前言
最近在开发过程中使用了大量的json作为前后端数据交换的方式,由于之前没有对json做过系统的学习,所有在使用过程中查阅了大量的文档与资料,这里主要记录了我在开发后对json以及fastjson使用的总结
JSON 介绍
JSON(javaScript Object Notation)是一种轻量级的数据交换格式。主要采用键值对({"name": "json"})的方式来保存和表示数据。JSON是JS对象的字符串表示法，它使用文本表示一个JS对象的信息，本质上是一个字符串。更多简介见介绍JSON。
fastjson 简介
在日志解析,前后端数据传输交互中,经常会遇到字符串(String)与json,XML等格式相互转换与解析，其中json以跨语言，跨前后端的优点在开发中被频繁使用，基本上可以说是标准的数据交换格式。fastjson是一个java语言编写的高性能且功能完善的JSON库，它采用一种“假定有序快速匹配”的算法，把JSON Parse 的性能提升到了极致。它的接口简单易用，已经被广泛使用在缓存序列化，协议交互，Web输出等各种应用场景中。
fastjson 常用 API
fastjson API 入口类是com.alibaba.fastjson.JSON,常用的序列化操作都可以在JSON类上的静态方法直接完成。
public static final Object parse(String text); // 把JSON文本parse为JSONObject或者JSONArray public static final JSONObject parseObject(String text)； // 把JSON文本parse成JSONObject ???public static final <T> T parseObject(String text, Class<T> clazz); // 把JSON文本parse为JavaBean public static final JSONArray parseArray(String text); // 把JSON文本parse成JSONArray public static final <T> List<T> parseArray(String text, Class<T> clazz); //把JSON文本parse成JavaBean集合 public static final String toJSONString(Object object); // 将JavaBean序列化为JSON文本 public static final String toJSONString(Object object, boolean prettyFormat); // 将JavaBean序列化为带格式的JSON文本 public static final Object toJSON(Object javaObject); //将JavaBean转换为JSONObject或者JSONArray。使用方法举例
//将JSON文本转换为java对象import com.alibaba.fastjson.JSON;Model model = JSON.parseObject(jsonStr, Model.class);有关类库的一些说明
- JSONArray : 相当于List
- JSONObject: 相当于Map<String,Object>
fastjson 使用实例
java对象与JSON字符串的互转
User测试类
/** * User测试类 * @author dmego */public class User { ???private String username; ???private String password; ???public User(){} ???public User(String username,String password){ ???????this.username = username; ???????this.password = password; ???} ???public String getUsername() { ???????return username; ???} ???public void setUsername(String username) { ???????this.username = username; ???} ???public String getPassword() { ???????return password; ???} ???public void setPassword(String password) { ???????this.password = password; ???} ???@Override ???public String toString() { ???????return "User [username=" + username + ", password=" + password + "]"; ???}}UserGroup测试类
import java.util.ArrayList;import java.util.List;/** * 用户组测试类 * @author dmego * */public class UserGroup { ???private String name; ?????private List<User> users = new ArrayList<User>(); ???public UserGroup(){} ???public UserGroup(String name,List<User> users){ ???????this.name = name; ???????this.users = users; ???} ???public String getName() { ???????return name; ???} ???public void setName(String name) { ???????this.name = name; ???} ???public List<User> getUsers() { ???????return users; ???} ???public void setUsers(List<User> users) { ???????this.users = users; ???} ???@Override ???public String toString() { ???????return "UserGroup [name=" + name + ", users=" + users + "]"; ???} ?}fastJson测试类
package demo;import java.util.ArrayList;import java.util.List;import org.junit.Test;import com.alibaba.fastjson.JSON;/** * fastJson测试类 * @author dmego * */public class TestFastJosn { ???/** ????* java对象转 json字符串 ?????*/ ???@Test ???public void objectTOJson(){ ???????//简单java类转json字符串 ???????User user = new User("dmego", "123456"); ???????String UserJson = JSON.toJSONString(user); ???????System.out.println("简单java类转json字符串:"+UserJson); ???????????????//List<Object>转json字符串 ???????User user1 = new User("zhangsan", "123123"); ???????User user2 = new User("lisi", "321321"); ???????List<User> users = new ArrayList<User>(); ???????users.add(user1); ???????users.add(user2); ???????String ListUserJson = JSON.toJSONString(users); ???????System.out.println("List<Object>转json字符串:"+ListUserJson); ??????????????????//复杂java类转json字符串 ???????UserGroup userGroup = new UserGroup("userGroup", users); ???????String userGroupJson = JSON.toJSONString(userGroup); ???????System.out.println("复杂java类转json字符串:"+userGroupJson); ??????????????????} ???????/** ????* json字符串转java对象 ????* 注：字符串中使用双引号需要转义 (" --> \"),这里使用的是单引号 ????*/ ???@Test ???public void JsonTOObject(){ ???????/* json字符串转简单java对象 ????????* 字符串：{"password":"123456","username":"dmego"}*/ ???????????????String jsonStr1 = "{‘password‘:‘123456‘,‘username‘:‘dmego‘}"; ???????User user = JSON.parseObject(jsonStr1, User.class); ???????System.out.println("json字符串转简单java对象:"+user.toString()); ???????????????/* ????????* json字符串转List<Object>对象 ????????* 字符串：[{"password":"123123","username":"zhangsan"},{"password":"321321","username":"lisi"}] ????????*/ ???????String jsonStr2 = "[{‘password‘:‘123123‘,‘username‘:‘zhangsan‘},{‘password‘:‘321321‘,‘username‘:‘lisi‘}]"; ???????List<User> users = JSON.parseArray(jsonStr2, User.class); ???????System.out.println("json字符串转List<Object>对象:"+users.toString()); ???????????????????/*json字符串转复杂java对象 ????????* 字符串：{"name":"userGroup","users":[{"password":"123123","username":"zhangsan"},{"password":"321321","username":"lisi"}]} ????????* */ ???????String jsonStr3 = "{‘name‘:‘userGroup‘,‘users‘:[{‘password‘:‘123123‘,‘username‘:‘zhangsan‘},{‘password‘:‘321321‘,‘username‘:‘lisi‘}]}"; ???????UserGroup userGroup = JSON.parseObject(jsonStr3, UserGroup.class); ???????System.out.println("json字符串转复杂java对象:"+userGroup); ?????}}输出结果
简单java类转json字符串:{"password":"123456","username":"dmego"}List<Object>转json字符串:[{"password":"123123","username":"zhangsan"},{"password":"321321","username":"lisi"}]复杂java类转json字符串:{"name":"userGroup","users":[{"password":"123123","username":"zhangsan"},{"password":"321321","username":"lisi"}]}json字符串转简单java对象:User [username=dmego, password=123456]json字符串转List<Object>对象:[User [username=zhangsan, password=123123], User [username=lisi, password=321321]]json字符串转复杂java对象:UserGroup [name=userGroup, users=[User [username=zhangsan, password=123123], User [username=lisi, password=321321]]]fastjson 解析复杂嵌套json字符串
这个实例是我在开发中用到的，先给出要解析的json字符串
[ ???{ ???????"id": "user_list", ???????"key": "id", ???????"tableName": "用户列表", ???????"className": "cn.dmego.domain.User", ???????"column": [ ???????????{ ???????????????"key": "rowIndex", ???????????????"header": "序号", ???????????????"width": "50", ???????????????"allowSort": "false" ???????????}, ???????????{ ???????????????"key": "id", ???????????????"header": "id", ???????????????"hidden": "true" ???????????}, ???????????{ ???????????????"key": "name", ???????????????"header": "姓名", ???????????????"width": "100", ???????????????"allowSort": "true" ???????????} ???????] ???}, ???{ ???????"id": "role_list", ???????"key": "id", ???????"tableName": "角色列表", ???????"className": "cn.dmego.domain.Role", ???????"column": [ ???????????{ ???????????????"key": "rowIndex", ???????????????"header": "序号", ???????????????"width": "50", ???????????????"allowSort": "false" ???????????}, ???????????{ ???????????????"key": "id", ???????????????"header": "id", ???????????????"hidden": "true" ???????????}, ???????????{ ???????????????"key": "name", ???????????????"header": "名称", ???????????????"width": "100", ???????????????"allowSort": "true" ???????????} ???????] ???}]要想解析这种复杂的字符串，首先得先定义好与之相符的java POJO 对象，经过观察，我们发现，这个是一个json对象数组，每一个对象里包含了许多属性，其中还有一个属性的类型也是对象数组。所有，我们从里到外，先定义最里面的对象：
public class Column { ???private String key; ???private String header; ???private String width; ???private String allowSort; ???private String hidden; ???????public String getKey() { ???????return key; ???} ???public void setKey(String key) { ???????this.key = key; ???} ???//这里省略部分getter与setter方法 }再定义外层的对象：
import java.util.List;import org.apache.commons.collections4.map.LinkedMap;public class Query { ???private String id; ???private String key; ???private String tableName; ???private String className; ???private List<LinkedMap<String, Object>> column; ????private List<Column> columnList; ???????public String getId() { ???????return id; ???} ???public void setId(String id) { ???????this.id = id; ???} ???//这里省略部分getter与setter方法 ????public List<LinkedMap<String, Object>> getColumn() { ???????return column; ???} ???public void setColumn(List<LinkedMap<String, Object>> column) { ???????this.column = column; ???} ???public List<Column> getColumnList() { ???????return columnList; ???} ???public void setColumnList(List<Column> columnList) { ???????this.columnList = columnList; ???}}我的这个json文件放置在类路径下，最后想将这个json字符串转化为List
???/** ????* 读取类路径下的配置文件 ????* 解析成对象数组并返回 ????* @throws IOException ????*/ ???@Test ???public List<Query> test() throws IOException { ???????// 读取类路径下的query.json文件 ???????ClassLoader cl = this.getClass().getClassLoader(); ???????InputStream inputStream = cl.getResourceAsStream("query.json"); ???????String jsontext = IOUtils.toString(inputStream, "utf8"); ???????// 先将字符jie串转为List数组 ???????List<Query> queryList = JSON.parseArray(jsontext, Query.class); ???????for (Query query : queryList) { ???????????List<Column> columnList = new ArrayList<Column>(); ???????????List<LinkedMap<String,Object>> columns = query.getColumn(); ???????????for (LinkedMap<String, Object> linkedMap : columns) { ???????????????//将map转化为java实体类 ???????????????Column column = (Column)map2Object(linkedMap, Column.class); ???????????????System.out.println(column.toString()); ???????????????columnList.add(column); ???????????} ???????????query.setColumnList(columnList); //为columnList属性赋值 ???????} ???????return queryList; ???} ???/** ????* Map转成实体对象 ????* @param map map实体对象包含属性 ????* @param clazz 实体对象类型 ????* @return ????*/ ???public static Object map2Object(Map<String, Object> map, Class<?> clazz) { ???????if (map == null) { ???????????return null; ???????} ???????Object obj = null; ???????try { ???????????obj = clazz.newInstance(); ???????????Field[] fields = obj.getClass().getDeclaredFields(); ???????????for (Field field : fields) { ???????????????int mod = field.getModifiers(); ???????????????if (Modifier.isStatic(mod) || Modifier.isFinal(mod)) { ???????????????????continue; ???????????????} ???????????????field.setAccessible(true); ???????????????String flag = (String) map.get(field.getName()); ???????????????if(flag != null){ ???????????????????if(flag.equals("false") || flag.equals("true")){ ???????????????????????field.set(obj, Boolean.parseBoolean(flag)); ???????????????????}else{ ???????????????????????field.set(obj, map.get(field.getName())); ???????????????????} ???????????????} ???????????????????????????} ???????} catch (Exception e) { ???????????e.printStackTrace(); ???????} ????????return obj; ???}fastjson
原文地址：https://www.cnblogs.com/abin-c/p/10323719.html