[Client] Java Client Add Pojo Support

[polyzos]

Search before asking

• I searched in the issues and found nothing similar.

Description

#1404 introduced a RowConverterUtils to handle the conversion between InternalRow <> POJOs.

Next, we need to use these utilities to allow the users to work with POJOs directly. For example

AppendWriter<User> writer = table.newAppend().createWriter(User.class);
User u = new User(1, "John");
writer.append(u)

We should handle the AppendWriter, UpsertWriter, the LogScanner and also ensure it can be used by operations like lookups, projections, and partial updates.

Willingness to contribute

• I'm willing to submit a PR!

[gyang94]

Is anyone working on this? If not, I'd like to take it.
Thinking: just leverage the existing PojoToRowConverter to convert a pojo object into a row in the writer.

[polyzos]

Hi @gyang94 👋 this issue has been addressed here #1404, but it is for internal use. The next step now is to add this to the java api directly, so users can write POJOS directly, and the work introduced in the PR above can take care of the conversion.

[gyang94]

Hi @polyzos got it, thanks for the explanation. Now we are going to add upsert(T record) and delete(T record) in UpsertWriter interfaces to allow users to input a pojo object directly, instead of manually convert pojo to row.
So what's the next for this issue? Directly implement these functions based on utils in #1404 , or design the interfaces and details first as Jark's comment have another design/FIP to do the final API expose. ?

[polyzos]

The two main steps should be:

1. to make the APIs - TableWriter and related implementations - generic
2. Provide implementations for the related API based on the converter

I'm not sure if we need a FIP here. To me, it seems like there is no design change, but rather it's about making the existing ones more generic. @wuchong WDTY?