在尝试了一些提供的解决方案之后，我能够从服务器检索响应但仍然无法显示我收到的JSON数组且应用程序崩溃，请帮助我：
Logcat错误
07-07 11:12:09.500: E/AndroidRuntime(1829): FATAL EXCEPTION: main
07-07 11:12:09.500: E/AndroidRuntime(1829): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.g2k/com.example.g2k.HotelSearch}: java.lang.NullPointerException: println needs a message
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.os.Handler.dispatchMessage(Handler.java:99)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.os.Looper.loop(Looper.java:137)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.ActivityThread.main(ActivityThread.java:5039)
07-07 11:12:09.500: E/AndroidRuntime(1829): at java.lang.reflect.Method.invokeNative(Native Method)
07-07 11:12:09.500: E/AndroidRuntime(1829): at java.lang.reflect.Method.invoke(Method.java:511)
07-07 11:12:09.500: E/AndroidRuntime(1829): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-07 11:12:09.500: E/AndroidRuntime(1829): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-07 11:12:09.500: E/AndroidRuntime(1829): at dalvik.system.NativeStart.main(Native Method)
07-07 11:12:09.500: E/AndroidRuntime(1829): Caused by: java.lang.NullPointerException: println needs a message
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.util.Log.println_native(Native Method)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.util.Log.v(Log.java:117)
07-07 11:12:09.500: E/AndroidRuntime(1829): at com.example.g2k.HotelSearch.onCreate(HotelSearch.java:22)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.Activity.performCreate(Activity.java:5104)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-07 11:12:09.500: E/AndroidRuntime(1829): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-07 11:12:09.500: E/AndroidRuntime(1829): ... 11 more
07-07 11:12:14.430: E/Trace(1848): error opening trace file: No such file or directory (2)
源代码：
public class HotelBook extends Activity {
private String resp;
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> hotelsList;
HashMap<String, String> map;
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_HOTEL = "hotels";
private static final String TAG_PID = "hotel_id";
private static final String TAG_NAME = "hotel_name";
private static final String TAG_AREA = "area";
private static final String TAG_RATING = "star_rating";
private static final String TAG_IMAGE = "image";
private static final String TAG_GOVRATE = "govrating";
private static final String TAG_PRICE = "price";
private String city_id = "feedbacktype2";
// products JSONArray
JSONArray hotels = null;
Button sendPostReqButton;
private static final String url = "http://10.0.2.2/android_connect/search_hotel.php";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_hotelbook);
// Hashmap for ListView
hotelsList = new ArrayList<HashMap<String, String>>();
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
.permitAll().build();
StrictMode.setThreadPolicy(policy);
sendPostReqButton = (Button) findViewById(R.id.button1);
addListenerOnButton();
}
public void addListenerOnButton() {
sendPostReqButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// Get the data
// Loading products in Background Thread
new GetHotel().execute();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_hotelbook, menu);
return true;
}
class GetHotel extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
/*
* pDialog = new ProgressDialog(HotelbookActivity.this);
* pDialog.setMessage("Loading hotels. Please wait...");
* pDialog.setIndeterminate(false); pDialog.setCancelable(false);
* pDialog.show();
*/
}
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("cityid", city_id));
// getting JSON string from URL
JSONObject json = null;
try {
json = jParser.makeHttpRequest(url, "GET", params);
} catch (IOException e1) {
// TODO Auto-generated catch block
// Check your log cat for JSON reponse
Log.e("All hotels: ", e1.toString());
}
// Check your log cat for JSON reponse
Log.d("All hotels: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = 1;
// json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
hotels = json.getJSONArray(TAG_HOTEL);
// looping through All Products
for (int i = 0; i < hotels.length(); i++) {
JSONObject c = hotels.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_PID);
String name = c.getString(TAG_NAME);
String area = c.getString(TAG_AREA);
String rating = c.getString(TAG_RATING);
String image = c.getString(TAG_IMAGE);
String price = c.getString(TAG_PRICE);
String govrate = c.getString(TAG_GOVRATE);
// creating new HashMap
map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_PID, id);
map.put(TAG_NAME, name);
map.put(TAG_AREA, area);
map.put(TAG_RATING, rating);
map.put(TAG_IMAGE, image);
map.put(TAG_PRICE, price);
map.put(TAG_GOVRATE, govrate);
// adding HashList to ArrayList
hotelsList.add(map);
}
} else {
}
} catch (JSONException e) {
Log.e("response error", json.toString(), e);
}
return null;
}
protected void onPostExecute(String file_url) {
Intent intent = new Intent(HotelBook.this, HotelSearch.class);
intent.putExtra("map", map);
startActivity(intent);
}
}
}
JSONParser类：
public class JSONParser {
InputStream is = null;
JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// function get json from url
// by making HTTP POST or GET method
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) throws IOException {
// 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");
}
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
} finally {
is.close();
}
// 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;
}
}
答案 0 :(得分：0)
您的logcat指向HotelbookActivity.java第154行，您可以在其中对null ed对象执行操作：
Caused by: java.lang.NullPointerException
07-05 08:36:07.533: E/AndroidRuntime(1073): at
com.example.go2kashmir.HotelbookActivity$GetHotel
.doInBackground(HotelbookActivity.java:154)
修改
如果你说第154行是json访问，那么这一行：
Log.d("All hotels: ", json.toString());
应记录：
All hotels: null
确认（在这种情况下不需要显式toString()）。记录您的jParser makeHttpRequest()做的原始响应，以查看服务器真正返回的内容。问题潜伏在那里。
答案 1 :(得分：0)
您没有按预期使用日志功能。第一个参数应该用于标识上下文，而消息应该是第二个参数。
相反，做一些像
这样的事情Log.d("MyActivity", "Object of interest is " + objectOfInterest);
这样，如果对象为null，您将收到一条日志消息，而不是异常。