Jackson Parser example in android

Jackson parser’s ObjectMapper for reading value and transforms it into a Java object.

ObjectMapper mapper = new ObjectMapper();
Person person1, person2, person3;
//read from an url
person1 = mapper.readValue(new URL("https://api.myjson.com/bins/hoh4j"), Person.class);

//read from a string
String personJsonStr = "{\"firstname\":\"John\",\"lastname\":\"Doe\"}";
person2 = mapper.readValue(personJsonStr, Person.class);

//read from a file
person3 = mapper.readValue(new File("/a/path/to/person.json"), Person.class);

Jackson parser’s ObjectMapper for writing to json string from Java object.

ObjectMapper mapper = new ObjectMapper();
Person person = new Person();

mapper.writeValue(new File("/a/path/to/person.json"), person);  // write to file
String jsonStr = mapper.writeValueAsString(person);            // write to string

The following are basic examples for setting up Jackson parser and how to use it in Android.

1. Jackson parser dependencies to be included in the gradle file.

compile 'com.fasterxml.jackson.core:jackson-databind:2.8.5'
compile 'com.fasterxml.jackson.core:jackson-core:2.8.5'
compile 'com.fasterxml.jackson.core:jackson-annotations:2.8.5'

2. Exclude META-INF/LICENSE in the android tag in the gradle file to avoid dup license file error in Android studio

packagingOptions {
    exclude 'META-INF/LICENSE'
}

3. Sample json string, https://api.myjson.com/bins/hoh4j

{
  "firstname": "John",
  "lastname": "Doe"
}

4. Sample model class with Jackson annotations for the above json string.

import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
        "firstname",
        "lastname"
})
public class Person {
    @JsonProperty("firstname")
    private String firstname;
    @JsonProperty("lastname")
    private String lastname;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("firstname")
    public String getFirstname() {
        return firstname;
    }

    @JsonProperty("firstname")
    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    @JsonProperty("lastname")
    public String getLastname() {
        return lastname;
    }

    @JsonProperty("lastname")
    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }
}

5. Json string to Java object using Jackson parser

private void jsonToObject() {
    final ObjectMapper mapper = new ObjectMapper();
    try {
        String personJsonStr = "{\"firstname\":\"John\",\"lastname\":\"Doe\"}";
        //Person person = mapper.readValue(new File(getFilesDir(), "person.json"), Person.class);    // read from file
        Person person = mapper.readValue(personJsonStr, Person.class);                               // read from json string
        tvDisplay.setText("json string -> object\n" + person.getFirstname() + " " + person.getLastname());
    } catch (IOException e) {
        e.printStackTrace();
        tvDisplay.setText(e.getMessage());
        progressBar.setVisibility(View.GONE);
    }
}

6. Json string from an url to Java object using Jackson parser in Android, since there is network involved, the INTERNET use-permission needs to be enabled in the manifest file and it has to run in a background thread.

private void jsonToObjectUrl() {
    final ObjectMapper mapper = new ObjectMapper();
    final Handler handler = new Handler();
    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                Person person = mapper.readValue(new URL("https://api.myjson.com/bins/hoh4j"), Person.class);                                 // read from url
                handler.post(new Runnable() {
                    @Override
                    public void run() {
                        tvDisplay.setText("json string -> object\n" + person.getFirstname() + " " + person.getLastname());
                    }
                });
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }).start();
}

7. Java object to Json string using Jackson parser.

private void objectToJson() {
    ObjectMapper mapper = new ObjectMapper();
    try {
        //mapper.writeValue(new File(getFilesDir(), "person.json"), person);  // write to file
        String jsonStr = mapper.writeValueAsString(person);                   // write to string
        tvDisplay.setText("object -> json string\n" + jsonStr);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
        tvDisplay.setText(e.getMessage());
    } catch (IOException e) {
        e.printStackTrace();
        tvDisplay.setText(e.getMessage());
    }
}

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