[fix][java-client] Returns immutable data set when use TableView.

[Technoboy-]

Fixes #14821

Master Issue: #14821

Motivation

Currently TableViewImpl methods that access the underlying map, e.g., TableViewImpl::KeySet() (https://github.com/apache/pulsar/blob/master/pulsar-client/src/main/java/org/apache/pulsar/client/impl/TableViewImpl.java#L141) returns views of the underlying map, which means users could modify the returned value and accidentally change the internal state of TableViewImpl.

It's better to return an immutable set to users.

Documentation

• no-need-doc

[mattisonchao]

@Technoboy-

Can we use Collections.unmodifiableSet() to return an immutable Set?
I'm not very deep in TableView , please let me know what you think if there are any mistakes.
Thanks!

[Technoboy-]

@Technoboy-

Can we use Collections.unmodifiableSet() to return an immutable Set? I'm not very deep in TableView , please let me know what you think if there are any mistakes. Thanks!

My first version is using immutable set like Collections.unmodifiableSet(). But users want to modify the data, and after talking with @nlu90, it's good to return a new data set for them.

[Technoboy-]

@Technoboy-
Can we use Collections.unmodifiableSet() to return an immutable Set? I'm not very deep in TableView , please let me know what you think if there are any mistakes. Thanks!

My first version is using immutable set like Collections.unmodifiableSet(). But users want to modify the data, and after talking with @nlu90, it's good to return a new data set for them.

Change to immutable set