Part 3 – POST Request – Coding in Flow

[embedyt] https://www.youtube.com/watch?v=GP5OyYDu_mU[/embedyt]

In part 3 of the Retrofit tutorial, we will learn how to make HTTP POST requests on a REST API to create new resources.
For this we use the @POST annotation in our interface, define the relative URL endpoint and pass the object that we want to send to the server as an argument that we annotate with @Body. The GSON converter will then serialize this object into the JSON format before it is uploaded to the server. If we want to serialize the object into another format (like XML or String), we can use a different ConverterFactory.
The same as in a GET request, the POST method returns a Call object that we can enqueue to execute it asynchronously. A successful POST request will return a 201 (Created) response code together with a response body in the onResponse callback.
Retrofit also supports form-urlencoded format (application/x-www-form-urlencoded). For this we have to annotate a POST method with @FormUrlEncoded and pass either single @Field arguments or a @FieldMap.

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Links & DependenciesComment.javaPost.javaactivity_main.xmlJsonPlaceHolderApi.javaMainActivity.javaAndroidManifest.xml

Retrofit + converter dependencies:

square.github.io/retrofit/

JSONPlaceHolder API:

jsonplaceholder.typicode.com/

package com.codinginflow.retrofitexample;

import com.google.gson.annotations.SerializedName;

public class Comment {

    private int postId;

    private int id;

    private String name;

    private String email;

    @SerializedName("body")
    private String text;

    public int getPostId() {
        return postId;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    public String getText() {
        return text;
    }
}

package com.codinginflow.retrofitexample;

import com.google.gson.annotations.SerializedName;

public class Post {

    private int userId;

    private Integer id;

    private String title;

    @SerializedName("body")
    private String text;

    public Post(int userId, String title, String text) {
        this.userId = userId;
        this.title = title;
        this.text = text;
    }

    public int getUserId() {
        return userId;
    }

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getText() {
        return text;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="8dp"
    tools:context=".MainActivity">

    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/text_view_result"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="#000" />

    </android.support.v4.widget.NestedScrollView>

</android.support.constraint.ConstraintLayout>

package com.codinginflow.retrofitexample;

import java.util.List;
import java.util.Map;

import retrofit2.Call;
import retrofit2.http.Body;
import retrofit2.http.Field;
import retrofit2.http.FieldMap;
import retrofit2.http.FormUrlEncoded;
import retrofit2.http.GET;
import retrofit2.http.POST;
import retrofit2.http.Path;
import retrofit2.http.Query;
import retrofit2.http.QueryMap;
import retrofit2.http.Url;

public interface JsonPlaceHolderApi {

    @GET("posts")
    Call<List<Post>> getPosts(
            @Query("userId") Integer[] userId,
            @Query("_sort") String sort,
            @Query("_order") String order
    );

    @GET("posts")
    Call<List<Post>> getPosts(@QueryMap Map<String, String> parameters);

    @GET("posts/{id}/comments")
    Call<List<Comment>> getComments(@Path("id") int postId);

    @GET
    Call<List<Comment>> getComments(@Url String url);

    @POST("posts")
    Call<Post> createPost(@Body Post post);

    @FormUrlEncoded
    @POST("posts")
    Call<Post> createPost(
            @Field("userId") int userId,
            @Field("title") String title,
            @Field("body") String text
    );

    @FormUrlEncoded
    @POST("posts")
    Call<Post> createPost(@FieldMap Map<String, String> fields);
}

package com.codinginflow.retrofitexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class MainActivity extends AppCompatActivity {
    private TextView textViewResult;

    private JsonPlaceHolderApi jsonPlaceHolderApi;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textViewResult = findViewById(R.id.text_view_result);

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://jsonplaceholder.typicode.com/")
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        jsonPlaceHolderApi = retrofit.create(JsonPlaceHolderApi.class);

        //getPosts();
        //getComments();
        createPost();
    }

    private void getPosts() {
        Map<String, String> parameters = new HashMap<>();
        parameters.put("userId", "1");
        parameters.put("_sort", "id");
        parameters.put("_order", "desc");

        Call<List<Post>> call = jsonPlaceHolderApi.getPosts(parameters);

        call.enqueue(new Callback<List<Post>>() {
            @Override
            public void onResponse(Call<List<Post>> call, Response<List<Post>> response) {

                if (!response.isSuccessful()) {
                    textViewResult.setText("Code: " + response.code());
                    return;
                }

                List<Post> posts = response.body();

                for (Post post : posts) {
                    String content = "";
                    content += "ID: " + post.getId() + "\n";
                    content += "User ID: " + post.getUserId() + "\n";
                    content += "Title: " + post.getTitle() + "\n";
                    content += "Text: " + post.getText() + "\n\n";

                    textViewResult.append(content);
                }
            }

            @Override
            public void onFailure(Call<List<Post>> call, Throwable t) {
                textViewResult.setText(t.getMessage());
            }
        });
    }

    private void getComments() {
        Call<List<Comment>> call = jsonPlaceHolderApi
                .getComments("https://jsonplaceholder.typicode.com/posts/3/comments");

        call.enqueue(new Callback<List<Comment>>() {
            @Override
            public void onResponse(Call<List<Comment>> call, Response<List<Comment>> response) {

                if (!response.isSuccessful()) {
                    textViewResult.setText("Code: " + response.code());
                    return;
                }

                List<Comment> comments = response.body();

                for (Comment comment : comments) {
                    String content = "";
                    content += "ID: " + comment.getId() + "\n";
                    content += "Post ID: " + comment.getPostId() + "\n";
                    content += "Name: " + comment.getName() + "\n";
                    content += "Email: " + comment.getEmail() + "\n";
                    content += "Text: " + comment.getText() + "\n\n";

                    textViewResult.append(content);
                }
            }

            @Override
            public void onFailure(Call<List<Comment>> call, Throwable t) {
                textViewResult.setText(t.getMessage());
            }
        });
    }

    private void createPost() {
        Post post = new Post(23, "New Title", "New Text");

        Map<String, String> fields = new HashMap<>();
        fields.put("userId", "25");
        fields.put("title", "New Title");

        Call<Post> call = jsonPlaceHolderApi.createPost(fields);

        call.enqueue(new Callback<Post>() {
            @Override
            public void onResponse(Call<Post> call, Response<Post> response) {

                if (!response.isSuccessful()) {
                    textViewResult.setText("Code: " + response.code());
                    return;
                }

                Post postResponse = response.body();

                String content = "";
                content += "Code: " + response.code() + "\n";
                content += "ID: " + postResponse.getId() + "\n";
                content += "User ID: " + postResponse.getUserId() + "\n";
                content += "Title: " + postResponse.getTitle() + "\n";
                content += "Text: " + postResponse.getText() + "\n\n";

                textViewResult.setText(content);
            }

            @Override
            public void onFailure(Call<Post> call, Throwable t) {
                textViewResult.setText(t.getMessage());
            }
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.retrofitexample">

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>