java - 如何在Android应用程序上从互联网获取json响应

Question

我正在尝试从 api 调用获取 json 响应。但是发生了一些错误。请告诉我我的代码有什么问题...我的代码是这样的。

private JSONObject responseJson;

private void apiRequest() {
    mQueue = Volley.newRequestQueue(MainActivity.this);
    String mRequestUrl = "http://hogehoge";
    JsonObjectRequest jsonOR = new JsonObjectRequest(Request.Method.GET, mRequestUrl, null, new Response.Listener<JSONObject>() {
        @Override
        public void onResponse(JSONObject response) {
            try {
                if (response.getJSONObject("response").has("error")) {
                    throw new NoSuchElementException(msg);
                }else{
                    responseJson = response;
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    // error
                }
            });

    jsonOR.setRetryPolicy(new DefaultRetryPolicy(5000, DefaultRetryPolicy.DEFAULT_MAX_RETRIES, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
    mQueue.add(jsonOR);
}

错误消息是这样的。

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.mymaterialapp/com.example.user.mymaterialapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.toString()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        at android.app.ActivityThread.access$800(ActivityThread.java:144)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)

位于 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.toString()' on a null object reference
    at com.example.user.mymaterialapp.MainActivity.onCreate(MainActivity.java:75)
    at android.app.Activity.performCreate(Activity.java:5933)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)

Answer 1

试试这个代码

public String callWebService(String serviceURL) {
            StringBuffer buff = new StringBuffer("");
            HttpClient client;
            BufferedReader in = null;

            try {

                HttpGet getRequest = new HttpGet(serviceURL);
                final HttpParams httpParams = new BasicHttpParams();
                HttpConnectionParams.setConnectionTimeout(httpParams, 5000);
                client = new DefaultHttpClient(httpParams);
                HttpResponse response = client.execute(getRequest);
                in = new BufferedReader(new InputStreamReader(response.getEntity()
                        .getContent()));
                String line = "";
                while ((line = in.readLine()) != null) {
                    buff.append(line);
                }
                in.close();
            } catch (Exception e) {
            }
            return buff.toString();
        }

它将返回 JSON