When specify exporter-jar by -Dotel.exporter.jar, the OtlpGrpcSpanExporter and OtlpGrpcMetricExporter are also installed

[lshangq]

Describe the bug
When specify exporter-jar by -Dotel.exporter.jar, the OtlpGrpcSpanExporter and OtlpGrpcMetricExporter are also installed.

logs as below
[grpc-default-executor-2] WARN io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporter - Failed to export spans. Error message: UNAVAILABLE: io exception
[grpc-default-executor-1] WARN io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporter - Failed to export metrics

Steps to reproduce
java -javaagent:path/to/opentelemetry-javaagent-all.jar
-Dotel.exporter.jar=path/to/external-exporter.jar
-jar myapp.jar

What did you expect to see?
When specify exporter-jar by -Dotel.exporter.jar, the default exporter includes OtlpGrpcSpanExporter and OtlpGrpcMetricExporter are not installed except for explict specification.

What did you see instead?
When specify exporter-jar by -Dotel.exporter.jar, the OtlpGrpcSpanExporter and OtlpGrpcMetricExporter are also installed.
What version are you using?
v0.15.0

Environment
openjdk version "1.8.0_202
OS: centos7.3

Additional context
Add any other context about the problem here.

[anuraaga]

This is definitely a change in behavior we should fix. In the meantime you may want to disable the default exporters with OTEL_TRACE_EXPORTER=none and OTEL_METRICS_EXPORTER=none

[lshangq]

Thanks, will it be fixed before release 1.0.0

[trask]

Closing, as we are moving from otel.exporter.jar to otel.javaagent.extensions in #2442, where this will be possible by providing a custom property source, e.g.

opentelemetry-java-instrumentation/testing/agent-exporter/src/main/java/io/opentelemetry/javaagent/testing/exporter/AgentTestingExporterPropertySource.java

Lines 13 to 22 in 25dd2cf

	@AutoService(PropertySource.class)
	public class AgentTestingExporterPropertySource implements PropertySource {
	@Override
	public Map<String, String> getProperties() {
	Map<String, String> properties = new HashMap<>();
	properties.put("otel.traces.exporter", "none");
	properties.put("otel.metrics.exporter", "none");
	return properties;
	}
	}