Parsing JSON using Jackson Library

Apart from being able to parse a json using the json libraries as shown here, another interesting way to parse a json is using the jackson library. To begin using this method, we add the following entry to our pom -

pom.xml

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.6.3</version>
</dependency>

And we use the following json file that we read from our resource folder -

sherlock.json

{
 "firstname": "Sherlock",
 "lastname": "Holmes",
 "address": {
  "street": "221B, Baker Street",
  "city": "London"
 },
 "books": ["A Study in Scarlet", "The Sign of the Four", "The Hound of the Baskervilles"]
}

The Jackson library essentially maps json elements to class variables. So, to map the values, a model consisting of one or more classes, having the same structure as the json is needed. For our current json, we need two classes - one for the original json and one for the address.

The two models are as follows -

Address.java

public class Address {
        String street;
        String city;

        //Getters and Setters
}

JsonEntry.java

import java.util.List;

import com.fasterxml.jackson.annotation.JsonProperty;

public class JsonEntry {
        @JsonProperty("firstname")
        String firstName;

        @JsonProperty("lastname")
        String lastName;

        Address address;
        List<String> books;

        //Getters and Setters
}

The JsonProperty annotation is used when the name of the json field varies from the variable name. It is not needed in the case when the name of the field is the same as the name of the variable.

The complete java file which parses and prints the json is given below -

JsonParser.java

package json.parser;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonParser {
 public static void main(String[] args) {
  String json;
  try {
   ClassLoader classLoader = JsonParser.class.getClassLoader();
   InputStream in = classLoader.getResourceAsStream("json/sherlock.json");
   json = convertToString(in);
   ObjectMapper mapper = new ObjectMapper();

   JsonEntry jsonParsed = parseJson(json, mapper);

   System.out.println("-----Printing Json--------------");
   printJson(jsonParsed);

   System.out.println("\n-----Pretty Printing Json--------------");
   prettyPrintJson(jsonParsed, mapper);
  } catch (Exception e) {
   e.printStackTrace();
  }
 }

 private static String convertToString(InputStream in) throws IOException {
  StringBuilder sb = new StringBuilder();
  BufferedReader br = new BufferedReader(new InputStreamReader(in));

  String line;

  while ((line = br.readLine()) != null) {
   sb.append(line).append("\n");
  }

  return sb.toString();

 }

 private static JsonEntry parseJson(String jsonString, ObjectMapper mapper) {
  JsonEntry jsonEntry = null;

  try {
   // Convert JSON string to Object
   jsonEntry = mapper.readValue(jsonString, JsonEntry.class);
  } catch (JsonGenerationException e) {
   e.printStackTrace();
  } catch (JsonMappingException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }

  return jsonEntry;

 }

 private static void printJson(JsonEntry json) {
  System.out.println("First Name: " + json.getFirstName());
  System.out.println("Last Name: " + json.getLastName());

  System.out.println("Street: " + json.getAddress().getStreet());
  System.out.println("City: " + json.getAddress().getCity());

  for (int i = 0; i < json.getBooks().size(); i++) {
   System.out.println("Book " + (i + 1) + ": " + json.getBooks().get(i));
  }
 }

 private static void prettyPrintJson(JsonEntry json, ObjectMapper mapper) throws JsonProcessingException {
  String prettyPrint = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(json);
  System.out.println(prettyPrint);
 }
}

The method parseJson() maps the json string to the object model definition. printJson() and prettyPrintJson()are simply outputting the values of the mapped json.


See also -
Parsing Json using Json Libraries