Upgrade to HttpComponents HttpClient 5.5

[sdeleuze]

Per https://hc.apache.org/status.html this is the new stable version + updating the Javadoc link will fix the build.

[the-vj]

Possibly only a theoretical problem, but still wondering, @sdeleuze:

• this is a minor version (not a patch) 3rd party library update for a patch version of Spring framework - does it not go against the rules of dependency management in the Spring ecosystem, while no obvious reason to do so in this case?

• Spring Framework 3.5.1 which will use this version of Spring Framework is not upgrading, and remains on version 5.4.4 - obviously all regression passed, but it sounds a bit more like luck rather than "design"?

[jhoeller]

@the-vj this is just the version that the core framework builds against, not a version that we bring onto anyone's classpath. This ensures that we are forward-compatible with HttpClient 5.5 while not having found any issues with running our support classes against HttpClient 5.4.x at runtime. We also support older HttpClient versions down to 5.1.x with the same arrangement still.

As far as we see, 5.4.x is being immediately superseded by 5.5.x, with no futher 5.4.x maintenance to be expected. So for a long-term supported branch such as Spring Framework 6.2.x, we need to be prepared for applications to use HttpClient 5.5.x - maybe not right now but soon. In such cases, we usually build against the latest version while ensuring runtime compatibility with older versions.

For a comparison, we also build against Hibernate ORM 5.6.x while the primary version used with Spring is Hibernate 6.6 these days. Like with many dependencies, we effectively support a user's version of choice within a range of supported versions.