Java 2

Week 4

Topics Covered

JSON file input
Operations with open source APIs

What is JSON?

JavaScript Object Notation (JSON) is a text file format for storing and transmitting data objects.
JSON filenames use the extension .json
JSON can be used to get data for Java objects
A JavaScript object starts with { and ends with }
Between the curly brackets are key:value pairs
- keys must be strings
- values can be strings, arrays, or objects
- each key value pair must be separated by a comma.
Below is an example of JSON representing a Message object.
Here is a more complex example representing a Person object.

{role: "test", content: "example"}

JSON Dependency

To read JSON, you need to add a dependency to the pom.xml file
- Google Gson
Create a new Java file called JsonDemo1. Add this code.
I am assigning the JSON string to a variable called responseBody to represent an HTTP response from a web server.

import com.google.gson.Gson;

public class JsonDemo1 {
    public static void main(String[] args) throws Exception {
        String responseBody = "{role: \"test\", content: \"example\"}";
        Gson gson = new Gson();
        Message message = gson.fromJson(responseBody, Message.class);
        System.out.println(message.role);
        System.out.println(message.content);
    }

    private static class Message {
        private String role;
        private String content;
    }
}

Handling Invalid JSON

In this example, I removed the comma from the string to make invalid JSON.
The fromJson() method throws a JsonSyntaxException when invalid JSON is found.

import com.google.gson.Gson;
import com.google.gson.JsonSyntaxException;

public class JsonDemo1 {
    public static void main(String[] args) throws Exception {
        String responseBody = "{role: \"test\" content: \"example\"}";
        Gson gson = new Gson();
        Message message = null;
        try {
            message = gson.fromJson(responseBody, Message.class);
        } catch(JsonSyntaxException e) {
            System.out.println("ERROR: " + e.getMessage());
            System.exit(0);
        }
        System.out.println(message.role);
        System.out.println(message.content);
    }

    private static class Message {
        private String role;
        private String content;
    }
}

JSON Dependencies

Instead of Google Gson, you can add these dependencies to the pom.xml file
- JSON In Java and Jackson Databind
  - org.json:json
  - com.fasterxml.jackson.core:jackson-databind

What is an API?

An application programming interface (API) is a way for two or more programs to communicate with each other.
APIs offer data and services to other pieces of software.
An API dictates how to write code to take advantage of that system's capabilities.

HTTP Dependency

To read JSON from a web server, you need to add a second dependency to the pom.xml file
- Square OkHttp
Create a new Java file called JsonDemo2. Add this code.
In this example, I only obtain the Person object's first name, last name, and email address.

import com.google.gson.Gson;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;


public class JsonDemo2 {
    private static final String API_URL = "https://randomuser.me/api/?format=json&seed=abc&results=1&nat=us";

    public static void main(String[] args) throws Exception {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url(API_URL)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);
        Gson gson = new Gson();
        APIResponse apiResponse = gson.fromJson(responseBody, APIResponse.class);
        for (Person person : apiResponse.results) {
            System.out.println(person.name.first + " " + person.name.last);
            System.out.println(person.email);
        }
    }

    private static class APIResponse {
        private Person[] results;
    }

    private static class Person {
        private Name name;
        private String email;
    }

    private static class Name {
        private String first;
        private String last;
    }
}

Get More Data

In this example, I add the Person object's location and street address.

import com.google.gson.Gson;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;


public class JsonDemo2 {
    private static final String API_URL = "https://randomuser.me/api/?format=json&seed=abc&results=1&nat=us";

    public static void main(String[] args) throws Exception {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url(API_URL)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);
        Gson gson = new Gson();
        APIResponse apiResponse = gson.fromJson(responseBody, APIResponse.class);
        for (Person person : apiResponse.results) {
            System.out.println(person.name.first + " " + person.name.last);
            System.out.printf("%d %s\n", person.location.street.number, person.location.street.name);
            System.out.printf("%s, %s %s\n", person.location.city, person.location.state, person.location.postcode);
            System.out.printf("Latitude: %.4f, Longitude: %.4f\n", person.location.coordinates.latitude, person.location.coordinates.longitude);
            System.out.println(person.email);
        }
    }

    private static class APIResponse {
        private Person[] results;
    }

    private static class Person {
        private Name name;
        private Location location;
        private String email;
    }

    private static class Name {
        private String first;
        private String last;
    }

    private static class Location {
        private Street street;
        private String city;
        private String state;
        private int postcode;
        private Coordinates coordinates;
    }

    private static class Street {
        private int number;
        private String name;
    }

    private static class Coordinates {
        private double latitude;
        private double longitude;
    }
}

Handling Exceptions

In this example, I try to assign a String to an int.
If you have an attribute that doesn't exist, it will be assigned its default value (Object is null, int is 0, etc.)

package edu.kirkwood;

import com.google.gson.Gson;
import com.google.gson.JsonSyntaxException;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;


public class JsonDemo2 {
    private static final String API_URL = "https://randomuser.me/api/?format=json&seed=abc&results=1&nat=us";

    public static void main(String[] args) throws Exception {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url(API_URL)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);
        Gson gson = new Gson();
        APIResponse apiResponse = null;
        try {
            apiResponse = gson.fromJson(responseBody, APIResponse.class);
        } catch(JsonSyntaxException e) {
            System.out.println("ERROR: " + e.getMessage());
            System.exit(0);
        }
        for (Person person : apiResponse.results) {
            System.out.println(person.name.first + " " + person.name.last);
            System.out.printf("%d %s\n", person.location.street.number, person.location.street.name);
            System.out.printf("%s, %s %s\n", person.location.city, person.location.state, person.location.postcode);
            System.out.printf("Latitude: %.4f, Longitude: %.4f\n", person.location.coordinates.latitude, person.location.coordinates.longitude);
            System.out.println(person.email);
        }
    }

    private static class APIResponse {
        private Person[] results;
    }

    private static class Person {
        private Name name;
        private Location location;
        private String email;
    }

    private static class Name {
        private String first;
        private String last;
    }

    private static class Location {
        private Street street;
        private String city;
        private String state;
        private int postcode;
        private Coordinates coordinates;
    }

    private static class Street {
        private int number;
        private int name;
    }

    private static class Coordinates {
        private double latitude;
        private double longitude;
    }
}

Handling Dates

Note the different date formats in the DateTimeFormatter class.
"1967-07-23T09:18:33.666Z" represents an Instant object.
Here I created an InstantDeserializer class with the help of Stack Overflow.

import com.google.gson.*;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

import java.lang.reflect.Type;
import java.time.Instant;

public class JsonDemo2 {
    private static final String API_URL = "https://randomuser.me/api/?format=json&seed=abc&results=1&nat=us";

    public static void main(String[] args) throws Exception {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url(API_URL)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);
        Gson gson = new GsonBuilder()
                .registerTypeAdapter(Instant.class, new InstantDeserializer())
                .create();
        APIResponse apiResponse = null;
        try {
            apiResponse = gson.fromJson(responseBody, APIResponse.class);
        } catch(JsonSyntaxException e) {
            System.out.println("ERROR: " + e.getMessage());
            System.exit(0);
        }
        for (Person person : apiResponse.results) {
            System.out.println(person.name.first + " " + person.name.last);
            System.out.printf("%d %s\n", person.location.street.number, person.location.street.name);
            System.out.printf("%s, %s %s\n", person.location.city, person.location.state, person.location.postcode);
            System.out.printf("Latitude: %.4f, Longitude: %.4f\n", person.location.coordinates.latitude, person.location.coordinates.longitude);
            System.out.println(person.email);
            System.out.printf("Born %s\n", person.dob.date);
        }
    }

    private static class InstantDeserializer implements JsonDeserializer<Instant> {
        @Override
        public Instant deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
            return Instant.parse(json.getAsString());
        }
    }

    private static class APIResponse {
        private Person[] results;
    }

    private static class Person {
        private Name name;
        private Location location;
        private String email;
        private DateOfBirth dob;
    }

    private static class Name {
        private String first;
        private String last;
    }

    private static class Location {
        private Street street;
        private String city;
        private String state;
        private int postcode;
        private Coordinates coordinates;
    }

    private static class Street {
        private int number;
        private String name;
    }

    private static class Coordinates {
        private double latitude;
        private double longitude;
    }

    private static class DateOfBirth {
        private Instant date;
    }
}

Comparing and Sorting

Implement the Comparable Interface in the RandomUser class.
Before printing users, sort them alphabetically.

import com.google.gson.*;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

import java.lang.reflect.Type;
import java.time.Instant;
import java.util.Arrays;

public class JsonDemo2 {
    private static final String API_URL = "https://randomuser.me/api/?format=json&seed=abc&results=5&nat=us";

    public static void main(String[] args) throws Exception {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url(API_URL)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);
        Gson gson = new GsonBuilder()
                .registerTypeAdapter(Instant.class, new InstantDeserializer())
                .create();
        APIResponse apiResponse = null;
        try {
            apiResponse = gson.fromJson(responseBody, APIResponse.class);
        } catch(JsonSyntaxException e) {
            System.out.println("ERROR: " + e.getMessage());
            System.exit(0);
        }
        Person[] people = apiResponse.results;
        Arrays.sort(people);
        for(Person person: people) {
            System.out.println(person.name.first + " " + person.name.last);
            System.out.printf("%d %s\n", person.location.street.number, person.location.street.name);
            System.out.printf("%s, %s %s\n", person.location.city, person.location.state, person.location.postcode);
            System.out.printf("Latitude: %.4f, Longitude: %.4f\n", person.location.coordinates.latitude, person.location.coordinates.longitude);
            System.out.println(person.email);
            System.out.printf("Born %s\n", person.dob.date);
            System.out.println();
        }
    }

    private static class InstantDeserializer implements JsonDeserializer<Instant> {
        @Override
        public Instant deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
            return Instant.parse(json.getAsString());
        }
    }

    private static class APIResponse {
        private Person[] results;
    }

    private static class Person implements Comparable<Person> {
        private Name name;
        private Location location;
        private String email;
        private DateOfBirth dob;
        
        @Override
        public int compareTo(Person o) {
            int result = this.name.last.compareTo(o.name.last);
            if (result == 0) {
                result = this.name.first.compareTo(o.name.first);
            }
            return result;
        }
    }

    private static class Name {
        private String first;
        private String last;
    }

    private static class Location {
        private Street street;
        private String city;
        private String state;
        private int postcode;
        private Coordinates coordinates;
    }

    private static class Street {
        private int number;
        private String name;
    }

    private static class Coordinates {
        private double latitude;
        private double longitude;
    }

    private static class DateOfBirth {
        private Instant date;
    }
}

JSON Dependencies

Instead of Square OkHttp, you can add this dependency to the pom.xml file
- Apache HttpClient
Here is some sample code to try.
https://www.baeldung.com/java-http-response-body-as-string

Movie API

Read the documentation for The Movie Database (TMDB) API.
This API requires you to register for an API key.
- When entering application details, enter something like this:
  - Application name: Java Web App
  - Application URL: https://yourname.azurewebsites.net/
  - Application Summary: Learning Java web development
Replace apiKey with your API Read Access Token
- Do not push this key to GitHub.

import com.google.gson.*;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

import java.io.IOException;
import java.lang.reflect.Type;
import java.time.*;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class JsonDemo3 {
    public static void main(String[] args) throws IOException {
        // Remove before pushing to GitHub
        String apiKey = "";

        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url("https://api.themoviedb.org/3/trending/movie/day?language=en-US")
                .get()
                .addHeader("accept", "application/json")
                .addHeader("Authorization", "Bearer " + apiKey)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);

        Gson gson = new GsonBuilder()
                .setPrettyPrinting()
                .registerTypeAdapter(LocalDate.class, new LocalDateDeserializer())
                .create();
//        JsonElement jsonElement = new JsonParser().parse(responseBody);
//        String json = gson.toJson(jsonElement);
//        System.out.print(json);
        MovieDBAPI movieDBAPI = null;
        try {
            movieDBAPI = gson.fromJson(responseBody, MovieDBAPI.class);
        } catch (JsonSyntaxException | JsonIOException e) {
            System.out.println(e.getMessage());
            System.exit(0);
        }

        for(Movie movie : movieDBAPI.results) {
            System.out.println("ID: " + movie.id);
            System.out.println("Title: " + movie.title);
            System.out.println("Overview: " + movie.overview);
            System.out.println("Genres: " + Arrays.toString(movie.genre_ids));
            System.out.println("Vote Average: " + movie.vote_average);
            System.out.println("Video: " + (movie.video ? "Yes" : "No"));
            System.out.println("Release Date: " + movie.release_date);
            System.out.println();
        }
    }

    private static class LocalDateDeserializer implements JsonDeserializer<LocalDate> {
        @Override
        public LocalDate deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
            return LocalDate.parse(json.getAsString());
        }
    }

    private static class MovieDBGenre {
        public Genre[] genres;
    }
    private static class Genre {
        public int id;
        public String name;
    }

    private static class MovieDBAPI {
        public Movie[] results;
    }
    private static class Movie {
        public int id;
        public String title;
        public String overview;
        public int[] genre_ids;
        public double vote_average;
        public boolean video;
        public LocalDate release_date;
    }
}

Genre Ids to Genres

Make a second API request to get Genre data.
Use this solution to convert the array of Genre objects into a List<Genre>.
Use this solution to retrieve a Genre by its id.
The filter() method requires a Predicate object.
- The object of type T is a Genre object.
- -> indicates a lamba expression
- The value after the -> must be a boolean expression.

import com.google.gson.*;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

import java.io.IOException;
import java.lang.reflect.Type;
import java.time.*;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class JsonDemo3 {
    public static void main(String[] args) throws IOException {
        // Remove before pushing to GitHub
        String apiKey = "";

        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url("https://api.themoviedb.org/3/trending/movie/day?language=en-US")
                .get()
                .addHeader("accept", "application/json")
                .addHeader("Authorization", "Bearer " + apiKey)
                .build();

        Request request2 = new Request.Builder()
                .url("https://api.themoviedb.org/3/genre/movie/list?language=en")
                .get()
                .addHeader("accept", "application/json")
                .addHeader("Authorization", "Bearer " + apiKey)
                .build();

        Response response = client.newCall(request).execute();
        String responseBody = response.body().string();
//        System.out.println(responseBody);

        Response response2 = client.newCall(request2).execute();
        String responseBody2 = response2.body().string();
//        System.out.println(responseBody2);

        Gson gson = new GsonBuilder()
                .setPrettyPrinting()
                .registerTypeAdapter(LocalDate.class, new LocalDateDeserializer())
                .create();
//        JsonElement jsonElement = new JsonParser().parse(responseBody);
//        String json = gson.toJson(jsonElement);
//        System.out.print(json);
        MovieDBAPI movieDBAPI = null;
        try {
            movieDBAPI = gson.fromJson(responseBody, MovieDBAPI.class);
        } catch (JsonSyntaxException | JsonIOException e) {
            System.out.println(e.getMessage());
            System.exit(0);
        }

        MovieDBGenre movieDBGenre = null;
        try {
            movieDBGenre = gson.fromJson(responseBody2, MovieDBGenre.class);
        } catch (JsonSyntaxException | JsonIOException e) {
            System.out.println(e.getMessage());
            System.exit(0);
        }
        Genre[] genres = movieDBGenre.genres;
        List<Genre> genresList = Arrays.asList(genres);

        for(Movie movie : movieDBAPI.results) {
            System.out.println("ID: " + movie.id);
            System.out.println("Title: " + movie.title);
            System.out.println("Overview: " + movie.overview);
//            System.out.println("Genres: " + Arrays.toString(movie.genre_ids));
            System.out.print("Genres: ");
            for(int id: movie.genre_ids){
                Genre genre = genresList.stream().filter(a -> a.id == id).collect(Collectors.toList()).get(0);
                System.out.print(genre.name + ", ");
            }
            System.out.println();
            System.out.println("Vote Average: " + movie.vote_average);
            System.out.println("Video: " + (movie.video ? "Yes" : "No"));
            System.out.println("Release Date: " + movie.release_date);
            System.out.println();
        }
    }

    private static class LocalDateDeserializer implements JsonDeserializer<LocalDate> {
        @Override
        public LocalDate deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
            return LocalDate.parse(json.getAsString());
        }
    }

    private static class MovieDBGenre {
        public Genre[] genres;
    }
    private static class Genre {
        public int id;
        public String name;
    }

    private static class MovieDBAPI {
        public Movie[] results;
    }
    private static class Movie {
        public int id;
        public String title;
        public String overview;
        public int[] genre_ids;
        public double vote_average;
        public boolean video;
        public LocalDate release_date;
    }
}