Sorting & Pagination

---

• Repository must implement PagingAndSortingRepository (JpaRepository already does)
• Example entity:

    @Entity
    @ToString
    @Getter @Setter
    public class Post {
    
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long idOfThis;
    
        private String text;
    
        @CreationTimestamp
        private LocalDateTime created;
    }

Sorting

• Example - Select from Post table, where Post.text contains substring, ordered by Post.text desceding: SQL:

  SELECT * FROM `post` WHERE `text` LIKE '%a%' ORDER BY `text` DESC;

  PostRepository.java:

  List<Post> findAllByTextContains(String substring, Sort sort);

  Usage of Sort:

  List<Post> posts = postRepository.findAllByTextContains("a", Sort.by("text").descending());

  Generated SQL query:

  SELECT
    post0_.id_of_this AS id_of_th1_0_,
    post0_.created AS created2_0_,
    post0_.text AS text3_0_
  FROM
    post post0_
  WHERE
    post0_.text LIKE '%a%' ESCAPE '\'
  ORDER BY post0_.text DESC

Pagination

• Example - Select Posts from table page-by-page - not everything at once, by taking advantage of SQL syntax LIMIT offset, count

  SQL

  SELECT * FROM `post` WHERE `text` LIKE '%a%' LIMIT 0, 10;

  PostRepository.java:

  Page<Post> findAllByTextContains(String substring, Pageable pageable);

  Usage of Pageable:

  Page<Post> posts = postRepository.findAllByTextContains("a", PageRequest.of(0, 5));

  Generated SQL query:

  select post0_.id_of_this as id_of_th1_0_, post0_.created as created2_0_, post0_.text as text3_0_ from post post0_ where post0_.text like '%a%' escape '\\' limit 5;
  select count(post0_.id_of_this) as col_0_0_ from post post0_ where post0_.text like '%a%' escape '\\';

Pagination & Sorting

• Example - Select from Post table, where Post.text contains substring, ordered by Post.text desceding, Post.idOfThis ascending, page-by-page:

  Pageable pageable = PageRequest.of(0, 10, Sort.by("text").descending().and(Sort.by("idOfThis").ascending()));
  Page<Post> posts;
  
  do {
      posts = postRepository.findAllByTextContains(str, pageable);
      posts.forEach(System.out::println);
      // Move to the next page
      pageable = pageable.next();
  
  // Stop when current page == total number of pages
  } while (posts.getTotalPages() > pageable.getPageNumber());

  Generated SQL queries:

  select post0_.id_of_this as id_of_th1_0_, post0_.created as created2_0_, post0_.text as text3_0_ from post post0_ where post0_.text like '%a%' escape '\\' order by post0_.text desc, post0_.id_of_this asc limit 10
  select count(post0_.id_of_this) as col_0_0_ from post post0_ where post0_.text like '%a%' escape '\\'
  select post0_.id_of_this as id_of_th1_0_, post0_.created as created2_0_, post0_.text as text3_0_ from post post0_ where post0_.text like '%a%' escape '\\' order by post0_.text desc, post0_.id_of_this asc limit 10, 10
  select count(post0_.id_of_this) as col_0_0_ from post post0_ where post0_.text like '%a%' escape '\\'
  select post0_.id_of_this as id_of_th1_0_, post0_.created as created2_0_, post0_.text as text3_0_ from post post0_ where post0_.text like '%a%' escape '\\' order by post0_.text desc, post0_.id_of_this asc limit 20, 10

Note

• You don't have to specify overloads for sorting and pagination for already supported methods by PagingAndSortingRepository interface. They are alredy defined:

  Iterable<T> findAll(Sort sort);
  Page<T> findAll(Pageable pageable);

Pagination and Thymeleaf

• Moving on the next page and previous page in view:

  Endpoint:

  model.addAttribute("posts", postRepository.findAll(PageRequest.of(pageNumber, 10));
  model.addAttribute("currentPage", pageNumber);

  View:

  <a th:if="${currentPage > 0}" th:href="@{/show(page=${currentPage - 1})}">Previous</a>
  <a th:if="${currentPage + 1 < posts.totalPages}" th:href="@{/show(page=${currentPage + 1})}">Next</a>

Spring Security Quickguide

• Turn off security: @SpringBootApplication(exclude = SecurityAutoConfiguration.class)
• Build project with Spring security dependency
• Dan Vega's amazing intro to Spring Security

Data model

1. Create entity for storing users, which implements UserDetails`:

   @Entity
   @Getter @Setter
   public class User implements UserDetails {
       ...
       private String username;
   
       @Column(length = 100)
       private String password;
   
       private boolean enabled;
   
       @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
       @JoinTable(
               name = "users_roles",
               joinColumns = @JoinColumn(name = "user_id"),
               inverseJoinColumns = @JoinColumn(name = "role_id")
       )
       private Set<Role> roles = new HashSet<>();
           
       @Override
       public Collection<? extends GrantedAuthority> getAuthorities() {
           return roles.stream()
                   .map(role -> new SimpleGrantedAuthority(role.getName()))
                   .collect(Collectors.toList());
       }
       ...
   }

2. Create entity for users' roles:

   @Entity
   @Getter @Setter
   public class Role {
       @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
       private Long id;
   
       private String name;
   
       @ManyToMany(mappedBy = "roles")
       private List<User> users;
   }

Service layer implementation

3. Implement interface UserDetailsService, which provides UserDetails:

   @Service
   @RequiredArgsConstructor
   public class UserDetailServiceImpl implements UserDetailsService {
       private final UserRepository userRepository;
   
       @Override
       public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
           Optional<User> user = userRepository.findByUsername(username);
   
           if (user.isEmpty()) {
               throw new UsernameNotFoundException(username);
           }
   
           return user.get();
       }
   }

Provide custom web security implementation

4. Provide custom implementation of WebSecurityConfigurerAdapter

   @Configuration
   @EnableWebSecurity
   @RequiredArgsConstructor
   public class SecurityConfiguration extends WebSecurityConfigurerAdapter {
   
       private final UserDetailsService userDetailsService;
   
       @Bean
       public PasswordEncoder encoder() {
           return new BCryptPasswordEncoder();
       }
   
       @Override
       protected void configure(AuthenticationManagerBuilder auth) throws Exception {
           auth.userDetailsService(userDetailsService);
       }
   
       @Override
       protected void configure(HttpSecurity http) throws Exception {
           http
                   .authorizeRequests()
                   .antMatchers("/posts/**").hasRole("USER")
                   .antMatchers("/**").permitAll()
                   .and()
                   .formLogin()
                   .and()
                   .logout();
       }
   }

How to

Log in & Log out

Navigate to /login and /logout.

Register new user

Saving new user is simple. Just make sure to handle password properly:

private final UserRepository userRepository;
private final PasswordEncoder passwordEncoder;

public void registerUser(String username, String password) throws UserAlreadyExistException {
    if (userRepository.findByUsername(username).isPresent()) {
        throw new UserAlreadyExistException(String.format("User %s already exists", username));
    }

    Role role = new Role();
    role.setName("ROLE_USER");

    User user = new User();
    user.setUsername(username);
    user.setEnabled(true);
    user.addRole(role);
    user.setPassword(passwordEncoder.encode(password));

    userRepository.save(user);
}