如何检查JSONArray在Java中是否为空? [英] how to check if a JSONArray is empty in java?

问题描述

我正在开发一个Android应用，该应用获取名为"WebUntis"的Web服务的json内容.我得到的Json内容如下:

I am working on an android app that get json content of a webservice called "WebUntis". The Json content i am getting looks like:

{"jsonrpc":"2.0","id":"req-002",
 "result":[
    {"id":125043,"date":20110117,"startTime":800,"endTime":850,
     "kl":[{"id":71}],
     "te":[{"id":23}],
     "su":[{"id":13}],
     "ro":[{"id":1}]},
    {"id":125127,"date":20110117,"startTime":1055,"endTime":1145,
     "kl":[{"id":71}],
     "te":[{"id":41}],
     "su":[{"id":19}],
     "ro":[{"id":31}]},
...]}

在结果数组中可以看到，还有其他数组，例如"kl"，"su"和"ro"

As you can see in the result-array there are also other arrays like "kl", "su" and "ro"

我正在获取这些数组的内容，然后将它们存储在arraylist中. 但是当这些数组之一为空时，就像;

I am getting the content of these array and then i store them in an arraylist. But when one of these array is empty, like;

    {"jsonrpc":"2.0","id":"req-002",
     "result":[
         {"id":125043,"date":20110117,"startTime":800,"endTime":850,
          "**kl":[]**,
          "te":[{"id":23}],
          "su":[{"id":13}],
          "ro":[{"id":1}]},
         {"id":125127,"date":20110117,"startTime":1055,"endTime":1145,
          "kl":[{"id":71}],
          "te":[{"id":41}],
          "su":[{"id":19}],
          "ro":[{"id":31}]},
...]}

我总是收到错误 IndexOutOfRangeException ， 但是我总是告诉它不应该使用空数组，这是我尝试过的:

I am always getting the error IndexOutOfRangeException, but I am always telling it that it should not take the empty arrays, this is what I have tried:

 JSONObject jsonResult = new JSONObject(s);
 // Get the result object
 JSONArray arr = jsonResult.getJSONArray("result");

 for (int i = 0; i < arr.length(); i++) {
    JSONObject c = arr.getJSONObject(i);
    anfangStunde[i] = c.getString("startTime");
    endeStunde[i] = c.getString("endTime");

    // get the jsonarrays (kl, su, ro)
    kl = c.getJSONArray("kl");
    su = c.getJSONArray("su");
    ro = c.getJSONArray("ro");

    // check if kl is not null
    if(kl != null){
       klassenID[i] = kl.getJSONObject(0).getString("id");
    }
    if (klassenID[i] != null) {
       klasse = webuntis.klassenMap.get(klassenID[i]);
       Log.d("ID und Klasse=", "" + klassenID[i] + ";" + klasse);
    }
    // get th ids
    fachID[i] = su.getJSONObject(0).getString("id");
    if (fachID[i] != null) {
       fach = webuntis.faecherMap.get(fachID[i]);
       Log.d("ID und Fach=", "" + fachID[i] + ";" + fach);
    }

    // "Start;Ende;Klasse;Fach;Raum" store in arraylist
    webuntis.stundenPlan.add(anfangStunde[i] + ";" + endeStunde[i] + ";" + klasse + ";" + fach);
    // Write Data into a file for offline use:
 }

有人可以帮助我吗?

推荐答案

如果数组在文件中定义，但为空，例如:

If the array is defined in the file but is empty, like:

...
"kl":[]
...

然后getJSONArray("kl")将返回一个 empty 数组，但该对象不是null.然后，如果您这样做:

Then getJSONArray("kl") will return an empty array, but the object is not null. Then, if you do this:

kl = c.getJSONArray("kl");
if(kl != null){
   klassenID[i] = kl.getJSONObject(0).getString("id");
}

kl不是 null，kl.getJSONObject(0)将引发异常-数组中没有第一个元素.

kl is not null and kl.getJSONObject(0) will throw an exception - there is no first element in the array.

相反，您可以检查length()，例如:

Instead you can check the length(), e.g.:

kl = c.getJSONArray("kl");
if(kl != null && kl.length() > 0 ){
   klassenID[i] = kl.getJSONObject(0).getString("id");
}

这篇关于如何检查JSONArray在Java中是否为空?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！