使用的对象存储使用的是 Cloudinary 上传图片时文档不完善,通过将图像转为data url解决

感觉突然像是卡住了一样，进入了倦怠期，也许是因为某个问题遇到了两三次还是没记住，让我有些灰心了（10.21）

进度：

update avatar

get user info

show email

get user’s posts and comments

Dependency Injection

The recommended way of dependency injection in Spring Boot is constructor injection. Here’s why it’s preferred and how to implement it:

1. Constructor Injection: This is the most recommended approach. Here’s how it works:

   @Service
   public class UserService {
       private final UserRepository userRepository;
       private final EmailService emailService;
   
       @Autowired // Optional in newer Spring versions
       public UserService(UserRepository userRepository, EmailService emailService) {
           this.userRepository = userRepository;
           this.emailService = emailService;
       }
   
       // Service methods...
   }
   

   Advantages:

   • Promotes immutability (dependencies can be final)
   • Makes dependencies explicit
   • Ensures the bean is fully initialized after construction
   • Easier to test (you can easily provide mock dependencies)
   • Prevents circular dependencies at compile-time

2. Setter Injection: While not as favored as constructor injection, setter injection can be useful in certain scenarios, particularly when dealing with optional dependencies:

   @Service
   public class UserService {
       private UserRepository userRepository;
   
       @Autowired
       public void setUserRepository(UserRepository userRepository) {
           this.userRepository = userRepository;
       }
   
       // Service methods...
   }
   

   Setter injection is less common but can be useful for optional dependencies or when you need to change dependencies at runtime.

3. Field Injection (Not Recommended): As discussed earlier, this method is generally discouraged:

   @Service
   public class UserService {
       @Autowired
       private UserRepository userRepository;
   
       // Service methods...
   }
   

Best Practices:

1. Use constructor injection for required dependencies.
2. Consider setter injection for optional dependencies.
3. Avoid field injection in most cases.
4. Use the @Autowired annotation on constructors (optional in newer Spring versions).
5. Keep your classes focused and try to limit the number of dependencies.

Would you like me to elaborate on any specific aspect of dependency injection or provide a more complex example?

Field Injection (not recommended)

Field injection in Spring Boot is generally not recommended for several reasons:

1. Immutability: Field injection makes it difficult to create immutable objects, as the fields need to be non-final to allow injection.

2. Testability: Classes using field injection are harder to unit test, as you can’t easily inject mock dependencies without using a Spring container or reflection.

3. Dependency hiding: Field injection can hide dependencies, making it less obvious what a class requires to function properly.

4. Circular dependencies: Field injection can more easily lead to circular dependency issues, which are harder to detect and resolve.

5. Inversion of Control (IoC) principle: Field injection violates the IoC principle to some extent, as the class is directly asking for its dependencies rather than having them provided.

6. Reflection use: Spring uses reflection to inject dependencies into private fields, which can have a minor performance impact and bypasses encapsulation.

Instead of field injection, constructor injection is typically recommended as it addresses these issues. It allows for immutable objects, makes dependencies explicit, and facilitates easier testing and better design.

Would you like me to elaborate on any of these points or provide an example of constructor injection?

User Id Exposure

Exposing a backend user ID in frontend code or APIs is generally not a good practice for several reasons, especially in public-facing applications. Here’s why:

Security Risks

• Enumeration Attacks: If user IDs are predictable (like auto-incrementing integers), attackers can guess and try to access other users’ data, leading to potential data breaches.
• User Impersonation: Exposing a backend ID might allow an attacker to impersonate another user if your application doesn’t properly authenticate requests.

Privacy Concerns

• Sensitive Information: In some cases, a user ID may be linked to personal data. Exposing these identifiers could lead to privacy violations, depending on the nature of the application.

Business Logic Exposure

• Insights into Structure: If your backend user IDs reveal too much about your data structure, an attacker could gain insights into how your system is designed, which may make it easier to exploit vulnerabilities.

Alternatives and Best Practices

• Use UUIDs or Random Identifiers: Instead of exposing sequential user IDs, consider using universally unique identifiers (UUIDs) or other random tokens that are harder to predict and manipulate.
• Tokenization: Use session tokens or API tokens that map to a user ID on the backend but don’t directly expose the ID itself.
• Limit Information: Only expose what is absolutely necessary for the frontend or API consumer. If there’s no need to show the user ID, don’t include it.
• Access Control: Ensure proper access control and authentication mechanisms so that even if a user ID is exposed, unauthorized users cannot exploit it.

In summary, it’s a best practice to avoid exposing backend user IDs unless necessary and only if adequate security measures are in place to mitigate risks.