解析json时clausule的位置

Question

我有一个应用程序，其中有不同的学生在不同的班级（在学校的课程）。我和学生们制作了一个JSON文件（在我的服务器上）。我设法让应用程序在ListView中显示所有学生，但现在我只想显示特定班级的学生。我尝试过很多东西，但到目前为止它还没有用。

所以我的问题是：有办法做到这一点吗？像SQL中的where子句一样？

这是我的JSON文件：

{
"studenten": [
    {

            "Naam": "Marina, Adams",
            "Studentnummer": "s1078544",
            "Klas": "INF1C",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
    {

            "Naam": "Beer, Boris",
            "Studentnummer": "s1074144",
            "Klas": "INF1A",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
   {

            "Naam": "Bootjes, Donald",
            "Studentnummer": "s1084511",
            "Klas": "INF1B",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
    {

            "Naam": "Deriksen, Johan",
            "Studentnummer": "s1089654",
            "Klas": "INF1D",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
{

            "Naam": "Donder, Berend",
            "Studentnummer": "s1074533",
            "Klas": "INF1E",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
{

            "Naam": "Evertsen, Maaike",
            "Studentnummer": "s1074577",
            "Klas": "INF1F",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
  {

            "Naam": "Frederiksen, Michiel",
            "Studentnummer": "s1087966",
            "Klas": "INF1G",
            "Groep" : "1",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
 {

            "Naam": "Gaffel, Lisa",
            "Studentnummer": "s1087512",
            "Klas": "INF1H",
            "Groep" : "1",
            "Cijfer":"",
            "Opmerkingen":""    

    },
 {

            "Naam": "Gerardsen, Mariëlle",
            "Studentnummer": "s1074159",
            "Klas": "INF1A",
            "Groep" : "2",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
  {

            "Naam": "Gokker, Yvonne",
            "Studentnummer": "s1071211",
            "Klas": "INF1B",
            "Groep" : "2",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
 {

            "Naam": "Hendriksen, Willem",
            "Studentnummer": "s1087869",
            "Klas": "INF1C",
            "Groep" : "2",
            "Cijfer":"",
            "Opmerkingen":""    

    },
 {

            "Naam": "Hokje, Dirk",
            "Studentnummer": "s1084514",
            "Klas": "INF1D",
            "Groep" : "2",
            "Cijfer":"", 
            "Opmerkingen":""    

    },
    {

            "Naam": "Imker, Lara",
            "Studentnummer": "s1071423",
            "Klas": "INF1E",
            "Groep" : "2",
            "Cijfer":"", 
            "Opmerkingen":""    

    }
]
}

这是我的Java类：

 package com.ipmedt4.challengeweek_v2;

 import android.annotation.TargetApi;
 import android.app.Activity;
 import android.app.ListActivity;
  import android.app.ProgressDialog;
  import android.content.Context;
  import android.content.Intent;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteException;
 import android.database.sqlite.SQLiteOpenHelper;
 import android.os.AsyncTask;
 import android.os.Build;
 import android.os.StrictMode;
 import android.support.v7.app.ActionBarActivity;
 import android.os.Bundle;
 import android.text.Editable;
 import android.text.TextWatcher;
 import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AdapterView;
 import android.widget.ArrayAdapter;
 import android.widget.Button;
 import android.widget.EditText;
 import android.widget.FilterQueryProvider;
 import android.widget.ListAdapter;
 import android.widget.ListView;
  import android.widget.SimpleAdapter;
 import android.widget.SimpleCursorAdapter;
 import android.widget.TextView;
 import android.widget.Toast;

 import org.apache.http.NameValuePair;
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;

 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;


public class Overzicht_Studenten1A extends ListActivity {

private ProgressDialog pDialog;

// URL to get contacts JSON
private static String url = "http://charlenemacdonald.com/allestudenten.json";

// JSON Node names
private static final String TAG_STUDENTEN = "studenten";
private static final String TAG_NAAM = "Naam";
private static final String TAG_STUDENTNUMMER = "Studentnummer";
private static final String TAG_KLAS = "Klas";
private static final String TAG_GROEP = "Groep";
private static final String TAG_CIJFER = "Cijfer";
private static final String TAG_OPMERKINGEN = "Opmerkingen";


// contacts JSONArray
JSONArray studenten= null;

// Hashmap for ListView
ArrayList<HashMap<String, String>> studentList;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_overzicht_studenten);
    if (android.os.Build.VERSION.SDK_INT > 9) {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
        System.out.println("*** My thread is nu geconfigureerd zodat het interverbinding toestaat");
    }

    studentList = new ArrayList<HashMap<String, String>>();

    ListView lv = (ListView) findViewById(android.R.id.list);
    // Listview on item click listener
    lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
            // getting values from selected ListItem
            String Naam = ((TextView) view.findViewById(R.id.Naam))
                    .getText().toString();
            String Studentnummer = ((TextView) view.findViewById(R.id.Studentnummer))
                    .getText().toString();
            String Klas = ((TextView) view.findViewById(R.id.Klas))
                    .getText().toString();
            String Groep = ((TextView) view.findViewById(R.id.Groep))
                    .getText().toString();

            // Starting single contact activity
            Intent in = new Intent(getApplicationContext(),
                    Beoordelingscherm.class);
            in.putExtra(TAG_NAAM, Naam);
            in.putExtra(TAG_STUDENTNUMMER, Studentnummer);
            in.putExtra(TAG_KLAS, Klas);
            startActivity(in);

        }
    });

    // Calling async task to get json
    new GetStudenten().execute();
}

/**
 * Async task class to get json by making HTTP call
 * */
private class GetStudenten extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(Overzicht_Studenten1A.this);
        pDialog.setMessage("Even geduld a.u.b., studenten worden geladen...");
        pDialog.setCancelable(false);
        pDialog.show();


    }

    @Override
    protected Void doInBackground(Void... arg0) {
        // Creating service handler class instance
        ServiceHandler sh = new ServiceHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);

        Log.d("Response: ", "> " + jsonStr);

        if (jsonStr != null) {
            try {
                JSONObject jsonObj = new JSONObject(jsonStr);

                // Getting JSON Array node
                studenten = jsonObj.getJSONArray(TAG_STUDENTEN);


                // looping through All Contacts
                for (int i = 0; i < studenten.length(); i++) {
                    JSONObject c = studenten.getJSONObject(i);


                    String Naam = c.getString(TAG_NAAM);
                    String Studentnummer = c.getString(TAG_STUDENTNUMMER);
                    String Klas = c.getString(TAG_KLAS);
                    String Groep = c.getString(TAG_GROEP);
                    String Cijfer = c.getString(TAG_CIJFER);
                    String Opmerkingen = c.getString(TAG_OPMERKINGEN);

                    // tmp hashmap for single contact
                    HashMap<String, String> student = new HashMap<String, String>();

                    // adding each child node to HashMap key => value

                    student.put(TAG_NAAM, Naam);
                    student.put(TAG_STUDENTNUMMER, Studentnummer);
                    student.put(TAG_KLAS, Klas);
                    student.put(TAG_GROEP, Groep);



                    // adding contact to contact list
                    studentList.add(student);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        } else {
            Log.e("ServiceHandler", "Couldn't get any data from the url");
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        // Dismiss the progress dialog
        if (pDialog.isShowing())
            pDialog.dismiss();
        /**
         * Updating parsed JSON data into ListView
         * */
        ListAdapter adapter = new SimpleAdapter(
                Overzicht_Studenten1A.this, studentList,
                R.layout.student_info, new String[] { TAG_NAAM, TAG_STUDENTNUMMER,
                TAG_KLAS, TAG_GROEP }, new int[] { R.id.Naam,
                R.id.Studentnummer, R.id.Klas, R.id.Groep });

        setListAdapter(adapter);
    }

}

 }

Answer 1

您可以在设置studentList时过滤某些klas值。

    //Just an example, you will probably want to set this somewhere else
    String klas = "INF1A";

    // Calling async task to get json
    new GetStudenten().execute(klas);

过滤更多类别：

   //Just an example, you will probably want to set this somewhere else
    String klas1 = "INF1A";
    String klas2 = "INF1B";

    // Calling async task to get json
    new GetStudenten().execute(klas1, klas2);

注意下面的类定义中的Void字符串intead：

private class GetStudenten extends AsyncTask<String, Void, Void> {

doInBackground现在接受一个String数组，用于＆＃34; ...＆＃34;符号见varargs：http://docs.oracle.com/javase/1.5.0/docs/guide/language/varargs.html

    @Override
    protected Void doInBackground(String... arg0) {
        HashSet<String> klasFilter = new HashSet<String>();
        for (int i = 0; i < arg0.length; i++){
           klasFilter.add(arg0[i]); 
        }

        // Creating service handler class instance
        ServiceHandler sh = new ServiceHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);

        Log.d("Response: ", "> " + jsonStr);

        if (jsonStr != null) {
            try {
                JSONObject jsonObj = new JSONObject(jsonStr);

                // Getting JSON Array node
                studenten = jsonObj.getJSONArray(TAG_STUDENTEN);

                // looping through All Contacts
                for (int i = 0; i < studenten.length(); i++) {
                    JSONObject c = studenten.getJSONObject(i);

                    String Naam = c.getString(TAG_NAAM);
                    String Studentnummer = c.getString(TAG_STUDENTNUMMER);
                    String Klas = c.getString(TAG_KLAS);
                    String Groep = c.getString(TAG_GROEP);
                    String Cijfer = c.getString(TAG_CIJFER);
                    String Opmerkingen = c.getString(TAG_OPMERKINGEN);

                    // tmp hashmap for single contact
                    HashMap<String, String> student = new HashMap<String, String>();

                    //only add student to list if in specified klasFilter
                    if (klasFilter.contains(Klas)){ 
                       // adding each child node to HashMap key => value
                       student.put(TAG_NAAM, Naam);
                       student.put(TAG_STUDENTNUMMER, Studentnummer);
                       student.put(TAG_KLAS, Klas);
                       student.put(TAG_GROEP, Groep);

                       // adding contact to contact list
                       studentList.add(student);
                     }
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        } else {
            Log.e("ServiceHandler", "Couldn't get any data from the url");
        }

        return null;
    }    
}