public SamplingPolicySettings readSettings() {
        SamplingPolicySettings samplingPolicySettings = new SamplingPolicySettings();
        if (Objects.nonNull(yamlData)) {
            readDefaultSamplingPolicy(samplingPolicySettings);
            readServicesSamplingPolicy(samplingPolicySettings);
        }
        return samplingPolicySettings;
    }
Read policy config file to {@link SamplingPolicySettings}
oap-server/analyzer/agent-analyzer/src/main/java/org/apache/skywalking/oap/server/analyzer/provider/trace/sampling/SamplingPolicySettingsReader.java