GraphQL for Java Developers: 04 - Data Fetchers

A tutorial on implementing GraphQL data fetchers in Java using Spring for GraphQL. Covers creating a controller with @QueryMapping and @SchemaMapping annotations to bind schema fields to Java methods, using the GraphiQL explorer to test queries, handling arguments with @Argument, defining input types vs output types, and implementing a mutation to add new records. Demonstrates querying a list of books, fetching a single book by ID, and adding a book via mutation with a BookInput record.