您好我有这个应用程序，允许用户注册到PHP本地主机数据库。我得到的1个错误是
＆＃39; java.lang.NullPointerException：尝试调用虚方法＆＃39; int java.lang.String.length（）＆＃39;在空对象引用＆＃39;
我不知道这意味着什么，任何人都可以帮我解决问题。
我崩溃的代码
public class BackgroundTask extends AsyncTask<String, Void, String> {
String register_url = "https://10.123.1.15/Fitnessplus/register.php";
String login_url = "https://10.123.1.15/Fitnessplus/login.php";
Context ctx;
Activity activity;
ProgressDialog progressDialog;
AlertDialog.Builder builder;
public BackgroundTask(Context ctx) {
this.ctx = ctx;
activity = (Activity) ctx;
}
@Override
protected void onPreExecute() {
builder = new AlertDialog.Builder(activity);
progressDialog = new ProgressDialog(ctx);
progressDialog.setTitle("Please wait");
progressDialog.setMessage("Connecting to server");
progressDialog.setIndeterminate(true);
progressDialog.setCancelable(false);
progressDialog.show();
}
@Override
protected String doInBackground(String... params) {
String method = params[0];
if (method.equals("register"))
{
try {
URL url = new URL(register_url);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
String name = params[1];
String email = params[2];
String password = params[3];
String data = URLEncoder.encode("name", "UTF-8") + "=" + URLEncoder.encode(name, "UTF-8") + "&" +
URLEncoder.encode("email", "UTF-8") + "=" + URLEncoder.encode(email, "UTF-8") + "&" +
URLEncoder.encode("password", "UTF-8") + "=" + URLEncoder.encode(password, "UTF-8");
bufferedWriter.write(data);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder stringBuilder = new StringBuilder();
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line + "\n");
}
httpURLConnection.disconnect();
Thread.sleep(5000);
return stringBuilder.toString().trim();
} catch (MalformedURLException e) {
e.printStackTrace();
throw new RuntimeException(e);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
} catch (InterruptedException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
else if (method.equals("login"))
{
try {
URL url = new URL(login_url);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
String email,password;
email = params[1];
password = params[2];
String data = URLEncoder.encode("email", "UTF-8") + "=" + URLEncoder.encode(email, "UTF-8") + "&" +
URLEncoder.encode("password", "UTF-8") + "=" + URLEncoder.encode(password, "UTF-8");
bufferedWriter.write(data);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder stringBuilder = new StringBuilder();
String line = "";
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line + "\n");
}
httpURLConnection.disconnect();
Thread.sleep(5000);
return stringBuilder.toString().trim();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (ProtocolException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
}
@Override
protected void onPostExecute(String json) {
try {
progressDialog.dismiss();
JSONObject jsonObject = new JSONObject(json);
JSONArray jsonArray = jsonObject.getJSONArray("server_response");
JSONObject JO = jsonArray.getJSONObject(0);
String code = JO.getString("code");
String message = JO.getString("message");
if (code.equals("reg_true"))
{
showDialog("Registration Success", message, code);
}
else if(code.equals("reg_false"));
{
showDialog("Registration failed", message, code);
}
if (code.equals("login_true"))
{
Intent intent = new Intent(activity,MainActivity.class);
intent.putExtra("message",message);
activity.startActivity(intent);
}
else if(code.equals("login_false"))
{
showDialog("Login Error",message,code);
}
} catch (JSONException e1) {
e1.printStackTrace();
}
}
public void showDialog(String title, String message, String code)
{
builder.setTitle(title);
if(code.equals("reg_true")|| code.equals("reg_false"))
{
builder.setMessage(message);
builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
activity.finish();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
else if (code.equals("login_false")) {
builder.setMessage(message);
builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
EditText email,password;
email = (EditText) activity.findViewById(R.id.email);
password = (EditText) activity.findViewById(R.id.password);
email.setText("");
password.setText("");
dialog.dismiss();
}
});
}
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
}
在线上似乎存在问题＆＃39; JSONObject jsonObject = new JSONObject（son）;＆＃39;
错误日志
04-27 19:25:32.070 7181-7181/com.example.kieranbroom.fitnessproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.kieranbroom.fitnessproject, PID: 7181
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
at org.json.JSONTokener.nextValue(JSONTokener.java:94)
at org.json.JSONObject.<init>(JSONObject.java:156)
at org.json.JSONObject.<init>(JSONObject.java:173)
at com.example.kieranbroom.fitnessproject.BackgroundTask.onPostExecute(BackgroundTask.java:167)
at com.example.kieranbroom.fitnessproject.BackgroundTask.onPostExecute(BackgroundTask.java:30)
at android.os.AsyncTask.finish(AsyncTask.java:651)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
答案 0 :(得分：0)
我正在使用此类从服务器发送和接收数据。
public class ServerConnector {
public final static int GET = 1;
public final static int POST = 2;
public ServerConnector() {
}
public String makeServiceCall(String requestURL, int TYPE) {
return this.makeServiceCall(requestURL, TYPE, null);
}
public String makeServiceCall(String requestURL, int TYPE, HashMap<String, String> postDataParams) {
String response = "";
try {
URL url;
url = new URL(requestURL);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(15000);
conn.setConnectTimeout(15000);
if (TYPE == POST) {
conn.setRequestMethod("POST");
conn.setDoInput(true);
conn.setDoOutput(true);
if (postDataParams != null) {
OutputStream os = conn.getOutputStream();
BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(os, "UTF-8"));
writer.write(getPostDataString(postDataParams));
writer.flush();
writer.close();
os.close();
}
int responseCode = conn.getResponseCode();
if (responseCode == HttpsURLConnection.HTTP_OK) {
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
while ((line = br.readLine()) != null) {
response += line;
}
} else {
response = "";
}
} else if (TYPE == GET) {
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.setDoOutput(true);
if (postDataParams != null) {
OutputStream os = conn.getOutputStream();
BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(os, "UTF-8"));
writer.write(getPostDataString(postDataParams));
writer.flush();
writer.close();
os.close();
}
int responseCode = conn.getResponseCode();
if (responseCode == HttpsURLConnection.HTTP_OK) {
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
while ((line = br.readLine()) != null) {
response += line;
//Log.d("ServerUtility", line);
}
} else {
response ="";
}
}
} catch (Exception e) {
e.printStackTrace();
}
return response;
}
private String getPostDataString(HashMap<String, String> params) throws UnsupportedEncodingException {
StringBuilder result = new StringBuilder();
boolean first = true;
for (Map.Entry<String, String> entry : params.entrySet()) {
if (first)
first = false;
else
result.append("&");
result.append(URLEncoder.encode(entry.getKey(), "UTF-8"));
result.append("=");
result.append(URLEncoder.encode(entry.getValue(), "UTF-8"));
}
return result.toString();
}
}
将keyValuePairList传递给BackgroundTask
public class BackgroundTask extends AsyncTask<HashMap<String, String>, Void, String>{
.
.
.
@Override
protected String doInBackground(HashMap<String, String>... params) {
ServerConnector serverConnector = new ServerConnector();
String response= serverConnector.makeServiceCall(url, ServerConnector.POST, params[0]);
return response;
}
现在打电话
HashMap<String, String> hashMapValues = new HashMap<>();
hashMapValues.add("mail","abcd@gmail.com");
new BackgroundTask(url).execute(hashMapValues);