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This question is regarding the better architecture to follow for API Development in Java using any RDBMS database backend.

Currently, we are using the below approach to fetch data from database and passing it to the client.

Here, Once the request is made to the rest controller (e.g. Spring Boot/Java EE), it makes a database procedure call which returns the database cursor. Using this cursor, the data will be parsed row by row and column by column (e.g Spring RowMapper/JDBC) into a list of POJOs. After that a JSON API (e.g. Jackson/GSON) serializes these POJOs to JSON response messages, which is then passed to client through the Rest controller.

We noticed some disadvantages with this approach

  • Performance Issue for large result sets
  • Many populated objects in the heap (too many POJOs) that keeps the garbage collector busy
  • Slow Development time (creating a POJO for every result set)

Now, we have come up with a new approach which increases the performance of the application, reduces the garbage collection and optimizes the development time. With this approach, once the request is made, a database procedure call is made which returns the JSON response using the in-database JSON API features (e.g. Oracle/SQL Server JSON APIs). This JSON Response is returned as a VARCHAR/CLOB and returned to the client using Java Rest controller.

This has been found to be more effective and productive compared to the traditional way of implementation because of the following benefits:

  • Better Performance because the JSON is generated when the data is fetched using the SQL commands
  • Less overhead on the garbage Collection because the serialization happens in the database
  • Fast Development as developers just need to worry about hand-coding their SQLs (at least in our team )

Can anyone please advise if it is better to serialize the data to JSON at database level instead of doing it in Middle Tier? Which is the better architecture ?

  • Since you are already using Spring, why not use an ORM (for example Hibernate) and Spring Data JPA? It will do the conversion to/from POJOs automatically for you, so that you don't need to write / maintain that yourself. Spring Web MVC will also automatically do the conversion to/from JSON for you. – Jesper Feb 27 at 15:15
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There are some downsides to your method.

  1. You could avoid the POJOs simply by serialising the native dataset returned by the database client.

  2. Usually your data structures don't exactly match your database table structure. eg joining tables

  3. Your database server is now doing work that you previously did in your application layer. This is less scaleable

  4. You can't apply any business logic

  5. Some clients might prefer XML

  6. You may have specific serialisation requirements which are hard to deal with on the DB eg type indicators, HATEOS links, versioning

  7. Compile time checks that your json can be deserialised to objects

So it might be faster for the cases where you are just doing CRUD DB operations via an API but its less performant at scale and less flexible.

In the general case it is accepted that you should try to decouple your data layer.

In your specific case maybe you only have a datalayer and are just forced to send queries via an API.

But I would wager that in the long term you will be better off with a decoupled solution.

Also. I would question whether POJO creation/garbage collection is actually a performance issue. Have you measured it?

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