如何解决错误`java.net.ConnectException: Failed to connect to localhost/127.0.0.1:8000`

Posted 2023-03-03

【中文标题】如何解决错误`java.net.ConnectException: Failed to connect to localhost/127.0.0.1:8000`

【英文标题】：How to solve the error `java.net.ConnectException: Failed to connect to localhost/127.0.0.1:8000`

【发布时间】：2021-01-22 15:49:55

【问题描述】：

我目前正在开发一个使用android-studio 和Kotlin 的应用程序以及一个使用django-rest-framework 的API 系统。

我想使用 android 模拟器访问我的本地服务器 127.0.0.1 以从 API 方法中获取一些值。

我检查了堆栈溢出站点和其他站点中的一些问题，并参考一些文章设置了我的代码，例如在AndroidManifest.xml 中添加一些代码，创建network_security_config.xml，更改Android emulator 的代理和更改 Django rest framework 项目中的一些代码。

即使当我点击本地服务器中的端点时，我也有如下错误代码：

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)

我该如何解决这个错误？

---

代码如下：

Android 项目

模拟器设置

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 框架项目

项目/settings.py

    #...      

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

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

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

API 端点

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

    
      "name": "myName.",
    

---

安卓工作室：3.3.2

蟒蛇：3.7.5

django-cors-headers: 2.4.0

djangorestframework：3.8.2

【问题讨论】：

hmmm localhost 是模拟器本身

这能回答你的问题吗？ How to connect to my http://localhost web server from Android Emulator

@Ryan M，谢谢你的评论，我已经提到了这个问题。但我无法解决我的错误...

【参考方案1】：

尝试打开cmd，然后在上面写ipconfig 之后，您获得了本地 IP 地址，然后尝试输入您的代码

例如，您从 cmd 获得 192.168.1.2，然后将其放入您的代码中，如下所示：

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

【讨论】：

感谢您的回答，在我将代码更改为您的回答后，错误消息更改为 ` W/System.err: org.json.JSONException: Value ype java.lang.字符串无法转换为 JSONObject`

您的连接问题已解决，但是，我认为您的 API 返回一个错误，通过 Postman 检查您的返回 API，如果它与您的 logcat 持续存在，那么它的问题来自您的 API 返回