java应用程序不从PHP Web服务检索JSON数据。Web服务运行良好
我的应用程序似乎没有正确地从PHP Web服务中提取JSON数据
访问webservice的函数以从数据库中获取所有数据记录会正确地生成JSON，但我的应用程序无法获取该数据，结果似乎是NullPointerException
LogCat向我发布以下信息：
更新：
注意到以下错误之前发生的黄色错误：
W/System.err(835): org.apache.http.conn.HttpHostConnectException: Connection to http:// localhost refused
如果我无法连接到本地主机上的Web服务，那么我就无法将JSON连接到我的应用程序。但为什么它会拒绝连接到本地主机呢
W/System.err(1159): at com.example.myfirstapp.MainActivity$LoadAllCars.doInBackground(MainActivity.java:113) W/System.err(1159): at com.example.myfirstapp.MainActivity$LoadAllCars.doInBackground(MainActivity.java:1) E/AndroidRuntime(1159): at com.example.myfirstapp.MainActivity$LoadAllCars.doInBackground(MainActivity.java:116) E/AndroidRuntime(1159): at com.example.myfirstapp.MainActivity$LoadAllCars.doInBackground(MainActivity.java:1) E/WindowManager(1159): at com.example.myfirstapp.MainActivity$LoadAllCars.onPreExecute(MainActivity.java:103)
第113行：JSONObject json = jParser.makeHttpRequest(url_all_cars, "GET", params);
第116行：Log.d("All Cars: ", json.toString());
main活动
package com.example.myfirstproject;
//imports
public class MainActivity extends ListActivity implements OnItemClickListener {
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> carsList;
// url to get all products list
private static String url_all_cars = "http://localhost/webservice/get_all_cars.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_CARS = "cars";
private static final String TAG_NAME = "name";
// products JSONArray
JSONArray cars = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Hashmap for ListView
carsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LoadAllcars().execute();
// Get listview
ListView lv = getListView();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
/**
* Background Async Task to Load all product by making HTTP Request
* */
class LoadAllcars extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Loading cars. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_cars, "GET", params);
// Check your log cat for JSON reponse
Log.d("All cars: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
cars = json.getJSONArray(TAG_CARS);
// looping through All Products
for (int i = 0; i < cars.length(); i++) {
JSONObject c = cars.getJSONObject(i);
// Storing each json item in variable
String title = c.getString(TAG_NAME);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_NAME, name);
// adding HashList to ArrayList
carsList.add(map);
}
} else {
// no products found
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("No cars found");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
MainActivity.this, carsList,
安卓.R.id.list, new String[] {TAG_NAME},
new int[] { R.id.title });
// updating listview
setListAdapter(adapter);
}
});
}
}
}
编辑
JSONParser:
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// 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;
}
}
# 1 楼答案
问题就在这里：
private static String url_all_cars = "http://localhost/webservice/get_all_cars.php";无法使用
localhost，因为模拟手机本身是localhost/127.0.0.1您需要将
localhost更改为10.0.2.2：private static String url_all_cars = "http://10.0.2.2/webservice/get_all_cars.php";# 2 楼答案
如果你在这一行得到一个空指针异常
JSONObject json=jParser。makeHttpRequest（url\u all\u cars，“GET”，params）
那么其中一个或多个东西必须为null。jParser被实例化，url字符串也是，params是一个列表，但是列表中没有任何内容。看看jParser内部，看看参数列表发生了什么。你需要它们吗？它需要它们吗
编辑
因此，jParser正在使用字符串生成器将列表（为空）转换为字符串。返回一个空的刺
因此，当您的url被发送到服务器时，它如下所示
所以是普通的url，但上面有一个问号。对吗
从您的httpresponse中记录statuscode和statusreason是有意义的，这样您就可以看到服务器正在响应什么，您可以这样做
编辑
url被设置为“localhost”，因此我认为它是在设备中查看，而不是在服务器上。改为输入服务器的ip
# 3 楼答案
我想你的问题可能是你从来没有在
params里放过任何东西。它只是一个空的List