JSON学习

来源：互联网发布：matlab矩阵的取值编辑：程序博客网时间：2024/06/06 01:31

1.json的定义

json(JavaScript Object Notation) 是一种轻量级的数据交换格式，能够在服务器之间交换数据。在json出现之前，通用的数据交换语言是XML，但是XML的生成与解析比较麻烦。json的规格非常简单，规定如下：

（1）并列的数据之间用逗号（"，"）分隔

（2）映射用冒号（“：”）

（3）并列数据的集合（数组）用方括号（“[]”）表示

（4）映射的集合（对象）用大括号（“{}”）表示

2.json的构建方式

json简单说就是javascript中的对象和数组，所以json的构建结构就有对象和数组两种，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“{}”扩起来的内容，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。

举例：

{ "firstName": "Brett" }

{ "firstName": "Brett", "lastName":"McLaughlin", "email": "aaaa" }

（2）数组

数组在js中是中括号“[]”扩起来的内容，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。

举例：

{ "people": [

{ "firstName": "Brett", "lastName":"McLaughlin", "email": "aaaa" },

{ "firstName": "Jason", "lastName":"Hunter", "email": "bbbb"},

{ "firstName": "Elliotte", "lastName":"Harold", "email": "cccc" }

]}

这不难理解。在这个示例中，只有一个名为 people的变量，值是包含三个条目的数组，每个条目是一个人的记录，其中包含名、姓和电子邮件地址。上面的示例演示如何用括号将记录组合成一个值。当然，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": "aaaa" },

{ "firstName": "Jason", "lastName":"Hunter", "email": "bbbb" },

{ "firstName": "Elliotte", "lastName":"Harold", "email": "cccc" }

"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" }

] }

这里最值得注意的是，能够表示多个值，每个值进而包含多个值。

3.操作json数据

例子

var people = { "programmers": [ { "firstName": "Brett", "lastName":"McLaughlin", "email": "aaaa" },

{ "firstName": "Jason", "lastName":"Hunter", "email": "bbbb" },

{ "firstName": "Elliotte", "lastName":"Harold", "email": "cccc" }

"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" }

] }

（1）访问数据

要想访问 programmers 列表的第一个条目的姓氏，可以这样写

people.programmers[0].lastName;

（2）修改数据

people.musicians[1].lastName = "Rachmaninov";

（3）换回字符串

如果不能轻松地将对象转换回本文提到的文本格式，那么所有数据修改都没有太大的价值。在 JavaScript 中这种转换也很简单：

String newJSONtext = people.toJSONString();

这样就行了！现在就获得了一个可以在任何地方使用的文本字符串，例如，可以将它用作 Ajax 应用程序中的请求字符串。

4.使用json串

（1）json串转化为java类

不同平台互通时，会涉及到json串的传递。比如A要调用B的API，B的返回数据的格式如下

{"OcsInstances":
{"OcsInstance":
[
{
"Bandwidth":4.5,"Capacity":128,"ConnectionDomain":"m.jst.ocs.aliyuncs.com","Connections":50,"OcsInstanceId":"0c44e4dcf27611e2","OcsInstanceStatus":"Available","Port":11211,"Qps":300,"RegionId":"cn-hangzhou-cm10-01","UserName":"0c44e4dcf27611e2"
},
{
"Bandwidth":4.5,"Capacity":128,"ConnectionDomain":"m.jst.ocs.aliyuncs.com","Connections":50,"OcsInstanceId":"0c5baaf0f27611e2","OcsInstanceName":"111","OcsInstanceStatus":"Available","Port":11211,"Qps":300,"RegionId":"cn-hangzhou-cm10-01","UserName":"0c5baaf0f27611e2"
},
{
"Bandwidth":4.5,"Capacity":128,"ConnectionDomain":"m.jst.ocs.aliyuncs.com","Connections":50,"OcsInstanceId":"6e66955af39511e2","OcsInstanceName":"123","OcsInstanceStatus":"Available","Port":11211,"Qps":300,"RegionId":"cn-hangzhou-cm10-01","UserName":"6e66955af39511e2"
},
{
"Bandwidth":4.5,"Capacity":256,"ConnectionDomain":"m.jst.ocs.aliyuncs.com","Connections":50,"OcsInstanceId":"f4f69cd2f39f11e2","OcsInstanceName":"123","OcsInstanceStatus":"Available","Port":11211,"Qps":300,"RegionId":"cn-hangzhou-cm10-01","UserName":"f4f69cd2f39f11e2"
}
]
},
"RequestId":"1F9F97DE-F6C5-4F13-9075-F335B5358E56"
}

假如B要获得每条记录中OcsInstanceId、OcsInstanceName、OcsInstanceStatus的值，那么B如何解析呢，B一般会封装一个类，来对json串进行解析，类如下

public class ModifyOcsInstanceAttributeResponse extends AliyunResponse {

   private OcsInstances ocsInstances;//这里的OcsInstances就是上面的映射，ocsInstances里面包含数组OcsInstance，后面会定义

   public OcsInstances getOcsInstances() {
       return ocsInstances;
   }

   public void setOcsInstances(OcsInstances ocsInstances) {
       this.ocsInstances = ocsInstances;
   }
    //ocsInstances里面包含数组OcsInstance
   public static class OcsInstances {
       private List<OcsInstance> ocsInstance;

       public List<OcsInstance> getOcsInstance() {
           return ocsInstance;
       }

       public void setOcsInstance(List<OcsInstance> ocsInstance) {
           this.ocsInstance = ocsInstance;
       }

   }
    //写OcsInstance的get、set三个属性（OcsInstanceId、OcsInstanceName、OcsInstanceStatus）的方法
   public static class OcsInstance implements Serializable {

       private String ocsInstanceId;
       private String ocsInstanceName;
       private String ocsInstanceStatus;

       public String getOcsInstanceId() {
           return ocsInstanceId;
       }

       public void setOcsInstanceId(String ocsInstanceId) {
           this.ocsInstanceId = ocsInstanceId;
       }

       public String getOcsInstanceName() {
           return ocsInstanceName;
       }

       public void setOcsInstanceName(String ocsInstanceName) {
           this.ocsInstanceName = ocsInstanceName;
       }

       public String getOcsInstanceStatus() {
           return ocsInstanceStatus;
       }

       public void setOcsInstanceStatus(String ocsInstanceStatus) {
           this.ocsInstanceStatus = ocsInstanceStatus;
       }

   }

}

（2）将后台数据以json串的形式给前端

比如后台数据为一个Map，我们要以json串的形式传给前台，我们可以这样写

 Map obj=new LinkedHashMap();  obj.put("name","foo");  obj.put("num",new Integer(100));  obj.put("balance",new Double(1000.21));  obj.put("is_vip",new Boolean(true));  obj.put("nickname",null);  String jsonText = JSONValue.toJSONString(obj);//将obj转化为json串的形式  System.out.print(jsonText);结果:{"name":"foo","num":100,"balance":1000.21,"is_vip":true,"nickname":null}