This guide walks you through the process of creating a Spring application connected to a MySQL Database (as opposed to an in-memory, embedded database, which most of the other guides and many sample applications use). It uses Spring Data JPA to access the database, but this is only one of many possible choices (for example, you could use plain Spring JDBC).
What You Will Build
You will create a MySQL database, build a Spring application, and connect it to the newly created database.
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Note
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MySQL is licensed with the GPL, so any program binary that you distribute with it must use the GPL, too. See the GNU General Public Licence. |
What You Need
Starting with Spring Initializr
You can use this pre-initialized project and click Generate to download a ZIP file. This project is configured to fit the examples in this tutorial.
To manually initialize the project:
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Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you.
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Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Java.
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Click Dependencies and select Spring Web, Spring Data JPA, and MySQL Driver.
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Click Generate.
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Download the resulting ZIP file, which is an archive of a web application that is configured with your choices.
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Note
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If your IDE has the Spring Initializr integration, you can complete this process from your IDE. |
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Note
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You can also fork the project from Github and open it in your IDE or other editor. |
Create the Database
Open a terminal (command prompt in Microsoft Windows) and open a MySQL client as a user who can create new users.
For example, on a Linux system, use the following command;
$ sudo mysql --password|
Note
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This connects to MySQL as root and allows access to the user from all hosts. This
is not the recommended way for a production server.
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To create a new database, run the following commands at the mysql prompt:
mysql> create database db_example; -- Creates the new database
mysql> create user 'springuser'@'%' identified by 'ThePassword'; -- Creates the user
mysql> grant all on db_example.* to 'springuser'@'%'; -- Gives all privileges to the new user on the newly created databaseCreate the application.properties File
Spring Boot gives you defaults on all things. For example, the default database is H2.
Consequently, when you want to use any other database, you must define the connection
attributes in the application.properties file.
Create a resource file called src/main/resources/application.properties, as the
following listing shows:
link:complete/src/main/resources/application.properties[]Here, spring.jpa.hibernate.ddl-auto can be none, update, create, or create-drop.
See the Hibernate documentation for details.
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none: The default forMySQL. No change is made to the database structure. -
update: Hibernate changes the database according to the given entity structures. -
create: Creates the database every time but does not drop it on close. -
create-drop: Creates the database and drops it whenSessionFactorycloses.
You must begin with either create or update, because you do not yet have the database
structure. After the first run, you can switch it to update or none, according to
program requirements. Use update when you want to make some change to the database
structure.
The default for H2 and other embedded databases is create-drop. For other databases,
such as MySQL, the default is none.
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Note
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It is a good security practice to, after your database is in a production state, set
this to none, revoke all privileges from the MySQL user connected to the Spring
application, and give the MySQL user only SELECT, UPDATE, INSERT, and DELETE. You
can read more about this at the end of this guide.
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Create the @Entity Model
You need to create the entity model, as the following listing
(in src/main/java/com/example/accessingdatamysql/User.java) shows:
link:complete/src/main/java/com/example/accessingdatamysql/User.java[]Hibernate automatically translates the entity into a table.
Create the Repository
You need to create the repository that holds user records, as the following listing
(in src/main/java/com/example/accessingdatamysql/UserRepository.java) shows:
link:complete/src/main/java/com/example/accessingdatamysql/UserRepository.java[]Spring automatically implements this repository interface in a bean that has the same name
(with a change in the caseโโโit is called userRepository).
Create a Controller
You need to create a controller to handle HTTP requests to your application, as the
following listing (in src/main/java/com/example/accessingdatamysql/MainController.java) shows:
link:complete/src/main/java/com/example/accessingdatamysql/MainController.java[]|
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The preceding example explicitly specifies POST and GET for the two endpoints.
By default, @RequestMapping maps all HTTP operations.
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Create an Application Class
Spring Initializr creates a simple class for the application. The following listing shows
the class that Initializr created for this example (in
src/main/java/com/example/accessingdatamysql/AccessingDataMysqlApplication.java):
link:initial/src/main/java/com/example/accessingdatamysql/AccessingDataMysqlApplication.java[]For this example, you need not modify the AccessingDataMysqlApplication class.
When you run the application, logging output is displayed. The service should be up and running within a few seconds.
Test the Application
Now that the application is running, you can test it by using curl or some similar tool.
You have two HTTP endpoints that you can test:
GET localhost:8080/demo/all: Gets all data.
POST localhost:8080/demo/add: Adds one user to the data.
The following curl command adds a user:
$ curl http://localhost:8080/demo/add -d name=First -d [email protected]The reply should be as follows:
SavedThe following command shows all the users:
$ curl http://localhost:8080/demo/allThe reply should be as follows:
[{"id":1,"name":"First","email":"[email protected]"}]Make Some Security Changes
When you are on a production environment, you may be exposed to SQL injection attacks. A
hacker may inject DROP TABLE or any other destructive SQL commands. So, as a security
practice, you should make some changes to your database before you expose the application
to your users.
The following command revokes all the privileges from the user associated with the Spring application:
mysql> revoke all on db_example.* from 'springuser'@'%';Now the Spring application cannot do anything in the database.
The application must have some privileges, so use the following command to grant the minimum privileges the application needs:
mysql> grant select, insert, delete, update on db_example.* to 'springuser'@'%';Removing all privileges and granting some privileges gives your Spring application the privileges necessary to make changes to only the data of the database and not the structure (schema).
When you want to make changes to the database:
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Regrant permissions.
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Change the
spring.jpa.hibernate.ddl-autotoupdate. -
Re-run your applications.
Then repeat the two commands shown here to make your application safe for production use again. Better still, use a dedicated migration tool, such as Flyway or Liquibase.
Summary
Congratulations! You have just developed a Spring application that is bound to a MySQL database and is ready for production!
See Also
The following guides may also be helpful: