Wise Compare Service

A Spring Boot service that compares money transfer offers across currencies and providers. The project exposes the same comparison capability through two controller approaches:

• REST API controller
• GraphQL controller

Project overview

The service uses:

• Spring Boot
• Spring Web
• Spring GraphQL
• Java 17+
• Maven Wrapper

The main comparison logic is handled by CompareService, and both controller styles call the same service method for consistent results.

Run the application

From the project root:

./mvnw spring-boot:run

The application runs with:

• REST base path: http://localhost:8082/api
• GraphQL endpoint: http://localhost:8082/api/graphql
• GraphiQL UI: http://localhost:8082/api/graphiql

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1) REST controller approach

The REST implementation is in CompareController and is annotated with @RestController.

Endpoint

GET /api/compare?sendAmount=1000&sourceCurrency=USD&targetCurrency=EUR

Example request

curl "http://localhost:8082/api/compare?sendAmount=1000&sourceCurrency=USD&targetCurrency=EUR"

Response shape

The endpoint returns a ComparisonResponse JSON object containing comparison data such as:

• source and target currency
• provider details
• quotes and rates
• logos and delivery estimates

This is the traditional HTTP-style controller approach, ideal for clients that expect standard REST endpoints and JSON responses.

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2) GraphQL controller approach

The GraphQL implementation is in CompareGqlController and is annotated with @Controller plus Spring GraphQL mapping annotations.

GraphQL schema

The schema is defined in src/main/resources/schema.graphqls and includes the query:

type Query {
  compare(
    amount: Int!
    sourceCurrency: String!
    targetCurrency: String!
  ): ComparisonResponse!
}

Example query

query {
  compare(amount: 1000, sourceCurrency: "USD", targetCurrency: "EUR") {
    amount
    sourceCurrency
    targetCurrency
    providers {
      name
      alias
      type
      quotes {
        rate
        fee
        receivedAmount
      }
    }
  }
}

Example request

curl -X POST "http://localhost:8082/api/graphql" \
  -H "Content-Type: application/json" \
  --data '{
    "query": "query { compare(amount: 1000, sourceCurrency: \"USD\", targetCurrency: \"EUR\") { amount sourceCurrency targetCurrency providers { name alias type quotes { rate fee receivedAmount } } } }"
  }'

This GraphQL approach is useful when you want a single query contract with flexible data selection and a schema-driven API.

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Which approach to use?

• Use the REST controller if you want a simple, resource-based endpoint pattern.
• Use the GraphQL controller if you want flexible querying and schema-driven response selection.

Both approaches use the same underlying CompareService, so the business logic remains consistent while the API exposure differs.