我目前正在开发一个需要消耗大量 JSON 数据的应用程序，并且在使用 Jackson 解析器执行此操作时遇到问题。我的类中有以下代码，我需要在其中解析数据：
HttpRequest request = HttpRequest.get("http://www.site.com/android/app/getAllUsers.php");
final Reader reader = request.reader();
final ObjectMapper mapper = new ObjectMapper();
final JsonFactory factory = mapper.getFactory();
class LoadAllUsers extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(VenuesListActivity.this);
pDialog.setMessage("Loading Users. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
try {
JsonParser jp = factory.createParser(reader);
while(jp.nextToken() == JsonToken.START_OBJECT) {
final User a = mapper.readValue(jp, User.class);
String fieldName = jp.getCurrentName();
if("users".equals(fieldName))
{
jp.nextToken();
while(jp.nextToken() != JsonToken.END_ARRAY)
{
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_ID, a.ID);
map.put(TAG_DATA2, a.data1);
map.put(TAG_DATA3, a.data2);
...
// adding HashList to ArrayList
usersList.add(map);
}
}
}
} catch (JsonParseException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all venues
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
setListAdapter(adapter);
}
});
}
}
然后我在一个类中设置了 POJO，如下所示：
public class User {
String ID;
String data1;
String data2;
...
public String getID() {
return ID;
}
public void setID(String iD) {
ID = iD;
}
public String getData1() {
return data1;
}
public void setData1(String data1) {
this.data1 = data1;
}
public String getData2() {
return data2;
}
public void setData2(String data2) {
this.data2 = data2;
}
...
}
下面我附上了我的 PHP 文件，该文件从我的数据库中收集数据以在调用时传递：
<?php
// array for JSON response $response = array(); // include db connect class require_once __DIR__ . '/dbConnect.php'; // connecting to db $db = new DB_CONNECT(); // get all users from users table $result = mysql_query("SELECT * FROM accounts") or die(mysql_error()); // check for empty result if (mysql_num_rows($result) > 0) {
// looping through all results
// users node
$response["users"] = array();
while ($row = mysql_fetch_array($result)) {
// temp user array
$venue = array();
$venue["ID"] = $row["ID"];
$venue["data1"] = $row["data1"];
$venue["data2"] = $row["data2"];
...
// push single user into final response array
array_push($response["users"], $venue);
}
// success
$response["success"] = 1;
// echoing JSON response
echo json_encode($response); } else {
// no users found
$response["success"] = 0;
$response["message"] = "No users found";
// echo no users JSON
echo json_encode($response); } ?>
当我运行我的代码时，我希望一切正常，但是我收到以下错误消息：
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.app.accs/com.app.accs.UsersListActivity}: android.os.NetworkOnMainThreadException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2297)
at android.app.ActivityThread.access$700(ActivityThread.java:152)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1282)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5328)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1125)
at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
at java.net.InetAddress.getAllByName(InetAddress.java:214)
at libcore.net.http.HttpConnection.<init>(HttpConnection.java:70)
at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)
at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:340)
at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:87)
at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:316)
at libcore.net.http.HttpEngine.connect(HttpEngine.java:311)
at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:290)
at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:240)
at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:282)
at libcore.net.http.HttpURLConnectionImpl.getHeaderField(HttpURLConnectionImpl.java:139)
at com.github.kevinsawicki.http.HttpRequest.header(HttpRequest.java:2025)
at com.github.kevinsawicki.http.HttpRequest.parameter(HttpRequest.java:2120)
at com.github.kevinsawicki.http.HttpRequest.charset(HttpRequest.java:2230)
at com.github.kevinsawicki.http.HttpRequest.reader(HttpRequest.java:1822)
at com.app.accs.UsersListActivity.<init>(UsersListActivity.java:107)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1319)
at android.app.Instrumentation.newActivity(Instrumentation.java:1071)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2164)
我希望有人可以帮助我，因为 JSON 文件可能包含 15,000 个用户条目的数组，我想使用这个流式处理来提高性能。我也不确定，但这可能与目标 SDK 有关，因此以下是有关该应用程序的更多信息：
android:minSdkVersion="11"
android:targetSdkVersion="17"
提前致谢。
** * *编辑* ** * *
您好，感谢您的回复，我一直在进一步研究这个问题，是的，这个异步任务是通过以下代码从 MainUI(onCreate) 执行的：
if(user == null || user.equals("All")){
// Loading users in Background Thread
new LoadAllUsers().execute();
}else{
// Load something else
}
这基本上是查看传递给该视图的一条名为“user”的数据，如果用户对象为空或它的值为“All”，则我执行 LoadAllUsers ASync 任务。如果我无法从主 UI 执行它，我该如何使用传递到此视图的数据来执行此操作？
谢谢您的帮助