This PR is was inspired from some work done on https://github.com/jord1e/graphql-java-asm-datafetcher

While it does not use any of the code, it uses the some of the idea.

That is could you dynamically generate a class that helps you fetch directly via method calls instead of reflection Method.invoke() calls

This uses JavaAssist to generate a peer class for each source class.

The generated class looks much like this

public class GeneratedUniqueName implements ByteCodeFetcher {

public Object fetch(Object sourceObject, String propertyName) {
   if (sourceObject == null) { return null; }
   graphql.schema.bytecode.SettersAndVoidPojo source = (graphql.schema.bytecode.SettersAndVoidPojo) sourceObject;
   if("name".equals(propertyName)) {
      return source.getName();
   } else {
      return null;
   }
}
}

Calling a method directly is 1.7 times after than use the same method.invoke. That sounds like a lot however its very quick so in the schema of all graphql processing its not a lot.

Benchmark                               Mode  Cnt         Score         Error  Units
ByteCodeGen.measureViaGeneratedClass   thrpt   15  67263591.084 ± 1577315.087  ops/s
ByteCodeGen.measureViaReflectedMethod  thrpt   15  39037523.623 ±  975625.383  ops/s

However we do get some improvements in object heavy benchmarks like the introspection one

Benchmark                                      Mode  Cnt  Score   Error  Units
IntrospectionBenchmark.benchMarkIntrospection  avgt   15  0.668 ± 0.069   s/op

vs master

Benchmark                                      Mode  Cnt  Score   Error  Units
IntrospectionBenchmark.benchMarkIntrospection  avgt   15  0.708 ± 0.078   s/op

This needs a few things to be ready.

We would need to shade Java assist - we dont want to expose this out to others.

We need a JVM wide switch to turn this on or off. Like the graphql.schema.PropertyDataFetcherHelper#setUseSetAccessible flag we have today.

I think we might turn if off in a release and let people opt in and then maybe invert that on another release.