ajax请求json数据异常：nested exception is net.sf.json.JSONException: java.lang.reflect.InvocationTargetExce

import java.text.SimpleDateFormat;

import net.sf.json.JsonConfig;
import net.sf.json.processors.JsonValueProcessor;

public class DateJsonValueProcessor implements JsonValueProcessor{

    private String format;

    public DateJsonValueProcessor(String format) {
        this.format = format;
    }

    public Object processArrayValue(Object value, JsonConfig jsonConfig) {
        return null;
    }

    public Object processObjectValue(String key, Object value,
            JsonConfig jsonConfig) {
        if (value == null) {
            return "";
        }
        if (value instanceof java.sql.Timestamp) {
            String str = new SimpleDateFormat(format)
                    .format((java.sql.Timestamp) value);
            return str;
        }
        if (value instanceof java.util.Date) {
            String str = new SimpleDateFormat(format)
                    .format((java.util.Date) value);
            return str;
        }

        return value.toString();
    }

}

JsonConfig cfg = new JsonConfig();  
cfg.registerJsonValueProcessor(java.util.Date.class,new DateJsonValueProcessor("yyyy-MM-dd"));  
JSONArray json = JSONArray.fromObject(users, cfg);

    @RequestMapping("/getAllJsonUser")
    public void getAllJsonUser(HttpServletResponse response){
        List<User> users = userService.listAll();
        System.out.println(users);
        JsonConfig cfg = new JsonConfig();  
        cfg.registerJsonValueProcessor(java.util.Date.class,new DateJsonValueProcessor("yyyy-MM-dd"));  
        JSONArray json = JSONArray.fromObject(users, cfg);
        JsonUtils.ajaxJson(json.toString(), response);
    }