Develop Reference

get a key value pair from a String json (simple object)

Im trying to get a key:value pair from a simple jsonString to add it after into a memory tab. If facing an issue cause my input is a string. and it looks like my loop isnot able to read the key value pair.
I read many topics about it, and im still in trouble with it. As you can see below
{"nom":"BRUN","prenom":"Albert","date_naiss":"10-10-1960","adr_email":"abrun#gmail.com","titre":"Mr","sexe":"F"}
and my method, find only on object... the result is the same in my loop
public static ArrayHandler jsonSimpleObjectToTab(String data) throws ParseException {
if( data instanceof String) {
final var jsonParser = new JSONParser();
final var object = jsonParser.parse(data);
final var array = new JSONArray();
array.put(object);
final var handler = new ArrayHandler("BW_funct_Struct");
for( KeyValuePair element : array) {
handler.addCell(element);
Log.warn(handler);
}
return handler;
} else {
throw new IllegalArgumentException("jsonSimpleObjectToTab: do not support complex object" + data + "to Tab");
}
}
i also tryed before to type my array as a List, Object etc, without the keyValuePair object, i would appreciate some help.
Thanks again dear StackOverFlowers ;)

You can try this :
const json = '{"nom":"BRUN","prenom":"Albert","date_naiss":"10-10-1960","adr_email":"abrun#gmail.com","titre":"Mr","sexe":"F"}';
map = new Map();
const obj = JSON.parse(json,(key,value) => {
map.set(key,value)
});
and you'll have every pair stored in map

Simply split the whole line at the commas and then split the resulting parts at the colon. This should give you the individual parts for your names and values.
Try:
supposing
String input = "\"nom\":\"BRUN\",\"prenom\":\"Albert\"";
then
String[] nameValuePairs = input.split(",");
for(String pair : nameValuePairs)
{
String[] nameValue = pair.split(":");
String name = nameValue[0]; // use it as you need it ...
String value = nameValue[1]; // use it as you need it ...
}

You can use TypeReference to convert to Map<String,String> so that you have key value pair.
String json = "{\"nom\":\"BRUN\",\"prenom\":\"Albert\",\"date_naiss\":\"10-10-1960\",\"adr_email\":\"abrun#gmail.com\",\"titre\":\"Mr\",\"sexe\":\"F\"}";
ObjectMapper objectMapper = new ObjectMapper();
TypeReference<Map<String,String>> typeReference = new TypeReference<Map<String, String>>() {
};
Map<String,String> map = objectMapper.readValue(json, typeReference);

I just answered a very similar question. The gist of it is that you need to parse your Json String into some Object. In your case you can parse it to Map. Here is the link to the question with my answer. But here is a short version: you can use any Json library but the recommended ones would be Jackson Json (also known as faster XML) or Gson(by Google) Here is their user guide site. To parse your Json text to a class instance you can use ObjectMapper class which is part of Jackson-Json library. For example
public <T> T readValue(String content,
TypeReference valueTypeRef)
throws IOException,
JsonParseException,
JsonMappingException
See Javadoc. But also I may suggest a very simple JsonUtils class which is a thin wrapper over ObjectMapper class. Your code could be as simple as this:
Map<String, Object> map;
try {
map = JsonUtils.readObjectFromJsonString(input , Map.class);
} catch(IOException ioe) {
....
}
Here is a Javadoc for JsonUtils class. This class is a part of MgntUtils open source library written and maintained by me. You can get it as Maven artifacts or from the Github

parsing large JSON with java/GSON, can't read the JSON structure

I'm trying to parse, using Java and GSON, a large (about 10GB) database dump in JSON format from the Musicbrainz.org
the JSON file has this structure. No '[' ']' to indicate that this is gonna be an array of objects, and no ',' between each object. Don't know why, but this JSON file is just like that.
{
"id": "d0ab06e1-751a-414b-a976-da72670391b1",
"name": "Arcing Wires",
"sort-name": "Arcing Wires"
}
{
"id": "6f0c2c16-dd7e-4268-a484-bc7b2ac78108",
"name": "Another",
"sort-name": "Another"
}
{
"id": "e062b6cd-5506-47b0-afdb-72f4279ec38c",
"name": "Agent S",
"sort-name": "Agent S"
}
and this is the code that I'm using:
try(JsonReader jsonReader = new JsonReader(
new InputStreamReader(
new FileInputStream(jsonFilePath), StandardCharsets.UTF_8))) {
Gson gson = new GsonBuilder().create();
jsonReader.beginArray();
while (jsonReader.hasNext()) {
Artist mapped = gson.fromJson(jsonReader, Artist.class);
//TODO do something with the object
}
}
jsonReader.endArray();
}
catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
and the class that I mapped is this:
public class Artist {
#SerializedName("id")
public String id;
#SerializedName("name")
public String name;
#SerializedName("sort-name")
public String sortName;
}
the error I'm getting:
Exception in thread "main" java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $
at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:350)
at DBLoader.parse(DBLoader.java:39)
at DBLoader.main(DBLoader.java:23)
I believe that the GSON expect a different structure from what I declared, but I don't understand how should I define this kind of JSON with no commas and no brackets.
Any clues?
thanks

JSON by default declares one top value only (and yes, this would be a valid JSON document), but there is JSON streaming that uses arbitrary techniques to concatenate multiple JSON elements into a single stream assuming that the stream consumer can parse it (read more). Gson supports a so-called lenient mode that turns off the "one top value only" mode (and does some more things irrelevant to the question) for JsonReader: setLenient. Having the lenient mode on, you can read JSON elements one by one, and it turns out that this mode can be used to parse/read line-delimited JSON and concatenated JSON values since they are simply delimited by zero or more whitespaces that are ignored by Gson (therefore more exotic record separator-delimited JSON and length-prefixed JSON are unsupported). The reason of why it does not work for you is that your initial code assumes that the stream contains a single JSON array (and it does not obviously: it is supposed to be a stream of elements that does not conform the JSON array syntax).
A simple generic JSON stream support might look like this (using Stream API for its more rich API than Iterator has, but it is fine to show an idea, and you can easily adapt it to iterators, callbacks, observable streams, whatever you like):
#UtilityClass
public final class JsonStreamSupport {
public static <T> Stream<T> parse(#WillNotClose final JsonReader jsonReader, final Function<? super JsonReader, ? extends T> readElement) {
final boolean isLenient = jsonReader.isLenient();
jsonReader.setLenient(true);
final Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<T>(Long.MAX_VALUE, Spliterator.ORDERED) {
#Override
public boolean tryAdvance(final Consumer<? super T> action) {
try {
final JsonToken token = jsonReader.peek();
if ( token == JsonToken.END_DOCUMENT ) {
return false;
}
// TODO: read more elements in batch
final T element = readElement.apply(jsonReader);
action.accept(element);
return true;
} catch ( final IOException ex ) {
throw new RuntimeException(ex);
}
}
};
return StreamSupport.stream(spliterator, false)
.onClose(() -> jsonReader.setLenient(isLenient));
}
}
And then:
JsonStreamSupport.<Artist>parse(jsonReader, jr -> gson.fromJson(jr, Artist.class))
.forEach(System.out::println);
Output (assuming Artist has Lombok-generated toString()):
Artist(id=d0ab06e1-751a-414b-a976-da72670391b1, name=Arcing Wires, sortName=Arcing Wires)
Artist(id=6f0c2c16-dd7e-4268-a484-bc7b2ac78108, name=Another, sortName=Another)
Artist(id=e062b6cd-5506-47b0-afdb-72f4279ec38c, name=Agent S, sortName=Agent S)
How many bytes does such an approach, JSON streaming, save so that it is used at the service you're trying to consume? I don't know.

It looks like jsonl format where every line is a valid JSON object. (read more here)
You can read file line by line and convert to object. I think it will works.

Create json object of undefined content

I am working with an exiting API that expects a "Metadata" field as part of its json payload. That "Metadata" field is a json object that is completely free-form. Currently, I need to read this data provided from another source, do some enrichment, then pass it on. I am struggling with how to define this "Metadata" object so that it can be any valid json object. OR, if that field was not provided, an empty json object.
I attempted to use org.json.JSONObject like so.
//meta is the json string read from the db
JSONObject jsonobject = new JSONObject(meta);
message.Metadata = jsonobject;
However, jackson, not unexpectedly, threw a serialization error:
com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.json.JSONObject and no properties discovered...
This is a critical requirement that I'm guessing I am missing some relatively obvious solution to. Any help would be greatly appreciated.
UPDATED FIX
As suggested by #shmosel I just switched the json object to a com.fasterxml.jackson.databind.JsonNode and all works beautifully.
// working code (rough of course)
ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode = null;
try {
rootNode = mapper.readTree(meta);
} catch (IOException e) {
e.printStackTrace();
}
message.Metadata = rootNode;

How to write bytearray to couchdb?

I want to send my object to couchdb using the ektorp java client. But I couldn't write my bytearray value to couchdb properly. My java object as follow:
If I convert bytearray to String:
The metadata value is saved on couchdb as "AgIGZm9vBmJhegA=" (base64), This means that "foobaz". Why is my bytearray value changed?
My example code :
private CouchDbInstance dbInstance;
private CouchDbConnector db;
...
Map<String, Object> doc = new HashMap<>();
doc.put("_id", "foo.com:http/");
byte[] serilazeData = IOUtils.serialize(writer, fieldValue);
doc.put("metadata", serilazeData);
...
db.update(doc);
My main code block
public void put(K key, T obj) {
final Map<String, Object> doc = new HashMap<>();
doc.put("_id", key.toString());
Schema schema = obj.getSchema();
List<Field> fields = schema.getFields();
for (int i = 0; i < fields.size(); i++) {
if (!obj.isDirty(i)) {
continue;
}
Field field = fields.get(i);
Schema.Type type = field.schema().getType();
Object fieldValue = obj.get(field.pos());
Schema fieldSchema = field.schema();
fieldValue = serializeFieldValue(fieldSchema, fieldValue);
doc.put(field.name(), fieldValue);
}
db.update(doc);
}
private Object serializeFieldValue(Schema fieldSchema, Object fieldValue ){
...
byte[] data = null;
try {
SpecificDatumWriter writer = getDatumWriter(fieldSchema);
data = IOUtils.serialize(writer, fieldValue);
} catch (IOException e) {
LOG.error(e.getMessage(), e);
}
fieldValue = data;
...
return fieldValue;
}

The value is the base64 encoded string "foobaz". You should probably post your code as well to get any meaningful feedback regarding this issue.
edit: Now that you provided code, is it possible, that the object you are trying to update already exists in the database? If yes you need to get it first or provide the proper existing revision id for the update. Otherwise the update will be rejected.

CouchDB stores JSON documents, and JSON does not support byte arrays, so I guess Ektorp is applying its own Base64 conversion during conversion of your object to JSON, before sending to CouchDB, and maybe that is skipping some characters in the byte array.
You might prefer to sidestep the Ektorp behaviour by applying your own Base64 serialisation before calling Ektorp, and then deserialise yourself after fetching the document from CouchDB. Or you could use something like Jackson, which will handle the object/JSON conversion behind the scenes, including byte arrays.

Ektorp uses Jackson for json serialization, I think jackson defaults to base64 for byte arrays. As long as you read/write with Ektorp you should not have any problems.
But I see in your code that you have some kind of type system of your own so that complicates things. I suggest you use POJOS instead of rolling your own since you won't get much help from ektorp and jackson if you are doing it yourself.

libgdx Json parsing

hi I'm trying to get all 'id' value from my json into my 'results' array.
I didn't really understood how the json class of libgdx works, but I know how json works itself.
Here is the json : http://pastebin.com/qu71EnMx
Here is my code :
Array<Integer> results = new Array<Integer>();
Json jsonObject = new Json(OutputType.json);
JsonReader jsonReader = new JsonReader();
JsonValue jv = null;
JsonValue jv_array = null;
//
try {
String str = jsonObject.toJson(jsonString);
jv = jsonReader.parse(str);
} catch (SerializationException e) {
//show error
}
//
try {
jv_array = jv.get("table");
} catch (SerializationException e) {
//show error
}
//
for (int i = 0; i < jv_array.size; i++) {
//
try {
jv_array.get(i).get("name").asString();
results.add(new sic_PlayerInfos(
jv_array.get(i).get("id").asInt()
));
} catch (SerializationException e) {
//show error
}
}
Here is the error I get : 'Nullpointer' on jv_array.size

Doing it this way will result in a very hacky, not maintainable code. Your JSON file looks very simple but your code is terrible if you parse the whole JSON file yourself. Just imagine how it will look like if you are having more than an id, which is probably going to happen.
The much more clean way is object oriented. Create an object structure, which resembles the structure of your JSON file. In your case this might look like the following:
public class Data {
public Array<TableEntry> table;
}
public class TableEntry {
public int id;
}
Now you can easily deserialize the JSON with libgdx without any custom serializers, because libgdx uses reflection to handle most standard cases.
Json json = new Json();
json.setTypeName(null);
json.setUsePrototypes(false);
json.setIgnoreUnknownFields(true);
json.setOutputType(OutputType.json);
// I'm using your file as a String here, but you can supply the file as well
Data data = json.fromJson(Data.class, "{\"table\": [{\"id\": 1},{\"id\": 2},{\"id\": 3},{\"id\": 4}]}");
Now you've got a plain old java object (POJO) which contains all the information you need and you can process it however you want.
Array<Integer> results = new Array<Integer>();
for (TableEntry entry : data.table) {
results.add(entry.id);
}
Done. Very clean code and easily extendable.