I've searched and couldn't find anything to suggest that Spring 4.0.0 is not fully backward compatible with Spring 3.x.
Is that indeed the case?
There are few API they have removed in the new version. You would not have any surprise changes with the new version, there could be slight changes in the API. But, you have to watch the deprecated APIs which will be the candidate for removal in the forthcoming versions.
Look at this document , they have included few backward compatibility changes and removal of the APIs.
The backward compatibility for object-mapper option of the and components has beed removed.
But there is not much changes mentioned in the document.
You should be safe if you have updated your third-party dependencies and updated any Spring deprecations in your project. Spring Framework project lead Juergen Hoeller writes in the blog Migrating from Spring Framework 3.2 to 4.0.1:
To a large degree, an upgrade from Spring Framework 3.2 (or earlier) to 4.0.1 should be as straightforward as a change of version numbers in your Maven POMs. Note that you may have to upgrade specific third-party dependencies to a recent enough version (e.g. Hibernate 3.6+, Quartz 1.8+, Jackson 1.8+, Tiles 2.2+)
Read the migration guide on GitHub for details.
I've prepared report on API changes for the Spring releases here: http://abi-laboratory.pro/java/tracker/timeline/spring-framework/
The report includes backward binary- (BC) and source-compatibility (SC) analysis results. The BC between 3.2.16 and 4.0.0 is estimated at 90.08% and SC is estimated at 88.70%.
The report is generated by the japi-compliance-checker tool.
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It should be backward compatible. I recently watched http://oredev.org/2013/wed-fri-conference/spring-4-on-java-8 and recall Juergen Hoeller saying that they designed Spring 4.0 to be easy to upgrade to from 3.2 its around the 47 minute mark in the video.
I take that to mean that there should be no compatibility issues.
Typically any breaking changes or incompatibility would be noted in the documentation. As you can see there is some deprecated code but it looks to be backwards compatible.
来源：https://stackoverflow.com/questions/20593135/spring-4-0-0-backward-compatibility