How to Add Token Swaps to Java Spring Boot

Java runs the financial world. With over 90% of Fortune 500 companies using Java and the language holding steady at third in the TIOBE Index with an 8.71% rating , it remains the default for enterprise backend systems. Now those same systems are moving on-chain: 84% of fintech companies include blockchain in their payment infrastructure , and enterprise blockchain spending hit $19 billion in 2025 . This guide shows you how to add token swap functionality to a Spring Boot application using a free REST API that requires no SDK, no API key, and no account. You send a GET request, receive executable calldata, and broadcast it to the blockchain. What You'll Need Java 17+ (LTS recommended) Spring Boot 3.x with spring-boot-starter-webflux (for WebClient) Jackson (included with Spring Boot) for JSON deserialization A wallet address for the sender parameter (the API returns calldata scoped to this address) No API key — the swap API is free and supports 46 EVM chains Add the WebFlux starter to y