php - 我在 Android 中将 JSON 对象解析为 String 时出错

Question

我想了解 Android 与 PHP 的关系，我在这个网站上找到了一段代码: demo web 所以，代码工作得很好，但是当我想做选择时，它说将 JSON 对象解析为字符串时出现错误。 我会给你代码的3部分。您可以在 Adob​​e 的网站中看到所有代码。

这里有两个代码:

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }


    public JSONObject getJSONFromUrl(final String url) {

        // Making HTTP request
        try {
            // Construct the client and the HTTP request.
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);

            // Execute the POST request and store the response locally.
            HttpResponse httpResponse = httpClient.execute(httpPost);
            // Extract data from the response.
            HttpEntity httpEntity = httpResponse.getEntity();
            // Open an inputStream with the data content.
            is = httpEntity.getContent();

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Create a BufferedReader to parse through the inputStream.
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            // Declare a string builder to help with the parsing.
            StringBuilder sb = new StringBuilder();
            // Declare a string to store the JSON object data in string form.
            String line = null;

            // Build the string until null.
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }

            // Close the input stream.
            is.close();
            // Convert the string builder data to an actual string.
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // Try to 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 the JSON Object.
        return jObj;

    }


    // function get json from url
    // by making HTTP POST or GET method
    public JSONObject makeHttpRequest(String url, String method,
            List<NameValuePair> params) {

        // Making HTTP request
        try {

            // check for request method
            if(method == "POST"){
                // request method is POST
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();

            }else if(method == "GET"){
                // request method is GET
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                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, "iso-8859-1"), 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;

    }
}

另一类:

package com.example.mysqltest;

import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class ReadComments extends ListActivity {

    // Progress Dialog
    private ProgressDialog pDialog;

    // php read comments script

    // localhost :
    // testing on your device
    // put your local ip instead, on windows, run CMD > ipconfig
    // or in mac's terminal type ifconfig and look for the ip under en0 or en1
    // private static final String READ_COMMENTS_URL =
    // "http://xxx.xxx.x.x:1234/webservice/comments.php";

    // testing on Emulator:
    private static final String READ_COMMENTS_URL = "http://10.0.2.2/webservice/comments.php";

    // testing from a real server:
    // private static final String READ_COMMENTS_URL =
    // "http://www.mybringback.com/webservice/comments.php";

    // JSON IDS:
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_TITLE = "title";
    private static final String TAG_POSTS = "posts";
    private static final String TAG_POST_ID = "post_id";
    private static final String TAG_USERNAME = "username";
    private static final String TAG_MESSAGE = "message";
    // it's important to note that the message is both in the parent branch of
    // our JSON tree that displays a "Post Available" or a "No Post Available"
    // message,
    // and there is also a message for each individual post, listed under the
    // "posts"
    // category, that displays what the user typed as their message.

    // An array of all of our comments
    private JSONArray mComments = null;
    // manages all of our comments in a list.
    private ArrayList<HashMap<String, String>> mCommentList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // note that use read_comments.xml instead of our single_post.xml
        setContentView(R.layout.read_comments);
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        // loading the comments via AsyncTask
        new LoadComments().execute();
    }

    public void addComment(View v) {
        Intent i = new Intent(ReadComments.this, AddComment.class);
        startActivity(i);
    }

    /**
     * Retrieves recent post data from the server.
     */
    public void updateJSONdata() {

        // Instantiate the arraylist to contain all the JSON data.
        // we are going to use a bunch of key-value pairs, referring
        // to the json element name, and the content, for example,
        // message it the tag, and "I'm awesome" as the content..

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

        // Bro, it's time to power up the J parser
        JSONParser jParser = new JSONParser();
        // Feed the beast our comments url, and it spits us
        // back a JSON object. Boo-yeah Jerome.
        JSONObject json = jParser.getJSONFromUrl(READ_COMMENTS_URL);

        // when parsing JSON stuff, we should probably
        // try to catch any exceptions:
        try {

            // I know I said we would check if "Posts were Avail." (success==1)
            // before we tried to read the individual posts, but I lied...
            // mComments will tell us how many "posts" or comments are
            // available
            mComments = json.getJSONArray(TAG_POSTS);

            // looping through all posts according to the json object returned
            for (int i = 0; i < mComments.length(); i++) {
                JSONObject c = mComments.getJSONObject(i);

                // gets the content of each tag
                String title = c.getString(TAG_TITLE);
                String content = c.getString(TAG_MESSAGE);
                String username = c.getString(TAG_USERNAME);

                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();

                map.put(TAG_TITLE, title);
                map.put(TAG_MESSAGE, content);
                map.put(TAG_USERNAME, username);

                // adding HashList to ArrayList
                mCommentList.add(map);

                // annndddd, our JSON data is up to date same with our array
                // list
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    /**
     * Inserts the parsed data into the listview.
     */
    private void updateList() {
        // For a ListActivity we need to set the List Adapter, and in order to do
        //that, we need to create a ListAdapter.  This SimpleAdapter,
        //will utilize our updated Hashmapped ArrayList, 
        //use our single_post xml template for each item in our list,
        //and place the appropriate info from the list to the
        //correct GUI id.  Order is important here.
        ListAdapter adapter = new SimpleAdapter(this, mCommentList,
                R.layout.single_post, new String[] { TAG_TITLE, TAG_MESSAGE,
                        TAG_USERNAME }, new int[] { R.id.title, R.id.message,
                        R.id.username });

        // I shouldn't have to comment on this one:
        setListAdapter(adapter);

        // Optional: when the user clicks a list item we 
        //could do something.  However, we will choose
        //to do nothing...
        ListView lv = getListView();    
        lv.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {

                // This method is triggered if an item is click within our
                // list. For our example we won't be using this, but
                // it is useful to know in real life applications.

            }
        });
    }

    public class LoadComments extends AsyncTask<Void, Void, Boolean> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(ReadComments.this);
            pDialog.setMessage("Loading Comments...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        @Override
        protected Boolean doInBackground(Void... arg0) {
            updateJSONdata();
            return null;

        }

        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            pDialog.dismiss();
            updateList();
        }
    }
}

这里有 php 代码:

*/
require("config.inc.php");


$query = "Select post_id,username,title,message FROM comments";


try {
    $stmt   = $db->prepare($query);
    $result = $stmt->execute($query_params);

}
catch (PDOException $ex) {
    $response["success"] = 0;
    $response["message"] = "Database Error!";
    die(json_encode($response));
}


$rows = $stmt->fetchAll();


if ($rows) {
    $response["success"] = 1;
    $response["message"] = "Post Available!";
    json_encode($response)
    $response["posts"]   = array();


    foreach ($rows as $row) {
        $post             = array();
        $post["post_id"]  = $row["post_id"];
        $post["username"] = $row["username"];
        $post["title"]    = $row["title"];
        $post["message"]  = $row["message"];


        //update our repsonse JSON data
        array_push($response["posts"], $post);
    }

    // echoing JSON response
    echo json_encode($response);


} else {
    $response["success"] = 0;
    $response["message"] = "No Post Available!";
    die(json_encode($response));
}

我希望你能帮助我，因为我喜欢Android，但我认为这段代码是为高级人员准备的。我仍在学习有关 JSON 的所有知识。

Answer 1

正如 Android API 文档中所说:

public JSONArray getJSONArray(字符串名称)

返回按名称映射的值(如果存在且为 JSONArray)。

抛出 如果映射不存在或者不是 JSONArray，则抛出 JSONException。

在您的情况下，您不会检查响应中的 JSON 对象是否具有值为 1 的字段 status。如果是 0，则 mComments = json.getJSONArray(TAG_POSTS); 行将抛出 JSONException。因为您的数组 posts 仅具有 status = 1