Spring RestDocs workaround for documenting nested arrays in the response

OperationResponseSubsectionPreprocessor.java

/*
 * This provides a workaround for the https://github.com/spring-projects/spring-restdocs/issues/569
 *
 * The basic idea is to create a OperationResponsePreprocessor that will extract
 * a subsection (described by a JSON pointer) from the original OperationResponse and allow
 * to create snippets from it.
 */
@AllArgsConstructor
class OperationResponseSubsectionPreprocessor implements OperationResponsePreprocessor {

    private ObjectMapper objectMapper;

    private String jsonPointer;

    @Override
    public OperationResponse preprocess(final OperationResponse response) {
        try {
            final var originalJson = this.objectMapper.readTree(response.getContent());
            final var subsectionJson = originalJson.at(jsonPointer);
            final var subsectionContent = this.objectMapper.writeValueAsBytes(subsectionJson);
            return new OperationResponseSubsection(response, subsectionContent);
        }
        catch (IOException e) {
            throw new RuntimeException("error while extracting JSON subsection", e);
        }
    }

    @AllArgsConstructor
    private static class OperationResponseSubsection implements OperationResponse {

        private final OperationResponse origin;

        private final byte[] content;

        @Override
        public HttpStatus getStatus() {
            return this.origin.getStatus();
        }

        @Override
        public int getStatusCode() {
            return this.getStatus().value();
        }

        @Override
        public HttpHeaders getHeaders() {
            return this.origin.getHeaders();
        }

        @Override
        public byte[] getContent() {
            return this.content;
        }

        @Override
        public String getContentAsString() {
            return new String(this.getContent());
        }
    }
}