//json-lib-2.2-jdk15.jar
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
1. //把java 对象列表转换为json对象数组，并转为字符串
    JSONArray array = JSONArray.fromObject(userlist);
    String jsonstr = array.toString();
2.//把java对象转换成json对象，并转化为字符串
  JSONObject object = JSONObject.fromObject(invite);
  Log4jInit.ysulogger.debug(object.toString());
3.//把JSON字符串转换为JAVA 对象数组
 String personstr = getRequest().getParameter("persons");
  JSONArray json = JSONArray.fromObject(personstr);
  List<InvoidPerson> persons = (List<InvoidPerson>)JSONArray.toCollection(json, nvoidPerson.class);
4.//把JSON字符串转换为JAVA 对象
 str = "{\"lendperson\":\"李四\",\"lendcompany\":\"有限公司\",\"checkperson\":\"李四\",
  \"lenddate\":\"2010-07-19T00:00:00\",\"lendcounts\":4,\"
  passports\":[{\"passportid\":\"d\",\"name\":\"李豫川\",\"passporttype\":\"K\"},
  {\"passportid\":\"K9051\",\"name\":\"李平\",\"passporttype\":\"K\"},
  {\"passportid\":\"K90517\",\"name\":\"袁寒梅\",\"passporttype\":\"K\"},
  {\"passportid\":\"K905199\",\"name\":\"贺明\",\"passporttype\":\"K\"}]}";
   JSONObject jsonobject = JSONObject.fromObject(str);
  PassportLendsEntity passportlends = null;
  try {
   //获取一个json数组
   JSONArray array = jsonobject.getJSONArray("passports");
   //将json数组 转换成 List<PassPortForLendsEntity>泛型
   List<PassPortForLendsEntity> list = new ArrayList<PassPortForLendsEntity>();
   for (int i = 0; i < array.size(); i++) {   
           JSONObject object = (JSONObject)array.get(i);  
           PassPortForLendsEntity passport = (PassPortForLendsEntity)JSONObject.toBean(object,
            PassPortForLendsEntity.class);
           if(passport != null){
           list.add(passport);
           }  
        }
   //转换PassportLendsEntity 实体类
   passportlends = (PassportLendsEntity)JSONObject.toBean(jsonobject, PassportLendsEntity.class);