Java parity mob spawning in rivers

In bedrock river biomes only salmon squid and drown can spawn making it impossible to build a hostile mob farm in bedrock over a river. With out a reliable way to determine when a river biome ends it causes an issue with players hostile mob farms. In java all mobs can spawn in a river biome if given a spawnable block and meeting the criteria for mob spawning. I would very much appreciate seeing this as i built a industrial sized hostile mob farm designed to put out 4k items (not a lot incomparison to java mob farms) And it simply does not work because the spawning platforms are at the edge of a river biome.