1hr37mins30secs de SpringBoot

2023-12-26 1595 words 8 minutes views

Contents

SpringBoot 2023

SpringBoot initializr

Dependencies:

SpringBoot DevTools
Spring Web
Spring Data JPA and Hibernate
PostgreSQL Driver

Starting the server

src
  - main
    - java
      - com.example.demo.DemoApplication
    - resources
      - static
      - templates
      - application.properties
  - test
    - java
    - resources

Create a simple API

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@RestController //To Make the class to serve restful endpoint
public class DemoController {}
  @GetMapping //To set Restful endpoint on method
  public List<String> hello() {
    return List.of("Hello", "World");
  }
}

Student Class

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public class Student {
    private Long id;
    private String name;
    private String email;
    private LocalDate dob;
    private Integer age;
}
// No arg constructor
// All args constructor
// constuctor w/ everything but without ID
// Getter & Setter
// toString

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@GetMapping
public List<Student> hello() {
  return List.of(
    new Student(
                1L, 
                "Mariam", 
                "mj@gmail.com", 
                LocalDate.of(2000, Month.FEBRUARY, 16),
                24
               )
  );
}

API Layer

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@RestController
@RequestMapping(path="api/v1/student")
public class StudentController {
  
  private final StudentService studentService;
  @Autowired
  public StudentController(StudentService studentService) {
    this.studentService = studentService;
  }
  
  @GetMapping
  public List<Student> getStudents() {
    
  }
}

Business Layer

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//@Component //To tell spring that this is a bean
@Service //More for semantics, exactly the same as component
public class StudentService {
  public List<Student> getStudents() {
    return List.of(
      new Student(
          1L,
          "chu",
          "cu@gmail",
           LocalDate.of(1998, Month.FEBRUARY, 5),
           26
      )
    );
  }
}

Properties File

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# Application.properties
spring.datasource.url=jdbc:postgresql://localhost:5432/student
spring.datasource.username=
spring.datasource.password=
# create-drop: ensure we have a clean state every time we run the app
spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgresSQLDialect
spring.jpa.properties.hibernate.format_sql=true

Connecting to Database

打開 shell，輸入 psql

\l 可以查看現有的資料庫清單

建立新的資料庫

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CREATE DATABASE student;

\du 可以查看現有角色 role

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	GRANT ALL PRIVILEGES ON DATABASE "student" TO {role_name};

\c student 連線進去此資料庫

\d 確認此資料庫有無relations (如果有app正在存取應該會顯示出來)

Run project -> Hikari-Pool started

JPA and @Entity

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@Entity //For Hibernate
@Table //For table in the datable
public class Student {
  // some fields
  @Id
  @SequenceGenerator(
    name="student_sequence", 
    sequenceName = "student_sequence",
    allocationSize=1)
  @GeneratedValue(
    strategy = GenerationType.SEQUENCE,
    generator = "student_sequence"
  )
  private Long id;
  private String name;
}

JPA repository

Implement data access layer

StudentRepository — 使用 xxx+Repository 命名，當程式要存取資料庫，尤其是使用JPA存取DB的時候

繼承JpaRepository，Generic#1 的 T 放 the type of object that we want this repository to work with；Generic#2 the ID for the type that we want.

@Repository — responsible for data access

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@Repository
public interface StudentRepository extends JpaRepository<Student, Long> {
  
}

在student service 使用student repository

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@Service
public class StudentService {
  private final StudentRepository studentRepository;
  @Autowired
  public StudentService(StudentRepository studentRepository) {
    this.studentRepository = studentRepository;
  }
  
  public List<Student> getStudents() {
    return studentRepository.findAll();
  }
}

Saving Students

建立一個學生配置檔，這樣啟動專案的時候就會將以下資料插入資料庫的table

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@Configuration
public class StudentConfig {
  @Bean
  CommandLineRunner commandLineRunner(StudentRepository repository) {
    return args -> {
      Student mariam = new Student(
                 "Mariam",
                 "mj@gmail.com",
                 LocalDate.of(2000, FEBRUARY, 16)
      );
      Student himmel = new Student(
                 "Himmel",
                 "hj@gmail.com",
                 LocalDate.of(1998, FEBRUARY, 5)
      );
      repository.saveAll(
        List.of(mariam, himmel)
      );
    };
  }
}

@Transient

存入資料庫table時，與其塞入年齡值，選擇直接讓系統藉由生日(dob)計算出年齡

使用 javax.persistence.*，如此以來之後如果把Hibernate換成其它provider，還是能正常運作

標註@Transient的類別欄位：There is no need for you to be a column in our database, meaning that age will be calculated first.

把 age 從 Student constructor 移除之後，在 getAge 方法中修改回傳值 Period.between(this.dob, LocalDate.now()).getYears();

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import javax.persistence.*;
import java.time.LocalDate;

@Entity 
@Table 
public class Student {
  @Id
  @SequenceGenerator(
    name="student_sequence", 
    sequenceName = "student_sequence",
    allocationSize=1)
  @GeneratedValue(
    strategy = GenerationType.SEQUENCE,
    generator = "student_sequence"
  )
  private Long id;
  private String name;
  private String email;
  private LocalDate dob;
  @Transient //This field
  private Integer age;
  
  public Student() {
  }
  public Student(Strng name, String email, LocalDate dob) {
    this.name = name;
    this.email = email;
    this.dob = dob;
  }
  // some getter and setter
  public Integer getAge() {
    return Period.between(this.dob, LocalDate.now()).getYears();
  }
}

PostMapping

Post is used when you want to add new resources to your system. 在這個例子就是新增一筆 Student。

在 StudentController.java 新增一個 registerNewStudent 方法

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@PostMapping
public void registerNewStudent(@RequestBody Student student) {
  studentService.addNewStudent(student);
}

在 StudentService.java 新增 addNewStudent 方法

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public void addNewStudent(Student student) {
  System.out.print(student); //sout
}

右鍵上面的 @PostMapping，點擊 Open in HTTP client

 ---Actions for URL---
 Go to declaration or usages
 Open in HTTP client ✅ click this ✅
 Show all endpoints of module

generated-requests.http

###
POST http://localhost:8080/api/vi/student
CONTENT-TYPE: application/json

{
  "firstName": "Alicia",
  "lastName": "Hadid",
  "email": "ha@gmail.com",
  "password": "passw0rd"
}

寫好 payload 之後，點擊 POST 左邊的綠色play按鈕，Run this request，就可以在 console 查看
步驟3~6也可以改用postman完成

Writing Business Logic

在StudentRepository寫自定義的商業邏輯

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@Repository
public interface StudentRepository extends JpaRepository<Student, Long> {
  //@Query("SELECT s FROM Student s WHERE s.email = ?1")
  Optional<Student> findStudentByEmail(String email);
}

在 StudentService.addNewStudent 方法加入判斷是否有重複 email 的商業邏輯

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public void addNewStudent(Student student) {
  Optional<Student> studentOptional = studentRepository.findStudentByEmail(student.getEmail());
  if (studentOptional.isPresent()) {
    throw new IllegalStateException("email taken"); 
    //could be improvised
  }
  studentRepository.save(student);
}

Testing post request

試著發送email與現有資料一樣的payload，結果發現 status為 500，但 message 是空的 ""

在 application.properties 加入錯誤訊息的顯示

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spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect
spring.jpa.properties.hibernate.format_sql=true

# 顯示 error message 的配置
server.error.include-message=always

Delete student

在 StudentController 加入 deleteStudent 方法

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@DeleteMapping(path = "{studentId}")
public void deleteStudent(
  @PathVariable("studentId") Long studentId) {
  studentService.deleteStudent(studentId);
}

在 StudentService 加入 deleteStudent 方法

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public void deleteStudent(Long studentId) {
  boolean exists = studentRepository.existsById(studentId);
  if (!exists) {
    throw new IllegalStateException(
      "student with id " + studentId + " does not exists");
  }
  studentRepository.deleteById(studentId);
}

測試這個方法，刪除 id 為 1 的學生

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###
DELETE http://localhost:8080/api/v1/student/1

Exercise

PutMapping - to update both name and email。要掛上@Transaction 標註。

StudentController:

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@PutMapping(path="{studentId}")
pubic void updateStudent(@PathVariable("studentId") Long studentId,
                        @RequestParam(required=false) String name,
                        @RequestParam(required=false) String email) {
  studentService.updateStudent(studentId, name, email);
}

StudentService:

When we use @Transactional annotation, the entity goes into managed state (參考 Spring Data JPA course).

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@Transactional
public void updateStudent(Long studentId, String name, String email) {
  Student student = studentRepository.findById(studentId)
    .orElseThrow(() -> new IllegalStateException(
            "student with id " + studentId + " does not exist."));
  //變更名字
  if (name != null && name.length() > 0 &&
      !Objects.equals(student.getName(), name)) {
    student.setName(name);
  }
  // change email
  if (email != null && email.length() > 0 &&
     !Objects.equals(student.getEmail(), email)) {
    Optional<Student> studentOptional = studentRepository.findStudentByEmail(email);
    // check that new email hasn't been taken
    if (studentOptional.isPresent()) {
      throw new IllegalStateException("email taken");
    }
    student.setEmail(email);
  }
}

測試更新一筆資料 request payload

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###
PUT http://localhost:8080/api/v1/student/1?name=Maria
Content-Type: application/json

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###
PUT http://localhost:8080/api/v1/student/1?name=Maria&email=already@gmail.com

10 SpringBoot mistakes

Leaking internals

洩漏 user 不需要知道的訊息，例如 Customer entity 的 password 欄位

方法… 使用 @JsonIgnore
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@Override @JsonIgnore public String getPassword() { return this.password; }

Not using Record … 好東西幹嘛不用

取代 class CustomerResponse

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record CustomerResponse (String name) {

}
// Before appearance of Record
class CustomerResponse {
  String name;
  //...
}

Not using dependency injection correctly

不要再用 new … initialize 物件，改用依賴注入

Beans, they are singleton, which means they are reused all over the shot.

需要有建構子較好，不用加物件的 setter

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public class Test {

  private final CustomerRepository customerRepository;

  //@Autowired ❌
  public Test(CustomerRepository customerRepository) {
    this.customerRepository = customerRepository;	 
  }
  // some codes

//  Setter injection ❌
//  public void setCustomerRepository(CustomerRepository customerRepository) {
//    this.customerRepository = customerRepository;
//  }
}

Separation of misconcern

Controller 不應該直接呼叫 Repository 的方法存許資料庫

Controller 的職責是處理 httpRequest、Service 處理商業邏輯、Repository與資料來源互動

Lack of ErrorHandling

以下程式碼為例，找不到就會拋出錯誤，message=“foo”，但statusCode=500

比較適切的回應是 404 error 才對

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@GetMapping("{id}")
private Customer getCustomer(@PathVariable Integer id) {
  return customerRepository.findById(id)
    .orElseThrow(() -> new RuntimeException("foo"));
}

最佳方式是寫自定義的錯誤處理機制

src.main.java.com.example.exception.ApiError

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package com.example.exception;

import java.time.LocalDateTime;

public record ApiError(String path,
                      String message,
                      int statusCode,
                      LocalDateTime localDateTime) {
}

DefaultExceptionHandler: 負責處理所有不同類型的例外

@ControllerAdvice

@ExcpetionHandler

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@ControllerAdvice
public class DefaultExceptionHandler {

  @ExceptionHandler(ResourceNotFoundException.class)
  public ResponseEntity<ApiError> handleException(ResourceNotFoundException e, HttpServletRequest request) {
    ApiError apiError = new ApiError(
      request.getRequestURI(),
      e.getMessage(),
      HttpStatus.NOT_FOUND.value(),
      LocalDateTime.now()
    );
    return new ResponseEntity<>(apiError, HttpStatus.NOT_FOUND);
  }

  @ExceptionHandler(InsufficientAuthenticationException.class)
  public ResponseEntity<ApiError> handleException(InsufficientAuthenticationException e, HttpServletRequest request) {
    ApiError apiError = new ApiError(
      request.getRequestURI(),
      e.getMessage(),
      HttpStatus.FORBIDDEN.value(),  // there
      LocalDateTime.now()
    );
    return new ResponseEntity<>(apiError, HttpStatus.FORBIDDEN);
  }

  @ExceptionHandler(BadCredentialException.class)
  public ResponseEntity<ApiError> handleException(BadCredentialException e, HttpServletRequest request) {
    ApiError apiError = new ApiError(
      request.getRequestURI(),
      e.getMessage(),
      HttpStatus.UNAUTHORIZED.value(),  // there
      LocalDateTime.now()
    );
    return new ResponseEntity<>(apiError, HttpStatus.UNAUTHORIZED);
  }

 // @ExceptionHandler(Exception.class)
  @ExceptionHandler({Exception.class, RuntimeException.class})
  public ResponseEntity<ApiError> handleException(Exception e, HttpServletRequest request) {
    ApiError apiError = new ApiError(
      request.getRequestURI(),
      e.getMessage(),
      HttpStatus.INTERNAL_SERVER_ERROR.value(),  // there
      LocalDateTime.now()
    );
    return new ResponseEntity<>(apiError, HttpStatus.INTERNAL_SERVER_ERROR);
  }
}

這樣的寫法就不會導致拋出容易使人混淆的 statusCode 了

見上述程式碼最後一個方法 @ExceptionHandler({Exception.class, RuntimeException.class})

Testing (NOOB Level)

@DataJpaTest

@TestContainers

整合測試使用的 @SpringBootTest

Not Using Annotation Validation

使用 Validation 標註可以減少很多 if 判斷

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@GetMapping("{id}")
private void getCustomer(@Validated CustomerRequest customerRequest) {
  // some codes
}

record CustomerRequest (@NonNull String name) {}

使用 @Validated + @NonNull 再加上自定義的 ExceptionHandler 捕獲錯誤，轉換成user看的懂的payload

Don’t log enough
- Know how to log (when to info, debug, warn)
- Don’t log frequently, because it could also impact the response round trip
Using xml to build Spring applications
Immutability