Let's begin by discussing a specific use case. There may arise a situation where we need to dynamically change the DATASOURCE. For instance, let's say you are developing a highly impressive RESTful API, and your clients are local banks. These banks have a preference for using their own integrated databases instead of the default database used by your service. Consequently, you end up with a RESTful API that needs to handle multiple databases.

To differentiate requests coming from different banks, you can utilize information from the request header or path. In Spring 2.0.1, an AbstractRoutingDataSource was introduced, which proves to be quite useful in this scenario. The basic concept is that a routing DataSource acts as an intermediary, allowing the determination of the 'real' DataSource dynamically at runtime.

• Spring Boot 2.2.0
• MySQL
• Spring Data JPA

• We will create two database ( database1 & database2). Each of the database will have one table EMPLOYEE
• We will expose a GET API with a path variable /{bank}/employees. Path variable {bank} will be replaced in run time. Example: -- http://localhost:8080/bank1/employees -- http://localhost:8080/bank2/employees
• If the path variable is bank1 application will serve data from the database1, if it is bank2 then from database2 and so on.

• We will write an interceptor, which will intercept every request and read the path variable, and based on the path variable we will decide which datasoruce to use (at startup one of the datasoruce will be selected as the default datasource)
• We will not let spring boot auto-configuration come our way to configure the data source. So we will disable the data-source and transaction-manager auto-configuration.
• We will configure two data source datasurce1, datasoruce2 and one transactionManager, one entityManagerFactory manually
• We will provide the corresponding property in the application.properties file to configure both data sources. Properties will look like the following:

		spring.datasource.driver-class-name.1=com.mysql.cj.jdbc.Driver 
		spring.datasource.url.1=jdbc:mysql://localhost:3306/database1 
		spring.datasource.username.1=root 
		spring.datasource.password.1=admin 
				 
		spring.datasource.driver-class-name.2=com.mysql.cj.jdbc.Driver 
		spring.datasource.url.2=jdbc:mysql://localhost:3306/database2 
		spring.datasource.username.2=root 
		spring.datasource.password.2=admin 
				 
		database.hibernate.schema_update = update 
		database.hibernate.dialect = org.hibernate.dialect.MySQL5Dialect 
		database.hibernate.show_sql = true 
		database.hibernate.format_sql = true 
				 
		server.port=8080

// database1
create table Employee
(
 id int auto_increment primary key,
 bankName varchar(255) null,
 name varchar(255) null
);
INSERT INTO database1.Employee (id, bankName, name) VALUES (1, 'Bank 1', 'ABC Bank');
// database2
create table Employee
(
 id int auto_increment primary key,
 bankName varchar(255) null,
 name varchar(255) null
);
INSERT INTO database2.Employee (id, bankName, name) VALUES (1, 'Bank 2', 'XYZ Bank');

With bank1 in the path

GET http://localhost:8080/bank1/employees

curl --location --request GET 'http://localhost:8080/bank1/employees'

With bank2 in the path

GET http://localhost:8080/bank2/employees

curl --location --request GET 'http://localhost:8080/bank2/employees'