[英]Android sending data to php and receiving issue nullpointerexception
我是android開發的新手,我不確定要讓代碼正常工作所缺少的內容。 嘗試創建登錄應用程序。 我使用dataoutputstream接收數據或發送數據的方式是否有問題? 有沒有一種更好的方法,它不會被淘汰和復雜化。 尋找最簡單易懂的解決方案。
在后台代碼中執行
@Override
protected Boolean doInBackground(String... params) {
DataOutputStream printout;
HttpURLConnection urlConn;
BufferedReader reader;
URL url;
String json;
JSONObject jObj;
//send POST login details to server
try {
url = new URL(SERVER_ADDRESS + "login.php");
urlConn = (HttpURLConnection) url.openConnection();
urlConn.setRequestMethod("POST");
urlConn.setDoOutput(true);
urlConn.setRequestProperty("Accept-Charset", "UTF-8");
urlConn.setReadTimeout(10000);
urlConn.setConnectTimeout(15000);
HashMap<String, String> map = new HashMap<String, String>();
map.put("username", params[0]);
map.put("password", params[1]);
StringBuilder sb = new StringBuilder();
for(HashMap.Entry<String, String> e : map.entrySet()){
if(sb.length() > 0){
sb.append("&");
}
sb.append(URLEncoder.encode(e.getKey(), "UTF-8")).append("=").append(URLEncoder.encode(e.getValue(), "UTF-8"));
}
String loginDetails = sb.toString();
printout = new DataOutputStream(urlConn.getOutputStream());
printout.writeBytes(loginDetails);
printout.flush();
printout.close();
reader = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));
StringBuilder sb2 = new StringBuilder();
String result = null;
while((result=reader.readLine())!=null) {
sb2.append(result + '\n');
Log.d("Results", sb2.toString());
};
json = result.toString();
jObj = new JSONObject(json);
JSONLogin = jObj.getBoolean(TAG_LOGINSTATUS);
Log.d("LoginStatus!!!!", JSONLogin.toString());
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (ProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
Log.d("JsonConvertion", "FAILED TO CONVERT JSON");
}
return JSONLogin;
}
堆棧錯誤
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: Process: com.httpkhronolog.khronolog, PID: 2459
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: java.lang.RuntimeException: An error occurred while executing doInBackground()
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at android.os.AsyncTask$3.done(AsyncTask.java:309)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.FutureTask.run(FutureTask.java:242)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.lang.Thread.run(Thread.java:818)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toString()' on a null object reference
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at com.httpkhronolog.khronolog.Login_Activity$checkUserDetails.doInBackground(Login_Activity.java:137)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at com.httpkhronolog.khronolog.Login_Activity$checkUserDetails.doInBackground(Login_Activity.java:79)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at android.os.AsyncTask$2.call(AsyncTask.java:295)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.FutureTask.run(FutureTask.java:237)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
10-18 22:43:34.169 2459-2523/? E/AndroidRuntime: at java.lang.Thread.run(Thread.java:818)
login.php
<?php
if($_SERVER["REQUEST_METHOD"] == "POST"){
// Establishing Connection with Server by passing server_name, user_id and password as a parameter
$connection = mysql_connect("localhost", "someusername", "Password");
// Selecting Database
$db = mysql_select_db("khronolo_systemdb", $connection);
$username = $_POST["username"];
$password = $_POST["password"];
$query = "SELECT * FROM user_table WHERE password='$password' AND email='$username';";
$result = mysql_query($query, $connection) or die (mysql_error($connection));
$rows = mysql_num_rows($result);
if ($rows == 1) {
$returnValue[] = array("loginStatus"=> "true");
echo json_encode($returnValue);
}
else {
$returnValue[] = array("loginStatus"=> "false");
echo json_encode($returnValue);
}
mysql_close($connection);
}
?>
代替
json = result.toString();
你應該做
json = sb2.toString();
您退出時的while循環中,結果將為null,因此執行result.toString()
將導致nullpointerexception。
您可以使用GSON庫來幫助您毫無障礙地獲取/設置響應值。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.