Android studio httpURLConnection 应用程序崩溃

Question

我是 Android 和 Java 开发的新手，我是一名 Web 开发人员，想学习 Android Studio 和 Java。

在学习新语言时，我首先要做的是一些数据库调用，在这个只是 JSON 调用中。

使用 httpURLConnection ，我在网上找到了示例，当我在 android studio 中运行它时，它可以在我的 main 函数中运行，但是当我将它放在 click 函数上的按钮内并在我的手机上运行我的应用程序时，我的应用程序崩溃了。

我也加了 到 AndroidManifest.xml 里面的 manifest 标签。

这是我得到的错误

11-22 19:47:46.354 24975-24975/com.example.adis.myapp I/System.out: I am here//////////////////////////////////////////
11-22 19:47:46.494 24975-24975/com.example.adis.myapp D/AndroidRuntime: Shutting down VM
11-22 19:47:46.494 24975-24975/com.example.adis.myapp W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x41659e00)
11-22 19:47:46.514 24975-24975/com.example.adis.myapp E/AndroidRuntime: FATAL EXCEPTION: main

                 Process: com.example.adis.myapp, PID: 24975
                    java.lang.IllegalStateException: Could not execute method for android:onClick
                        at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
                ive Method)
                     Caused by: java.lang.reflect.InvocationTargetException
                        at java.lang.reflect.Method.invokeNative(Native Method)
                        at java.lang.reflect.Method.invoke(Method.java:515)
                        at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
                        at android.view.View.performClick(View.java:4457) 
                        at android.view.View$PerformClick.run(View.java:18491) 
                        at android.os.Handler.handleCallback(Handler.java:733) 
                        at android.os.Handler.dispatchMessage(Handler.java:95) 
                        at android.os.Looper.loop(Looper.java:136) 
                        at android.app.ActivityThread.main(ActivityThread.java:5333) 
                        at java.lang.reflect.Method.invokeNative(Native Method) 
                        at java.lang.reflect.Method.invoke(Method.java:515) 
                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:895) 
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711) 
                        at dalvik.system.NativeStart.main(Native Method) 
                     Caused by: android.os.NetworkOnMainThreadException
                        at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1148)
                        at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
                        at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
                        at java.net.InetAddress.getAllByName(InetAddress.java:214)
                        at com.android.okhttp.internal.Dns$1.getAllByName(Dns.java:28)
                        at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:216)
                        at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:122)
                        at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:292)
                        at com.android.okhttp.internal.http.HttpEngine.sendSocketRequest(HttpEngine.java:255)
                        at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:206)
                        at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:345)
                        at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:296)
                        at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponseCode(HttpURLConnectionImpl.java:503)
                        at com.example.adis.myapp.MainActivity.loginFunction(MainActivity.java:85)
                        at java.lang.reflect.Method.invokeNative(Native Method) 
                        at java.lang.reflect.Method.invoke(Method.java:515) 
                        at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
                        at android.view.View.performClick(View.java:4457) 
                        at android.view.View$PerformClick.run(View.java:18491) 
                        at android.os.Handler.handleCallback(Handler.java:733) 
                        at android.os.Handler.dispatchMessage(Handler.java:95) 
                        at android.os.Looper.loop(Looper.java:136) 
                        at android.app.ActivityThread.main(ActivityThread.java:5333) 
                        at java.lang.reflect.Method.invokeNative(Native Method) 
                        at java.lang.reflect.Method.invoke(Method.java:515) 
                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:895) 
                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711) 
                        at dalvik.system.NativeStart.main(Native Method) 
11-22 19:47:46.524 923-1275/? W/ActivityManager:   Force finishing activity com.example.adis.myapp/.MainActivity

这是我的 onClick 函数

public void loginFunction(View view) throws IOException, JSONException {


    System.out.println("I am here//////////////////////////////////////////");
    try {

        URL url = new URL("http://echo.jsontest.com/insert-key-here/insert-value-here/key/value");
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setRequestProperty("Accept", "application/json");

        if (conn.getResponseCode() != 200) {
            throw new RuntimeException("Failed : HTTP error code : "
                    + conn.getResponseCode());
        }

        BufferedReader br = new BufferedReader(new InputStreamReader(
                (conn.getInputStream())));

        String output;
        System.out.println("Output from Server .... \n");
        while ((output = br.readLine()) != null) {
            System.out.println(output);
        }

        conn.disconnect();

    } catch (MalformedURLException e) {

        e.printStackTrace();

    } catch (IOException e) {

        e.printStackTrace();

    }



}

如果你看到一些即使是 java 初学者也应该看到的愚蠢错误，请对我严厉，因为我没有。

感谢您的光临:)

Answer 1

您不能在主线程上建立网络连接，因为这会冻结 UI 线程并使您的应用无响应。这就是引发异常的原因。

您可以使按钮触发新线程或 AsyncTask 以完成操作。

示例： How to fix android.os.NetworkOnMainThreadException?

Answer 2

1. 将此添加到您的 AndroidManifest.xml 之前的 Application 标记：-

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

2. 即使在微不足道的互联网连接上，HTTP 请求也可能需要大量时间，从而冻结主 UI 线程。您可以做的是在按下按钮时启动一个新的 AsyncTask。

   将代码放在单独的类中，例如：-

   public class HTTPRequestTask extends AsyncTask<Void, Void, Void> {
   
   @Override
   protected Void doInBackground(Void... params){
   System.out.println("I am   here//////////////////////////////////////////");
   try {
   URL url = new URL("http://echo.jsontest.com/insert-key-here/insert-value-here/key/value");
   HttpURLConnection conn = (HttpURLConnection) url.openConnection();
   conn.setRequestMethod("GET");
   conn.setRequestProperty("Accept", "application/json");
   
   if (conn.getResponseCode() != 200) {
       throw new RuntimeException("Failed : HTTP error code : "
               + conn.getResponseCode());
   }
   
   BufferedReader br = new BufferedReader(new InputStreamReader(
           (conn.getInputStream())));
   
   String output;
   System.out.println("Output from Server .... \n");
   while ((output = br.readLine()) != null) {
       System.out.println(output);
   }
   
   conn.disconnect();
   
   } catch (MalformedURLException e) {
   
      e.printStackTrace();
   
   } catch (IOException e) {
   
      e.printStackTrace();
   
   }
   

   并修改 onClickButton 如下：-

   OnButtonclick(...){ ... HTTPRequestTask testTask =new HTTPRequestTask(); testTask.execute(); ...}

   PS - 我已将新类命名为 HTTPRequestTask。你可以选择你自己的名字。