JSON 字符串 与 java 对象之间互相转换

首先引入maven需要依赖的jar：
<dependency>
    <groupId>net.sf.json-lib</groupId>
    <artifactId>json-lib</artifactId>
    <version>2.4</version>
    <classifier>jdk15</classifier>
</dependency>


需要导入的类：
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
    JSONArrayarray = JSONArray.fromObject(userlist);
    Stringjsonstr = 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, InvoidPerson.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\"}]}";
  
  JSONObjectjsonobject = JSONObject.fromObject(str);
  PassportLendsEntitypassportlends = null;
  
  try {
   //获取一个json数组
   JSONArrayarray = jsonobject.getJSONArray("passports");
   //将json数组 转换成List<PassPortForLendsEntity>泛型
   List<PassPortForLendsEntity>list = newArrayList<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);
   
5.如果只想取JSON字符串的某几个字段，就没必要转成Java对象，直接转成对象数组，再把数组转成对象，再去某个字段的值
JSONArray listArray = dataObject.getJSONArray("list");
for (int i =0; i < listArray.size(); i++){
    tmp = listArray.getJSONObject(i);
    float longitude = tmp.getString("longitude");
}