Java

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Gson基本使用

下面对json做json->object;object->json操作：

{ "code": 200, "msg": "success", "newslist": [ { "ctime": "2016-03-31", "title": "奇虎360宣布通过私有化决议", "description": "互联网头条", "picUrl": "http://t1.qpic.cn/mblogpic/f01a972dbcc1060fd456/2000", "url": "http://mp.weixin.qq.com/s?__biz=MjM5OTMyODA2MA==&idx=1&mid=402594468&sn=5cd644536b472a283cc1d3f5124a0cab" }, { "ctime": "2016-03-31", "title": "小本生意做什么挣钱十七大小本生意推荐", "description": "创业最前线", "picUrl": "http://zxpic.gtimg.com/infonew/0/wechat_pics_-4225297.jpg/640", "url": "http://mp.weixin.qq.com/s?__biz=MzA3NjgzNDUwMQ==&idx=2&mid=401864059&sn=cfa082e38ba38c7e673b1ce0a075faee" } ] }

首先需要写一个Object类，作为这个json的实体类。这里我使用的IDE为Android Studio,使用GsonFormat插件能一键转换为Object对象。自己写的时候，顺着符号{``[来写即可，遇到{表示该字段为对象，遇到[表明该字段为数组或是集合。 转换后的对象如下 Weather.java

package com.raise.raisestudy.gson.entity; import java.util.List; /** * Created by raise.yang on 16/08/15. */ public class NewsInfo { /** * code : 200 * msg : success * newslist : [{"ctime":"2016-03-31","title":"奇虎360宣布通过私有化决议","description":"互联网头条","picUrl":"http://t1.qpic.cn/mblogpic/f01a972dbcc1060fd456/2000","url":"http://mp.weixin.qq.com/s?__biz=MjM5OTMyODA2MA==&idx=1&mid=402594468&sn=5cd644536b472a283cc1d3f5124a0cab"},{"ctime":"2016-03-31","title":"小本生意做什么挣钱十七大小本生意推荐","description":"创业最前线","picUrl":"http://zxpic.gtimg.com/infonew/0/wechat_pics_-4225297.jpg/640","url":"http://mp.weixin.qq.com/s?__biz=MzA3NjgzNDUwMQ==&idx=2&mid=401864059&sn=cfa082e38ba38c7e673b1ce0a075faee"}] */ private int code; private String msg; /** * ctime : 2016-03-31 * title : 奇虎360宣布通过私有化决议 * description : 互联网头条 * picUrl : http://t1.qpic.cn/mblogpic/f01a972dbcc1060fd456/2000 * url : http://mp.weixin.qq.com/s?__biz=MjM5OTMyODA2MA==&idx=1&mid=402594468&sn=5cd644536b472a283cc1d3f5124a0cab */ private List<NewslistBean> newslist; public int getCode() { return code; } public void setCode(int code) { this.code = code; } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } public List<NewslistBean> getNewslist() { return newslist; } public void setNewslist(List<NewslistBean> newslist) { this.newslist = newslist; } public static class NewslistBean { private String ctime; private String title; private String description; private String picUrl; private String url; public String getCtime() { return ctime; } public void setCtime(String ctime) { this.ctime = ctime; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public String getPicUrl() { return picUrl; } public void setPicUrl(String picUrl) { this.picUrl = picUrl; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } } }

准备工作已做好，下面看Gson如何解析：

json,object互转

String json = ...; Gson gson = new Gson(); //json -> object NewsInfo newsInfo = gson.fromJson(json, NewsInfo.class); //object ->json gson.toJson(newsInfo);

数组的处理

Gson gson = new Gson(); int[] ints = {1, 2, 3, 4, 5}; String[] strings = {"abc", "def", "ghi"}; // Serialization gson.toJson(ints); // ==> [1,2,3,4,5] gson.toJson(strings); // ==> ["abc", "def", "ghi"] // Deserialization int[] ints2 = gson.fromJson("[1,2,3,4,5]", int[].class); // ==> ints2 will be same as ints

泛型的处理

泛型的解析，需要通过Gson提供的TypeToken类，获取一个Type.

class Foo<T> { T value; } Gson gson = new Gson(); Foo<Bar> foo = new Foo<Bar>(); Type fooType = new TypeToken<Foo<Bar>>() {}.getType(); gson.toJson(foo,fooType); gson.fromJson(json, fooType);

null对象的处理

当一个对象的某个属性值为null时，Gson在生成json时会忽略掉这个属性。 Persion对象如下：

public class Person { public double height; public String name; public int age; public Person(double height, String name, int age) { this.height = height; this.name = name; this.age = age; } //...get(),set() }

比如：

Gson gson = new Gson(); Person person = new Person(1.72,null,10); Log.d(TAG,gson.toJson(person));// -->{"age":10,"height":1.72}

GsonBuilder

Gson对象有一个很强大的工厂类GsonBuilder，它可以在创建一个特定的Gson对象，用来制定转换规则。 若需要显示 null 对象：

Gson gson = new GsonBuilder().serializeNulls().create(); Person person = new Person(1.72,null,10); Log.d(TAG,gson.toJson(person));// -->{"age":10,"height":1.72,"name":null}

日期的处理

在Person类增加了下例字段：

public Date birthday;

默认日期格式：

Gson gson = new GsonBuilder().serializeNulls().create(); Person person = new Person(1.72,null,10,new Date()); Log.d(TAG,gson.toJson(person));// -->{"age":10,"birthday":"Aug 15, 2016 19:42:52","height":1.72,"name":null}

使用GsonBuilder格式化后的日志格式：

Gson gson = new GsonBuilder(). serializeNulls() .setDateFormat("yyyyMMdd") .create(); Person person = new Person(1.72,null,10,new Date()); Log.d(TAG,gson.toJson(person));// -->{"age":10,"birthday":"20160815","height":1.72,"name":null}

修改映射key名称

后端人员有时下发json也不安套路出牌，若后端下发给我们的是以下json:

{"age":10,"birthday":"20160815","height":1.72,"person_name":null}

但是我们移动端根本不需要这么详细的定义，还是想像之前一样使用name来表示姓名，那可不可以呢，当然可以，使用注解@SerializedName即可，这样Person修改为：

public double height; @SerializedName("person_name") public String name; public int age; public Date birthday;

@SerializedName可以指定转换时，字段的key。

Gson gson = new GsonBuilder(). serializeNulls() .setDateFormat("yyyyMMdd") .create(); String person_json = "{\"age\":10,\"birthday\":\"20160815\",\"height\":1.72,\"person_name\":null}"; Person person = gson.fromJson(person_json, Person.class); Log.d(TAG,person.toString());// -->Person{height=1.72, name='null', age=10, birthday=20160815}

忽略某些字段

当我们收到Person信息时，为了持久化数据，应该保存在数据库中，因此会增加一个id字段，Person字段修改如下：

public double _id;//新增 public double height; @SerializedName("person_name") public String name; public int age; public Date birthday;

当然，从后端下发下来的json不带_id字段也可以直接使用gson.fromJson()自动转换为Person对象，但是当我们将Person转换为json上传到后端时，如果不做处理，会自动的增加_id这个字段,如下：

Gson gson = new GsonBuilder(). serializeNulls() .setDateFormat("yyyyMMdd") .create(); Person person = new Person(1,1.70,"raise",10, new Date()); Log.d(TAG,gson.toJson(person));// -->{"_id":1.0,"age":10,"birthday":"20160816","height":1.7,"person_name":"raise"}

很明显，我们应该在生成json时，想办法踢掉这个_id字段，这是Gson提供了新的注解@Expose，用来显示哪些字段需要转换。 使用了新的注解后，记得在GsonBuilder时增加excludeFieldsWithoutExposeAnnotation()方法，转换的json就不带_id字段： Person

public double _id; @Expose //需要显示转换的字段 public double height; @Expose @SerializedName("person_name") public String name; @Expose public int age; @Expose public Date birthday; Gson gson = new GsonBuilder() .serializeNulls() .excludeFieldsWithoutExposeAnnotation()//只转换带@Expose注解的字段 .setDateFormat("yyyyMMdd") .create(); Person person = new Person(1,1.70,"raise",10, new Date()); Log.d(TAG,gson.toJson(person));// -->{"age":10,"birthday":"20160816","height":1.7,"person_name":"raise"}

参考资料： http://www.studytrails.com/java/json/java-google-json-parse-json-to-java.jsp http://blog.csdn.net/lk_blog/article/details/7685169