我是android新手，我尝试使用这样的类从url解析json：
package com.***.exchanger;
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.client.ClientProtocolException;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj;
static String json = "";
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url) {
// Making HTTP request
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpGet httpPost = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
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, "UTF-8"), 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;
}
}
当我在没有 asynctask 的情况下进行解析时 - 一切都很好，我得到了 json 结果，等等......
但现在我的代码是这样的：
public class ExchangerListActivity extends ListActivity {
private static String url;
private static final String TAG_BANKS = "bank";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_Exc_count = "exch_count";
private static final String TAG_central_office_address = "central_office_address";
JSONArray banks = null;
JSONObject json;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_exchanger_list);
url = "http://192.168.1.4:3000/banks.json";
JSONParser jParser = new JSONParser();
JSONObject json = jParser.getJSONFromUrl(url);
ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();
listViewLoaderTask.execute(json);
}
private class ListViewLoaderTask extends AsyncTask<JSONObject, Void, ListAdapter>{
JSONObject jObject;
/** Doing the parsing of xml data in a non-ui thread */
@Override
protected ListAdapter doInBackground(JSONObject... strJson) {
url = "http://192.168.1.4:3000/banks.json";
ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();
JSONParser jParser = new JSONParser();
JSONObject json = jParser.getJSONFromUrl(url);
try {
banks = json.getJSONArray(TAG_BANKS);
for(int i = 0; i < banks.length(); i++){
JSONObject c = banks.getJSONObject(i);
String id = c.getString(TAG_ID);
String name = c.getString(TAG_NAME);
String central_office_address = c.getString(TAG_central_office_address);
String exchangers_list_count = c.getString(TAG_Exc_count);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_ID, id);
map.put(TAG_NAME, name);
map.put(TAG_central_office_address, central_office_address);
map.put(TAG_Exc_count, exchangers_list_count);
contactList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
final ListAdapter adapter = new SimpleAdapter(ExchangerListActivity.this, contactList,
R.layout.bank_list,
new String[] { TAG_NAME, TAG_central_office_address, TAG_Exc_count }, new int[] {
R.id.bank_name, R.id.central_office_address, R.id.exchangers_list_count});
return adapter;
}
/** Invoked by the Android system on "doInBackground" is executed completely */
/** This will be executed in ui thread */
@Override
protected void onPostExecute(ListAdapter adapter) {
/** Getting a reference to listview of main.xml layout file */
ListView listView = ExchangerListActivity.this.getListView();
/** Setting the adapter containing the country list to listview */
listView.setAdapter(adapter);
//setListAdapter(adapter);
/*
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
*/
@SuppressWarnings("unchecked")
@Override
public void onItemClick(AdapterView<?> parent, android.view.View view,
int position, long id) {
Intent in = new Intent(getApplicationContext(), BankExchangersListActivity.class);
String a = ((Map<String, String>) adapter.getItem(position)).get(TAG_ID);
in.putExtra("Bank_id", a);
startActivity(in);
}
});
*/ } }
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.exchanger_list, menu);
return true;
}
}
然后我得到错误：
05-02 20:16:21.749: E/AndroidRuntime(4057): FATAL EXCEPTION: main
05-02 20:16:21.749: E/AndroidRuntime(4057): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pavel.exchanger/com.pavel.exchanger.ExchangerListActivity}: android.os.NetworkOnMainThreadException
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.os.Handler.dispatchMessage(Handler.java:99)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.os.Looper.loop(Looper.java:137)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.ActivityThread.main(ActivityThread.java:5041)
05-02 20:16:21.749: E/AndroidRuntime(4057): at java.lang.reflect.Method.invokeNative(Native Method)
05-02 20:16:21.749: E/AndroidRuntime(4057): at java.lang.reflect.Method.invoke(Method.java:511)
05-02 20:16:21.749: E/AndroidRuntime(4057): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-02 20:16:21.749: E/AndroidRuntime(4057): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-02 20:16:21.749: E/AndroidRuntime(4057): at dalvik.system.NativeStart.main(Native Method)
05-02 20:16:21.749: E/AndroidRuntime(4057): Caused by: android.os.NetworkOnMainThreadException
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117)
05-02 20:16:21.749: E/AndroidRuntime(4057): at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
05-02 20:16:21.749: E/AndroidRuntime(4057): at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
05-02 20:16:21.749: E/AndroidRuntime(4057): at libcore.io.IoBridge.connect(IoBridge.java:112)
05-02 20:16:21.749: E/AndroidRuntime(4057): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
05-02 20:16:21.749: E/AndroidRuntime(4057): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)
05-02 20:16:21.749: E/AndroidRuntime(4057): at java.net.Socket.connect(Socket.java:842)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:144)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
05-02 20:16:21.749: E/AndroidRuntime(4057): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
05-02 20:16:21.749: E/AndroidRuntime(4057): at com.pavel.exchanger.JSONParser.getJSONFromUrl(JSONParser.java:39)
05-02 20:16:21.749: E/AndroidRuntime(4057): at com.pavel.exchanger.ExchangerListActivity.onCreate(ExchangerListActivity.java:45)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.Activity.performCreate(Activity.java:5104)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
05-02 20:16:21.749: E/AndroidRuntime(4057): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
05-02 20:16:21.749: E/AndroidRuntime(4057): ... 11 more
我做错了什么？如何运行我的活动以进行 json 解析和显示？