[REQ] Java client code that works with Java 8 and little else

[alexec]

I need to generate client for many (100s to 1000s of API specifications) to be used by many (100s to 1000s) of consumers.

• Many of these are on older stacks, e.g. Java 8.
• Variety of platforms, some Spring, some Vert.X, and a mixture of current and older versions.
• Avoid dependency conflicts, i.e. use minimum dependencies.

Describe the solution you'd like

A lowest common denominator client.

Describe alternatives you've considered

I'd use native, but that is Java 11+.

What's the most widely compatible option? Should I write my own using HTTPUrlConnection?

[wing328]

I'd use native, but that is Java 11+.

what about the default which is okhttp-gson? it should work with JDK8

[Eric-Telavox]

Same thing forme, i am sitting with an older code base using Java and i cant i my life get the maven plugin or the cli generator to make me a client that works. Either there is miss matching in file names, packeges or imports.

Maven pluggin 7.0.0 is not able to run under Java 8 så i need to go back to an older version, but still just issues. Spent to much time on this and do someone know if there is a known version and setup for generating a Java client using an OpenApi 3.0.1 spec, using Java 1.8 and Maven.

[alexec]

My conclusion is: Unless you have a need to integrate with a specific framework, use native for Java 11+ and apache-httpclient for Java 8+.

I spend several hours testing out the different Java generator libraries and evaluating them. Here is that tabulated:

I may have made mistakes, please correct and I'll update.

Commentary:

• The java generator has ~14 library options. Python and Javascript have just two, Golang just one. This seems a Java only problem.
• All the generator create between 3k and 6k LOC.
• I focussed on runtime code, test and docs don't count to cost.
• Generated code consists of about 20%-40% files that you will not need (e.g. Android manifests when you're writing a service, Gradle build files when you use Maven).
• Most generate test files, but they always pass, so little need for these.
• Most generate Markdown docs, this duplicates of the source code comments, so little need for these either.
• You cannot choose one library and later easily switch to another because the interfaces are different. We would benefit from a Simple Http Facade for Java (like SLF4J).
• Many use either Apache or OkHttp under the hood.
• Some are more friendly to testing, e.g. by have their ApiClient or DefaultAPI an interface rather than a class.
• Many use SLF4J for logging.
• Most use GSON or Jackson for JSON marshaling.

Here are the runtime dependencies of native:

Here are the runtime dependencies of apache-httpclient:

In this list, I've struck out dependencies that Maven identified as unused. You could probably remove them.

[Eric-Telavox]

@alexec

Awesome writing, thank you. And yes the Java generator feels awful i agree. I am not a fun of Java in the first hand but this have been such a mess to get going. What i ended upp doing is made my self a script that first clean out old generated god, then generate new one with a .openapi-ignore file so it just generates the client code that i want, and some supporting files. And since the Java8 generator is so buggy and not able to place the package and the folder structure in a good way i just used some terminal move command and then som folder cleaning with the script.....

I can see why anyone could use this in a production environment.