public static Analyzer build(final String metricName,
                                 final String filterExpression,
                                 final String expression,
                                 final MeterSystem meterSystem) {
        Expression e = DSL.parse(metricName, expression);
        FilterExpression filter = null;
        if (!Strings.isNullOrEmpty(filterExpression)) {
            filter = new FilterExpression(filterExpression);
        }
        ExpressionParsingContext ctx = e.parse();
        Analyzer analyzer = new Analyzer(metricName, filter, e, meterSystem, ctx);
        analyzer.init();
        return analyzer;
    }
Analyzer analyses DSL expression with input samples, then to generate meter-system metrics.
oap-server/analyzer/meter-analyzer/src/main/java/org/apache/skywalking/oap/meter/analyzer/Analyzer.java