JSON 的说明

JSON 是什么？
JSON的全称是JavaScript Object Notation，是一种轻量级的数据交换格式。JSON与XML具有相同的特性，例如易于人编写和阅读，易于机器生成和解析。但是JSON比XML数据传输的有效性要高出很多。JSON完全独立与编程语言，使用文本格式保存。
JSON数据有两种结构：
• Name-Value 对构成的集合，类似于Java中的Map。
• Value的有序列表，类似于Java中的Array。
一个JSON格式的数据示例：
{
  "Name": "Apple",
  "Expiry": "2007/10/11 13:54",
  "Price": 3.99,
  "Sizes": [
    "Small",
    "Medium",
    "Large"
  ]
}
更多关于JSON数据格式的说明参看JSON官方网站：http://www.json.org（中文内容参看：http://www.json.org/json-zh.html）
GWT与JSON
GWT中支持的客户端服务器端方法调用和数据传递的标准格式是RPC。 JSON并不是GWT支持的标准的数据传递格式。那么如何使用JSON来作为GWT的数据传递格式呢？需要以下几步。
第一，引用HTTP和JSON支持。
第二，在客户端创建JSON数据，提交到服务器
第三，在服务器上重写数据格式解析的代码，使之支持JSON格式的数据
第四，在服务器上组织JSON格式的数据，返回给客户端。
第五，客户端解析服务器传回的JSON数据，正确的显示
引用HTTP和JSON支持
找到.gwt.xml文件，在其中的
<inherits name='com.google.gwt.user.User'/>
在之后添加如下的内容：
    <inherits name="com.google.gwt.json.JSON"/>
    <inherits name="com.google.gwt.http.HTTP"/>
其中com.google.gwt.json.JSON指的是要使用JSON，com.google.gwt.http.HTTP值得是通过HTTP调用服务器上的服务方法。
客户端构造JSON数据
客户端需要使用com.google.gwt.json.client包内的类来组装JSON格式的数据，数据格式如下：

数据类型 说明
JSONArray JSONValue构成的数组类型
JSONBoolean JSON boolean值
JSONException 访问JSON结构的数据出错的情况下可以抛出此异常
JSONNull JSON Null根式的数据
JSONNumber JSON Number类型的数据
JSONObject JSON Object类型的数据
JSONParser 将String格式的JSON数据解析为JSONValue类型的数据
JSONString JSON String类型的数据
JSONValue 所有JSON类型值的超级类型

组合一个简单的JSON数据： 
JSONObject input = new JSONObject();
JSONString value = new JSONString("mazhao");
input.put("name", value);
JSON数据格式为：{name: "mazhao"}
组合一个包含数组类型的复杂JSON数据：
JSONObject input = new JSONObject();
JSONString value = new JSONString("mazhao");
input.put("name", value);
JSONArray arrayValue = new JSONArray();
arrayValue.set(0, new JSONString("array item 0"));
arrayValue.set(1, new JSONString("array item 1"));
arrayValue.set(2, new JSONString("array item 2"));
input.put("array", arrayValue);    
JSON数据格式为：
{name: "mazhao",
  array: {"array item 0", "array item 1", "array item 2"}}
注意上述的JSON类型的数据，使用的都是com.google.gwt.json.client包内的类型。这些类型最终会被编译为JavaScript执行。
服务端重写数据解析代码，支持JSON格式的数据
在服务器上，需要使用JSON Java支持类才能将JSON格式的数据转换为各种类型的数据，当然也可以自己写一些解析用的代码。这里我们使用了www.json.org上的代码来完成。这组代码与com.google.gwt.json.client的代码很相似，只是在org.json包内部。
怎么解析JSON术诀呢？针对上述中的复杂的JSON数据：
{name: "mazhao",
  array: {"array item 0", "array item 1", "array item 2"}}
可以使用如下的方式解析：
JSONObject jsonObject = new JSONObject(payload);
String name = jsonObject.getString("name");
System.out.println("name is:" + name);
JSONArray jsonArray = jsonObject.getJSONArray("array");
for(int i = 0; i < jsonArray.length(); i++) {
    System.out.println("item " + i + " :" + jsonArray.getString(i));
}
其中payload指的是上述的JSON格式的数据。
那么如何写GWT 的Service来得到Payload的数据呢？需要两点，第一，需要建立一个Service类，第二，覆盖父类的processCall方法。
示例代码：
package com.jpleasure.gwt.json.server;
import com.google.gwt.user.client.rpc.SerializationException;
import com.google.gwt.user.server.rpc.RemoteServiceServlet;
import com.jpleasure.gwt.json.client.HelloWorldService;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
/**
* Created by IntelliJ IDEA.
* User: vaio
* Date: 2007-9-4
* Time: 22:08:31
* To change this template use File | Settings | File Templates.
*/
public class HelloWorldServiceImpl extends RemoteServiceServlet implements HelloWorldService {
    public String processCall(String payload) throws SerializationException {
        try {
            JSONObject jsonObject = new JSONObject(payload);
            String name = jsonObject.getString("name");
            System.out.println("name is:" + name);
            JSONArray jsonArray = jsonObject.getJSONArray("array");
            for(int i = 0; i < jsonArray.length(); i++) {
                System.out.println("item " + i + " :" + jsonArray.getString(i));
            }
        } catch (JSONException e) {
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        }
        return "success";   
    }
}
在服务器上组织JSON格式的数据，返回给客户端
同上
客户端解析服务器传回的JSON数据，正确的显示
同上


Struts2返回json需要jsonplugin-0[1].25的包

然后我们的配置文件中需要继承json-default
Java代码 
1. <?xml version="1.0" encoding="UTF-8" ?>  
2. <!DOCTYPE struts PUBLIC  
3.         "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" 
4.         "http://struts.apache.org/dtds/struts-2.0.dtd">  
5.  
6. <struts>  
7.  
8.     <package name="com.action.testJson" extends="json-default" namespace="/" >  
9.         <action name="jsonUser" class="com.action.testJson.JsonAction" method="testUser">  
10.             <result type="json"/>  
11.         </action>  
12.         <!-- Add actions here -->  
13.     </package>  
14. </struts> 
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
        "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
        "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>

    <package name="com.action.testJson" extends="json-default" namespace="/" >
        <action name="jsonUser" class="com.action.testJson.JsonAction" method="testUser">
        <result type="json"/>
        </action>
        <!-- Add actions here -->
    </package>
</struts>


然后我们的Action中需要返回的json信息需要加上注解
Java代码 
1. //pizza  
2. package com.action.testJson;  
3.  
4. import java.util.ArrayList;  
5. import java.util.List;  
6.  
7. import com.googlecode.jsonplugin.annotations.JSON;  
8. import com.opensymphony.xwork2.ActionSupport;  
9.  
10. public class JsonAction extends ActionSupport {  
11.  
12.     private static final long serialVersionUID = -4082165361641669835L;  
13.       
14.     Users user=new Users();  
15.     List userList=new ArrayList();  
16.       
17.       
18.     public String testUser(){  
19.         System.out.println("in the json Acton");  
20.         userInit();  
21.         userList.add(user);  
22.         return SUCCESS;  
23.     }  
24.           
25.     public void userInit(){  
26.         user.setAge(1);  
27.         user.setName("张泽峰");  
28.         user.setPassword("nofengPassword");  
29.     }  
30.       
31.     @JSON(name="userString")  
32.     public Users getUser() {  
33.         return user;  
34.     }  
35.  
36.     @JSON(name="userList")  
37.     public List getUserList() {  
38.         return userList;  
39.     }  
40.       
41.     public void setUser(Users user) {  
42.         this.user = user;  
43.     }  
44.  
45.     public void setUserList(List userList) {  
46.         this.userList = userList;  
47.     }  
48.  
49.
50. } 
JSON Plugin
的说明
Edit Page    Browse Space    Add Page    Add News
Added by Musachy Barroso, last edited by ghostroller on Jul 04, 2008  (view change) SHOW COMMENT 
Name
JSON Plugin
Publisher Musachy Barroso

License Open Source (ASL2)
Version 0.30
Compatibility Struts 2.0.6 or later
Homepage http://code.google.com/p/jsonplugin/ 

Download http://code.google.com/p/jsonplugin/downloads/list 

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Overview
The JSON plugin provides a "json" result type that serializes actions into JSON. The serialization process is recursive, meaning that the whole object graph, starting on the action class (base class not included) will be serialized (root object can be customized using the "root" attribute). If the interceptor is used, the action will be populated from the JSON content in the request, these are the rules of the interceptor:
1. The "content-type" must be "application/json"
2. The JSON content must be well formed, see json.org  for grammar.
3. Action must have a public "setter" method for fields that must be populated.
4. Supported types for population are: Primitives (int,long...String), Date, List, Map, Primitive Arrays, Other class (more on this later), and Array of Other class.
5. Any object in JSON, that is to be populated inside a list, or a map, will be of type Map (mapping from properties to values), any whole number will be of type Long, any decimal number will be of type Double, and any array of type List.
Given this JSON string:
{
   "doubleValue": 10.10,
   "nestedBean": {
      "name": "Mr Bean"
   },
   "list": ["A", 10, 20.20, {
      "firstName": "El Zorro"
   }],
   "array": [10, 20]
}
The action must have a "setDoubleValue" method, taking either a "float" or a "double" argument (the interceptor will convert the value to the right one). There must be a "setNestedBean" whose argument type can be any class, that has a "setName" method taking as argument an "String". There must be a "setList" method that takes a "List" as argument, that list will contain: "A" (String), 10 (Long), 20.20 (Double), Map ("firstName" -> "El Zorro"). The "setArray" method can take as parameter either a "List", or any numeric array.
Installation
This plugin can be installed by copying the plugin jar into your application's /WEB-INF/lib directory. No other files need to be copied or created.
To use maven, add this to your pom:
<dependencies>
   ...
   <dependency>
       <groupId>com.googlecode</groupId>
       <artifactId>jsonplugin</artifactId>
       <version>0.26</version>
   </dependency>
   ...
</dependencies>
<repository>
    <id>Maven Plugin Repository</id>
    <url>http://struts2plugin-maven-repo.googlecode.com/svn/trunk/</url>
    <snapshots>
      <enabled>false</enabled>
    </snapshots>
    <releases>
      <enabled>true</enabled>
    </releases>
</repository>
Customizing Serialization and Deserialization
Use the JSON annotation to customize the serialization/deserialization process. Available JSON annotation fields:
Name Description Default Value Serialization Deserialization
name Customize field name empty yes no
serialize Include in serialization true yes no
deserialize Include in deserialization true no yes
format Format used to format/parse a Date field "yyyy-MM-dd'T'HH:mm:ss" yes yes
Excluding properties
A comma-delimited list of regular expressions can be passed to the JSON Result and Interceptor, properties matching any of these regular expressions will be ignored on the serialization process:
<!-- Result fragment -->
<result type="json">
  <param name="excludeProperties">
    login.password,
    studentList.*\.sin
  </param>
</result>

<!-- Interceptor fragment -->
<interceptor-ref name="json">
  <param name="enableSMD">true</param>
  <param name="excludeProperties">
    login.password,
    studentList.*\.sin
  </param>
</interceptor-ref>
Including properties
A comma-delimited list of regular expressions can be passed to the JSON Result to restrict which properties will be serialized. ONLY properties matching any of these regular expressions will be included in the serialized output.

Note
Exclude property expressions take precedence over include property expressions. That is, if you use include and exclude property expressions on the same result, include property expressions will not be applied if an exclude exclude property expression matches a property first.
<!-- Result fragment -->
<result type="json">
  <param name="includeProperties">
    ^entries\[\d+\]\.clientNumber,
    ^entries\[\d+\]\.scheduleNumber,
    ^entries\[\d+\]\.createUserId
  </param>
</result>
Root Object
Use the "root" attribute(OGNL expression) to specify the root object to be serialized.
<result type="json">
  <param name="root">
    person.job
  </param>
</result>
The "root" attribute(OGNL expression) can also be used on the interceptor to specify the object that must be populated, make sure this object is not null.
<interceptor-ref name="json">
  <param name="root">bean1.bean2</param>
</interceptor-ref>
Wrap with Comments

wrapWithComments can turn safe JSON text into dangerous text. For example,
["*/ alert('XSS'); /*"]
Thanks to Douglas Crockford for the tip!
If the "wrapWithComments" (false by default) attribute is set to true, the generated JSON is wrapped with comments like:
/* {
   "doubleVal": 10.10,
   "nestedBean": {
      "name": "Mr Bean"
   },
   "list": ["A", 10, 20.20, {
      "firstName": "El Zorro"
   }],
   "array": [10, 20]
} */
This can be used to avoid potential Javascript Hijacks . To strip those comments use:
var responseObject = eval("("+data.substring(data.indexOf("\/\*")+2, data.lastIndexOf("\*\/"))+")");
Base Classes
By default properties defined on base classes of the "root" object won't be serialized, to serialize properties in all base classes (up to Object) set "ignoreHierarchy" to false in the JSON result:
<result type="json">
  <param name="ignoreHierarchy">false</param>
</result>
Enumerations
By default, an Enum is serialized as a name=value pair where value = name().
public enum AnEnum {
     ValueA,
     ValueB
  }

  JSON:  "myEnum":"ValueA"
Use the "enumAsBean" result parameter to serialize Enum's as a bean with a special property _name with value name(). All properties of the enum are also serialized.
public enum AnEnum {
     ValueA("A"),
     ValueB("B");

     private String val;
    
     public AnEnum(val) {
        this.val = val;
     }
     public getVal() {
        return val;
     }
   }

  JSON:  myEnum: { "_name": "ValueA", "val": "A" }
Enable this parameter through struts.xml:
<result type="json">
  <param name="enumAsBean">true</param>
</result>
Compressing the output.
Set the enableGZIP attribute to true to gzip the generated json response. The request must include "gzip" in the "Accept-Encoding" header for this to work.
<result type="json">
  <param name="enableGZIP">true</param>
</result>
Example
Setup Action
This simple action has some fields:
Example:
import java.util.HashMap;
import java.util.Map;

import com.opensymphony.xwork2.Action;

public class JSONExample {
    private String field1 = "str";
    private int[] ints = {10, 20};
    private Map map = new HashMap();
    private String customName = "custom";

    //'transient' fields are not serialized
    private transient String field2;

    //fields without getter method are not serialized
    private String field3;

    public String execute() {
        map.put("John", "Galt");
        return Action.SUCCESS;
    }

    public String getField1() {
        return field1;
    }

    public void setField1(String field1) {
        this.field1 = field1;
    }

    public int[] getInts() {
        return ints;
    }

    public void setInts(int[] ints) {
        this.ints = ints;
    }

    public Map getMap() {
        return map;
    }

    public void setMap(Map map) {
        this.map = map;
    }

    @JSON(name="newName")
    public String getCustomName() {
        return this.customName;
    }
}
Write the mapping for the action
1. Add the map inside a package that extends "json-default"
2. Add a result of type "json"
Example:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
    "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>

  <package name="example"  extends="json-default">
     <action name="JSONExample" class="example.JSONExample">
        <result type="json"/>
     </action>
  </package>

</struts>
JSON example output
{ 
   "field1" : "str",
   "ints": [10, 20],
   "map": {
       "John":"Galt"
   },
   "newName": "custom"
}
JSON RPC
The json plugin can be used to execute action methods from javascript and return the output. This feature was developed with Dojo in mind, so it uses Simple Method Definition  to advertise the remote service. Let's work it out with an example(useless as most examples).
First write the action:
package smd;

import com.googlecode.jsonplugin.annotations.SMDMethod;
import com.opensymphony.xwork2.Action;

public class SMDAction {
    public String smd() {
        return Action.SUCCESS;
    }
   
    @SMDMethod
    public Bean doSomething(Bean bean, int quantity) {
        bean.setPrice(quantity * 10);
        return bean;
    }
}
Methods that will be called remotely must be annotated with the SMDMethod annotation, for security reasons. The method will take a bean object, modify its price and return it. The action can be annotated with the SMD annotation to customize the generated SMD (more on that soon), and parameters can be annotated with SMDMethodParameter. As you can see, we have a "dummy", smd method. This method will be used to generate the Simple Method Definition (a definition of all the services provided by this class), using the "json" result.
The bean class:
package smd;

public class Bean {
    private String type;
    private int price;
   
    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

}
The mapping:
<package name="RPC" namespace="/nodecorate" extends="json-default">
    <action name="SMDAction" class="smd.SMDAction" method="smd">
        <interceptor-ref name="json">
            <param name="enableSMD">true</param>
        </interceptor-ref>
        <result type="json">
             <param name="enableSMD">true</param>
        </result>
    </action>
</package>
Nothing special here, except that both the interceptor and the result must be applied to the action, and "enableSMD" must be enabled for both.
Now the javascript code:
<s:url id="smdUrl" namespace="/nodecorate" action="SMDAction" />
<script type="text/javascript">
    //load dojo RPC
    dojo.require("dojo.rpc.*");
   
    //create service object(proxy) using SMD (generated by the json result)
    var service = new dojo.rpc.JsonService("${smdUrl}");
   
    //function called when remote method returns
    var callback = function(bean) {
        alert("Price for " + bean.type + " is " + bean.price);
    };
   
    //parameter
    var bean = {type: "Mocca"};
   
    //execute remote method
    var defered = service.doSomething(bean, 5);

    //attach callback to defered object
    defered.addCallback(callback);
</script>
Dojo's JsonService will make a request to the action to load the SMD, which will return a JSON object with the definition of the available remote methods, using that information Dojo creates a "proxy" for those methods. Because of the asynchronous nature of the request, when the method is executed, a deferred object is returned, to which a callback function can be attached. The callback function will receive as a parameter the object returned from your action. That's it.
Proxied objects
(V0.20) As annotations are not inherited in Java, some user might experience problems while trying to serialize objects that are proxied. eg. when you have attached AOP interceptors to your action.
In this situation, the plugin will not detect the annotations on methods in your action.
To overcome this, set the "ignoreInterfaces" result parameter to false (true by default) to request that the plugin inspects all interfaces and superclasses of the action for annotations on the action's methods.
NOTE: This parameter should only be set to false if your action could be a proxy as there is a performance cost caused by recursion through the interfaces.
<action name="contact" class="package.ContactAction" method="smd">
   <interceptor-ref name="json">
      <param name="enableSMD">true</param>
      <param name="ignoreSMDMethodInterfaces">false</param>
   </interceptor-ref>
   <result type="json">
      <param name="enableSMD">true</param>
      <param name="ignoreInterfaces">false</param>
   </result>
   <interceptor-ref name="default"/>
</action>



在Struts 2中使用JSon ajax支持
来源： 作者： 发布时间：2007-12-19  

　　JSON插件提供了一种名为json的ResultType，一旦为某个Action指定了一个类型为json的Result，则该Result无需映射到任何视图资源。因为JSON插件会负责将Action里的状态信息序列化成JSON格式的数据，并将该数据返回给客户端页面的JavaScript。
　　简单地说，JSON插件允许我们在JavaScript中异步调用Action，而且Action不再需要使用视图资源来显示该Action里的状态信息，而是由JSON插件负责将Action里的状态信息返回给调用页面——通过这种方式，就能够完成Ajax交互。
　　Struts2提供了一种可插拔方式来管理插件，安装Struts2的JSON插件和安装普通插件并没有太大的区别，相同只需要将Struts2插件的JAR文档复制到Web应用的WEB-INF/lib路径下即可。
　　安装JSON插件按如下步骤进行：
　　（1）登陆http://code.google.com/p/jsonplugin/downloads/list站点，下载Struts2的JSON插件的最新版本，当前最新版本是0.7，我们能够下载该版本的JSON插件。
　　（2）将下载到的jsonplugin-0.7.jar文档复制到Web应用的WEB-INF路径下，即可完成JSON插件的安装。
　　实现Actio逻辑
　　假设wo,en输入页面中包含了三个表单域，这三个表单域对于三个请求参数，因此应该使用Action来封装这三个请求参数。三个表单域的name分别为field1、field2和field3。
　　处理该请求的Action类代码如下：
public class JSONExample
{
　//封装请求参数的三个属性
　private String field1;
　private transient String field2;
　private String field3;
　//封装处理结果的属性
　private int[] ints = {10, 20};
　private Map map = new HashMap();
　private String customName = "custom";
　//三个请求参数对应的setter和getter方法
　public String getField1()
　{
　　return field1;
　}
　public void setField1(String field1)
　{
　　this.field1 = field1;
　}
　//此处省略了field1和field2两个字段的setter和getter方法
　...
　//封装处理结果的属性的setter和getter方法
　public int[] getInts()
　{
　　return ints;
　}
　public void setInts(int[] ints)
　{
　　this.ints = ints;
　}
　public Map getMap()
　{
　　return map;
　}
　public void setMap(Map map)
　{
　　this.map = map;
　}
　//使用注释语法来改变该属性序列化后的属性名
　@JSON(name="newName")
　public String getCustomName()
　{
　　return this.customName;
　}
　public String execute()
　{
　　map.put("name", "yeeku");
　　return Action.SUCCESS;
　}
}
　　在上面代码中，使用了JSON注释，注释时指定了name域，name域指定Action属性被序列化成JSON对象的属性名。除此之外，JSON注释还支持如下几个域：
　　serialize：配置是否序列化该属性
　　deserialize：配置是否反序列化该属性。
　　format：配置用于格式化输出、解析日期表单域的格式。例如"yyyy-MM-dd'T'HH:mm:ss"。
　　配置该Action和配置普通Action存在小小的区别，应该为该Action配置类型为json的Result。而这个Result无需配置任何视图资源。
　　配置该Action的struts.xml文档代码如下：
＜?xml version="1.0" encoding="GBK"?＞
＜!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd"＞
＜struts＞
　＜constant name="struts.i18n.encoding" value="UTF-8"/＞
　＜package name="example" extends="json-default"＞
　　＜action name="JSONExample" class="lee.JSONExample"＞
　　　＜result type="json"/＞
　　＜/action＞
　＜/package＞
＜/struts＞
　　在上面配置文档中有两个值得注意的地方：
　　第一个地方是配置struts.i18n.encoding常量时，不再是使用GBK编码，而是UTF-8编码，这是因为Ajax的POST请求都是以UTF-8的方式进行编码的。
　　第二个地方是配置包时，自己的包继承了json-default包，而不再继承默认的default包，这是因为只有在该包下才有json类型的Result。