JSON 的含义？
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。
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
在之后添加如下的内容：
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：
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);
JSON arrayValue = new JSON();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);JSON json = jsonObject.getJSON("array");for(int i = 0; i < json.length(); i++) { System.out.println("item " + i + " :" + json.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.JSON;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); JSON json = jsonObject.getJSON("array"); for(int i = 0; i < json.length(); i++) { System.out.println("item " + i + " :" + json.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.
2.
3. "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
4. "http://struts.apache.org/dtds/struts-2.0.dtd">
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
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.List;
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 List();
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
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Added by Musachy Barroso, last edited by ghostroller on Jul 04, 2008 (view change) show comment hide comment
Comment: change "ignoreInterfaces" to "ignoreSMDMethodInterfaces" in interceptor parametersView page history
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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 s, Other class (more on this later), and 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 "set" method can take as parameter either a "List", or any numeric array.
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:
...
...
Use the JSON annotation to customize the serialization/deserialization process. Available JSON annotation fields:
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:
"excludeProperties">
login.password,
studentList.*\.sin
"enableSMD">true
"excludeProperties">
login.password,
studentList.*\.sin
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.
"includeProperties">
^entries\[\d+\]\.clientNumber,
^entries\[\d+\]\.scheduleNumber,
^entries\[\d+\]\.createUserId
Use the "root" attribute(OGNL expression) to specify the root object to be serialized.
"root">
person.job
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.
"root">bean1.bean2
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("\*\/"))+")");
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:
"ignoreHierarchy">false
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:
"enumAsBean">true
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.
"enableGZIP">true
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;
}
}
1. Add the map inside a package that extends "json-default"
2. Add a result of type "json"
Example:
"1.0" encoding="UTF-8" ?>
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
{
"field1" : "str",
"ints": [10, 20],
"map": {
"John":"Galt"
},
"newName": "custom"
}
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:
"enableSMD">true
"enableSMD">true
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:
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.
(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.
"enableSMD">true
"ignoreSMDMethodInterfaces">false
"enableSMD">true
"ignoreInterfaces">false
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