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Java Microservices: A Practical Guide

You can use this guide to understand what Java microservices are, how you will develop and create them. And also get an overview of libraries for developing Java microservices.


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Content



The basics of Java microservices


To get a real idea of ​​Java microservices, it makes sense to start with the very basics: the infamous monolith in Java, what it is and what its advantages or disadvantages are.


What is a Java monolith?


Imagine that you are working for a bank or a fintech startup. You provide users with a mobile application that they can use to open a new bank account.


This Java code requires a controller class, which, simplifiedly , looks something like the one shown below.


@Controller
class BankController {

    @PostMapping("/users/register")
    public void register(RegistrationForm form) {
        validate(form);
        riskCheck(form);
        openBankAccount(form);
        // etc..
    }
}

Do you want to:


  1. Validate the registration form.
  2. Check the risk at the user's address to decide whether you want to open a bank account for him or not.
  3. Open bank account

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@Controller
class BankController {

    @Autowired
    private HttpClient httpClient;

    @PostMapping("/users/register")
    public void register(RegistrationForm form) {
        validate(form);
        httpClient.send(riskRequest, responseHandler());
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        // etc..
    }
}

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@Service
class UserService {

    public void register(User user) {
        String email = user.getEmail();
        String username =  email.substring(0, email.indexOf("@"));
        // ...
    }
}

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class UserService {

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        // ...
    }
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class BillingService {

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     public void bill(User user, Plan plan) {
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        rabbitTemplate.convertAndSend(exchange, routingkey, invoice);
        // ...
    }
}

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@Controller
class LoginController {

    // ...

    @PostMapping("/login")
    public boolean login(String username, String password) {
        User user = userDao.findByUserName(username);
        if (user == null) {
            // handle non existing user case
            return false;
        }
        if (!user.getPassword().equals(hashed(password))) {
            // handle wrong password case
            return false;
        }
        // 'Yay, Logged in!';
        // set some cookies, do whatever you want
        return true;
    }
}

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How many database connections should your Java monolith (connection pool) open on your database server?


Why? How many active users can (approximately) scale your monolith at the same time?


Answer


Leave your answer to these questions in the comments section. I look forward to all the answers.


Now make your choice yourself


If you are still here with me: Thanks for reading!

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