How to make a GET request on Android?

Question

I previously developed a real time currency converter program, and would like to export it as an Android app. To do so, I am using a GET request with RestTemplate to get the rate between 2 currencies. However, I then get this error: android.os.NetworkOnMainThreadException

Here is the code I first tried:

   public void displayResult(View view) {

    TextView output = (TextView) findViewById(R.id.conversion);
    output.setInputType(InputType.TYPE_CLASS_NUMBER);
    output.setText(String.valueOf(convert()));
}

float convert() {

    EditText textBaseCurrency = (EditText) findViewById(R.id.BASE_CURRENCY);
    EditText textTargetCurrency = (EditText) findViewById(R.id.TARGET_CURRENCY);
    EditText textAmount = (EditText) findViewById(R.id.AMOUNT);

    String baseCurrency = textBaseCurrency.getText().toString().toUpperCase();
    String targetCurrency = textTargetCurrency.getText().toString().toUpperCase();
    float amount = Integer.parseInt(textAmount.getText().toString());

    restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
    String url = "https://v6.exchangerate-api.com/v6/" + API_KEY + "/latest/" + baseCurrency;
    ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class);
    System.out.println(responseEntity);

    ObjectMapper mapper = new ObjectMapper();
    JsonNode root = null;
    try {
        root = mapper.readTree(responseEntity.getBody());
    } catch (IOException e) {
        e.printStackTrace();
    }
    JsonNode name = root.get(conversionRates);
    JsonNode rates = name.get(targetCurrency);
    float rate = rates.floatValue();
    float newAmount = rate * amount;

    return newAmount;
}

I saw that the solution would be to use AsyncTask. I tried it, but I wasn't successful:

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


    public class Connection extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... voids) {

        EditText textBaseCurrency = (EditText) findViewById(R.id.BASE_CURRENCY);
        EditText textTargetCurrency = (EditText) findViewById(R.id.TARGET_CURRENCY);
        EditText textAmount = (EditText) findViewById(R.id.AMOUNT);

        String baseCurrency = textBaseCurrency.getText().toString().toUpperCase();
        String targetCurrency = textTargetCurrency.getText().toString().toUpperCase();
        float amount = Integer.parseInt(textAmount.getText().toString());

        restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
        String url = "https://v6.exchangerate-api.com/v6/" + API_KEY + "/latest/" + baseCurrency;
        ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class);
        System.out.println(responseEntity);

        ObjectMapper mapper = new ObjectMapper();
        JsonNode root = null;
        try {
            root = mapper.readTree(responseEntity.getBody());
        } catch (IOException e) {
            e.printStackTrace();
        }
        JsonNode name = root.get(conversionRates);
        JsonNode rates = name.get(targetCurrency);
        float rate = rates.floatValue();
        float newAmount = rate * amount;

        return null;
    }

Moreover, this is now deprecated.

My gradle.build file:

    packagingOptions{
    exclude 'META-INF/notice.txt'
    exclude 'META-INF/license.txt'
}dependencies {
implementation fileTree(dir: "libs", include: ["*.jar"])
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'androidx.constraintlayout:constraintlayout:2.0.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test.ext:junit:1.1.2'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
implementation 'com.fasterxml.jackson.core:jackson-databind:2.9.10.6'
implementation 'javax.xml.stream:stax-api:1.0'
implementation 'org.springframework.android:spring-android-rest-template:1.0.1.RELEASE'

}

I also added <uses-permission android:name="android.permission.INTERNET" /> in my AndroidManifest.xml

`I saw that the solution would be to use AsyncTask. I tried it, but I wasn't successful.` - show what you have tried, this is proper approach. You ma exchange `AsyncTask` for some other solution, e.g. like [HERE](https://stackoverflow.com/questions/58767733/android-asynctask-api-deprecating-in-android-11-what-are-the-alternatives) — snachmsm, Sep 07 '20 at 13:17

Vikas · Answer 1 · 2020-09-08T15:16:28.317

1

You need to do your api process im background thread instead of Main thread

Use Async Task Use Retrofit Use Runnable

Choose one from these. There are many more

edited Sep 08 '20 at 15:16

answered Sep 07 '20 at 13:19

Vikas

432
4
17

Hassan Yousefzadeh · Accepted Answer · 2020-09-07T13:29:02.230

You can use some library like to do this:

but first of all you should add this permission:

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

but the easiest way is :

class RequestTask extends AsyncTask<String, String, String>{

    @Override
    protected String doInBackground(String... uri) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpResponse response;
        String responseString = null;
        try {
            response = httpclient.execute(new HttpGet(uri[0]));
            StatusLine statusLine = response.getStatusLine();
            if(statusLine.getStatusCode() == HttpStatus.SC_OK){
                ByteArrayOutputStream out = new ByteArrayOutputStream();
                response.getEntity().writeTo(out);
                responseString = out.toString();
                out.close();
            } else{
                //Closes the connection.
                response.getEntity().getContent().close();
                throw new IOException(statusLine.getReasonPhrase());
            }
        } catch (ClientProtocolException e) {
            //TODO Handle problems..
        } catch (IOException e) {
            //TODO Handle problems..
        }
        return responseString;
    }
    
    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        //Do anything with response..
    }
}

You then can make a request by:

   new RequestTask().execute("https://v6.exchangerate-api.com/v6/" + API_KEY + "/latest/" + baseCurrency);

keep in mind if you use this application on android 9 you should use this attribute to your AndroidManifest.xml where you allow all http for all requests:

<application android:usesCleartextTraffic="true">
</application>

But in case you want some more configurations for different links, for instance, allowing HTTP for some domains but not other domains you must provide res/xml/networkSecurityConfig.xml file.

To do this in Android 9 Pie you will have to set a networkSecurityConfig in your Manifest application tag like this:

<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
    <application android:networkSecurityConfig="@xml/network_security_config">




    </application>
</manifest>

Then in your xml folder you now have to create a file named network_security_config just like the way you have named it in the Manifest and from there the content of your file should be like this to enable all requests without encryptions:

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <base-config cleartextTrafficPermitted="true">
        <trust-anchors>
            <certificates src="system" />
        </trust-anchors>
    </base-config>
</network-security-config>

but note this:

HttpClient is not supported any more in sdk 23. You have to use URLConnection or downgrade to sdk 22 (compile 'com.android.support:appcompat-v7:22.2.0')

If you need sdk 23, add this to your gradle:

android {
    useLibrary 'org.apache.http.legacy'
}

You also may try to download and include HttpClient.jar directly into your project or use OkHttp instead

score 1 · Answer 3 · answered Sep 07 '20 at 13:23

You cannot execute HTTP requests in the main thread as it . You need to run them on a different thread and then run a callback in the main thread.
Yes, you could use an AsyncTask but the code would be really verbose and I personally don't like AsyncTasks

However I'll suggest you to use more advanced libraries that work great like Retrofit or OkHttp

score 1 · Answer 4 · answered Sep 07 '20 at 13:26

You have to perform Network related operations on a Separate thread... You can use AsyncTask

private class DownloadFilesTask extends AsyncTask<Void, Void, Float> {
    protected Float doInBackground(Void) {
         // put the convert function definition
    }

    protected void onPostExecute(Float result) {
        // update the UI after background processes completes
    }
}

Define this class as a subclass of that activity, then call it like

new MyTask().execute();

How to make a GET request on Android?

4 Answers4