Java: Parse Json with Jackson

Using Jackson we can easily deserialize a JSON Object into a Java Object. The following example takes a file Person.json and creates a new Person java object using the contents.

Jackson by default will map the keys in the json file to the fields in your java object. Notice the key names in Person.json map to the fields in the java Person object.

• Line 2 in Person.json maps to line 10 in Person.java
• Line 3 in Person.json maps to line 11 in Person.java
• Line 4 in Person.json maps to line 12 in Person.java

Person.json

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{
    "firstName": "John",
    "lastName": "Smith",
    "age": 25
}

1. Create a new ObjectMapper
   On line 69 we create ObjectMapper which is what reads the json file and produces a Java Object.
   
   
2. Call mapper.readValue to deserialize
   mapper.readValue takes 2 arguments. The first argument in this example is a new File object using the path to the Person.json object relative to the base of our project directory. The second argument is the class that is produced, in this exmaple this is the Person.class seen from lines 9 through 25.
   

JacksonJson.java

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package nibs.io.json;

import java.io.File;

import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonJson {

    public static class Person {
        private String firstName;
        private String lastName;
        private int age;

        public String getFirstName() {
            return firstName;
        }

        public String getLastName() {
            return lastName;
        }

        public int getAge() {
            return age;
        }
    }

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        Person person = mapper.readValue(new File("./Person.json"), Person.class);
        System.out.println(person.getFirstName());
        System.out.println(person.getLastName());
        System.out.println(person.getAge());
    }

}

Console Output

John
Smith
25

Reference: http://wiki.fasterxml.com/JacksonHome