Convert InputStream into JSON

Question

I am using json-rpc-1.0.jar.Below is my code. I need to convert InputStream object into JSON since the response is in JSON.

I did verify the json response obtained from Zappos API. It is valid.

PrintWriter out = resp.getWriter();
String jsonString = null;
URL url = new URL("http://api.zappos.com/Search?term=boots&key=my_key");
InputStream inputStream = url.openConnection().getInputStream();
resp.setContentType("application/json");

JSONSerializer jsonSerializer = new JSONSerializer();
try {
   jsonString = jsonSerializer.toJSON(inputStream);
} catch (MarshallException e) {
 e.printStackTrace();
    }
out.print(jsonString);

I get the below mentioned exception:

com.metaparadigm.jsonrpc.MarshallException: can't marshall sun.net.www.protocol.http.HttpURLConnection$HttpInputStream
    at com.metaparadigm.jsonrpc.JSONSerializer.marshall(JSONSerializer.java:251)
    at com.metaparadigm.jsonrpc.JSONSerializer.toJSON(JSONSerializer.java:259)
    at Communicator.doGet(Communicator.java:33)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
    at filters.ExampleFilter.doFilter(ExampleFilter.java:149)

Answer 1

Make use of Jackson JSON parser.

Refer - Jackson Home

The only thing you need to do -

ObjectMapper mapper = new ObjectMapper();
Map<String, Object> jsonMap = mapper.readValue(inputStream, Map.class);

Now jsonMap will contain the JSON.

Answer 2

ObjectMapper.readTree(InputStream) easily let's you get nested JSON with JsonNodes.

public void testMakeCall() throws IOException {
    URL url = new URL("https://api.coindesk.com/v1/bpi/historical/close.json?start=2010-07-17&end=2018-07-03");
    HttpURLConnection httpcon = (HttpURLConnection) url.openConnection();
    httpcon.addRequestProperty("User-Agent", "Mozilla/4.0");
    InputStream is = httpcon.getInputStream();

    try {
        ObjectMapper mapper = new ObjectMapper();
        JsonNode jsonMap = mapper.readTree(is);
        JsonNode bpi = jsonMap.get("bpi");
        JsonNode day1 = bpi.get("2010-07-18");

        System.out.println(bpi.toString());
        System.out.println(day1.toString());
    } finally {
        is.close();
    }
}

Result:

{"2010-07-18":0.0858,"2010-07-19":0.0808,...}

0.0858

Answer 3

Better to save memory by having output as Stream<JsonNode>

    private fun InputStream.toJsonNodeStream(): Stream<JsonNode> {
        return StreamSupport.stream(
                Spliterators.spliteratorUnknownSize(this.toJsonNodeIterator(), Spliterator.ORDERED),
                false
        )
    }

    private fun InputStream.toJsonNodeIterator(): Iterator<JsonNode> {
        val jsonParser = objectMapper.factory.createParser(this)

        return object: Iterator<JsonNode> {

            override fun hasNext(): Boolean {
                var token = jsonParser.nextToken()
                while (token != null) {
                    if (token == JsonToken.START_OBJECT) {
                        return true
                    }
                    token = jsonParser.nextToken()
                }
                return false
            }

            override fun next(): JsonNode {
                return jsonParser.readValueAsTree()
            }
        }
    }