Fixing Moco API POST JSON Parameter Extraction with a Custom JsonExtractor

During API virtualization with Moco, the example provided in the official documentation only supports extracting query parameters, which means a POST request that sends JSON data cannot be processed correctly.

The original ParamRequestExtractor class extends HttpRequestExtractor<String[]> and retrieves values from request.getQueries(), which works for URL‑encoded query strings but not for JSON payloads.

To solve this, a new JsonExtractor class is implemented. It reads the request content via request.getContent().toString(), parses the string into a JSONObject, extracts the value associated with the specified key, and returns it as a String[]. If parsing fails, an empty string array is returned.

public class JsonExtractor extends HttpRequestExtractor<String[]> {
    private final String param;
    public JsonExtractor(final String param) { this.param = param; }
    @Override
    protected Optional<String[]> doExtract(HttpRequest request) {
        try {
            String s = request.getContent().toString();
            String value = JSONObject.fromObject(s).getString(param);
            return fromNullable(new String[]{value});
        } catch (Exception e) {
            return fromNullable(new String[]{""});
        }
    }
    public static RequestExtractor<String[]> queryJson(final String param) {
        return new JsonExtractor(checkNotNullOrEmpty(param, "参数不能为空！"));
    }
}

In Groovy scripts, two helper methods are added:

/** get request parameter equality for GET */
static RequestMatcher eqArgs(String key, String value) {
    eq query(key), value
}
/** post request JSON parameter equality */
static RequestMatcher eqParams(String key, String value) {
    eq queryJson(key), value
}

These methods allow test definitions to compare query parameters ( eqArgs) and JSON body parameters ( eqParams) directly.

Groovy, being a JVM‑based dynamic language, offers strong Java compatibility—most Java files can be renamed to .groovy and compiled without changes, and vice‑versa. This compatibility reduces learning costs and enables seamless use of Java libraries. Modern IDEs such as IntelliJ provide robust Groovy support, and build tools like Gradle (which is Groovy‑based) often feel more convenient than Maven.