Is @Autowired annotation mandatory on constructor in Spring boot

Question

Is it mandatory to put @Autowired if I am using constructor DI?

Answer 1

Is @Autowired annotation mandatory for a constructor?

No.

After Spring 4.3 If your class has only single constructor then there is no need to put @Autowired.

Before Spring 4.3:

package com.example.service;
    
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
    
@Service
public class DatabaseAccountService implements AccountService {
    
    private final RiskAssessor riskAssessor;
    
    @Autowired
    public DatabaseAccountService(RiskAssessor riskAssessor) {
        this.riskAssessor = riskAssessor;
    }
    
    // ...
}

After:

@Service
public class DatabaseAccountService implements AccountService {
    
    private final RiskAssessor riskAssessor;
    
    public DatabaseAccountService(RiskAssessor riskAssessor) {
        this.riskAssessor = riskAssessor;
    }
    
    // ...
}

Extra: With Lombok, after Spring 4.3

With Lombok you can use @RequiredArgsConstructor to make the code even cleaner:

@Service
@RequiredArgsConstructor
public class DatabaseAccountService implements AccountService {
    private final RiskAssessor riskAssessor; 
}