转载：https://www.cnblogs.com/Ming8006/p/6944954.html
常用操作包括以下内容：
- 对象与（JsonObject或JsonArray）与String的互换
- String转换为（JsonObject或JsonArray）如何保持顺序
- Eval的使用
- 值为null的（JsonObject或JsonArray）转换为String时如何保存
代码：
package Demo.Sample1;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.JSONPath;import com.alibaba.fastjson.parser.Feature;import com.alibaba.fastjson.serializer.SerializerFeature;public class Sample { ???public static void main(String[] args) { ???????????????Group group = GenerateGroup(); ???????String ss="{\"id\":1.1,\"name\":\"admin\",\"users\":[{\"id\":2.2,\"name\":\"guest\"},{\"id\":3.3,\"name\":\"root\"}]}"; ???????????????Group groupWithNull=GenerateGroupWithNull(); ???????????????BasicObjectToStringCompare(); ???????JsonObjectToStringCompare(ss); ???????NJsonObjectToStringCompare(group); ???????JsonStringSequence(group, ss); ???????????????JsonEval(ss,"$.users"); ???????DealWithNullToStringString(groupWithNull); ???????????} ???????public static void BasicObjectToStringCompare() ???{ ???????System.out.println("---------- 基元类型 toString() toJSONString() 比较: ----------"); ???????System.out.println("ZifuChuan"); ???????System.out.println(JSON.toJSONString("ZifuChuan")); ???????System.out.println(true); ???????System.out.println(JSON.toJSONString(true)); ???????System.out.println(1.1); ???????System.out.println(JSON.toJSONString(1.1)); ???} ???????public static String NJsonObjectToStringCompare(Group group) { ???????String jsonString = JSON.toJSONString(group); ???????System.out.println("---------- 非JsonObject toString() toJSONString() 比较: ----------"); ???????System.out.println(group.toString()); ???????System.out.println(JSON.toJSONString(group)); ???????return jsonString; ???} ???????public static String JsonObjectToStringCompare(String ss) { ???????Object o=JSON.parse(ss,Feature.OrderedField); ???????System.out.println("---------- JsonObject toString() toJSONString() 比较: ----------"); ???????System.out.println(o.toString()); ???????System.out.println(JSON.toJSONString(o)); ???????return ss; ???} ???????public static void JsonStringSequence(Group group, String jsonString) { ???????System.out.println("---------- 是否有序: ----------"); ???????Object o=JSON.parse(jsonString); ???????System.out.println(o.toString());; ???????????????Object o1=JSON.parse(jsonString,Feature.OrderedField); ???????System.out.println(o1.toString()); ???????????????Object o2 = JSON.toJSON(group); ???????System.out.println(o2.toString()); ???} ???????public static void JsonEval(String ss,String jsonPath) { ???????System.out.println("---------- Json Eval: ----------"); ???????????????Object o3=JSONPath.eval(JSON.parse(ss,Feature.OrderedField),jsonPath); ???????System.out.println(o3.toString()); ???} ???public static void DealWithNullToStringString(Group groupWithNull) { ???????System.out.println("---------- JsonObject with null emlement: ----------"); ???????System.out.println(JSON.toJSONString(groupWithNull)); ???????System.out.println(JSON.toJSONString(groupWithNull,SerializerFeature.WriteMapNullValue)); ???} ???????private static Group GenerateGroup() { ???????Group group = new Group(); ???????group.setId(1.1); ???????group.setName("admin"); ???????User guestUser = new User(); ???????guestUser.setId(2.2); ???????guestUser.setName("guest"); ???????User rootUser = new User(); ???????rootUser.setId(3.3); ???????rootUser.setName("root"); ???????group.addUser(guestUser); ???????group.addUser(rootUser); ???????return group; ???} ???????private static Group GenerateGroupWithNull() { ???????Group group = new Group(); ???????group.setId(1.1); ???????group.setName(""); ???????User guestUser1 = new User(); ???????guestUser1.setId(null); ???????guestUser1.setName("guest"); ???????User guestUser2 = new User(); ???????guestUser2.setId(3.3); ???????????????User guestUser3 = new User(); ???????????????group.addUser(guestUser1); ???????group.addUser(guestUser2); ???????group.addUser(guestUser3); ???????return group; ???}}结果：
---------- 基元类型 toString() toJSONString() 比较: ----------ZifuChuan"ZifuChuan"truetrue1.11.1---------- JsonObject toString() toJSONString() 比较: ----------{"id":1.1,"name":"admin","users":[{"id":2.2,"name":"guest"},{"id":3.3,"name":"root"}]}{"id":1.1,"name":"admin","users":[{"id":2.2,"name":"guest"},{"id":3.3,"name":"root"}]}---------- 非JsonObject toString() toJSONString() 比较: ----------Demo.Sample1.Group@23ab930d{"id":1.1,"name":"admin","users":[{"id":2.2,"name":"guest"},{"id":3.3,"name":"root"}]}---------- 是否有序: ----------{"name":"admin","id":1.1,"users":[{"name":"guest","id":2.2},{"name":"root","id":3.3}]}{"id":1.1,"name":"admin","users":[{"id":2.2,"name":"guest"},{"id":3.3,"name":"root"}]}{"name":"admin","id":1.1,"users":[{"name":"guest","id":2.2},{"name":"root","id":3.3}]}---------- Json Eval: ----------[{"id":2.2,"name":"guest"},{"id":3.3,"name":"root"}]---------- JsonObject with null emlement: ----------{"id":1.1,"name":"","users":[{"name":"guest"},{"id":3.3},{}]}{"id":1.1,"name":"","users":[{"id":null,"name":"guest"},{"id":3.3,"name":null},{"id":null,"name":null}]}参考：
[1] Introducing JSON
http://www.json.org/
[2] FastJson 教程
https://www.w3cschool.cn/fastjson/%20
FastJson的常用操作
原文地址：http://www.cnblogs.com/MasterJ/p/7906309.html