Java reading json with Jackson - embedded array

Question

I have a JSON file that contains an array within it. I'm able to read the data fine but unsure of how I would print the array values out. Below I'm manually selecting the 3rd car. I need to show all cars. Not all persons have the same number of cars available. Some have 1 some have 3.... I keep running into null error when I try different kinds of loops.

Thanks!

try {
    ObjectMapper mapper = new ObjectMapper();
    InputStream inputStream = new FileInputStream(new File("/Users/blah/Downloads/persons.json"));
    TypeReference<List<Person>> typeReference = new TypeReference<List<Person>>() {};
    List<Person> persons = mapper.readValue(inputStream, typeReference);
    for (Person p : persons) {
        System.out.printf("name is %s city is %s cars available %s%n",
        p.getFirstName(),
        p.getAddress().getCity(),
        p.getCars()[2]);
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (JsonParseException e) {
    e.printStackTrace();
} catch (JsonMappingException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

JSON Example:

[
  {
    "firstName": "Leanne Graham",
    "lastName": "Bret",
    "age": 25,
    "address": {
      "street": "123 Main St",
      "city": "Bellevue",
      "zip": "90007"
    },
    "cars": [
      "Toyota Corolla",
      "Honda Civic",
    ]
  },
  {
    "firstName": "Steve Graham",
    "lastName": "Bret",
    "age": 25,
    "address": {
      "street": "123 Main St",
      "city": "Bellevue",
      "zip": "90007"
    },
    "cars": [
      "Toyota Corolla",
      "Honda Civic",
      "Infiniti G35"
    ]
  },
  {
    "firstName": "Sally Graham",
    "lastName": "Bret",
    "age": 25,
    "address": {
      "street": "123 Main St",
      "city": "Bellevue",
      "zip": "90007"
    },
    "cars": [
      "Toyota Corolla",
      "Honda Civic",
      "Infiniti G35"
    ]
  }
]

Why do you accept the latest and the less informative answer ? Do you really find it more helpfull ? — azro
– azro, Commented Jul 19, 2020 at 13:14
first what ? The appearing order is random and changes. As advice, always take a few seconds to choose a one for a reason ;) — azro
– azro, Commented Jul 19, 2020 at 13:18
@azro As I see it my answer is 2 minutes older than yours. Apart from that, it doesn't really matter, does it? Our answers are very similar and this accept wouldn't add that much to your 24,000 reputation, so I don't see the damage here. — bkis
– bkis, Commented Jul 19, 2020 at 15:20

bkis · Accepted Answer · 2020-07-19 12:44:35Z

1

You can use Arrays.toString(p.getCars()) for that.
BTW you should implement (override) the toString() method in your Person class. toString() is meant to give a meaningful string representation of an object. If you have done so, you can just go

for (Person p : persons) System.out.println(p);

edited Jul 19, 2020 at 12:44

answered Jul 19, 2020 at 12:38

bkis

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Comments

azro · Accepted Answer · 2020-07-19 12:40:21Z

1

You should implement that in the toString of the Person class, and to print the whole array use Arrays.toString()

public class Person{        
    public String toString(){         
        return String.format("name is %s city is %s cars available %s", p.getFirstName(),
                             p.getAddress().getCity(), Arrays.toString(p.getCars()));
    }
}

And use

for (Person p : persons) {
    System.out.println(p);
}

answered Jul 19, 2020 at 12:40

azro

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