我有一个忘记密码 Activity ，它连接到 mysql 数据库并生成新密码。然而; json 对象总是返回空指针异常。 php 脚本有一个用于测试的 html 表单，并且它运行完美，因此错误肯定存在于 java 代码中。
这是 Json Parser 类:
package test.example.com.test;
import android.util.Log;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// function get json from url
// by making HTTP POST or GET mehtod
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
// Making HTTP request
try {
// check for request method
if(method == "POST"){
// request method is POST
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}else if(method == "GET"){
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
这是异步任务:
class ForgetPass extends AsyncTask<String, String, String> {
boolean failure = false;
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(forg1.this);
pDialog.setTitle("Generating New Password...");
pDialog.setCancelable(true);
pDialog.setIndeterminate(false);
pDialog.show();
}
@Override
protected String doInBackground(String... args) {
// TODO Auto-generated method stub
// Check for success tag
int success;
String Email;
Email = etMailfrpass.getText().toString();
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("Email", Email));
JSONObject json5 = js.makeHttpRequest(
FORGET_URL, "POST", params);
// Log.d("Ibrahim forget pass", "Ibrahim forget pass");
success = json5.getInt(TAG_SUCCESS);
if (success == 1) {
//Log.d("Password generated", json5.toString());
pDialog.dismiss();
return json5.getString(TAG_MESSAGE);
} else {
// Log.d("generation Failure!", json5.getString(TAG_MESSAGE));
return json5.getString(TAG_MESSAGE);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url1) {
// dismiss the dialog once product deleted
pDialog.dismiss();
if (file_url1 != null) {
Toast.makeText(forg1.this, file_url1, Toast.LENGTH_LONG).show();
}
}
}
这是日志，错误位于 json.getInt
05-08 11:12:28.336 16229-16554/test.example.com.test E/JSON Parser﹕ Error parsing data org.json.JSONException: Value fetet of type java.lang.String cannot be converted to JSONObject
05-08 11:12:28.336 16229-16554/test.example.com.test W/dalvikvm﹕ threadid=11: thread exiting with uncaught exception (group=0x40aa5228)
05-08 11:12:28.346 16229-16554/test.example.com.test E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:278)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:864)
Caused by: java.lang.NullPointerException
at test.example.com.test.forg1$ForgetPass.doInBackground(forg1.java:107)
at test.example.com.test.forg1$ForgetPass.doInBackground(forg1.java:73)
at android.os.AsyncTask$2.call(AsyncTask.java:264)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:864)
最佳答案
假设出现问题，因此这部分在 jObj 中返回 null:
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
现在您的AsyncTask尝试在返回的jObj中调用getString()方法，该方法本身为空(每当成功为1时或不):
if (success == 1) {
//Log.d("Password generated", json5.toString());
pDialog.dismiss();
return json5.getString(TAG_MESSAGE);
} else {
// Log.d("generation Failure!", json5.getString(TAG_MESSAGE));
return json5.getString(TAG_MESSAGE);
}
现在您就可以使用 NPE 了。
关于java - 异步任务中的json空指针错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30119147/