import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
public class test {
public static void main(String[] args) {
aaa a = new aaa();
a.setId("1");
a.setUsername("张三");
a.setPassword("1234");
String aaString ="{\"id\": \"1\",\r\n" +
" \"username\": \"张三\",\r\n" +
" \"password\":\"123456\"}";
aaa parseObject = JSONObject.parseObject(aaString,aaa.class);
String id = parseObject.getId();
String jsonString = JSON.toJSONString(parseObject);
System.out.println("====="+id);
System.out.println("====="+jsonString);
}