Question

以下是我用来读取存储在assets文件夹中的JSON文件的代码。

public class ReadJson extends Activity {
public String loadJSONFromAsset() {
    String json1 = null;
    try {

        InputStream is = getAssets().open("jsonfile1.json");
        int size = is.available();
        byte[] buffer = new byte[size];
        is.read(buffer);
        is.close();
        json1 = new String(buffer, "UTF-8");
    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return json1;
} 
}

该应用程序崩溃并显示

"Attempt to invoke virtual method 'android.content.res.AssetManager android.content.Context.getAssets()' on a null object reference" exception.

如何解决这个问题？

Answer 1

试试这段代码：

BufferedReader reader = null;
try {
reader = new BufferedReader(
    new InputStreamReader(getAssets().open("jsonfile1.json")));

// do reading, usually loop until end of file reading  
String mLine;
while ((mLine = reader.readLine()) != null) {
   //process line
   ...
}
} catch (IOException e) {
//log the exception
} finally {
if (reader != null) {
     try {
         reader.close();
     } catch (IOException e) {
         //log the exception
     }
 }
 }

确保您的文件路径是否存在

Answer 2

您可以尝试下面的内容。

try{
    StringBuilder buf=new StringBuilder();
    InputStream json = getAssets().open("jsonfile1.json");
    BufferedReader in = new BufferedReader(new InputStreamReader(json, "UTF-8"));
    String str;

    while ((str=in.readLine()) != null) {
      buf.append(str);
    }

    in.close();
} catch(Exception e){

}

确保您的jsonfile1.json是资产文件夹的文件。

Answer 3

您何时致电public class ReadJson extends Activity { @Override protected void onCreate(Bundle savedInstaceState) { super.onCreate(savedInstaceState); loadJSONFromAsset(); // call after super.onCreate()!!!! /// ... } }？看起来你在创建Activity之前调用它。请尝试以下方法：

<!-- Auth0's lock widget library -->
<script type="text/javascript" src="https://cdn.auth0.com/js/lock-9.0.js"></script>
<!-- Angular cookie wrapper library for client cookies -->
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.8/angular-cookies.js"></script>
<!-- Auth0's Angular SDK Library -->
<script type="text/javascript" src="https://cdn.auth0.com/w2/auth0-angular-4.js"></script>
<!-- Angular wrapper for localStorage and sessionStorage. Defaults to ng-cookies if not available -->
<script src="http://cdn.rawgit.com/auth0/angular-storage/master/dist/angular-storage.js" type="text/javascript"> </script>
<!-- Angular wrapper library for JWT-->
<script src="http://cdn.rawgit.com/auth0/angular-jwt/master/dist/angular-jwt.js" type="text/javascript"> </script>

无法在android中读取JSON文件

3 个答案: