Drop outdated readme hiding in java src (#3852)

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/export/README.md

@@ -1,123 +0,0 @@
-# OpenTelemetry metrics export framework
-
-The metrics world split between "pushed based" and "pull based" libraries and backends, and because
-of this, the OpenTelemetry export framework needs to address all the possible combinations.
-
-To achieve the support for "pushed based" and "pull based" libraries the OpenTelemetry defines two
-interfaces that helps with this:
-* MetricProducer - is the interface that a "pull based" library should implement in order to make
-data available to OpenTelemetry exporters.
-* MetricExporter - is an interface that every OpenTelemetry exporter should implement in order to
-allow "push based" libraries to push metrics to the backend.
-
-Here are some examples on how different libraries will interact with pull/push backends.
-
-**Push backend:**
-
-```java
-import io.opentelemetry.sdk.metrics.export.MetricExporter;
-import io.opentelemetry.sdk.metrics.export.MetricProducer;
-
-/**
- * Simple implementation of the MetricExporter that pushes data to the backend.
- */
-public final class PushMetricExporter implements MetricExporter {
-  @Override
-  ResultCode export(Collection<MetricData> metrics) {
-    // A "push based" library calls to export metrics
-    return pushToBackend(metrics);
-  }
-}
-
-/**
- * Class to build and register MeterProvider globally. MeterProvider is
- * initialized with PeriodicMetricReader which wraps the MetricsExporter
- * and automatically reads and exports the metrics every export interval.
- */
-public final class PushExporter {
-  // The number of milliseconds between metric exports.
-  private static final long METRIC_EXPORT_INTERVAL_MS = 800L;
-
-  private final PushMetricExporter metricExporter;
-  // This will be used to create instruments
-  private final SdkMeterProvider meterProvider;
-
-  public PushExporter() {
-    metricExporter = new PushMetricExporter();
-    // Create an instance of PeriodicMetricReaderFactory and configure it
-    // to export via the Metrics exporter
-    MetricReaderFactory periodicReaderFactory =
-        PeriodicMetricReader.create(
-            metricExporter, Duration.ofMillis(METRIC_EXPORT_INTERVAL_MS));
-    meterProvider =
-        SdkMeterProvider.builder()
-            .registerMetricReader(periodicReaderFactory)
-            .buildAndRegisterGlobal();
-  }
-
-  // Can be accessed by any "push based" library to export metrics.
-  public MetricExporter getMetricExporter() {
-    return metricExporter;
-  }
-
-  // GlobalMeterProvider can also be used to achieve the same.
-  public SdkMeterProvider getSdkMeterProvider() {
-    return meterProvider;
-  }
-
-}
-```
-
-**Pull backend:**
-
-```java
-import io.opentelemetry.sdk.metrics.data.MetricData;
-import io.opentelemetry.sdk.metrics.export.MetricExporter;
-import io.opentelemetry.sdk.metrics.export.MetricProducer;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-
-/**
- * Simple implementation of the MetricExporter that stores data in memory and makes them available
- * via MetricProducer interface.
- */
-public final class PullMetricExporter implements MetricExporter, MetricProducer {
-  private final List<MetricData> metricsBuffer = new ArrayList<>();
-
-  @Override
-  synchronized ResultCode export(Collection<MetricData> metrics) {
-    metricsBuffer.addAll(metrics);
-    return ResultCode.SUCCESS;
-  }
-
-  synchronized Collection<MetricData> getAllMetrics() {
-    List<MetricData> ret = metricsBuffer;
-    metricsBuffer = new ArrayList<>();
-    return ret;
-  }
-}
-
-public final class PullExporter {
-  private final PullMetricExporter metricExporter;
-  private final Collection<MetricProducer> producers;
-
-  public PushExporter(Collection<MetricProducer> producers) {
-    metricExporter = new PullMetricExporter();
-    producers = Collections.unmodifiableCollection(new ArrayList<>(producers));
-  }
-
-  // Can be accessed by any "push based" library to export metrics.
-  public MetricExporter getMetricExporter() {
-    return metricExporter;
-  }
-
-  private void onPullRequest() {
-    // Iterate over all producers and the PullMetricExporter and export all metrics.
-    for (MetricProducer metricProducer : producers) {
-      Collection<MetricData> metrics = metricProducer.getAllMetrics();
-      // Do something with metrics
-    }
-  }
-}
-```