private FieldExtractor getAnnotationExtractByUrl(Class clazz, Field field) {
        FieldExtractor fieldExtractor = null;
        ExtractByUrl extractByUrl = field.getAnnotation(ExtractByUrl.class);
        if (extractByUrl != null) {
            String regexPattern = extractByUrl.value();
            if (regexPattern.trim().equals("")) {
                regexPattern = ".*";
            }
            fieldExtractor = new FieldExtractor(field,
                    new RegexSelector(regexPattern), new Url(), extractByUrl.notNull(),
                    extractByUrl.multi() || List.class.isAssignableFrom(field.getType()));
            Method setterMethod = getSetterMethod(clazz, field);
            if (setterMethod != null) {
                fieldExtractor.setSetterMethod(setterMethod);
            }
        }
        return fieldExtractor;
    }
The main internal logic of page model extractor.

@author code4crafter@gmail.com <br>
@since 0.2.0
webmagic-extension/src/main/java/us/codecraft/webmagic/model/PageModelExtractor.java