JavaWeb中Ajax 对 Json 格式的解析

Ajax 对 Json 格式的解析

       一、JSON介绍

        JSON建构有两种结构
json简单说就是javascript中的对象和数组，所以这两种结构就是对象和数组两种结构，通过这两种结构可以表示各种复杂的结构
1、对象：对象在js中表示为“{}”括起来的内容，数据结构为 {key：value,key：value,...}的键值对的结构，在面向对象的语言中，key为对象的属性，value为对应的属性值，所以很容易理解，取值方法为对象.key 获取属性值，这个属性值的类型可以是 数字、字符串、数组、对象几种。
2、数组：数组在js中是中括号“[]”括起来的内容，数据结构为 ["java","javascript","vb",...]，取值方式和所有语言中一样，使用索引获取，字段值的类型可以是 数字、字符串、数组、对象几种。经过对象、数组2种结构就可以组合成复杂的数据结构了。

       基于上述组成原理，JSON 可以将 JavaScript 对象中表示的一组数据转换为字符串，然后就可以在函数之间轻松地传递这个字符串，或者在异步应用程序中将字符串从 Web 客户机传递给服务器端程序，同样，JSON 也可以将 Java对象中表示的一组数据转换为字符串，传递给前端的Ajax来解析。

        按照最简单的形式，可以用下面这样的 JSON 表示名称/值对：{ "firstName": "Brett"}

        这样的键/值对也可以是多个：{"name":"aaa","sex":"男","age":"20"}

        从语法方面来看，这与名称/值对相比并没有很大的优势，但是在这种情况下 JSON 更容易使用，而且可读性更好。

值的数组---当需要表示一组值时，JSON 不但能够提高可读性，而且可以减少复杂性。

如果使用 JSON，就只需将多个带花括号的记录分组在一起：

{ "people": [  { "firstName": "Brett", "lastName":"McLaughlin", "email": "111111" },  { "firstName": "Jason", "lastName":"Hunter", "email": "22222" },  { "firstName": "Elliotte", "lastName":"Harold", "email": "33333" }]}

可以使用相同的语法表示多个值（每个值包含多个记录）：

{ "programmers": [  { "firstName": "Brett", "lastName":"McLaughlin", "email": "3333" },  { "firstName": "Jason", "lastName":"Hunter", "email": "1222" },  { "firstName": "Elliotte", "lastName":"Harold", "email": "3333" } ],"authors": [  { "firstName": "Isaac", "lastName": "Asimov", "genre": "science fiction" },  { "firstName": "Tad", "lastName": "Williams", "genre": "fantasy" },  { "firstName": "Frank", "lastName": "Peretti", "genre": "christian fiction" } ],"musicians": [  { "firstName": "Eric", "lastName": "Clapton", "instrument": "guitar" },  { "firstName": "Sergei", "lastName": "Rachmaninoff", "instrument": "piano" } ]}

Json也可以这样写：

{ "listaccountsresponse" : { "count":1 ,"account" : [  {"id":5,"name":"xian1","accounttype":0,"domainid" :2,"domain":"Server","receivedbytes":649444,"sentbytes":175467975,"vmlimit":"20","vmtotal":2,"vmavailable" :"18","iplimit":"20","iptotal":1,"ipavailable":"19","volumelimit":"20","volumetotal":2,"volumeavailable" :"18","snapshotlimit":"20","snapshottotal":0,"snapshotavailable":"20","templatelimit":"20","templatetotal" :0,"templateavailable":"20","vmstopped":0,"vmrunning":2,"state":"enabled","user":[{"id":5,"username" :"xian1","firstname":"Eric","lastname":"Tang","email":"[e-mail]","created":"2012-03-22T09 :36:44+0800","state":"enabled","account":"xian1","accounttype":0,"domainid":2,"domain":"Server","timezone" :"Asia/Shanghai"}]} ] } }

注：Json在ajax开发中用得越来越多，当然在后端（php,java等也有很多在使用），一般程序输出来的json代码都缩成一行了，对于前端开发人员的可读性是非常差，非常难以使用。

      JSON格式取代了xml给网络传输带来了很大的便利,但是却没有了xml的一目了然,尤其是json数据很长的时候,我们会陷入繁琐复杂的数据节点查找中：一时没有办法判断JSON数据格式是否正确,是否少或多符号而导致程序不能解析。但是国人的一款在线工具 BeJson 给众多程序员带来了一阵凉风。

 下面推荐几个在线格式化json数据的工具:

       json.parser.online.fr(浏览器中使用，强力推荐)
       http://www.kjson.com/
       http://www.bejson.com/go.php?u=http://www.bejson.com/index.php
       http://jsonformatter.curiousconcept.com/ 

二、ajax对Json格式数据的解析 

1.对简单json格式的解析：

{ "firstName": "Brett"}

写道:

$.ajax({url:"这里是你要请求的地址",data:{"id":id}, //以键/值对的形式async : false,dataType : "json",success : function(data) {alert("firstName = " + data.firstName);}});

注：这里的data是你从后台穿过来的Json字符传串。

 后台写法：

response.setCharacterEncoding("utf-8");response.setContentType("text/json;charset=UTF-8");PrintWriter out = null;String count = "<span style="color: #000000;">{ "firstName": "Brett" }</span>;try {out = response.getWriter();} catch (Exception e) {e.printStackTrace();}out.print(count);out.flush();

这样就能在前台页面弹出提示框：firstName = Brett。

 2.多个键/值对和上面的情况一样

3.解析Json如下数组：

{  { "firstName": "Brett", "lastName":"McLaughlin", "email": "111111" },  { "firstName": "Jason", "lastName":"Hunter", "email": "22222" },  { "firstName": "Elliotte", "lastName":"Harold", "email": "33333" }}

$.ajax({url:"这里是你要请求的地址",data:{"id":id}, //以键/值对的形式async : false,dataType : "json",success : function(data) {for(int i = 0; i < data.length; i++) { //循环后台传过来的Json数组     var datas = data[i];     alert(datas.firstName);     alert(datas.lastName);     alert(datas.email);}}});

4.解析如下Json数据

{ "programmers": [  { "firstName": "Brett", "lastName":"McLaughlin", "email": "3333" },  { "firstName": "Jason", "lastName":"Hunter", "email": "1222" },  { "firstName": "Elliotte", "lastName":"Harold", "email": "3333" } ],"authors": [  { "firstName": "Isaac", "lastName": "Asimov", "genre": "science fiction" },  { "firstName": "Tad", "lastName": "Williams", "genre": "fantasy" },  { "firstName": "Frank", "lastName": "Peretti", "genre": "christian fiction" } ],"musicians": [  { "firstName": "Eric", "lastName": "Clapton", "instrument": "guitar" },  { "firstName": "Sergei", "lastName": "Rachmaninoff", "instrument": "piano" } ]}

$.ajax({url:"这里是你要请求的地址",data:{"id":id}, //以键/值对的形式async : false,dataType : "json",success : function(data) {var pro = data.programmers; // pro为programmers的一个数组for(int i = 0; i < pro.length; i++) { //循环后台传过来的Json数组     var datas = pro[i];     alert(pro.firstName);     alert(pro.lastName);     alert(pro.email);}var aut = data.authors; // aut为authors的一个数组for(int i = 0; i < aut.length; i++) { //循环后台传过来的Json数组     var datas = aut[i];     alert(aut.firstName);     alert(aut.lastName);     alert(aut.genre);}var mus = data.musicians; // aut为authors的一个数组for(int i = 0; i < mus.length; i++) { //循环后台传过来的Json数组     var datas = mus[i];     alert(mus.firstName);     alert(mus.lastName);     alert(mus.instrument);}}});

5.

{ "listaccountsresponse" : { "count":1 ,"account" : [  {"id":5,"name":"xian1","accounttype":0,"domainid" :2,"domain":"Server","receivedbytes":649444,"sentbytes":175467975,"vmlimit":"20","vmtotal":2,"vmavailable" :"18","iplimit":"20","iptotal":1,"ipavailable":"19","volumelimit":"20","volumetotal":2,"volumeavailable" :"18","snapshotlimit":"20","snapshottotal":0,"snapshotavailable":"20","templatelimit":"20","templatetotal" :0,"templateavailable":"20","vmstopped":0,"vmrunning":2,"state":"enabled","user":[{"id":5,"username" :"xian1","firstname":"Eric","lastname":"Tang","email":"[e-mail]","created":"2012-03-22T09 :36:44+0800","state":"enabled","account":"xian1","accounttype":0,"domainid":2,"domain":"Server","timezone" :"Asia/Shanghai"}]} ] } }

$.ajax({url:"这里是你要请求的地址",data:{"id":id}, //以键/值对的形式async : false,dataType : "json",success : function(data) {var accounts = data.listaccountsresponse.account; //取到“account”中的数据for(int i = 0; i < accounts.length; i++) { //循环后台传过来的Json数组     var datas = accounts[i];     alert(datas.id);     alert(datas.name);     alert(datas.accounttype);     ..........}}});

-------------------------------这里是自己写的一个后台传值------------------------------------------

@RequestMapping(value="/applyVm/listApplyVmCount", method={RequestMethod.GET, RequestMethod.POST})public void listApplyVmCount(HttpServletRequest request, HttpServletResponse response) {response.setCharacterEncoding("utf-8");response.setContentType("text/json;charset=UTF-8");PrintWriter out = null;String count = "";try {out = response.getWriter();Map<String, Integer> map = applyVmService.findApplyVmCount();Gson gson = new Gson();count = gson.toJson(map);} catch (Exception e) {e.printStackTrace();}out.print(count);out.flush();} 

本文参考：http://xiaoxiong-it.iteye.com/blog/1485121