Gson的基础用法

想要使用Gson，首先得导入Gson.jar，网上很多，随便搜一下就可以。 下面是Gson的一些基本的使用方法，我目前能用到的就这么多。 因为我是做Android开发的，最常使用Json的情景，就是客户端发送请求到服务器，服务器返回Json数据，客户端解析为相关的Java类对象，然后展示信息。所以，下面先演示一下用Gson根据一个类生成Json和根据Json串解析为一个类对象： 首先创建一个演示类User： class User{ String name; int age; @SerializedName(value="emailAddress", alternate={"email","email_address"}) String emailAddress; @Override public String toString() { return "User [name=" + name + ", age=" + age + ", emailAddress=" + emailAddress + "]"; } public User(String name, int age) { super(); this.name = name; this.age = age; } public User() { super(); }} 接着先创建一个Gson对象： Gson gson = new Gson(); 下面就是生成json串的代码： User user = new User("wcc", 25);String userString = gson.toJson(user, User.class); userString的值为： {"name":"wcc","age":25} 接着将刚生成的Json串再解析为User对象： // 将Json串解析成User对象User newUser = gson.fromJson(userString, User.class); 打印出的newUser结果为： User [name=wcc, age=25, emailAddress=null] 下面说一下注解@SerializedName的使用，它用于解决Json串的字段和相对应的类的字段不匹配的问题。 举个例子： Json串是这样的： String jsonString = "{\"name\":\"wcc\",\"age\":25,\"email_address\":\"bj\"}"; 而相应类的字段是这样的： String emailAddress; 如果直接解析结果为： User [name=wcc, age=25, emailAddress=null] 在字段上加上@SerializedName注解： @SerializedName("email_address") tring emailAddress; 结果就变为这样了： User [name=wcc, age=25, emailAddress=bj] 这还没完，如果Json串里有多个对象，且可能出现多个不同的email字段，如：email、email_address、emailAddress，这种情况可以用@SerializedName的alternate属性解决： @SerializedName(value="emailAddress", alternate={"email","email_address"})String emailAddress; 再说说通过TypeToken使用泛型，为什么要使用TypeToken呢？因为Gson是通过反射起作用的，像List<String>.class,List<Integer>.class最后得到的都是同一个字节码List.class，所以通过TypeToken可以区别不同的泛型。 下面通过解析一个Json数组说明： String jsonArray = "['shenmu','changshengjie','zhetian']"; 将上面的数组解析成一个Java数组比较简单，只要这样就行了： String[] strArr = gson.fromJson(jsonArray, String[].class); 但是想要将其解析成List，就需要借助TypeToken： List<String> list = gson.fromJson(jsonArray, new TypeToken<List<String>>(){}.getType()); 因为TypeToken的Constructor is not visible，所以要用匿名内部类的方式调用，输出list： [shenmu, changshengjie, zhetian] 好了，基础知识已经具备，下面来解析一个比较复杂的Json： String jsArray = "[{'boardid': 'tech_bbs'," + "'clkNum': 0," + " 'digest': ''," + "'docid': 'BUGQFHA500097U7U'}," + "{'boardid': 'tech_bbs'," + "'clkNum': 0," + " 'digest': ''," + "'docid': 'BUGQFHA500097U7U'}," + "{'boardid': 'tech_bbs'," + "'clkNum': 0," + " 'digest': ''," + "'docid': 'BUGQFHA500097U7U'}]"; 上面的Json数组具有三个内容相同的对象，不管它是什么，反正是一个对象就行了，下面将它解析成一个List，其中的每一个元素都是一个Data对象，首先看Data的定义： class Data{ String boardid; int clkNum; String digest; String docid; @Override public String toString() { return "Data [boardid=" + boardid + ", clkNum=" + clkNum + ", digest=" + digest + ", docid=" + docid + "]"; } public Data(String boardid, int clkNum, String digest, String docid) { super(); this.boardid = boardid; this.clkNum = clkNum; this.digest = digest; this.docid = docid; } public Data() { }} 上面的定义很好理解，就是声明了一些字段，下面是解析的代码： List<Data> dl = gson.fromJson(jsArray, new TypeToken<List<Data>>(){}.getType()); 一句话搞定，输出： [Data [boardid=tech_bbs, clkNum=0, digest=, docid=BUGQFHA500097U7U], Data [boardid=tech_bbs, clkNum=0, digest=, docid=BUGQFHA500097U7U], Data [boardid=tech_bbs, clkNum=0, digest=, docid=BUGQFHA500097U7U]] 最后解析一个对我来说很复杂的Json串，非常长： static String superString = "{" +"'V9LG4B3A0': [" +"{" +"'topicImg':'http://vimg3.ws.126.net/image/snapshot/2016/8/O/N/VBSN1KMON.jpg'," +"'videosource':'新媒体'," +"'mp4Hd_url':'http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/HD/jDXFt0488-mobile.mp4'," +"'topicDesc':'好的音乐铸就好的电影，不定期将为大家推荐各类经典影片，一起跟着音乐看电影吧！'," +"'topicSid':'VBSN1KMOH'," +"'cover':'http://vimg2.ws.126.net/image/snapshot/2016/8/0/2/VBTJGJQ02.jpg'," +"'title':'「跟着音乐看电影」第四期：爆裂鼓手'," +"'playCount': 11575," +"'replyBoard':'video_bbs'," +"'sectiontitle':''," +"'replyid':'BTJGJQ01008535RB'," +"'description':'本期推荐的是2014年上映的剧情音乐电影《爆裂鼓手》，推荐音乐Caravan。'," +"'mp4_url':'http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/SD/jDXFt0488-mobile.mp4'," +"'length': 304," +"'playersize': 0," +"'m3u8Hd_url':'http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/HD/movie_index.m3u8'," +"'vid':'VBTJGJQ01'," +"'m3u8_url':'http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/SD/movie_index.m3u8'," +"'ptime':'2016-08-15 17:20:25'," +"'topicName':'跟着音乐看电影'" +"}," +"{" +"'topicImg':'http://vimg1.ws.126.net/image/snapshot/2016/3/U/K/VBI02N0UK.jpg'," +"'videosource':'新媒体'," +"'mp4Hd_url':'http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/HD/aObgM2410-mobile.mp4'," +"'topicDesc':'奇葩事的大盘点。'," +"'topicSid':'VBI02N0UI'," +"'cover':'http://vimg1.ws.126.net/image/snapshot/2016/8/7/U/VBTJIF17U.jpg'," +"'title':'快放假拉横幅了多少时间'," +"'playCount': 5113," +"'replyBoard':'video_bbs'," +"'videoTopic': {" +"'alias':'奇葩事的大盘点。'," +"'tname':'奇葩剧情'," +"'ename':'T1460515713166'," +"'tid':'T1460515713166'" +"}," +"'sectiontitle':''," +"'replyid':'BTJIBJNG008535RB'," +"'description':'快放假拉横幅了多少时间'," +"'mp4_url':'http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/SD/aObgM2410-mobile.mp4'," +"'length': 120," +"'playersize': 1," +"'m3u8Hd_url':'http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/HD/movie_index.m3u8'," +"'vid':'VBTJIBJNG'," +"'m3u8_url':'http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/SD/movie_index.m3u8'," +"'ptime':'2016-08-15 17:13:44'," +"'topicName':'奇葩剧情'" +"}]}"; 上面的Json串首先是一个对象，这个对象里有一个数组，数组里又有两个子对象，子对象里又可能含对象，所以我们要定义三个相对应的Java类，首先看最里面的对象对应的类，即节点videoTopic对应的类的定义： class VideoTopic{ String alias; String tname; String ename; String tid; @Override public String toString() { return "VideoTopic [alias=" + alias + ", tname=" + tname + ", ename=" + ename + ", tid=" + tid + "]"; }} 再看数组里的对象对应的类的定义： public class NewsBean { String topicImg; String videosource; String mp4Hd_url; String topicDesc; String topicSid ; String cover; String title; int playCount; String replyBoard; VideoTopic videoTopic; String sectiontitle; String replyid; String description; String mp4_url; int length; int playersize; String m3u8Hd_url; String vid; String m3u8_url; String ptime; String topicName; @Override public String toString() { return "NewsBean [topicImg=" + topicImg + ", videosource=" + videosource + ", mp4Hd_url=" + mp4Hd_url + ", topicDesc=" + topicDesc + ", topicSid=" + topicSid + ", cover=" + cover + ", title=" + title + ", playCount=" + playCount + ", replyBoard=" + replyBoard + ", videoTopic=" + videoTopic + ", sectiontitle=" + sectiontitle + ", replyid=" + replyid + ", description=" + description + ", mp4_url=" + mp4_url + ", length=" + length + ", playersize=" + playersize + ", m3u8Hd_url=" + m3u8Hd_url + ", vid=" + vid + ", m3u8_url=" + m3u8_url + ", ptime=" + ptime + ", topicName=" + topicName + "]"; } } 看到上面的类，将VideoTopic对象作为类成员进行声明了，这样解析的时候，相关的节点videoTopic就会被解析为VideoTopic对象并作为对应的NewsBean对象的成员存在。最后看一下最外层对象所对应的类的定义： public class Wrapper { List<NewsBean> V9LG4B3A0;} 因为该对象里面有一个数组，所以我把它定义为List。下面是解析的代码，很简单： Wrapper w = gson.fromJson(superString, Wrapper.class); 遍历，并输出其中的内容： List<NewsBean> newsList = w.V9LG4B3A0; for(NewsBean n : newsList) System.out.println(n+"\n"); 输出结果： NewsBean [topicImg=http://vimg3.ws.126.net/image/snapshot/2016/8/O/N/VBSN1KMON.jpg, videosource=新媒体, mp4Hd_url=http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/HD/jDXFt0488-mobile.mp4, topicDesc=好的音乐铸就好的电影，不定期将为大家推荐各类经典影片，一起跟着音乐看电影吧！, topicSid=VBSN1KMOH, cover=http://vimg2.ws.126.net/image/snapshot/2016/8/0/2/VBTJGJQ02.jpg, title=「跟着音乐看电影」第四期：爆裂鼓手, playCount=11575, replyBoard=video_bbs, videoTopic=null, sectiontitle=, replyid=BTJGJQ01008535RB, description=本期推荐的是2014年上映的剧情音乐电影《爆裂鼓手》，推荐音乐Caravan。, mp4_url=http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/SD/jDXFt0488-mobile.mp4, length=304, playersize=0, m3u8Hd_url=http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/HD/movie_index.m3u8, vid=VBTJGJQ01, m3u8_url=http://flv2.bn.netease.com/videolib3/1608/15/jDXFt0488/SD/movie_index.m3u8, ptime=2016-08-15 17:20:25, topicName=跟着音乐看电影]NewsBean [topicImg=http://vimg1.ws.126.net/image/snapshot/2016/3/U/K/VBI02N0UK.jpg, videosource=新媒体, mp4Hd_url=http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/HD/aObgM2410-mobile.mp4, topicDesc=奇葩事的大盘点。, topicSid=VBI02N0UI, cover=http://vimg1.ws.126.net/image/snapshot/2016/8/7/U/VBTJIF17U.jpg, title=快放假拉横幅了多少时间, playCount=5113, replyBoard=video_bbs, videoTopic=VideoTopic [alias=奇葩事的大盘点。, tname=奇葩剧情, ename=T1460515713166, tid=T1460515713166], sectiontitle=, replyid=BTJIBJNG008535RB, description=快放假拉横幅了多少时间, mp4_url=http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/SD/aObgM2410-mobile.mp4, length=120, playersize=1, m3u8Hd_url=http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/HD/movie_index.m3u8, vid=VBTJIBJNG, m3u8_url=http://flv2.bn.netease.com/videolib3/1608/15/aObgM2410/SD/movie_index.m3u8, ptime=2016-08-15 17:13:44, topicName=奇葩剧情] 最后，想要更深入的了解Gson的用法，可以去 http://www.jianshu.com/p/e740196225a4看看，我在这里只是梳理一下自己所学。