Add CustomMetricFilter

src/main/java/me/crespel/karaplan/web/filter/CustomMetricFilter.java

@@ -0,0 +1,38 @@
+package me.crespel.karaplan.web.filter;
+
+import java.io.IOException;
+
+import org.springframework.stereotype.Component;
+import org.springframework.web.filter.GenericFilterBean;
+
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.metrics.LongCounter;
+import io.opentelemetry.api.metrics.Meter;
+import jakarta.servlet.FilterChain;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.ServletRequest;
+import jakarta.servlet.ServletResponse;
+import jakarta.servlet.http.HttpServletRequest;
+
+@Component
+public class CustomMetricFilter extends GenericFilterBean {
+
+	private final LongCounter apiCallsCounter;
+
+	public CustomMetricFilter(OpenTelemetry otel) {
+		Meter meter = otel.getMeter("karaplan");
+		this.apiCallsCounter = meter.counterBuilder("karaplan.api.calls").setDescription("Number of KaraPlan API calls").build();
+	}
+
+	@Override
+	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
+		HttpServletRequest httpRequest = (HttpServletRequest) request;
+		if (httpRequest.getRequestURI() != null && httpRequest.getRequestURI().startsWith("/api/")) {
+			Attributes attrs = Attributes.builder().put("method", httpRequest.getMethod()).build();
+			apiCallsCounter.add(1, attrs);
+		}
+		chain.doFilter(request, response);
+	}
+
+}