HttpUrlConnection not connecting to the server

Question

I'm new to Android development, and with some consulting on the internet I came up with the following code to connect to a Url, POST a string content and read it's response.

private static java.lang.String getRequest(java.lang.String Url, java.lang.String PostContent)
{
    java.lang.StringBuilder content = new java.lang.StringBuilder();
    try
    {
        java.lang.String line;
        java.net.URL url = new java.net.URL(Url);
        if (cweb.companion.MainActivity.url.startsWith("https"))
        {
            javax.net.ssl.HttpsURLConnection httpsConnection = (javax.net.ssl.HttpsURLConnection)url.openConnection();
            httpsConnection.setSSLSocketFactory((javax.net.ssl.SSLSocketFactory)javax.net.ssl.SSLSocketFactory.getDefault());
            httpsConnection.setRequestMethod("POST");
            httpsConnection.setDoOutput(true);
            httpsConnection.setRequestProperty("Content-Type", "text/plain");
            httpsConnection.addRequestProperty("Content-Length", java.lang.String.valueOf(PostContent.length()));
            java.io.OutputStreamWriter wr = new java.io.OutputStreamWriter(httpsConnection.getOutputStream());
            wr.write(PostContent);
            wr.flush();
            wr.close();
            java.io.BufferedReader bufferedReader = new java.io.BufferedReader(new java.io.InputStreamReader(httpsConnection.getInputStream()));
            while ((line = bufferedReader.readLine()) != null) { content.append(line + "\n"); }
            bufferedReader.close();
        }
        else
        {
            java.net.HttpURLConnection httpConnection = (java.net.HttpURLConnection)url.openConnection();
            httpConnection.setRequestMethod("POST");
            httpConnection.setDoOutput(true);
            httpConnection.setRequestProperty("Content-Type", "text/plain");
            httpConnection.addRequestProperty("Content-Length", java.lang.String.valueOf(PostContent.length()));
            java.io.OutputStreamWriter wr = new java.io.OutputStreamWriter(httpConnection.getOutputStream());
            wr.write(PostContent);
            wr.flush();
            wr.close();
            java.io.BufferedReader bufferedReader = new java.io.BufferedReader(new java.io.InputStreamReader(httpConnection.getInputStream()));
            while ((line = bufferedReader.readLine()) != null) { content.append(line + "\n"); }
            bufferedReader.close();
        }
        return content.toString();
    } catch (java.lang.Exception e) { return "ERROR{" + e.getMessage() + "}"; }
}

I left it very "duplicated" to help me debugging (I know could push out some code to other methods).

That code is in the MainActivity that implements like this:

public class MainActivity extends androidx.appcompat.app.AppCompatActivity
{
    private static java.lang.String getRequest(java.lang.String Url, java.lang.String PostContent)
    {
        //my code (as posted earlier)
    }

    @Override protected void onCreate(android.os.Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_main);
        //here i call the code to something like:
        java.lang.String retHTTP = getRequest("http://httpaddress.example.com", "hello world!");
        java.lang.String retHTTPS = getRequest("https://httpsaddress.example.com", "hello world!");
    }
}

If I target a HTTPS address the function throws and empty exception and ends (the getMessage() method of the Exception is a null/empty string) and if it targets a HTTP address it gives me a "Cleartext HTTP traffic to localhost not permitted" message.

My manifest and Gradle are like this:

Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:targetSandboxVersion="1" package="cweb.companion">
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <application
        android:usesCleartextTraffic="true"
        android:allowBackup="true"
        android:icon="@drawable/logo_standard"
        android:label="@string/app_name"
        android:roundIcon="@drawable/logo_standard"
        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>

Gradle

apply plugin: 'my.application.com'
android
    {
        compileSdkVersion 29
        buildToolsVersion "29.0.3"
        defaultConfig
                {
                    applicationId "my.application.com"
                    minSdkVersion 23
                    targetSdkVersion 29
                    versionCode 1
                    versionName "1.0"
                    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
                }
        buildTypes
                {
                    release
                            {
                                minifyEnabled true
                                proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
                            }
                }
        sourceSets { main { assets.srcDirs = ['src/main/assets', 'src/main/assets/'] } }
    }
dependencies
    {
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        implementation 'androidx.appcompat:appcompat:1.0.2'
        implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
        testImplementation 'junit:junit:4.12'
        androidTestImplementation 'androidx.test.ext:junit:1.1.0'
        androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'
    }

So, why the connection does not happen (I have the server side code as well and nothing is even sent to it, in both cases)?

It will be very easy for you if you use [retrofit](https://github.com/square/retrofit) or some other client library. Few lines of code will do what you want. — Afsar edrisy, Feb 28 '20 at 13:22
I don't work with `HttpUrlConnection` but every Http call shouldn't be done at main thread. It just won't work. But yeah, `Retrofit` will be better alternative and it even have built-in thread handling. — SkypeDogg, Feb 28 '20 at 13:24
@Afsaredrisy maybe, but i'm knew to this IDE and language, so merge things is complicated, but wouldn't it work? is anything wrong here? — SammuelMiranda, Feb 28 '20 at 13:24
@SkypeDogg did not know that, so have to be in a different class? — SammuelMiranda, Feb 28 '20 at 13:26
For Http call you need add network security config file see [this](https://stackoverflow.com/questions/45940861/android-8-cleartext-http-traffic-not-permitted) & You should call `getRequest()` method from background thread use [Asyncktask](https://developer.android.com/reference/android/os/AsyncTask) or Handler for that — Afsar edrisy, Feb 28 '20 at 13:27
Just make the call inside `AsyncTask` even inside same activity — SkypeDogg, Feb 28 '20 at 13:27
Are you using a real device or an emulated device to test? I had the same Problem with a Samsung S9. After an update it started to throw a security exception for HTTP and only HTTPS calls were permitted. — Dominik Wuttke, Feb 28 '20 at 13:29
@Afsaredrisy tryed that post before nothing changed with the security file, but never done in a Asynctask so maybe the problem is there as well (requires both) - i'll read about AsyncTask and try to implement to see if it solves the issue. — SammuelMiranda, Feb 28 '20 at 13:29
@SammuelMiranda Here you have great explanation of `AsyncTask`: https://stackoverflow.com/a/25647882/7074278 . Happy Coding ;) — SkypeDogg, Feb 28 '20 at 13:31

score 1 · Accepted Answer · answered Feb 28 '20 at 14:00

For HTTP request as you said that you have added security configuration to your project then here is working HTTP call

...

 java.net.URL url = new java.net.URL(Url);
          ...
         else
        {
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5000000);
            conn.setRequestProperty("Content-Type", "text/plain; charset=UTF-8");
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setRequestMethod("POST");
            OutputStream os = conn.getOutputStream();
            os.write(PostContent.getBytes("UTF-8"));
            os.close();
            // read the response
            InputStream in = new BufferedInputStream(conn.getInputStream());

            String result = IOUtils.toString(in, "UTF-8");
            conn.disconnect();
            return result;
        }
    } catch (java.lang.Exception e) { return "ERROR{" + e.getMessage() + "}"; }

...

Now consider to do network operation on background thread So you can make a call to getRequest method as follows.


  protected void onCreate(android.os.Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_main);
        //here you call the code to something like in Background thread:
        new AsyncTask<Void, Void, Void>() {
            @Override
            protected Void doInBackground(Void... voids) {
                java.lang.String retHTTP = getRequest("http://httpaddress.example.com", "hello world!");
                return null;
            }
        }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);

    }

Same you can success HTTPS as well with SSL.

Note: Use implementation 'org.apache.commons:commons-io:1.3.2' for IOUtils in app.gradle file.

everything freezes at conn.getOutputStream() so far, still working on it though - i'll update my question with the code changes as soon as i exhaust all attempts — SammuelMiranda, Feb 28 '20 at 14:39
worked! did not put the implementation tag though, but used the xml solution with only the tag (no domain tag) - in the end isn't exactly like your post but took a lot from it and for the "how to do asynctask" post as well. Thanks everyone for the help! — SammuelMiranda, Feb 28 '20 at 17:26

HttpUrlConnection not connecting to the server

1 Answers1