Android 输入流和输出流答案

【问题标题】：Android inputStream and outputStreamAndroid 输入流和输出流
【发布时间】：2019-01-25 19:43:07
【问题描述】：

我试图使用 HTTP-Post 来获取一些 MySQL 数据库信息。使用 HttpUrlConnection 和 OutputStreamWriter，我得到：

08-19 21:47:38.883 28462-28668/com.squareb0x.playground W/System.err: java.net.ProtocolException: cannot write request body after response has been read
    at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getOutputStream(HttpURLConnectionImpl.java:255)
    at com.squareb0x.playground.LoadscreenActivity$getDB.doInBackground(LoadscreenActivity.java:231)
    at com.squareb0x.playground.LoadscreenActivity$getDB.doInBackground(LoadscreenActivity.java:212)
    at android.os.AsyncTask$2.call(AsyncTask.java:295)
    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
    at java.lang.Thread.run(Thread.java:818)
08-19 21:47:38.883 28462-28462/com.squareb0x.playground W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
    at com.squareb0x.playground.LoadscreenActivity.Backload_ResourcesDownload(LoadscreenActivity.java:165)
    at com.squareb0x.playground.LoadscreenActivity$2.onPostExecute(LoadscreenActivity.java:147)
    at com.squareb0x.playground.LoadscreenActivity$2.onPostExecute(LoadscreenActivity.java:137)
    at android.os.AsyncTask.finish(AsyncTask.java:651)
    at android.os.AsyncTask.access$500(AsyncTask.java:180)
    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:7331)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

代码是：

protected String doInBackground(String... params){
        String serverURL = params[0];
        try {
            url = new URL(serverURL);
            if (httpURLConnection == null){
                httpURLConnection = (HttpURLConnection) url.openConnection();
                httpURLConnection.setReadTimeout(5000);
                httpURLConnection.setConnectTimeout(5000);
                httpURLConnection.setDefaultUseCaches(false);
                httpURLConnection.setDoInput(true);
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setRequestProperty("content-type", "application/x-www-form-urlencoded");
               httpURLConnection.connect();
                int response_status_code = httpURLConnection.getResponseCode();
                StringBuffer stringBuffer = new StringBuffer();
                stringBuffer.append("client").append(encryptString(playground_specific_channel, AES_playground_key, "AES"));
                OutputStreamWriter outputStreamWriter = new OutputStreamWriter((httpURLConnection.getOutputStream()), "UTF-8");
                PrintWriter printWriter = new PrintWriter(outputStreamWriter);
                printWriter.write(stringBuffer.toString());
                printWriter.flush();
                ...
            } else {
                ...
            }
        } catch (MalformedURLException e){
          ...
        } catch (Exception e){
           ...
        }
    }

有人说是PHP文件的问题，但是我跑了一个PHP验证，没有关系。有什么问题？

【问题讨论】：

标签： php android android-asynctask httpurlconnection

【解决方案1】：

您需要将对“getResponseCode()”的调用移至所有输出流/打印机写入的下方。 HTTP 响应代码仅在请求完全发送后可用；读取http响应码后，无法向http服务器写入额外数据。

【讨论】：