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Nacho Zve De La Torre
Asked: 2020-07-17 12:35:49 +0800 CST 2020-07-17 12:35:49 +0800 CST

How to read Json from a file in Java with Simple JSON library?

  • 772

I have the following code that throws me an error at runtime and I don't know where the problem is:

THE ERROR:

Exception reading configuration file java.lang.ClassCastException: org.json.simple.JSONObject cannot be cast to org.json.simple.JSONArray

My code:

 public static void readJson(){


    try {

        JSONParser parser = new JSONParser();
        JSONArray jsonArray = (JSONArray) parser.parse(new FileReader("/home/incentivate/Desktop/config.cfg"));

        for (Object object : jsonArray)
        {
          JSONObject config = (JSONObject) object;

          String verb = (String) config.get("verb");
          System.out.println(verb);

          String host = (String) config.get("host");
          System.out.println(host);

          String port = (String) config.get("port");
          System.out.println(port);

          String method = (String) config.get("method");
          System.out.println(method);

        }

    } catch (Exception e) {
        System.out.println("Excepcion leyendo fichero de configuracion " + e);
    }

}

This is what my config.cfg looks like in case you need it:

{"verb"  :"POST",
 "host"  :"192.169.3.243",
 "port"  :"8080",
 "method":"API/DOCUMENTS/"}

What I need is to get each value of the JSON inside a JAVA variable so that I can continue using them.

I am using Java 8 and the Simple JSON library.

java

1 Answers

  1. Best Answer

    The error indicates that the type being read is actually a JSONObject not a JSONArray. So it should be enough to put:

    public static void readJson(){
      try {

        JSONParser parser = new JSONParser();
        Object object =  parser.parse(new FileReader("/home/incentivate/Desktop/config.cfg"));


          JSONObject config = (JSONObject) object;

          String verb = (String) config.get("verb");
          System.out.println(verb);

          String host = (String) config.get("host");
          System.out.println(host);

          String port = (String) config.get("port");
          System.out.println(port);

          String method = (String) config.get("method");
          System.out.println(method);


    } catch (Exception e) {
        System.out.println("Excepcion leyendo fichero de configuracion " + e);
    }
   }

    Since your configuration file has only one element with several properties, a JSONArray is not necessary.

    • 2