I have an InputStream containing an array of JSON objects. Each individual object can be parsed to a Java class Person using Jackson's ObjectMapper:
public class Person {
public String name;
public Int age;
...
}
InputStream myStream = connection.getInputStream(); // [{name: "xx", age: 00}, {...}]
ObjectMapper objectMapper = new ObjectMapper();
How do I parse the JSON-stream into a new Stream<Person> using Jackson without having all the data in the memory?
You can do something like
private void parseJson(InputStream is) throws IOException {
// Create and configure an ObjectMapper instance
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
// Create a JsonParser instance
try (JsonParser jsonParser = mapper.getFactory().createParser(is)) {
// Check the first token
if (jsonParser.nextToken() != JsonToken.START_ARRAY) {
throw new IllegalStateException("Expected content to be an array");
}
// Iterate over the tokens until the end of the array
while (jsonParser.nextToken() != JsonToken.END_ARRAY) {
// Read a contact instance using ObjectMapper and do something with it
Person person= mapper.readValue(jsonParser, Person.class);
}
}
}
Stream<Person>, but each individual Person as a variable. It should be possible to transfer those to a stream?
The answer by SJN is on the right track, but it still does not convert the InputStream to a Stream. JsonParser actually has a readValuesAs method that returns an iterator. Converting this iterator into a Stream is then straightforward.
Stream<Person> toStream(InputStream inputStream) throws IOException {
ObjectMapper objectMapper = new ObjectMapper();
JsonParser jsonParser = objectMapper.getFactory().createParser(inputStream);
if (jsonParser.nextToken() != JsonToken.START_ARRAY) {
throw new IllegalStateException("Not an array");
}
jsonParser.nextToken(); // advance jsonParser to start of first object
Iterator<Person> iterator = jsonParser.readValuesAs(Person.class);
return StreamSupport.stream(
Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED),
false);
}
[]). You can consider adding one more if-statement: if (jsonParser.nextToken() == JsonToken.END_ARRAY) { return Stream.empty(); }