Provide Stream output for transformers

[snuyanzin]

The problem with current method like net.datafaker.transformations.JsonTransformer#generate(net.datafaker.transformations.Schema<IN,?>, int) it generates the whole String and then returns it. As a result for bigger numbers it consumes larger amount of memory and e.g. such test fails with OutOfMemory

@Test
    void test2() {
        BaseFaker faker = new BaseFaker(new Random(10L));
        Schema<Object, ?> schema = Schema.of(
            field("Text", () -> faker.name().firstName()),
            field("Bool", () -> faker.name().lastName())
        );

        JsonTransformer<Object> transformer = JsonTransformer.builder().build();
        String json = transformer.generate(schema, 50_000_000);
        System.out.println(json);
    }

There is not so much we can do about this method since anyway with such approach we need somehow to store that giant string value.

Another approach is instead of generation the final string value we could generate a stream of values and return it.

[snuyanzin]

partially covered with https://github.com/datafaker-net/datafaker/pull/1177 however not all formats are supported yet

[RVRhub]

Do I understand correctly that this proposal suggests implementing a solution similar to the one used for JsonTransformer, but also for:

• XmlTransformer
• JavaObjectTransformer
• SqlTransformer

[snuyanzin]

yes you are right

[gatear]

My PR covers the SQL transformer support https://github.com/datafaker-net/datafaker/pull/1264

[gatear]

Also a PR for JavaObjectTransformer https://github.com/datafaker-net/datafaker/pull/1313