Jackson parser behavior when encountering integer, nulls, and empty strings.

app_build.gradle

android {
    ...
    
    packagingOptions {
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/NOTICE'
    }
}

dependencies {
    ...

    compile 'com.google.code.gson:gson:2.3.1'
    
    compile 'com.fasterxml.jackson.core:jackson-databind:2.5.1'
    compile 'com.fasterxml.jackson.core:jackson-annotations:2.5.1'

    testCompile 'junit:junit:4.12'
    testCompile "org.mockito:mockito-core:1.9.5"
}

GsonParser.java

import com.google.gson.Gson;

import java.io.IOException;

public class GsonParser implements Parser {
    @Override
    public <T> T parse(String json, Class<T> clazz) throws IOException {
        return new Gson().fromJson(json, clazz);
    }
}

JacksonParser.java

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class JacksonParser implements Parser {
    @Override
    public <T> T parse(String json, Class<T> clazz) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.readValue(json, clazz);
    }
}

Parser.java

import java.io.IOException;

public interface Parser {
    <T> T parse(String json, Class<T> clazz) throws IOException;
}

ParsersTests.java

import org.junit.Assert;
import org.junit.Ignore;
import org.junit.Test;

import java.io.IOException;

public class ParserTest {
    @Test
    public void testJacksonParseNormalJson() throws IOException {
        Parser parser = new JacksonParser();
        testParseNormalJson(parser);
    }

    @Test
    public void testJacksonParseNullJson() throws IOException {
        Parser parser = new JacksonParser();
        testParseNullJson(parser);
    }

    @Test
    public void testJacksonParseEmptyStringAsNullJson() throws IOException {
        Parser parser = new JacksonParser();
        testParseEmptyStringAsNullJson(parser);
    }

    @Test
    public void testGsonParseNormalJson() throws IOException {
        Parser parser = new GsonParser();
        testParseNormalJson(parser);
    }

    @Test
    public void testGsonParseNullJson() throws IOException {
        Parser parser = new GsonParser();
        testParseNullJson(parser);
    }

    @Test
    public void testGsonParseEmptyStringAsNullJson() throws IOException {
        Parser parser = new GsonParser();
        testParseEmptyStringAsNullJson(parser);
    }

    private void testParseNormalJson(Parser parser) throws IOException {
        Person person = parser.parse("{\"name\": \"Bob\", \"age\": 30, \"pets\": 1}", Person.class);

        Assert.assertEquals("Bob", person.getName());
        Assert.assertNotNull(person.getAge());
        Assert.assertEquals(30, person.getAge().intValue());
        Assert.assertEquals(1, person.getPets());
    }

    private void testParseNullJson(Parser parser) throws IOException {
        Person person = parser.parse("{\"name\": \"Bob\", \"age\": null, \"pets\": null}", Person.class);

        Assert.assertEquals("Bob", person.getName());
        Assert.assertNull(person.getAge());
        Assert.assertEquals(-1, person.getPets());
    }

    private void testParseEmptyStringAsNullJson(Parser parser) throws IOException {
        Person person = parser.parse("{\"name\": \"Bob\", \"age\": \"\", \"pets\": \"\"}", Person.class);

        Assert.assertEquals("Bob", person.getName());
        Assert.assertNull(person.getAge());
        Assert.assertEquals(-1, person.getPets());
    }
}

Person.java

import com.fasterxml.jackson.annotation.JsonProperty;

public class Person {
    @JsonProperty("name")
    String name;

    @JsonProperty("age")
    Integer age;

    int pets;

    public String getName() {
        return name;
    }

    public Integer getAge() {
        return age;
    }

    public int getPets() {
        return pets;
    }

    @JsonProperty("pets")
    void setPets(Object pets) {
        if (pets == null) {
            this.pets = -1;
        } else if ("".equals(pets)) {
            this.pets = -1;
        } else {
            this.pets = (Integer) pets;
        }
    }
}