Android studio post запрос json

POST запросы в Android. Как?

Решил попробовать пописать под Android, соответственно появилось очень большое количество вопросов. Кому не трудно ответьте пожалуйста.

Пытаюсь сделать, чтобы приложение работало с неким API, общение с помощью json , но у меня не получается написать класс, как например на шарпе, в который я передаю адрес, параметры и выполняю POST запрос, например как здесь https://stackoverflow.com/questions/4015324/http-request-with-post.

Насколько я понял приложение на Android не может выполнить POST запрос из обычного метода, нужно использовать AsyncTask<> — тут я вообще ничего не понял, начиная от самого синтаксиса, а именно doInBackground(String. params) — String. это перечисления параметров при вызове метода типа doInBackground(str1, str2, str3) или как?

В общем я не прошу написать за меня готовый код, прошу помочь понять принцип как работать с POST запросами в Android, хотя бы один конкретный пример: отправка POST (json) и получение ответа так же в json и немного теории, пжлст)).

как я понял первое это тип входящего значения, второй тип промежуточного значения(. ), третий это тип возвращаемого значения, верно? Что есть промежуточное значение?

4 ответа 4

AsyncTask лучше один раз попробовать, и потом забыть про них. То же самое касается и HttpUrlConnection . В настоящий момент основной библиотекой для взаимодействия с Rest сервером в Android считается Retorofti. На официальном сайте есть примеры. Так же их не мало и на сторонних ресурсах, например здесь. Приведу лишь пример POST запроса.

Для этого нам потребуется класс-модель, в которую преобразуется полученный от сервера Json, класс-модель для тела запроса и интерфейс с методом аннотированным специальной анотацией.

Допустим сервер имеет метод, который добавляет почтовые адреса пользователю, и возвращает какую то информацию о статусе операции. В теле запроса сервер принимает обычный массив из строк, а результат возвращает в виде Json.

Сначала создаем модель ответа сервера(поля объявлены как public с целью уменьшения кода, в реальном приложении лучше использовать private + get/set методы):

Теперь создаем интерфейс, через который будет происходить взаимодействие с сервером.

Аннотация над методом означает что будет выполнен POST запрос, аннотация @Body указывает на то, что этот объект должен быть передан в теле запроса.

Далее необходимо создать сервера. Делается это так:

Вызывая метод enqueue() вы говорите что бы запрос выполнился асинхронно. В конце результат придет в переданный callback где его можно обработать. Вот в принципе и все. Данная библиотека не ограничивается одним лишь POST запросом, она умеет делать все, что нужно для разработки клиент-серверного приложения.

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Sending a JSON POST request in Android

I am new to Andorid and understand the following method of sending post requests are deprecated in Android 22 and later. Would anyone have a working sample of Android code using the URLCONNECTION method seding a JSON POST request (I guess this is the basic model not using import org.apache.http.client).

4 Answers 4

its time to use volley bro ,android networking library that’s fast and much more better then http request in performance. few features of volley.

1. Request queuing and prioritization
2. Effective request cache and memory management
3. Extensibility and customization of the library to our needs
4. Cancelling the requests

here u can do the same thing with volley first of all set the dependencies

after that create a singleton class

this is as it is just copy and paste and name it AppController then make a few changes in manifest add it in your application tag of manifest

and finally last one is to make a json request and here is how u can do it .

and with volley you can make almost any type of request by extending the volley class but in default we have

1.StringRequest 2. JsonObjectRequest 3. JsonArrayRequest

and in above we have used JsonObjectRequest

I know this is not a direct answer to your problem but i hope this helps you some how little or more.

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How To Send json Object to the server from my android app

I’m at a bit of a loss as to how to send a json object from my android application to the database

As I am new to this I’m not too sure where I’ve gone wrong, I’ve pulled the data from the XML and I have no clue how to then post the object to our server.

any advice would be really appreciated

4 Answers 4

You need to be using an AsyncTask class to communicate with your server. Something like this:

This is in your onCreate method.

This is a new class within you activity class.

The line: httpURLConnection.setRequestMethod(«POST»); makes this an HTTP POST request and should be handled as a POST request on your server.

Then on your server you will need to create a new JSON object from the «PostData» which has been sent in the HTTP POST request. If you let us know what language you are using on your server then we can write up some code for you.

You should use web service to send data from your app to your server because it will make your work easy and smooth. For that you have to create web service in any server side language like php,.net or even you can use jsp(java server page).

You have to pass all items from your Edittexts to web service.Work of adding data to server will be handled by web service

As per your current code implementation you have onPostExecute method but there is no onPreExecute and doInBackgound method. Starting from Android 3.0 all network operations need to be done on the background thread. So you need to use Asynctask that will perform the actual sending of the request in the background and in the onPostExecute handle the result returned by the doInbackground method.

Here is what you need to do.

1. Create a Asynctask class and override all the necessary methods.
2. The sendDeviceDetails method will eventually go inside the doInBackgound method.
3. onPostExecute will handle the result returned.

As far as sending a JSON object is concerned, you can do it as follows,

Code snippet borrowed from here

This is just one of the ways. You can go for an Asynctask implementation as well.

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How to send a JSON object over Request with Android?

I want to send the following JSON text

to a web service and read the response. I know to how to read JSON. The problem is that the above JSON object must be sent in a variable name jason .

How can I do this from android? What are the steps such as creating request object, setting content headers, etc.

8 Answers 8

Sending a json object from Android is easy if you use Apache HTTP Client. Here’s a code sample on how to do it. You should create a new thread for network activities so as not to lock up the UI thread.

You could also use Google Gson to send and retrieve JSON.

Android doesn’t have special code for sending and receiving HTTP, you can use standard Java code. I’d recommend using the Apache HTTP client, which comes with Android. Here’s a snippet of code I used to send an HTTP POST.

I don’t understand what sending the object in a variable named «jason» has to do with anything. If you’re not sure what exactly the server wants, consider writing a test program to send various strings to the server until you know what format it needs to be in.

HttpPost is deprecated by Android Api Level 22. So, Use HttpUrlConnection for further.

There’s a surprisingly nice library for Android HTTP available at the link below:

Simple requests are very easy:

It’s all asynchronous, works well with Android and safe to call from your UI thread. The responseHandler will run on the same thread you created it from (typically, your UI thread). It even has a built-in resonseHandler for JSON, but I prefer to use google gson.

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How to Send JSON Data in a POST Request in Android

Retrofit2 is a powerful HTTP client library developed by Square used in Android and Java development. I have put together a tutorial with code samples in Java covering how to send JSON data in a HTTP POST request within an Android app using Retrofit2.

To send JSON data in a POST request in Android using Retrofit2 you need to complete the following steps.

1. Obtain the dependencies for Retrofit2 using Gradle
2. Create the model for the API request and response
3. Create a Java interface representing the service and including Retrofit2 annotations
4. Set up the HTTP client using a singleton pattern within your app
5. Invoke the HTTP client generating the request and handling the response and errors
6. Configure the app manifest to give permission to access the internet

Continue reading this post to deep dive into what Retrofit2 is and how it can be used to generate a POST request containing JSON data with code samples available in this article in Java.

I have also added some information to the tutorial around an alternative approach for sending data in a POST request with Retrofit2 by using URL parameters instead of a JSON body inside the request.

Android HTTP JSON Body Post Request in Java Using Retrofit2 Example

We will be creating a very basic Android app for this tutorial to demonstrate how to make a HTTP POST request containing a JSON body using Retrofit2.

Please see a screenshot of the Android app will be creating. The app contains a basic form that is used to capture a comment which is like something that you might see on a social media app or a news app with articles the public can comment on.

As you can see it contains the following:

• Three fields for capturing a Comment including a title, a body and an author
• A radio button group containing three different options for creating the HTTP POST request using Retrofit2
• And a button to send the HTTP POST request containing the data about the Comment

I have uploaded the code for the Android app being created in this tutorial in GitHub – https://github.com/learntodroid/PostRequestwithJSON

For the purposes of this tutorial I have written code for a very basic API using Python and the library Flask which is configured to respond with the same Comment sent to the API in POST request from the Android app.

If you are interested in the code for the API written in Python using the Flask library it is also available on GitHub – https://github.com/learntodroid/PostRequestFlaskApi

If you want to run this API make sure you have Python and PyPi installed on your local machine where you are running the Android emulator and follow the brief instructions in the Readme to retrieve the dependencies for Flask and run the API.

Step 1: Obtaining the Retrofit2 Dependencies

In this tutorial we will be making use of various 3rd party libraries to simplify the effort required to integrate our Android app with an API to make a POST request.

The 3rd party libraries we will use include Retrofit2, OkHttp3 and GSON. Each of the libraries will be retrieved into our Android project using Gradle.

Retrofit2

Retrofit2 is a HTTP client for Android and Java developed by Square which allows you to use a Java interface to simplify the process of integrating with a HTTP API.

To retrieve the Retrofit2 library using Gradle include the following implementation dependency inside your app’s build.gradle file (see a complete build.gradle file at the end of this section which covers all required dependencies).

Retrofit2 requires Java 8, to include Java 8 in an Android project, update your app’s build.gradle file to include compile options.

OkHttp3

OkHttp3 is a HTTP client for Java and Kotlin developed by Square.

For the purposes of this tutorial we will be using the logging interceptor included in the OkHttp3 library to give us visibility of the HTTP request and response logs for our Android app within Logcat.

To get an idea of what we will be able to see in Logcat using the OkHttp3 logging interceptor, have a look at the screenshot below

To retrieve the logging interceptor from the OkHttp3 library using Gradle include the following implementation dependency inside your app’s build.gradle file.

Gson is a Java library by Google that supports converting objects in Java into JSON format and back otherwise known as serialization and deserialization.

Retrofit2 has added support for different converters including GSON to support serialization and deserialization when handling an API’s request and response.

To retrieve the GSON converter from the Retrofit2 library using Gradle include the following implementation dependency inside your app’s build.gradle file.

The list of converters supported by Retrofit2 are:

Example ‘build.gradle’ Containing Retrofit2, OkHttp3 & GSON Dependencies

Please see the example build.gradle file covering all the dependencies highlighted in the section above.

Step 2: Creating the Model for the API Request and Response

The comments we will capture in our Android app with contain three attributes entered by the user. These three attributes will all be strings and will contain the comment author, a title for the comment and a body for the comment.

When we will be make a POST request to the API, we will use the GSON library to transform a Comment object into a JSON string (serialization) to send inside the body of the request.

If the request was correctly formatted the API will request with the same JSON file we can then use GSON to transform that JSON string and transform it into a Comment object (deserialization).

When building the model class, use the @SerializedName(string) annotation against each field to set the name of the attribute as it will appear in the JSON file. By default GSON will use the variable name in Java if there is no @SerializedName(string) annotation provided.

Please see the example class below containing the model for a comment.

Step 3: Creating a Java Interface for the API with Retrofit2

In this section of the tutorial we will be creating a Java interface and use the Retrofit2 library to add annotations to methods in the interface that will represent the operations exposed on the API.

Please see the example Java interface using Retrofit2 annotations to describe the API will we be using to submit Comments.

In this section we will focus the createComment(Comment) method defined on line 14.

Line 13, contains both the request method and path that will be called on the API when the createComment(Comment) method is invoked. In this case we are using a POST request so we use the “@POST” Retrofit2 annotation. We will be sending the POST request to the “/comments” end point on the API so inside we pass the path as a parameter to the “@POST” annotation.

The full list of request methods supported by Retrofit2 are:

On line 14, we are defining the method for creating a comment and we are passing a @Body annotation with a Comment object as a parameter. Providing an @Body annotation with a Comment as a parameter indicates that we will be providing a request body when we invoke this API which in our case will be a JSON payload containing the details of the comment.

The finally, the createComment(Comment) method returns a Call object. This means that when we invoke the API to create the comment we expect to see a request body containing a JSON body that we will deserialize into a Comment object (in our case using Gson).

Step 4: Setting Up the HTTP Client

In this part of the tutorial we will setting up access to the HTTP client using Retrofit2 inside a repository class that follows the singleton pattern. This will enable us in the next step of tutorial to retrieve the instance of the repository then invoke the API to create a comment.

Please see the code below containing the CommentsRepository class which initialises the HTTP client using Retrofit2 inside the constructor.

Inside the constructor prior to setting up the API using Retrofit2 first we create an interceptor using the OkHttp3 library that we will use to allow us to log the HTTP request and responses inside Logcat. We create also use the OkHttp3 library for it’s HTTP client when interacting with the API.

Using the Retrofit2 API builder we provide it with the base url of the API, we set the client to the OkHttp3 client and specify we will be using the Gson library for converting API request and response payloads.

With regards to the base url, I have set it to use the host of “http://10.0.2.2” and the port number 5000. This is because I will use flask to run on it’s default port which is port 5000, and run it on the same host as where I am running the Android emulator.

You cannot use “localhost” as the host for the Android emulator because as I learned in this helpful Stackoverflow answer localhost on the Android emulator will point to the emulator’s own loopback service and you need to use “10.0.2.2” instead to access your local machine.

And finally we create a reference to the web service using the interface of the API we defined in step 3.

Step 5: Invoking the API using Retrofit2

In this section of the tutorial for sending a JSON payload inside a POST request using Retrofit2 we will be creating our Activity that will invoke the API using Retrofit2.

Please see the code below containing the CommentsActivity class which invokes the HTTP client with a POST request using Retrofit2 when the button is clicked.

Inside the onCreate(Bundle) method we will get access to the single instance of the CommentsRepository which we will use in the OnClickListener assigned to the Button to generate a HTTP request to the Comments API.

Inside the OnClickListener we first create the Comment object using the comment title, comment author and comment body captured by the use.

Then using a switch statement check for which radio button was selected, in this section I will only cover the option sending the JSON payload which is defined in lines 55 – 66.

To invoke the API we access the CommentService on the CommentRepository and call the createComment(Comment) method passing the Comment object we created based on the user input.

We call the createComment(Comment) method using enqueue which allows use to define a callback method in case of either a response (defined in an onResponse method) or failure (defined in a onFailure method).

In the onResponse method we expect to see a Comment object in the response and we use a toast to show the comment text which is present inside the HTTP response JSON body that gets deserialized into a Comment object using Gson.

In the onFailure method we simply display the error encountered using a toast, this may occur if the API is down, if there are connectivity issues, or there is a coding error on the server side API.

I have also included the layout resource below which I used for the CommentActivity class.

Step 6: Configure the Manifest to Access the Internet

One final thing you will need to do to ensure you have connectivity to the API is to enable the permission to access the internet (android.permission.INTERNET) inside your Android Manifest for your app.

In addition to this, if you are going to use the Flask API I wrote and don’t want to configure a HTTPS certificate for the API, you will need to add an attribute in the application tag (by setting “android:usesCleartextTraffic” to “true”) inside the Android Manifest to specify that you want to send clear text traffic in your Android app. Warning: Sending clear text traffic should not be done in production for security reasons.

See the sample AndroidManifest.xml file below the shows how to configure the use of clear text traffic and setting the permission to access the internet.

Demonstration

Now if you run your Android app with the API running, and include the comment details and click the button, you should see something like the following in Logcat.

Sending Data in URL Parameters using a POST Request with Retrofit2

Retrofit2 also has support for sending data in a POST request using parameters within the URL.

To achieve this using Retrofit2 inside the interface class you need to add @FormUrlEncoded annotation above the method name. For an example of this check out lines 16 and 20 in the interface code shared in Step 3 of this tutorial you will see the use of the @FormUrlEncoded annotation.

To see the difference in the logs when using the @FormUrlEncoded annotation compare the Logcat results from the Demo section above to the results using the @FormUrlEncoded annotation below.

As you can see one difference is that the Content-Type in the header of the request is to set “application/x-www-form-urlencoded”. Another difference is that instead of a request body the the title, comment and author appear in an encoded format in the URL.

How to Use @Field and @FieldMap in Retrofit2

When making a request to an API defined in Retrofit2 you opt to pass the attributes to be sent in the request as a set of fields or as a set of key value pairs.

Using @Field Annotation in Retrofit2

If you check out line 18 in the interface code shared in Step 3 of this tutorial you will see the use of the @Field annotation. Each of the field names and their data types are defined in the method parameters inside the interface.

If you have a look at line 69 in the activity code shared in Step 5 of this tutorial you will see that instead of passing the Comment object as a parameter to the createComment method, the title, comment and author are passed as individual strings instead.

Using @FieldSet Annotation in Retrofit2

If you check out line 22 in the interface code shared in Step 3 of this tutorial you will see the use of the @FieldMap annotation. A Map contain keys that are Strings and values that are Strings are defined as a parameter for that method inside the interface.

If you have a look at lines 83 to 87 in the activity code shared in Step 5 of this tutorial you will see that instead of passing the Comment object as a parameter to the createComment method, a HashMap is passed as an parameter. This HashMap contains key value pairs of which the field names are defined as the keys and the comment title, comment body and comment author are defined as the values.

Further Reading

If you want to learn using the Model View ViewModel software design pattern with Retrofit2 to integrate your Android app with an API, check out the other post I wrote below that goes into this.

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