异步的Android JSON解析器android-空指针异常 [英] Async android json parser android- null pointer exception
本文介绍了异步的Android JSON解析器android-空指针异常的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
从我的最后一个职位，被T知道，我需要使用JSON用于从URL解析异步任务，都做相同的，附在下面，
公共类ReadJson扩展ListActivity {
私有静态字符串URL =http://docs.blackberry.com/sampledata.json;私有静态最后弦乐TAG_VTYPE =vehicleType;
私有静态最后弦乐TAG_VCOLOR =vehicleColor;
私有静态最后弦乐TAG_FUEL =燃料;
私有静态最后弦乐TAG_TREAD =treadType;ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT; jsonlist =新的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;（）;LV的ListView;
@覆盖
保护无效的onCreate（捆绑savedInstanceState）{
super.onCreate（savedInstanceState）;
的setContentView（R.layout.activity_read_json）;
新ProgressTask（ReadJson.this）.execute（）;
}
私有类ProgressTask扩展的AsyncTask＆LT;弦乐，太虚，布尔＆GT; {
私人ProgressDialog对话框;
//私有列表＆LT;消息＆GT;消息;
公共ProgressTask（ListActivity活动）{
上下文=活动;
对话框=新ProgressDialog（背景）;
}
/ **进度对话框，显示该备份处理用户。 * /
/ **应用程序上下文。 * /
私人上下文的背景下;
在preExecute保护无效（）{
this.dialog.setMessage（进步启动）;
this.dialog.show（）;
}
@覆盖
保护无效onPostExecute（最终布尔成功）{
如果（dialog.isShowing（））{
dialog.dismiss（）;
}
ListAdapter适配器=新SimpleAdapter（背景下，jsonlist，
R.layout.list_item，新的String [] {TAG_VTYPE，TAG_VCOLOR，
TAG_FUEL，TAG_TREAD}，新的INT [] {
R.id.vehicleType，R.id.vehicleColor，R.id.fuel，
R.id.treadType}）;
setListAdapter（适配器）;
//选择单个ListView项
LV = getListView（）;
}
保护布尔doInBackground（最终字符串参数... args）{
JSONParser jParser =新JSONParser（）;
JSONArray JSON = jParser.getJSONFromUrl（URL）;
的for（int i = 0; I＆LT; json.length（）;我++）{
尝试{
JSONObject的C = json.getJSONObject（I）
字符串由Vtype = c.getString（TAG_VTYPE）;
字符串vcolor = c.getString（TAG_VCOLOR）;
字符串vfuel = c.getString（TAG_FUEL）;
字符串vtread = c.getString（TAG_TREAD）;
HashMap的＆LT;字符串，字符串＆GT;地图=新的HashMap＆LT;字符串，字符串＆GT;（）;
map.put（TAG_VTYPE，由Vtype）;
map.put（TAG_VCOLOR，vcolor）;
map.put（TAG_FUEL，vfuel）;
map.put（TAG_TREAD，vtread）;
jsonlist.add（地图）;
}赶上（JSONException E）{
e.printStackTrace（）;
}
}
返回null;
}
}
}
当我执行，我得到空指针异常错误的行ASYC后台执行，的for（int i = 0; I＆LT; json.length（）;我++），试了好东西，但没有工作，任何帮助将gr8ly AP preciated !!
编辑1：添加解析器code
进口java.io.BufferedReader中;
进口java.io.IOException异常;
进口的java.io.InputStream;
进口java.io.InputStreamReader中;
进口java.io.UnsupportedEncodingException;进口org.apache.http.HttpEntity;
进口org.apache.http.Htt presponse;
进口org.apache.http.StatusLine;
进口org.apache.http.client.ClientProtocolException;
进口org.apache.http.client.HttpClient;
进口org.apache.http.client.methods.HttpGet;
进口org.apache.http.client.methods.HttpPost;
进口org.apache.http.impl.client.DefaultHttpClient;
进口org.json.JSONArray;
进口org.json.JSONException;
进口org.json.JSONObject;进口android.util.Log;公共类JSONParser { 静态InputStream为= NULL;
静态JSONArray jarray = NULL;
静态JSON字符串=; //构造
公共JSONParser（）{ } 公共JSONArray getJSONFromUrl（字符串URL）{ StringBuilder的建设者=新的StringBuilder（）;
HttpClient的客户端=新DefaultHttpClient（）;
HTTPGET HTTPGET =新HTTPGET（URL）;
尝试{
HTT presponse响应= client.execute（HTTPGET）;
状态行状态行= response.getStatusLine（）;
INT状态code = statusLine.getStatus code（）;
如果（状态code == 200）{
HttpEntity实体= response.getEntity（）;
InputStream的内容= entity.getContent（）;
读者的BufferedReader =新的BufferedReader（新的InputStreamReader（内容））;
串线;
而（（行= reader.readLine（））！= NULL）{
builder.append（线）;
}
}其他{
Log.e（==＆gt;中，无法下载文件）;
}
}赶上（ClientProtocolException E）{
e.printStackTrace（）;
}赶上（IOException异常五）{
e.printStackTrace（）;
} //尝试分析字符串到一个JSON对象
尝试{
jarray =新JSONArray（builder.toString（））;
}赶上（JSONException E）{
Log.e（JSON解析器，错误分析数据+ e.toString（））;
} //返回JSON字符串
返回jarray; }
}
解决方案
试试这个获取JSON
公共静态字符串getJSONString（字符串URL）{
字符串jsonString = NULL;
HttpURLConnection的linkConnection = NULL;
尝试{
网址linkurl =新的URL（网址）;
linkConnection =（HttpURLConnection类）linkurl.openConnection（）;
INT响应code = linkConnection.getResponse code（）;
如果（响应code == HttpURLConnection.HTTP_OK）{
InputStream的linkinStream = linkConnection.getInputStream（）;
ByteArrayOutputStream BAOS =新ByteArrayOutputStream（）;
INT J = 0;
而（（J = linkinStream.read（））！= - 1）{
baos.write（J）;
}
字节[]数据= baos.toByteArray（）;
jsonString =新的String（数据）;
}
}赶上（例外五）{
e.printStackTrace（）;
} {最后
如果（linkConnection！= NULL）{
linkConnection.disconnect（）;
}
}
返回jsonString;
}公共静态布尔isNetworkAvailable（活动活动）{
ConnectivityManager连接=（ConnectivityManager）活动
.getSystemService（Context.CONNECTIVITY_SERVICE）;
如果（连接== NULL）{
返回false;
}其他{
的NetworkInfo []信息= connectivity.getAllNetworkInfo（）;
如果（信息！= NULL）{
的for（int i = 0; I＆LT; info.length;我++）{
如果（资讯[I] .getState（）== NetworkInfo.State.CONNECTED）{
返回true;
}
}
}
}
返回false;
}
使用isNetworkAvailable检查连接
和我分析这样
{尝试 JSONObject的jObjectm =新的JSONObject（结果）;
JSONObject的jObject = jObjectm.getJSONObject（项目）;
如果（jObject！= NULL）
{
迭代器＆LT;＆GT;的iterator1 = jObject.keys（）;
LinkedHashMap的＆LT;弦乐，LinkedHashMap的＆LT;弦乐，对象＆gt; ＆GT; inneritem =新的LinkedHashMap＆LT;弦乐，LinkedHashMap的＆LT;弦乐，对象＆gt; ＆GT;（）;
而（iterator1.hasNext（））{
项目hashitem =新项目（）;
字符串键1 =（字符串）iterator1.next（）;
JSONObject的jObject1 = jObject.getJSONObject（键1）;
迭代器＆LT;＆GT;迭代= jObject1.keys（）;
LinkedHashMap的＆LT;弦乐，对象＆gt; inneritem1 =新的LinkedHashMap＆LT;弦乐，对象＆gt;（）;
而（iterator.hasNext（））{
字符串键=（字符串）iterator.next（）; inneritem1.put（键，jObject1.get（密钥））;
}
hashitem.setItem（KEY1，inneritem1）;
inneritem.put（KEY1，inneritem1）;
arrayOfList.add（hashitem）;
}
}
}赶上（JSONException E）{ 的System.out.println（NO JSON数据中发现）;
}
From my last post, got t know that, i need to use async task for json parsing from url, have done the same and attached below,
public class ReadJson extends ListActivity {
private static String url = "http://docs.blackberry.com/sampledata.json";
private static final String TAG_VTYPE = "vehicleType";
private static final String TAG_VCOLOR = "vehicleColor";
private static final String TAG_FUEL = "fuel";
private static final String TAG_TREAD = "treadType";
ArrayList<HashMap<String, String>> jsonlist = new ArrayList<HashMap<String, String>>();
ListView lv ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_read_json);
new ProgressTask(ReadJson.this).execute();
}
private class ProgressTask extends AsyncTask<String, Void, Boolean> {
private ProgressDialog dialog;
// private List<Message> messages;
public ProgressTask(ListActivity activity) {
context = activity;
dialog = new ProgressDialog(context);
}
/** progress dialog to show user that the backup is processing. */
/** application context. */
private Context context;
protected void onPreExecute() {
this.dialog.setMessage("Progress start");
this.dialog.show();
}
@Override
protected void onPostExecute(final Boolean success) {
if (dialog.isShowing()) {
dialog.dismiss();
}
ListAdapter adapter = new SimpleAdapter(context, jsonlist,
R.layout.list_item, new String[] { TAG_VTYPE, TAG_VCOLOR,
TAG_FUEL, TAG_TREAD }, new int[] {
R.id.vehicleType, R.id.vehicleColor, R.id.fuel,
R.id.treadType });
setListAdapter(adapter);
// selecting single ListView item
lv = getListView();
}
protected Boolean doInBackground(final String... args) {
JSONParser jParser = new JSONParser();
JSONArray json = jParser.getJSONFromUrl(url);
for (int i = 0; i < json.length(); i++) {
try {
JSONObject c = json.getJSONObject(i);
String vtype = c.getString(TAG_VTYPE);
String vcolor = c.getString(TAG_VCOLOR);
String vfuel = c.getString(TAG_FUEL);
String vtread = c.getString(TAG_TREAD);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_VTYPE, vtype);
map.put(TAG_VCOLOR, vcolor);
map.put(TAG_FUEL, vfuel);
map.put(TAG_TREAD, vtread);
jsonlist.add(map);
} catch (JSONException e) {
e.printStackTrace();
}
}
return null;
}
}
}
When i execute this, i get null pointer exception for error executing in asyc background in the line, for (int i = 0; i < json.length(); i++), tried several things but not working, any help will be gr8ly appreciated!!
Edit 1: added parser code
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONArray jarray = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONArray getJSONFromUrl(String url) {
StringBuilder builder = new StringBuilder();
HttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
try {
HttpResponse response = client.execute(httpGet);
StatusLine statusLine = response.getStatusLine();
int statusCode = statusLine.getStatusCode();
if (statusCode == 200) {
HttpEntity entity = response.getEntity();
InputStream content = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(content));
String line;
while ((line = reader.readLine()) != null) {
builder.append(line);
}
} else {
Log.e("==>", "Failed to download file");
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
// try parse the string to a JSON object
try {
jarray = new JSONArray( builder.toString());
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jarray;
}
}
解决方案
Try this for getting json
public static String getJSONString(String url) {
String jsonString = null;
HttpURLConnection linkConnection = null;
try {
URL linkurl = new URL(url);
linkConnection = (HttpURLConnection) linkurl.openConnection();
int responseCode = linkConnection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
InputStream linkinStream = linkConnection.getInputStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int j = 0;
while ((j = linkinStream.read()) != -1) {
baos.write(j);
}
byte[] data = baos.toByteArray();
jsonString = new String(data);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (linkConnection != null) {
linkConnection.disconnect();
}
}
return jsonString;
}
public static boolean isNetworkAvailable(Activity activity) {
ConnectivityManager connectivity = (ConnectivityManager) activity
.getSystemService(Context.CONNECTIVITY_SERVICE);
if (connectivity == null) {
return false;
} else {
NetworkInfo[] info = connectivity.getAllNetworkInfo();
if (info != null) {
for (int i = 0; i < info.length; i++) {
if (info[i].getState() == NetworkInfo.State.CONNECTED) {
return true;
}
}
}
}
return false;
}
use isNetworkAvailable for checking connection
and i parsed this way
try {
JSONObject jObjectm = new JSONObject(result);
JSONObject jObject=jObjectm.getJSONObject("items");
if(jObject!=null)
{
Iterator<?> iterator1=jObject.keys();
LinkedHashMap<String,LinkedHashMap<String, Object> > inneritem = new LinkedHashMap<String, LinkedHashMap<String, Object> >();
while (iterator1.hasNext() ){
Item hashitem=new Item();
String key1 = (String)iterator1.next();
JSONObject jObject1=jObject.getJSONObject(key1);
Iterator<?> iterator=jObject1.keys();
LinkedHashMap<String, Object> inneritem1 = new LinkedHashMap<String, Object>();
while (iterator.hasNext() ){
String key =(String) iterator.next();
inneritem1.put(key, jObject1.get(key));
}
hashitem.setItem(key1,inneritem1);
inneritem.put(key1,inneritem1);
arrayOfList.add(hashitem);
}
}
} catch (JSONException e) {
System.out.println("NO Json data found");
}
这篇关于异步的Android JSON解析器android-空指针异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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