如何使用 Jackson 从对象流生成 JSON 流

Question

I have a Stream of objects and an outgoing HttpServletResponse :

public class Person {
    public String name;
    public Int age;
    ...
}

@RequestMapping(value = "/my/path", produces = MediaType.APPLICATION_JSON_VALUE)
    public void getPersons(HttpServletRequest request, HttpServletResponse response) {
        Stream<Person> stream = getMyStream();

        // write stream of JSON array to response: [{name: "xx", age: 00}, {...}]
    }

How to I generate JSON using Jackson and stream this to the response without filling the memory with all the data?

Answer 1

Jackson comes with a generic StreamSerializer . You get it when you add the Jdk8Module to your ObjectMapper .

ObjectMapper objectMapper = new ObjectMapper()
        .registerModule(new Jdk8Module());

Having done that you can serialize your Stream<Person> very easily:

Stream<Person> stream = getMyStream();
OutputStream out = response.getOutputStream();
objectMapper.writeValue(out, stream);

Then the JSON output will look like this:

[{"name":"Alice","age":30},{"name":"Bob","age":31},{"name":"Charlie","age":32}]