Get started with the basics of Thymeleaf and Spring Boot and how to use them to create scalable applications.

Spring Boot Development for Java Programmers

This module will teach us how to build easily scalable applications with Thymeleaf and Spring Boot. We will combine Thymeleaf and Spring Boot with Spring Data and Spring Security.

This module will give us all the basics for developing an application using Thymeleaf and Spring Boot. Throughout the module, we will build an application of a fictional basketball team called Thyme Wizards. We will also learn to use unit and integration tests to ensure proper code functionality and create a maintainable code base that we can expand upon.

By the end of this module, we will have some great new skills working with the Spring Boot framework, which employers will love.

Building Scalable Applications with Thymeleaf and Spring Boot

## Customizing messages
Using the internationalization support we set up earlier, we can change the error messages to something more user-friendly, and have them translated for each language.

We can change the error message for all validation errors of a certain type (e.g., all `@NotNull` violations) or we can precisely change the message for a single property on a single model attribute.

This is an example of the four options:

NotBlank=The property '{0}' should not be blank.
NotBlank.email=Please enter the email address.
NotBlank.java.lang.String=The string should not be empty.
NotBlank.user.birthday=Please enter the birthday of the user.

* **`NotBlank`**: This will affect all fields from all objects that use the `@NotBlank` validation annotation. The `{0}` is replaced with the name of the field. An example error message would be: 
  ```java
  The property First name should not be blank.
  ```

* **`NotBlank.email`**: This will affect all fields named email from all objects that use the `@NotBlank` validation annotation.
* **`NotBlank.java.lang.String`**: This will affect all fields from all objects that use the `@NotBlank` validation annotation and are of type `java.lang.String`.
* **`NotBlank.user.birthday`**: This message will only be shown for the birthday field of a model
attribute named user that is annotated with `@NotBlank`.

## Applying user-friendly messages approach
Let's apply this to our example by adding the following code to our `messages.properties` file placed at `src/main/resources/i18n/messages.properties`:

# Customizing messages
Using the internationalization support we set up earlier, we can change the error messages to something more user-friendly, and have them translated for each language.

We can change the error message for all validation errors of a certain type (e.g., all `@NotNull` violations) or we can precisely change the message for a single property on a single model attribute.

This is an example of the four options:

* **`NotBlank`**: This will affect all fields from all objects that use the `@NotBlank` validation annotation. The `{0}` is replaced with the name of the field. An example error message would be: 
  ```java
  The property First name should not be blank.
  ```

* **`NotBlank.email`**: This will affect all fields named email from all objects that use the `@NotBlank` validation annotation.
* **`NotBlank.java.lang.String`**: This will affect all fields from all objects that use the `@NotBlank` validation annotation and are of type `java.lang.String`.
* **`NotBlank.user.birthday`**: This message will only be shown for the birthday field of a model
attribute named user that is annotated with `@NotBlank`.

# Applying user-friendly messages approach
Let's apply this to our example by adding the following code to our `messages.properties` file placed at `src/main/resources/i18n/messages.properties`:

Learn how to add customized user-friendly messages on invalid inputs.

What are Spring Boot and Thymeleaf?

Thymeleaf Introduction

Thyme Wizards

Fragments

Layouts

Controllers

Internationalization

Database Connection

Displaying Data

Forms

Data Editing

Implement Deletion of an Entity

Security

Security - Users from Database

Testing

Testing Using Cypress

Various Tips and Tricks - I

Various Tips and Tricks - II

Appendix

Conclusion

Custom Error Messages

Customizing messages