[feature]: Add sampling documentation for java (#4199)

Co-authored-by: opentelemetrybot <[email protected]>
Co-authored-by: Konstantinos Kolios <[email protected]>
Co-authored-by: Austin Parker <[email protected]>
Co-authored-by: Phillip Carter <[email protected]>
Co-authored-by: Fabrizio Ferri-Benedetti <[email protected]>

content/en/docs/languages/java/sampling.md

@@ -0,0 +1,45 @@
+---
+title: Sampling
+weight: 80
+---
+
+[Sampling](/docs/concepts/sampling/) is a process that restricts the amount of
+spans that are generated by a system. Which sampler to use depends on your
+needs. In general, decide which sampler to use at the start of a trace and allow
+the sampling decision to propagate to other services.
+
+A sampler can be set on the tracer provider using the `setSampler` method, as
+follows:
+
+```java
+import io.opentelemetry.sdk.trace.SdkTracerProvider;
+import io.opentelemetry.sdk.trace.samplers.Sampler;
+
+public class Example {
+  public static void main(String[] args) {
+    // Configure the tracer provider with the desired sampler
+    SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
+      .setSampler(Sampler.alwaysOn()) // Set to always sample traces
+      // or
+      .setSampler(Sampler.alwaysOff()) // Set to never sample traces
+      // or
+      .setSampler(Sampler.traceIdRatioBased(0.5)) // Set to sample a fraction of traces
+      .build();
+  }
+}
+```
+
+The `alwaysOn` value means that every span is sampled, while `alwaysOff` means
+that no span is sampled. When you’re getting started, or in a development
+environment, use `alwaysOn`.
+
+Other samplers include:
+
+- `traceIdRatioBased`, which samples a fraction of spans, based on the fraction
+  given to the sampler. If you set `0.5`, half of all the spans are sampled.
+- `parentBased`, which uses the parent span to make sampling decisions, if
+  present. By default, the tracer provider uses a parentBased sampler with the
+  `alwaysOn` sampler.
+
+When in a production environment, consider using the `parentBased` sampler with
+the `traceIdRatioBased` sampler.