openrtb-core/src/main/java/com/google/openrtb/json/OpenRtbJsonWriter.java
public String writeBidRequest(BidRequest req) throws IOException {
    try (StringWriter writer = new StringWriter()) {
      writeBidRequest(req, writer);
      return writer.toString();
    }
  }
public String writeBidRequest(BidRequest req) throws IOException {
    try (StringWriter writer = new StringWriter()) {
      writeBidRequest(req, writer);
      return writer.toString();
    }
  }
Serializes a {@link BidRequest} to JSON, returned as a {@code String}.