有一个JSON输出：
{"status":"error","data":null,"message":"required parameters not available."}
要访问它，有一个JSON Parsing java 类和一个User Function java 类。
我在JSONAsyncTask 中的 LoginActivity 上访问此文件时感到困惑。该任务引发空指针异常。我真的认为不提及“状态”是造成这种情况的原因……但这就是真正的原因吗？我是android新手，所以我没有好主意。请帮忙。代码如下：
JSONParser.java
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
static int GET = '1';
static int POST ='2';
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url, List<NameValuePair> params, int method) throws URISyntaxException {
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpResponse httpResponse = null;
HttpEntity httpentity = null;
try {
switch (method) {
case 1:
if(params!=null){
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
}
Log.e("URL", url);
HttpGet httpGet = new HttpGet(url);
httpResponse = httpClient.execute(httpGet);
httpentity = httpResponse.getEntity();
break;
case 2:
HttpPost postrequest = new HttpPost(url);
postrequest.setEntity(new UrlEncodedFormEntity(params));
httpResponse = httpClient.execute(postrequest);
httpentity = httpResponse.getEntity();
break;
}
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();
Log.e("JSON", json);
} 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;
}
}
用户函数.java
public class UserFunctions {
private JSONParser jsonParser;
private static String url_login = "http://10.0.0.2/blamethestars2/public/api/user/login";
static int GET = '1';
static int POST ='2';
// constructor
public UserFunctions(){
jsonParser = new JSONParser();
}
public JSONObject login(String username, String password){
JSONObject json = null;
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("email", username));
params.add(new BasicNameValuePair("password", password));
try {
json = jsonParser.getJSONFromUrl(url_login, params, POST);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return json;
}
}
登录活动.java
public class LoginActivity extends Activity{
EditText username, password;
String user, pass;
Button submit;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sign_in);
username = (EditText)findViewById(R.id.user_email);
password = (EditText)findViewById(R.id.user_password);
submit = (Button)findViewById(R.id.user_submit);
submit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
user = username.getText().toString();
pass = password.getText().toString();
if(user.length()<1 || pass.length()<1){
Toast.makeText(getApplicationContext(), "fill user name and pass", Toast.LENGTH_SHORT).show();
}else{
new Asynconnection().execute();
}
}
});
}
public class Asynconnection extends AsyncTask<Void, Void, Void>{
JSONObject jsarray;
@Override
protected Void doInBackground(Void... params) {
UserFunctions users = new UserFunctions();
jsarray = users.login(user, pass);
return null;
}
}
}
现在我只是想检查 api 响应是否出现在 logcat 上
日志错误：
04-18 16:07:01.190: W/System.err(874): java.lang.NullPointerException
04-18 16:07:01.260: W/System.err(874): at com.example.btshome.library.JSONParser.getJSONFromUrl(JSONParser.java:66)
04-18 16:07:01.260: W/System.err(874): at com.example.btshome.library.UserFunctions.login(UserFunctions.java:38)
04-18 16:07:01.270: W/System.err(874): at com.example.btshome.LoginActivity$Asynconnection.doInBackground(LoginActivity.java:54)
04-18 16:07:01.270: W/System.err(874): at com.example.btshome.LoginActivity$Asynconnection.doInBackground(LoginActivity.java:1)
04-18 16:07:01.280: W/System.err(874): at android.os.AsyncTask$2.call(AsyncTask.java:287)
04-18 16:07:01.280: W/System.err(874): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
04-18 16:07:01.280: W/System.err(874): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
04-18 16:07:01.293: W/System.err(874): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
04-18 16:07:01.293: W/System.err(874): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
04-18 16:07:01.300: W/System.err(874): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
04-18 16:07:01.320: W/System.err(874): at java.lang.Thread.run(Thread.java:856)