Unable to execute Java program with Json-simple jar file

Question

I am trying to write a simple Java program which writes JSON data to a file. I am compiling it with the JSON simple jar file but I am getting an error. Below is what I have done:

//JsonSimpleWriteExample.java

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;

import java.io.FileWriter;
import java.io.IOException;

public class JsonSimpleWriteExample {

public static void main(String[] args) {

    JSONObject obj = new JSONObject();
    obj.put("name", "mkyong.com");
    obj.put("age", new Integer(100));

    JSONArray list = new JSONArray();
    list.add("msg 1");
    list.add("msg 2");
    list.add("msg 3");

    obj.put("messages", list);

    try (FileWriter file = new FileWriter("f:\\test.json")) {

        file.write(obj.toJSONString());
        file.flush();

    } catch (IOException e) {
        e.printStackTrace();
    }

    System.out.print(obj);

  }

 }

To compile the above program in a terminal, I am doing:

javac -cp json-simple-1.1.1.jar JsonSimpleWriteExample.java

I downloaded the json-simple-1.1.1.jar file from http://www.java2s.com/Code/Jar/j/json-simple.htm

I am getting the below error:

Note: JsonSimpleWriteExample.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

I am using MacOS. Can anybody help me figure out the issue.

When I try running my class file I get the below error:

$ java JsonSimpleWriteExample

Error that I got:

  Exception in thread "main" java.lang.NoClassDefFoundError: org/json/simple/JSONObject
at JsonSimpleWriteExample.main(JsonSimpleWriteExample.java:11)
  Caused by: java.lang.ClassNotFoundException: org.json.simple.JSONObject
  at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
  ... 1 more

Answer 1

As you have it, you compile using the external jar file, so that the compiler finds the symbols you use during compilation time.

javac -cp json-simple-1.1.1.jar JsonSimpleWriteExample.java

The same has to be done at runtime:

java JsonSimpleWriteExample -cp ./json-simple-1.1.1.jar

In your example, this is the output:

{"name":"mkyong.com","messages":["msg 1","msg 2","msg 3"],"age":100}

As @Pshemo said, those "errors" you get are actually warnings. You can see more about unchecked or unsafe ops here and here .

Answer 2

import org.json.simple.JSONObject;

JSONObject jsonObject = (JSONObject) yourOrginalObject;

//code for get all keys from json
Set<String> keys=jsonObject.keySet();

//iterate the keys

//get values by passing keys
jsonObject.get(pass individual keys);