How to solve the error `java.net.ConnectException: Failed to connect to localhost/127.0.0.1:8000`

Question

I'm currently developing an application using android-studio with Kotlin and an API system using django-rest-framework.

I want to access my local server 127.0.0.1 with an android emulator to get some value from the API method.

I checked some questions in the stack overflow site and other sites and I set my codes up referring to some articles, like adding some code in an AndroidManifest.xml, making a network_security_config.xml, changing a proxy of Android emulator and changing some code in Django rest framework project.

even though when I hit an endpoint in my local server I have error codes like below:

2020-10-07 22:37:39.318 7247-7247/com.sample.apitest I/System.out: checked
2020-10-07 22:37:39.358 7247-7280/com.sample.apitest D/NetworkSecurityConfig: Using Network Security Config from resource network_security_config debugBuild: true
2020-10-07 22:37:39.392 7247-7280/com.sample.apitest W/System.err: java.net.ConnectException: Failed to connect to localhost/127.0.0.1:8000
2020-10-07 22:37:39.394 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.io.RealConnection.connectSocket(RealConnection.java:143)
2020-10-07 22:37:39.394 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.io.RealConnection.connect(RealConnection.java:112)
2020-10-07 22:37:39.394 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.http.StreamAllocation.findConnection(StreamAllocation.java:184)
2020-10-07 22:37:39.395 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.http.StreamAllocation.findHealthyConnection(StreamAllocation.java:126)
2020-10-07 22:37:39.395 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.http.StreamAllocation.newStream(StreamAllocation.java:95)
2020-10-07 22:37:39.395 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:281)
2020-10-07 22:37:39.396 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:224)
2020-10-07 22:37:39.396 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:461)
2020-10-07 22:37:39.396 7247-7280/com.sample.apitest W/System.err:     at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:127)
2020-10-07 22:37:39.397 7247-7280/com.sample.apitest W/System.err:     at com.sample.apitest.MainActivity$HitAPITask.doInBackground(MainActivity.kt:49)
2020-10-07 22:37:39.397 7247-7280/com.sample.apitest W/System.err:     at com.sample.apitest.MainActivity$HitAPITask.doInBackground(MainActivity.kt:39)
2020-10-07 22:37:39.397 7247-7280/com.sample.apitest W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:333)
2020-10-07 22:37:39.397 7247-7280/com.sample.apitest W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
2020-10-07 22:37:39.397 7247-7280/com.sample.apitest W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
2020-10-07 22:37:39.397 7247-7280/com.sample.apitest W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
2020-10-07 22:37:39.398 7247-7280/com.sample.apitest W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
2020-10-07 22:37:39.398 7247-7280/com.sample.apitest W/System.err:     at java.lang.Thread.run(Thread.java:764)

How could I solve this error?

---

Here are the codes:

Android project

emulator settings

AndroidManifest.xml

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

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

    <application
            android:networkSecurityConfig="@xml/network_security_config"
            android:usesCleartextTraffic="true"

            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"
            tools:ignore="GoogleAppIndexingWarning"
            tools:targetApi="n">
        <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>

network_security_config.xml

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">localhost</domain>
    </domain-config>
</network-security-config>

MainActivity.kt

package com.sample.apitest

import android.os.AsyncTask
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import org.json.JSONException
import org.json.JSONObject
import java.io.BufferedReader
import java.io.IOException
import java.io.InputStreamReader
import java.net.HttpURLConnection
import java.net.MalformedURLException
import java.net.URL

class MainActivity : AppCompatActivity() {

    var name: TextView? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        name = findViewById(R.id.textView)
        val button = findViewById<Button>(R.id.button)

        button.setOnClickListener {
            println("checked")
            HitAPITask().execute("http://localhost:8000/api/name/")

        }
    }

    inner class HitAPITask : AsyncTask<String, String, String>() {

        override fun doInBackground(vararg params: String?): String? {
            var connection: HttpURLConnection? = null
            var reader: BufferedReader? = null
            val buffer: StringBuffer

            try {
                val url = URL(params[0])
                connection = url.openConnection() as HttpURLConnection
                connection.connect()

                val stream = connection.inputStream
                reader = BufferedReader(InputStreamReader(stream))
                buffer = StringBuffer()
                var line: String?
                while (true) {
                    line = reader.readLine()
                    if (line == null) {
                        break
                    }
                    buffer.append(line)
                }

                var jsonText = buffer.toString()

                val jsonObj = JSONObject(jsonText)
                val plant_name: String = jsonObj.getString("name")

                return plant_name
            } catch (e: MalformedURLException) {
                e.printStackTrace()
            } catch (e: IOException) {
                e.printStackTrace()
            } catch (e: JSONException) {
                e.printStackTrace()
            } finally {
                connection?.disconnect()
                try {
                    reader?.close()
                } catch (e: IOException) {
                    e.printStackTrace()
                }
            }
            return null
        }

        override fun onPostExecute(result: String?) {
            super.onPostExecute(result)
            if (result == null) return

            name!!.text = result
        }
    }
}

build.gradle

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.sample.apitest"
        minSdkVersion 16
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:2.0.1'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

---

Django rest framework project

project/settings.py

    #...      

INSTALLED_APPS = [
    #...
    'corsheaders',
]

MIDDLEWARE = [
    #...
    'corsheaders.middleware.CorsMiddleware',
    'django.middleware.common.CommonMiddleware',
]

CORS_ORIGIN_WHITELIST = [
    'http://10.0.2.2:8000'
]

API endpoint

[ Method = GET ] http://127.0.0.1:8000/api/name/

    {
      "name": "myName.",
    }

---

android-studio: 3.3.2

python: 3.7.5

django-cors-headers: 2.4.0

djangorestframework: 3.8.2

Answer 1

Try open cmd and then write ipconfig on it after that you got your local ip address then try to put on your code

for example you got 192.168.1.2 from your cmd then put it to your code like this:

HitAPITask().execute("http://192.168.1.2/api/name/")