Java Json-lib note

JSON array: convert to Java JSONArray.
JSONArray instance: convert to List.
List: convert to Java JSONArray.
JSONArray instance: convert to JSON array(String).
ClassCastException.
You can not use iterator() for enhanced for-loop.

JSON(string) array, Java List and Java JSONArray

JSON array: convert to Java JSONArray.
It thinks JSON string as a String object which formated by JSON. Therefore invoke JSONArray.fromObject(), return a JSONArray instance.
```
jsonArray = JSONArray.fromObject( "[1, 2, 3]" );
```
JSONArray instance: convert to List.
Invoke JSONArray.toCollection(), pass class of target. However, it is still an unchecked or unsafe operations.
```
List<Integer> idList;
idList = (List<Integer>) JSONArray.toCollection(jsonArray, Integer.class);
```

List: convert to Java JSONArray.

jsonArray = JSONArray.fromObject( idList );

JSONArray instance: convert to JSON array(String).
```
System.out.println( jsonArray.toString() );
```

import java.util.*;
import net.sf.json.JSONArray;

public class ArrayAndJson {
    
    public static void
    main(String[] args) {
        String jsonString;
        List<Integer> idList;
        JSONArray jsonArray;

        jsonString = "[1 ,2 ,3]";

        // JSON array: convert to Java JSONArray

        jsonArray = JSONArray.fromObject( jsonString );

        System.out.println(jsonArray.toString());
            
        
        // JSONArray instance: convert to List

        // Warning: unchecked or unsafe operations.

        idList = (List<Integer>) JSONArray.toCollection(jsonArray, Integer.class);

        System.out.println(idList.toString());
        

        idList.add(9);

        // List: convert to Java JSONArray.

        jsonArray = JSONArray.fromObject( idList );

        // JSONArray instance: convert to JSON array(String).

        System.out.println( jsonArray.toString() );

    }
}

JSONArray iterator and exception.

ClassCastException.
Even you pass class to toCollection(), toCollection() won't throw this exception. It is only raised when you try to get an element from collection to variable.
You can not use iterator() for enhanced for-loop.
Method iterator() is not iterable by enhanced for-loop, because it fotgets to add interface Iterable into its implements list. It only lists JSON, List and Comparable.
```
    public final class JSONArray
       extends Object
       implements JSON, List, Comparable
    
```
http://json-lib.sourceforge.net/apidocs/jdk15/net/sf/json/JSONArray.html
http://blogs.sun.com/CoreJavaTechTips/entry/using_enhanced_for_loops_with

import java.util.*;
import net.sf.json.JSONArray;

public class ArrayAndJson2 {
    
    public static void
    main(String[] args) {
        String jsonString;
        List<Integer> idList;
        JSONArray jsonArray;

        jsonString = "[1 ,"x" ,3]";
        jsonArray = JSONArray.fromObject( jsonString );

        try {
            Integer i;
            for (Iterator iter = jsonArray.iterator();
                iter.hasNext();
                )
            {
                i = (Integer) iter.next(); // throws ClassCastException

                System.out.println( i );
            }
        }
        catch (ClassCastException e) {
            System.out.println("There is an element of unexcepted type in JSONArray. " 
                + e.getMessage());
        }

        // No exception riase...

        idList = (List<Integer>) JSONArray.toCollection(jsonArray, Integer.class);

        try {
            for (int i : idList) // throws ClassCastException

            {
                System.out.println( i );
            }
        }
        catch (ClassCastException e) {
            System.out.println("There is an element of unexcepted type in List. " 
                + e.getMessage());
        }

    }
}

樂多舊網址: http://blog.roodo.com/rocksaying/archives/11126901.html