flattr4j is a free open source Java library for using the Flattr API and adding Flattr buttons to JSP web sites.

It primarily targets for business grade Flattr integration, e.g. on servers, web sites and full-featured desktop applications, but it can also be used on Android devices.

flattr4j is actively maintained! The release rate is low because flattr4j is mature and stable, and there have been only very few changes to the Flattr API recently.


  • Lightweight and easy to use
  • Covers the entire Flattr API
  • Also runs on Android
  • JSP tag library for inserting static and javascript Flattr buttons
  • Helps through the OAuth authentication process at Flattr, no OAuth knowledge is needed
  • With Maven and Spring support
  • Spring Social provider available (currently beta)


Examples and How-Tos

  • First Steps: How to use flattr4j at all
  • Open Data API: How to access the Open Services API
  • REST API: How to access the Flattr Services API
  • CRUD: How to Create, Read, Update and Delete Things
  • Async API: How to access Flattr asynchronously



  • Spring: How to integrate flattr4j in Spring
  • Taglib: How to use the JavaScript API and add Flattr buttons to your JSPs
  • Android: How to use flattr4j on Android devices




flattr4j needs at least Java 1.6 or Android API level 8 (earlier levels should work, but are untested).

flattr4j version 2 requires json.org. If you use Maven, the dependency is loaded automatically. Android API provides it, so flattr4j-core does not need additional libraries on Android devices.

Up to version 2.11, flattr4j also required Apache HttpComponents 4.


flattr4j is released under GNU General Public License Version 3, GNU Lesser General Public License Version 3, Apache License 2.0.

flattr4j is not related to or supported by Flattr AB.