Parse all jsons that are concatenated in one string in Java

Question

I have a number of json objects concatenated into one string, and need to parse all of them. Simple example:

String jsonStr = "{"name":"peter","age":40}{"name":"laura","age":50}"

When using an ObjectMapper of jackson to parse this, it finds and reads the first json correctly, and drops the rest of the string.

ObjectMapper objectMapper = new ObjectMapper();
JsonNode rootNode = objectMapper.readTree(jsonStr);
System.out.println(rootNode);

Gives output {"name":"peter","age":20}

Is there any way (in Jackson or another framework) of e.g. returning the number of read characters, or the rest of the string, or an array of JsonNodes?

I found questions with the same goal in JavaScript and in Python, where it was recommended to split by }{ or regex to reformat this to a json array, but I still hope for a more elegant solution.

Answer 1

You don't need to modify your input as suggested by others, just use below code.

Main Method

public static void main(String[] args) throws IOException {

    ObjectMapper mapper = new ObjectMapper();
    JsonFactory factory = new JsonFactory(mapper);

    JsonParser parser = factory.createParser(new File("config.json"));
    // factory.createParser(String) and many other overload methods
    // available, byte[], char[], InputStream etc.

    Iterator<Person> persons = parser.readValuesAs(Person.class);
    while(persons.hasNext()) {
        Person p = persons.next();
        System.out.printf("%s: %d%n", p.getName(), p.getAge());
    }
}

Person Class

public class Person {

    private String name;
    private int age;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}  

config.json file

{"name":"peter","age":40}{"name":"laura","age":50}

Program Output

peter: 40
laura: 50

Library used

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.9.5</version>
</dependency>

Answer 2

In Json, an object structure starts with { and ends with }. Hence ObjectMapper thinks that there is nothing more to process as soon as it encounters }.

In Json an array is indicated with []. So if you wish to have multiple elements / objects it needs to be enclosed with [] and a comma separating individual objects

"[
  {"name":"peter","age":40},
  {"name":"laura","age":50}
]"

Answer 3

You can wrap the input with brackets [] and then replace every }{ with },{, and then finally parse the string as array:

String input = "{\"name\":\"peter\",\"age\":40}{\"name\":\"laura\",\"age\":50}"
String jsonArray = "[" + input.replace("}{", "},{") + "]";

ObjectMapper mapper = new ObjectMapper();
JsonNode parsedJsonArray = mapper.readTree(jsonArray);

Answer 4

you have to modify your JSON

String jsonStr = "[{\"name\":\"peter\",\"age\":40},{\"name\":\"laura\",\"age\":50}]";

There are multiple ways to convert JSON into java object.

1st Way

public JsonNode convertIntoJsonNode(String jsonStr)
    {
        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode rootNode = null;
        try {
            rootNode = objectMapper.readTree(jsonStr);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return rootNode;
    }

2nd Ways // check also imports

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
// User Model
    class User{
        private String name;
        private Integer age;
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public Integer getAge() {
            return age;
        }
        public void setAge(Integer age) {
            this.age = age;
        }
        @Override
        public String toString() {
            return "User [name=" + name + ", age=" + age + "]";
        }
    }
//Coversion Method
public List<User> convertIntoObject(String jsonStr)
    {
        ObjectMapper objectMapper = new ObjectMapper();
        User[] myObjects = null;
        try {
            myObjects = objectMapper.readValue(jsonStr, User[].class);


        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return Arrays.asList(myObjects);
    }

3rd way you can directly parse without array

public List<User> convertIntothirdway(String jsonStr)
    {
        ObjectMapper objectMapper = new ObjectMapper();
        List<User> userList = null;
        try {
             userList = objectMapper.readValue(jsonStr, new TypeReference<List<User>>(){});
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return userList;
    }

4th way

List<User> userList = mapper.readValue(jsonInput, mapper.getTypeFactory().constructCollectionType(List.class, User.class));