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load schema from .sql to create orm mapping in springboot

Is there any way to Load the database schema from .sql or json or textfile to create the ORM mapping with JPA/Hibernate to database in spring-boot while starting up the server.

Spring Boot enables you to use database migration tools such as Liquibase and Flyway, you can read more about that on Spring's official documentation.
Edit: From the docs
85.5 Use a Higher-level Database Migration Tool
Spring Boot supports two higher-level migration tools: Flyway and Liquibase.
85.5.1 Execute Flyway Database Migrations on Startup
To automatically run Flyway database migrations on startup, add the org.flywaydb:flyway-core to your classpath.
The migrations are scripts in the form V__.sql (with an underscore-separated version, such as ‘1’ or ‘2_1’). By default, they are in a folder called classpath:db/migration, but you can modify that location by setting spring.flyway.locations. This is a comma-separated list of one or more classpath: or filesystem: locations. For example, the following configuration would search for scripts in both the default classpath location and the /opt/migration directory:
spring.flyway.locations=classpath:db/migration,filesystem:/opt/migration
You can also add a special {vendor} placeholder to use vendor-specific scripts. Assume the following:
spring.flyway.locations=classpath:db/migration/{vendor}
Rather than using db/migration, the preceding configuration sets the folder to use according to the type of the database (such as db/migration/mysql for MySQL). The list of supported databases is available in DatabaseDriver.
FlywayProperties provides most of Flyway’s settings and a small set of additional properties that can be used to disable the migrations or switch off the location checking. If you need more control over the configuration, consider registering a FlywayConfigurationCustomizer bean.
Spring Boot calls Flyway.migrate() to perform the database migration. If you would like more control, provide a #Bean that implements FlywayMigrationStrategy.
Flyway supports SQL and Java callbacks. To use SQL-based callbacks, place the callback scripts in the classpath:db/migration folder. To use Java-based callbacks, create one or more beans that implement Callback. Any such beans are automatically registered with Flyway. They can be ordered by using #Order or by implementing Ordered. Beans that implement the deprecated FlywayCallback interface can also be detected, however they cannot be used alongside Callback beans.
By default, Flyway autowires the (#Primary) DataSource in your context and uses that for migrations. If you like to use a different DataSource, you can create one and mark its #Bean as #FlywayDataSource. If you do so and want two data sources, remember to create another one and mark it as #Primary. Alternatively, you can use Flyway’s native DataSource by setting spring.flyway.[url,user,password] in external properties. Setting either spring.flyway.url or spring.flyway.user is sufficient to cause Flyway to use its own DataSource. If any of the three properties has not be set, the value of its equivalent spring.datasource property will be used.
There is a Flyway sample so that you can see how to set things up.
You can also use Flyway to provide data for specific scenarios. For example, you can place test-specific migrations in src/test/resources and they are run only when your application starts for testing. Also, you can use profile-specific configuration to customize spring.flyway.locations so that certain migrations run only when a particular profile is active. For example, in application-dev.properties, you might specify the following setting:
spring.flyway.locations=classpath:/db/migration,classpath:/dev/db/migration
With that setup, migrations in dev/db/migration run only when the dev profile is active.
85.5.2 Execute Liquibase Database Migrations on Startup
To automatically run Liquibase database migrations on startup, add the org.liquibase:liquibase-core to your classpath.
By default, the master change log is read from db/changelog/db.changelog-master.yaml, but you can change the location by setting spring.liquibase.change-log. In addition to YAML, Liquibase also supports JSON, XML, and SQL change log formats.
By default, Liquibase autowires the (#Primary) DataSource in your context and uses that for migrations. If you need to use a different DataSource, you can create one and mark its #Bean as #LiquibaseDataSource. If you do so and you want two data sources, remember to create another one and mark it as #Primary. Alternatively, you can use Liquibase’s native DataSource by setting spring.liquibase.[url,user,password] in external properties. Setting either spring.liquibase.url or spring.liquibase.user is sufficient to cause Liquibase to use its own DataSource. If any of the three properties has not be set, the value of its equivalent spring.datasource property will be used.
See LiquibaseProperties for details about available settings such as contexts, the default schema, and others.
There is a Liquibase sample so that you can see how to set things up.
Spring also supports a database initialization on its own, the official docs are here.
Spring Boot can automatically create the schema (DDL scripts) of your DataSource and initialize it (DML scripts). It loads SQL from the standard root classpath locations: schema.sql and data.sql, respectively.

MyBatis Spring DYNAMIC number of multiple databases Java configuration

This is fairly straight forward with a simple Spring DAO approach. However, using MyBatis, is there a way to setup multiple potential datasources?
The best approach I can think of is to use an ArraList of a Bean each containing datasource.driverclass,datasource.url, datasource.username, datasource.password etc.
The values for the datasources are stored in individual properties files. There could be 1 or 10 of these property files (or more).
So for example, one application startup all the property files would be loaded one at a time into an ArrayList. Then, based on the NAME=value line from the property file, we would know which datasource to hit.
So http:localhost:8080/name=db1
... would access all the data from the datasource configured with the name "09". Each property file would contain:
name=db1
datasource.driverclass=jdbc:sqlserver
datasource.url=jdbc:sqlserver://localhost:1433;databaseName=someDBname
datasource.username=user1
datasource.password=pass1
So the identifier here is "name=db1".
Would the best approach from a MyBatis implementation utilise an ArrayList of Beans?

Here are some leads if you want to keep up with multiple DB:
Anyway, I would say datasources shall be managed in the server confiquration instead of in the App.
Then Mybatis main configuration file must be placed in a location added to the classpath, but outside of the app package, because every new datasource must be referenced there inside an environment element.
And for every user request or session (in case of a web app), the configuration will be parsed because SqlSessionFactoryBuilder.build(reader, environment=NAME); must be called to choose the environment (=> the DB).

I ended up using a hierarchical application.yml file detailing the multitenant connection values, based on a selected tenant code.

How can I configure persistence.xml to point to MongoDB

My project uses Morphia to map my Java entities to MongoDB. What I want to achieve is to create a persistence.xml and configure it so that I will not have to configure properties from source code. How can I achieve this ?

Morphia doesn't use persistence.xml. You'll have to use the annotations.

Using persistence.xml to create a Session to query the database?

I am familiar with using Hibernate and the hibernate.cfg.xml file to create a Session.
However, I have a persistence.xml file within my project, not the hibernate.cfg.xml file.
How do I use it to create a Session that I can then use to query my database?

If you want to use persistance.xml you should use EntityManager. How to use EntityManager you can find in Hibernate, JPA – Part 1 tutorial.
The key config file for JPA is persistence.xml. This lives in the
META-INF directory. It details what the persistence driver to use
and what JNDI data source to connect to. Additional properties can
also be specified, in this case we’ll include some Hibernate
properties.
Next pat is about Hibernate, JPA & Spring MVC – Part 2.

Hibernate, load schema from file

In Hibernate, I can use hbm2dll tool to import data files after hibernate generates the schema from my model. This is fine, but I want to load the file with my database schema and make hibernate use that instead of generating one.
Let's say I have some database configured in my hibernate config
<property name="javax.persistence.jdbc.url" value="jdbc:hsqldb:."/>
Now before I run my test I want to load the db with some schema defined in my schema.sql file. And I don't want to use Spring, I know there is support for it there.
I know I could use hibernate.hbm2ddl to generate schema when SessionFactory is created but I'd rather want to load my manually defined schema. Something like <jdbc:embedded-database> from spring-jdbc.
Is there any support for that in Hibernate?

link1 and link2 might help you out.
Also you can set hibernate.hbm2ddl to none, and add your import.sql file in the classpath which will be executed at the server startup.