What's the best way to create an InputStream from a Jackson JsonNode?

Question

I would like to find the most clever way to create an InputStream from a JsonNode, of the Java library Jackson.

Until now I have done:

IOUtils.toInputStream(jsonNode.toString());

But this way converts the JsonNode into a String before creating the InputStream.

ex of need:

org.apache.http.entity.InputStreamEntity entity = new InputStreamEntity(IOUtils.toInputStream(jsonNode.toString()));

Answer 1

1. In most cases JSON is written as UTF-8 and you can save some memory, if you directly generate byte array using ObjectMapper.

   ObjectMapper objectMapper = new ObjectMapper();
   JsonNode json = ...; 
   byte[] bytes = objectMapper.writeValueAsBytes(json);
   

   Specifically, Apache HTTP client provides ByteArrayEntity for use with byte array. For other uses, there is a ByteArrayInputStream.

   Of course, ObjectMapper should be created only once and reused.

2. If you really want JSON to be written in a streaming manner, it is possible to use a pair of PipedInputStream and PipedOutputStream, however, as JavaDoc states

   Typically, data is read from a PipedInputStream object by one thread and data is written to the corresponding PipedOutputStream by some other thread. Attempting to use both objects from a single thread is not recommended, as it may deadlock the thread.

   Example:

   ObjectMapper objectMapper = new ObjectMapper();
   JsonNode json = ...; 
   
   PipedInputStream in = new PipedInputStream();
   
   new Thread(() -> {
       try {
           IOUtils.copy(in, System.out);
       } catch (IOException e) {
           ...
       }
   }).start();
   
   try (
       PipedOutputStream out = new PipedOutputStream(in);
       JsonGenerator gen = objectMapper.getFactory().createGenerator(out);
   ) {
       gen.writeTree(json);
   } catch (IOException e) {
       ...
   }