return new HashMap<String, Object>() {
-      {
-        put("user", userWithToken);
-      }
-    };
+    Map<String, Object> response = new HashMap<>();
+    response.put("user", userWithToken);
+    return response;
   }
 }
 

src/main/java/io/spring/api/security/AuthorizationHeaderParser.java

@@ -0,0 +1,26 @@
+package io.spring.api.security;
+
+import java.util.Optional;
+
+public class AuthorizationHeaderParser {
+  private static final String BEARER_PREFIX = "Bearer ";
+  private static final int TOKEN_INDEX = 1;
+
+  public static Optional<String> extractToken(String authorizationHeader) {
+    if (authorizationHeader == null) {
+      return Optional.empty();
+    }
+
+    String[] parts = authorizationHeader.split(" ");
+    if (parts.length < 2) {
+      return Optional.empty();
+    }
+
+    return Optional.ofNullable(parts[TOKEN_INDEX]);
+  }
+
+  public static String extractTokenOrThrow(String authorizationHeader) {
+    return extractToken(authorizationHeader)
+        .orElseThrow(() -> new IllegalArgumentException("Invalid authorization header"));
+  }
+}

src/main/java/io/spring/api/security/JwtTokenFilter.java

@@ -48,15 +48,6 @@ protected void doFilterInternal(
   }
 
   private Optional<String> getTokenString(String header) {
-    if (header == null) {
-      return Optional.empty();
-    } else {
-      String[] split = header.split(" ");
-      if (split.length < 2) {
-        return Optional.empty();
-      } else {
-        return Optional.ofNullable(split[1]);
-      }
-    }
+    return AuthorizationHeaderParser.extractToken(header);
   }
 }

src/main/java/io/spring/application/Page.java

@@ -1,31 +1,36 @@
 package io.spring.application;
 
-import lombok.Data;
-import lombok.NoArgsConstructor;
+import lombok.Getter;
 
-@NoArgsConstructor
-@Data
+@Getter
 public class Page {
+  private static final int DEFAULT_OFFSET = 0;
+  private static final int DEFAULT_LIMIT = 20;
   private static final int MAX_LIMIT = 100;
-  private int offset = 0;
-  private int limit = 20;
+  private static final int MIN_OFFSET = 0;
+  private static final int MIN_LIMIT = 1;
+
+  private final int offset;
+  private final int limit;
+
+  public Page() {
+    this.offset = DEFAULT_OFFSET;
+    this.limit = DEFAULT_LIMIT;
+  }
 
   public Page(int offset, int limit) {
-    setOffset(offset);
-    setLimit(limit);
+    this.offset = validateOffset(offset);
+    this.limit = validateLimit(limit);
   }
 
-  private void setOffset(int offset) {
-    if (offset > 0) {
-      this.offset = offset;
-    }
+  private int validateOffset(int offset) {
+    return Math.max(offset, MIN_OFFSET);
   }
 
-  private void setLimit(int limit) {
-    if (limit > MAX_LIMIT) {
-      this.limit = MAX_LIMIT;
-    } else if (limit > 0) {
-      this.limit = limit;
+  private int validateLimit(int limit) {
+    if (limit < MIN_LIMIT) {
+      return DEFAULT_LIMIT;
     }
+    return Math.min(limit, MAX_LIMIT);
   }
 }

src/main/java/io/spring/application/user/UserService.java

@@ -77,30 +77,31 @@ public boolean isValid(UpdateUserCommand value, ConstraintValidatorContext conte
     String inputUsername = value.getParam().getUsername();
     final User targetUser = value.getTargetUser();
 
-    boolean isEmailValid =
-        userRepository.findByEmail(inputEmail).map(user -> user.equals(targetUser)).orElse(true);
-    boolean isUsernameValid =
-        userRepository
-            .findByUsername(inputUsername)
-            .map(user -> user.equals(targetUser))
-            .orElse(true);
+    boolean isEmailValid = isFieldAvailableForUser(inputEmail, targetUser, userRepository::findByEmail);
+    boolean isUsernameValid = isFieldAvailableForUser(inputUsername, targetUser, userRepository::findByUsername);
+
     if (isEmailValid && isUsernameValid) {
       return true;
-    } else {
-      context.disableDefaultConstraintViolation();
-      if (!isEmailValid) {
-        context
-            .buildConstraintViolationWithTemplate("email already exist")
-            .addPropertyNode("email")
-            .addConstraintViolation();
-      }
-      if (!isUsernameValid) {
-        context
-            .buildConstraintViolationWithTemplate("username already exist")
-            .addPropertyNode("username")
-            .addConstraintViolation();
-      }
-      return false;
     }
+
+    context.disableDefaultConstraintViolation();
+    if (!isEmailValid) {
+      addConstraintViolation(context, "email", "email already exist");
+    }
+    if (!isUsernameValid) {
+      addConstraintViolation(context, "username", "username already exist");
+    }
+    return false;
+  }
+
+  private boolean isFieldAvailableForUser(String fieldValue, User targetUser, java.util.function.Function<String, java.util.Optional<User>> finder) {
+    return finder.apply(fieldValue).map(user -> user.equals(targetUser)).orElse(true);
+  }
+
+  private void addConstraintViolation(ConstraintValidatorContext context, String property, String message) {
+    context
+        .buildConstraintViolationWithTemplate(message)
+        .addPropertyNode(property)
+        .addConstraintViolation();
   }
 }

src/main/java/io/spring/core/article/Article.java

@@ -49,17 +49,23 @@ public Article(
   }
 
   public void update(String title, String description, String body) {
-    if (!Util.isEmpty(title)) {
+    boolean updated = false;
+
+    if (!Util.isNullOrEmpty(title)) {
       this.title = title;
       this.slug = toSlug(title);
-      this.updatedAt = new DateTime();
+      updated = true;
     }
-    if (!Util.isEmpty(description)) {
+    if (!Util.isNullOrEmpty(description)) {
       this.description = description;
-      this.updatedAt = new DateTime();
+      updated = true;
     }
-    if (!Util.isEmpty(body)) {
+    if (!Util.isNullOrEmpty(body)) {
       this.body = body;
+      updated = true;
+    }
+
+    if (updated) {
       this.updatedAt = new DateTime();
     }
   }

src/main/java/io/spring/core/user/User.java

@@ -27,23 +27,23 @@ public User(String email, String username, String password, String bio, String i
   }
 
   public void update(String email, String username, String password, String bio, String image) {
-    if (!Util.isEmpty(email)) {
+    if (!Util.isNullOrEmpty(email)) {
       this.email = email;
     }
 
-    if (!Util.isEmpty(username)) {
+    if (!Util.isNullOrEmpty(username)) {
       this.username = username;
     }
 
-    if (!Util.isEmpty(password)) {
+    if (!Util.isNullOrEmpty(password)) {
       this.password = password;
     }
 
-    if (!Util.isEmpty(bio)) {
+    if (!Util.isNullOrEmpty(bio)) {
       this.bio = bio;
     }
 
-    if (!Util.isEmpty(image)) {
+    if (!Util.isNullOrEmpty(image)) {
       this.image = image;
     }
   }