validate if is valite for several output

validate if is valite for several output

https://github.com/apache/incubator-wayang/blob/77a5d3b5854f59b9cad1f9e9921b849ccc5cca58/python/src/pywy/platforms/jvm/execution.py#L80

```python

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from pywy.core import Executor, ChannelDescriptor
from pywy.core import PywyPlan
from pywy.platforms.jvm.channels import DISPATCHABLE_CHANNEL_DESCRIPTOR
from pywy.platforms.jvm.graph import NodeDispatch, WGraphDispatch
from pywy.platforms.jvm.operator import JVMExecutionOperator
from pywy.platforms.jvm.serializable.wayang_jvm_operator import WayangJVMOperator

class JVMExecutor(Executor):

def __init__(self):
super(JVMExecutor, self).__init__()

def execute(self, plan):
pywyPlan: PywyPlan = plan
graph = WGraphDispatch(pywyPlan.sinks)

# TODO get this information by a configuration and ideally by the context
descriptor_default: ChannelDescriptor = DISPATCHABLE_CHANNEL_DESCRIPTOR

def execute(op_current: NodeDispatch, op_next: NodeDispatch):
if op_current is None:
return

jvm_current: JVMExecutionOperator = op_current.current
if jvm_current.outputs == 0:
jvm_current.execute(jvm_current.inputChannel, [])
return

if op_next is None:
return

jvm_next: JVMExecutionOperator = op_next.current
outputs = jvm_current.get_output_channeldescriptors()
inputs = jvm_next.get_input_channeldescriptors()

intersect = outputs.intersection(inputs)
if len(intersect) == 0:
raise Exception(
"The operator(A) {} can't connect with (B) {}, "
"because the output of (A) is {} and the input of (B) is {} ".format(
jvm_current,
jvm_next,
outputs,
inputs
)
)

if len(intersect) > 1:
if descriptor_default is None:
raise Exception(
"The interaction between the operator (A) {} and (B) {}, "
"can't be decided because are several channel availables {}".format(
jvm_current,
jvm_next,
intersect
)
)
descriptor = descriptor_default
else:
descriptor = intersect.pop()

# TODO validate if is valite for several output
jvm_current.outputChannel[0] = descriptor.create_instance()

jvm_current.execute(jvm_current.inputChannel, jvm_current.outputChannel)

jvm_next.inputChannel = jvm_current.outputChannel

graph.traversal(graph.starting_nodes, execute)

magic: JVMExecutionOperator = graph.starting_nodes[0].current

magic.translate_context.generate_request()

```

a881b024a8724f7b7a1f77afa7a269acaf1fa2a1

Start in python/src/pywy/platforms/jvm/execution.py around JVMExecutor.execute and the TODO near line 80. Trace how get_output_channeldescriptors(), outputChannel, and the downstream operator are handled when an operator has several outputs. The issue does not define the expected validation behavior, so done requires agreeing on that rule and confirming the multi-output path handles it.

Written by the indexing model from the issue text.