我是JSON的新手。我试图在我的应用程序中解析一个简单的JSON文件。
文件是：
[
{
"itemName": "Backtrack",
"messgae": "Backtrack is going to start soon.Participants please report to the venues",
},
{
"itemName": "Lan-Gaming",
"messgae": "Lan-Gaming is going to start soon.Participants please report to the venues",
},
{
"itemName": "Deadlock",
"messgae": "Deadlock is going to start soon.Participants please report to the venues",
}
]
据我所知，我尝试了但应用程序崩溃了。它提供了以下控制台：
11-02 22:48:36.955 4913-4929/?
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: Process: com.defcomdevs.jsonparsing, PID: 4913
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: java.lang.RuntimeException: An error occured while executing doInBackground()
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at android.os.AsyncTask$3.done(AsyncTask.java:300)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.FutureTask.run(FutureTask.java:242)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.lang.Thread.run(Thread.java:841)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: Caused by: java.lang.NullPointerException
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at com.defcomdevs.jsonparsing.MainActivity$ProgressTask.doInBackground(MainActivity.java:87)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at com.defcomdevs.jsonparsing.MainActivity$ProgressTask.doInBackground(MainActivity.java:45)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at android.os.AsyncTask$2.call(AsyncTask.java:288)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.FutureTask.run(FutureTask.java:237)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
11-02 22:48:36.955 4913-4929/? E/AndroidRuntime: at java.lang.Thread.run(Thread.java:841)
11-02 22:48:36.955 559-886/? W/ActivityManager: Force finishing activity com.defcomdevs.jsonparsing/.MainActivity
基本上在后台函数中发生错误。我的java文件是：
package com.defcomdevs.jsonparsing;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
public class MainActivity extends ListActivity {
private Context context;
private static String url = "http://192.168.1.3/test.json"; //url for the terget page
private static final String VTYPE = "Type";
private static final String ITEMID = "ITEM";
private static final String ITEMMSG="MESSAGE";
private static final String VCOLOR = "Color";
private static final String FUEL = "Fuel";
private static final String TREAD = "Tread"; //properties of the page
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_main);
new ProgressTask(MainActivity.this).execute();
}
private class ProgressTask extends AsyncTask<String, Void, Boolean> {
private ProgressDialog dialog; //spinning symbol @ loading
private ListActivity activity;
private Context context;
public ProgressTask(ListActivity activity) {
this.activity = activity;
context = activity;
dialog = new ProgressDialog(context);
}
@Override
protected void onPreExecute() {
this.dialog.setMessage("Fetching data...Please wait");
this.dialog.show(); //shows the dialog before parsing data from page
}
@Override
protected void onPostExecute(Boolean result) {
if (dialog.isShowing()) {
dialog.dismiss();
}
ListAdapter adapter = new SimpleAdapter(context, jsonlist,
R.layout.list_item, new String[]{ITEMID,ITEMMSG}, new int[]{R.id.vehicleType,
R.id.vehicleColor});
setListAdapter(adapter);
lv = getListView(); //todo after the data has been obtained
}
@Override
protected Boolean doInBackground(String... params) {
JSONParser jParser = new JSONParser();
JSONArray json = jParser.getJSONFromUrl(url); //parser to parse from page
for (int i = 0; i < json.length(); i++) {
try {
JSONObject c = json.getJSONObject(i); //each node is assigned here
String name = c.getString("itemName");
String mssg = c.getString("messgae");
//details of the entity
HashMap<String, String> map = new HashMap<String, String>();
map.put(ITEMID, name);
map.put(ITEMMSG, mssg);
jsonlist.add(map);
} catch (JSONException e) {
e.printStackTrace();
}
}
return false;
}
}
}
JSON解析器：
package com.defcomdevs.jsonparsing;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
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.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import android.util.Log;
public class JSONParser {
static InputStream iStream = null;
static JSONArray jarray = null;
static String json = "";
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 {
jarray = new JSONArray(builder.toString());
} catch(JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
return jarray;
}
}
请帮忙。
答案 0 :(得分：1)
你的json中有语法错误。 messgae结尾处不应该有逗号。这是正确的json：
[
{
"itemName": "Backtrack",
"messgae": "Backtrack is going to start soon.Participants please report to the venues"
},
{
"itemName": "Lan-Gaming",
"messgae": "Lan-Gaming is going to start soon.Participants please report to the venues"
},
{
"itemName": "Deadlock",
"messgae": "Deadlock is going to start soon.Participants please report to the venues"
}
]