Modularity and Decoupling, The Right Way

Creating and maintaining a Java codebase is not an easy task, especially with a codebase with thousands of tests. We often try to solve this problem with new libraries, frameworks and even new languages that can create a false sense of decoupling and modularity.
But the answer is not in the libraries, nor in the frameworks. The answer is in the core of the Java language itself and it has been there since the early stages.
In this talk, you will learn how to organize your codebase in such a way that your code is really decoupled and modularized, and so that you don't have to modify your tests when you decide to change some implementation details (like choosing a different HTTP library or a different database abstraction layer).

Transcript

1. Modularity and
   @CarlosChacin
   Decoupling
   The Right Way
   https://goo.gl/fsmi85
   

   View Slide

2. ● Replace your http client changing only 1 or 2 lines?
   ● Rename an interface method changing only 1 or 2 lines?
   ● Have unit tests without a mocking framework?
   ● Rename an impl without changing mocks in tests?
   ● Hide your implementation details?
   ● Instantiate your application without a DI framework?
   Can you...
   

   View Slide

3. Am I in troubles
   with this new
   codebase?
   

   View Slide

4. find . -name \*.java -exec grep 'public class' {} \; | wc -l
   

   View Slide

5. find . -name \*.java -exec grep 'void' {} \; | wc -l
   

   View Slide

6. package com.example.app.domain;
   public class CacheImpl implements Cache {
   @Inject
   public Cache(final Jedis jedis) {
   }
   }
   @ExtendWith(MockitoExtension.class)
   class CacheImplTest {
   @Test
   void test(@Mock Jedis jedis) throws Exception {
   when(jedis.get(“a”)).thenReturn(“b”);
   assertThat(cache.get(“a”)).isEqualTo(“b”);
   verify(jedis).get(“a”);
   }
   }
   

   View Slide

7. Decoupling
   

   View Slide

8. One class depends on
   another
   

   View Slide

9. We need to test one class
   

   View Slide

10. Now we have ...
    

    View Slide

11. How we usually
    “decouple”?
    

    View Slide

12. How we usually
    “decouple”?
    

    View Slide

13. View Slide

14. 3 classes instead of 2?
    

    View Slide

15. And to test it ...
    

    View Slide

16. Example App
    

    View Slide

17. View Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    

    View Slide

18. View Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    

    View Slide

19. View Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    @Inject @Inject
    @Inject
    @Inject
    @Inject
    @Inject
    

    View Slide

20. Device Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    @Inject @Inject
    @Inject
    @Inject
    @Inject
    @Inject
    

    View Slide

21. Request key
    In Cache? Get from DB
    Return value Save on Cache
    YES
    NO
    

    View Slide

22. Modularizing
    Packaging
    

    View Slide

23. View Slide

24. View Slide

25. View Slide

26. Device Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    @Inject @Inject
    @Inject
    @Inject
    @Inject
    @Inject
    

    View Slide

27. public interface CustomerCache {
    void saveToCache(final Customer customer);
    Optional getFromCache(final UUID id);
    void method1();
    String method2();
    }
    

    View Slide

28. public interface CustomerCache {
    void saveToCache(final Customer customer);
    Optional getFromCache(final UUID id);
    void method1();
    String method2();
    }
    @Alternative
    public class FileSystemCache implements CustomerCache {
    @Override
    public void saveToCache(Customer customer) {
    System.out.println("SAVED TO FILE SYSTEM");
    }
    @Override
    public Optional getFromCache(UUID id) {
    System.out.println("RETRIEVED FROM FILE SYSTEM");
    return Optional.empty();
    }
    @Override
    public void method1() {}
    @Override
    public String method2() { return null; }
    }
    

    View Slide

29. Device Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    @Inject @Inject
    @Inject
    @Inject
    @Inject
    @Inject
    

    View Slide

30. public interface CustomerRepository {
    public void saveToDb(final Customer customer);
    public Optional getFromDb(final UUID id);
    public void method1();
    public String method2();
    }
    

    View Slide

31. public interface CustomerRepository {
    public void saveToDb(final Customer customer);
    public Optional getFromDb(final UUID id);
    public void method1();
    public String method2();
    }
    @Alternative
    public class DbRepository implements CustomerRepository {
    @Override
    public void saveToDb(Customer customer) {
    System.out.println("SAVED TO DATABASE");
    }
    @Override
    public Optional getFromDb(UUID id) {
    System.out.println("RETRIEVED FROM DATABASE");
    return Optional.empty();
    }
    @Override
    public void method1() {}
    @Override
    public String method2() { return null; }
    }
    

    View Slide

32. Device Logic
    Cache
    Persistence
    Redis
    File System
    PostgreSQL
    Json API
    CustomerDTO
    @Inject @Inject
    @Inject
    @Inject
    @Inject
    @Inject
    

    View Slide

33. public Optional find(final UUID id) {
    Optional cachedCustomer = this.cache.getFromCache(id);
    if (cachedCustomer.isPresent()) {
    return cachedCustomer;
    } else {
    Optional dbCustomer = this.repository.getFromDb(id);
    if (dbCustomer.isPresent()) {
    this.cache.saveToCache(dbCustomer.get());
    return dbCustomer;
    }
    }
    return Optional.empty();
    }
    

    View Slide

34. public class CustomerEndpoint {
    private final CustomerService service;
    @Inject
    public CustomerEndpoint(final CustomerService service) {
    this.service = service;
    }
    public void create(Customer customer) {
    service.create(customer);
    }
    public Optional find(UUID id) {
    return service.find(id);
    }
    }
    

    View Slide

35. @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

36. Issues
    

    View Slide

37. View Slide

38. View Slide

39. View Slide

40. View Slide

41. View Slide

42. And how do we solve it?
    

    View Slide

43. View Slide

44. Unit Test
    

    View Slide

45. View Slide

46. View Slide

47. View Slide

48. Layers
    Package by Layer
    

    View Slide

49. Data
    Layers
    Package by Layer
    

    View Slide

50. Domain
    Data
    Layers
    Package by Layer
    

    View Slide

51. Presentation
    Domain
    Data
    Layers
    Package by Layer
    

    View Slide

52. Presentation
    Domain
    Data
    Layers
    Package by Layer
    

    View Slide

53. Presentation
    Domain
    Data
    Layers
    Package by Layer
    

    View Slide

54. Presentation
    Domain
    Data
    Layers
    Package by Layer
    

    View Slide

55. Presentation
    Domain
    Data
    Layers
    Package by Layer Modularized by Speculation
    Splitted before is too big
    

    View Slide

56. Presentation
    Domain
    Data
    Layers
    Layers
    Package by Feature
    Package by Layer
    

    View Slide

57. Presentation
    Domain
    Data
    Layers
    Layers
    Package by Feature
    Package by Layer
    

    View Slide

58. Presentation
    Domain
    Data
    Layers
    Layers
    Package by Feature
    Package by Layer
    

    View Slide

59. Presentation
    Domain
    Data
    Layers
    Layers
    Package by Feature
    Package by Layer
    

    View Slide

60. Presentation
    Domain
    Data
    Layers
    Layers
    Package by Feature
    Package by Layer
    

    View Slide

61. Presentation
    Domain
    Data
    Layers
    Layers
    Package by Feature
    Package by Layer
    

    View Slide

62. Layers
    Package by Feature
    Modularized by cohesiveness
    Splitted after is too big
    

    View Slide

63. Presentation
    Domain
    Data
    

    View Slide

64. Let’s fix it
    

    View Slide

65. Package by Feat.
    

    View Slide

66. Do we know
    what is this app
    about?
    

    View Slide

67. View Slide

68. View Slide

69. View Slide

70. View Slide

71. View Slide

72. View Slide

73. Fix Visibility
    

    View Slide

74. public interface Cache {}
    public final class Customer {}
    public final class CustomerEndpoint {}
    public interface CustomerEndpointFactory {}
    public final class DbRepository {}
    public final class FileSystemCache {}
    public final class HttpRepository {}
    public final class RedisCache {}
    public interface Repository {}
    public final class Service {}
    

    View Slide

75. public interface Cache {}
    public final class Customer {}
    public final class CustomerEndpoint {}
    public interface CustomerEndpointFactory {}
    public final class DbRepository {}
    public final class FileSystemCache {}
    public final class HttpRepository {}
    public final class RedisCache {}
    public interface Repository {}
    public final class Service {}
    

    View Slide

76. public interface Cache {}
    public final class Customer {}
    public final class CustomerEndpoint {}
    public interface CustomerEndpointFactory {}
    public final class DbRepository {}
    public final class FileSystemCache {}
    public final class HttpRepository {}
    public final class RedisCache {}
    public interface Repository {}
    public final class Service {}
    

    View Slide

77. public interface Cache {}
    public final class Customer {}
    public final class CustomerEndpoint {}
    public interface CustomerEndpointFactory {}
    public final class DbRepository {}
    public final class FileSystemCache {}
    public final class HttpRepository {}
    public final class RedisCache {}
    public interface Repository {}
    public final class Service {}
    

    View Slide

78. View Slide

79. Decoupling
    

    View Slide

80. View Slide

81. public class CustomerService {
    private final CustomerRepository repository;
    private final CustomerCache cache;
    @Inject
    public CustomerService(final CustomerRepository repository, final CustomerCache cache) {
    this.repository = repository;
    this.cache = cache;
    }
    public void create(final Customer customer) {
    this.repository.saveToDb(customer);
    this.cache.saveToCache(customer);
    }
    public Optional find(final UUID id) {
    final Optional cachedCustomer = this.cache.getFromCache(id);
    if (cachedCustomer.isPresent()) {
    return cachedCustomer;
    } else {
    final Optional dbCustomer = this.repository.getFromDb(id);
    if (dbCustomer.isPresent()) {
    this.cache.saveToCache(dbCustomer.get());
    return dbCustomer;
    }
    }
    return Optional.empty();
    }
    }
    

    View Slide

82. public class CustomerService {
    private final CustomerRepository repository;
    private final CustomerCache cache;
    @Inject
    public CustomerService(final CustomerRepository repository, final CustomerCache cache) {
    this.repository = repository;
    this.cache = cache;
    }
    public void create(final Customer customer) {
    this.repository.saveToDb(customer);
    this.cache.saveToCache(customer);
    }
    public Optional find(final UUID id) {
    final Optional cachedCustomer = this.cache.getFromCache(id);
    if (cachedCustomer.isPresent()) {
    return cachedCustomer;
    } else {
    final Optional dbCustomer = this.repository.getFromDb(id);
    if (dbCustomer.isPresent()) {
    this.cache.saveToCache(dbCustomer.get());
    return dbCustomer;
    }
    }
    return Optional.empty();
    }
    }
    

    View Slide

83. public class CustomerService {
    private final CustomerRepository repository;
    private final CustomerCache cache;
    @Inject
    public CustomerService(final CustomerRepository repository, final CustomerCache cache) {
    this.repository = repository;
    this.cache = cache;
    }
    public void create(final Customer customer) {
    this.repository.saveToDb(customer);
    this.cache.saveToCache(customer);
    }
    public Optional find(final UUID id) {
    final Optional cachedCustomer = this.cache.getFromCache(id);
    if (cachedCustomer.isPresent()) {
    return cachedCustomer;
    } else {
    final Optional dbCustomer = this.repository.getFromDb(id);
    if (dbCustomer.isPresent()) {
    this.cache.saveToCache(dbCustomer.get());
    return dbCustomer;
    }
    }
    return Optional.empty();
    }
    }
    

    View Slide

84. @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

85. @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

86. View Slide

87. Why do we need it?
    

    View Slide

88. @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

89. @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

90. var cache = new Cache() {
    @Override
    public void saveToCache(Customer customer) {}
    @Override
    public Optional getFromCache(UUID id) {
    return Optional.empty();
    }
    @Override
    public void method1() {}
    @Override
    public String method2() { return null; }
    };
    @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

91. var cache = new Cache() {
    @Override
    public void saveToCache(Customer customer) {}
    @Override
    public Optional getFromCache(UUID id) {
    return Optional.empty();
    }
    @Override
    public void method1() {}
    @Override
    public String method2() { return null; }
    };
    @Test
    @DisplayName("return customer from db when not present in cache")
    void return_customer_from_db_when_not_present_in_cache(
    @Mock CustomerRepository repository,
    @Mock CustomerCache cache) throws Exception {
    // Given
    var customer = Customer.create(id, id.toString());
    when(cache.getFromCache(id)).thenReturn(Optional.empty());
    when(repository.getFromDb(id)).thenReturn(Optional.of(customer));
    // When
    var sut = new CustomerService(repository, cache);
    // Then
    assertThat(sut.find(id)).contains(Customer.create(id, id.toString()));
    verify(cache).saveToCache(customer);
    }
    

    View Slide

92. Are we really
    decoupled?
    

    View Slide

93. View Slide

94. View Slide

95. SAM
    

    View Slide

96. public interface Function {
    R apply(T t);
    }
    public interface Consumer {
    void accept(T t);
    }
    public interface Supplier {
    T get();
    }
    

    View Slide

97. public interface Function {
    R apply(T t);
    }
    public interface Consumer {
    void accept(T t);
    }
    public interface Supplier {
    T get();
    }
    Function>
    getFromCache
    Function>
    getFromDb
    Consumer
    saveToCache
    Consumer
    saveToDb
    

    View Slide

98. package java.util.function;
    public interface Function {
    R apply(T t);
    }
    public interface Consumer {
    void accept(T t);
    }
    public interface Supplier {
    T get();
    }
    Function>
    getFromCache
    Function>
    getFromDb
    Consumer
    saveToCache
    Consumer
    saveToDb
    

    View Slide

99. @Inject
    public CustomerService(
    CustomerRepository repository,
    CustomerCache cache) {
    this.repository = repository;
    this.cache = cache;
    }
    What is really required to build this class?
    

    View Slide

100. @Inject
     CustomerService(
     Function> getFromCache,
     Function> getFromDb,
     Consumer saveToDb,
     Consumer saveToCache) {
     // Omitted
     }
     ● No More Coupling with Repository / Cache
     ● We know explicitly what is required from this class
     

     View Slide

101. Removing Mocks
     

     View Slide

102. when(cache.getFromCache(id))
     .thenReturn(Optional.empty());
     when(repo.getFromDb(id))
     .thenReturn(Optional.of(cust));
     

     View Slide

103. var sut = new Service(
     uuid -> Optional.empty(),
     uuid -> Optional.of(customer),
     cust -> {},
     cust -> {}
     );
     ● No More Coupling with Repository / Cache
     ● No more mocks
     ● No more tests refactors because renames in production code
     when(cache.getFromCache(id))
     .thenReturn(Optional.empty());
     when(repo.getFromDb(id))
     .thenReturn(Optional.of(cust));
     

     View Slide

104. var sut = new Service(
     uuid -> Optional.empty(),
     uuid -> Optional.of(customer),
     cust -> {},
     cust -> {}
     );
     ● No More Coupling with Repository / Cache
     ● No more mocks
     ● No more tests refactors because renames in production code
     when(cache.getFromCache(id))
     .thenReturn(Optional.empty());
     when(repo.getFromDb(id))
     .thenReturn(Optional.of(cust));
     

     View Slide

105. var sut = new Service(
     uuid -> Optional.empty(),
     uuid -> Optional.of(customer),
     cust -> {},
     cust -> {}
     );
     ● No More Coupling with Repository / Cache
     ● No more mocks
     ● No more tests refactors because renames in production code
     when(cache.getFromCache(id))
     .thenReturn(Optional.empty());
     when(repo.getFromDb(id))
     .thenReturn(Optional.of(cust));
     

     View Slide

106. var sut = new Service(
     uuid -> Optional.empty(),
     uuid -> Optional.of(customer),
     cust -> {},
     cust -> {}
     );
     ● No More Coupling with Repository / Cache
     ● No more mocks
     ● No more tests refactors because renames in production code
     when(cache.getFromCache(id))
     .thenReturn(Optional.empty());
     when(repo.getFromDb(id))
     .thenReturn(Optional.of(cust));
     

     View Slide

107. public interface AppFactory {
     static CustomerEndpoint endpoint() {
     var dbRepository = new DbRepository();
     var fileSystemCache = new FileSystemCache();
     var service = new Service(
     fileSystemCache::getFromCache,
     dbRepository::getFromDb,
     dbRepository::saveToDb,
     fileSystemCache::saveToCache
     );
     return new CustomerEndpoint(
     service::find,
     service::create
     );
     }
     }
     

     View Slide

108. Recap
     

     View Slide

109. View Slide

110. View Slide

111. View Slide

112. View Slide

113. ● Higher modularity
     ● Easier code navigation
     ● Higher level of abstraction
     ● Separates both features and layers
     ● More readable and maintainable structure
     ● More cohesion
     ● Much easier to scale
     ● Less chance to accidentally modify unrelated classes or files
     ● Much easier to add or remove application features
     By looking at the structure you can already tell
     what the app is all about
     

     View Slide

114. ★ Replace your http client changing only 1 or 2 lines
     ★ Rename an interface method changing only 1 or 2 lines
     ★ Have unit tests without a mocking framework
     ★ Rename an impl without changing mocks in tests
     ★ Hide your implementation details
     ★ Instantiate your application without a DI framework
     Yes you can...
     

     View Slide

115. And it’s easier than you think
     

     View Slide

116. Gracias...
     

     View Slide

117. github.com/cchacin/nomo
     

     View Slide

118. Questions?
     Comments?
     

     View Slide