JSON(JavaScript Object Notation)内容详解(Android操作JSON)

1. 什么是 JSON

      JSON概念很简单，JSON 是一种轻量级的数据格式，他基于 javascript语法的子集，即数组和对象表示。由于使用的是 javascript 语法，因此JSON 定义可以包含在javascript文件中，对其的访问无需通过基于 XML 的语言来额外解析。不过在使用 JSON 之前，很重要的一点是理解 javascript中数组及对象字面量的特殊语法。

1.1 数组字面量

         数组字面量，是用一对方括号括起一组用逗号隔开的 javascript 值，例如：

        var aNames=["hello", 12, true , null];

1.2 对象字面量

        对象字面量，是通过两个花括号来定义的。在花括号内可以放置任意数量的“名称-值”对，定义格 式字符串值”。除了最后一行外，每个“名称-值”对后必须有一个逗号（这与Perl 中的联合数组的定义有些类似）。例如：

        var oCar = {

               "color": "red",       

              "doors" : 4,

               "paidFor" : true

        };

1.3 混合字面量

      我们可以混用对象和数组字面量，来创建一个对象数组，或一个包含数组的对象。例如：

{comments:[
{
id:1,
author:"someone1",
url:"http://someone1.x2design.net",
content:"hello"
},
{
id:2,
author:"someone2",
url:"http://someone2.x2design.net",
content:"hello"
},
{
id:3,
author:"someone3",
url:"http://someone3.x2design.net",
content:"hello"
}
]};

1、JSON是用来进行服务器和客户端数据传输的

2、JSON数据是一系列键值对的集合

3、JSON已经被大多数开发人员接受，在网络数据的传输当中应用非常广泛

JSON PK XML哪个更好?

JSON相对于XML来讲解析稍微方便一些。

JSON和XML的数据可读性基本相同

JSON和XML同样拥有丰富的解析手段

JSON相对于XML来讲，数据体积小

JSON与JavaScript的交互更加方便

JSON对数据的描述性相对于XML较差

一个JSON的例子：

    "name":"Michael";

    "address":

    {

        "city":"Beijing",

        "street":"Chaoyang Road",

        "postcode":100025

      }

}

{

    "name":"Michael";

    "address":

    {

        "city":"Beijing",

        "street":"Chaoyang Road",

        "postcode":100025

      }

}

说明：JSON官方网站:http://www.json.org/

Google JSON类库:http://code.google.com/p/google-gson/

看下面的例子：

Activity类：

public class MainActivity extends Activity {
    private String jsonData = "[{\"name\":\"Michael\",\"age\":20},{\"name\":\"Mike\",\"age\":21}]";
    private Button button ;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button = (Button)findViewById(R.id.buttonId);
        button.setOnClickListener(new ButtonListener());
    }

    private class ButtonListener implements OnClickListener {

        public void onClick(View v) {
            JsonUtils jsonUtils = new JsonUtils();
            jsonUtils.parseJson(jsonData);
        }

    }
}

public class MainActivity extends Activity {
	private String jsonData = "[{\"name\":\"Michael\",\"age\":20},{\"name\":\"Mike\",\"age\":21}]";
	private Button button ;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button = (Button)findViewById(R.id.buttonId);
        button.setOnClickListener(new ButtonListener());
    }
    
    private class ButtonListener implements OnClickListener {

		public void onClick(View v) {
			JsonUtils jsonUtils = new JsonUtils();
			jsonUtils.parseJson(jsonData);
		}
    	
    }
}

工具类：

 

public class JsonUtils {
    public void parseJson(String jsonData){
        try{
            //如果需要解析JSON数据，首要要生成一个JsonReader对象
            JsonReader reader = new JsonReader(new StringReader(jsonData));
            //开始解析数组
            reader.beginArray();
            //判断是否下一个JSON对象
            while(reader.hasNext()){
                //开始解析对象
                reader.beginObject();
                //判断有没键值对
                while(reader.hasNext()){
                    //得到下一个键
                    String tagName = reader.nextName();
                    if(tagName.equals("name")){
                        //得到键所对应的值
                        System.out.println("name--->" + reader.nextString());
                    }
                    else if(tagName.equals("age")){
                        System.out.println("age--->" + reader.nextInt());
                    }
                }
                //解析对象结束
                reader.endObject();
            }
            //解析数组结束
            reader.endArray();
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }
}

public class JsonUtils {
	public void parseJson(String jsonData){
		try{
			//如果需要解析JSON数据，首要要生成一个JsonReader对象
			JsonReader reader = new JsonReader(new StringReader(jsonData));
			//开始解析数组
			reader.beginArray();
			//判断是否下一个JSON对象
			while(reader.hasNext()){
				//开始解析对象
				reader.beginObject();
				//判断有没键值对
				while(reader.hasNext()){
					//得到下一个键
					String tagName = reader.nextName();
					if(tagName.equals("name")){
						//得到键所对应的值
						System.out.println("name--->" + reader.nextString());
					}
					else if(tagName.equals("age")){
						System.out.println("age--->" + reader.nextInt());
					}
				}
				//解析对象结束
				reader.endObject();
			}
			//解析数组结束
			reader.endArray();
		}
		catch(Exception e){
			e.printStackTrace();
		}
	}
}

一个JSON：[{"name":"zhangsan","age":20},{"name":"lisi","age":30}]
步骤：

1>开始解析数组

2>开始解析对象

3>解析键值对

4>解析键值对

5>解析对象结束

6>开始解析对象

7>解析键值对

8>解析键值对

9>解析对象结束

10>解析数组结束

只要理解上面的解析流程，学习JSON应该不是很难。

在看下面的这个例子：

User.java类

 

public class User {
    private String name ;
    private int age ;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

public class User {
	private String name ;
	private int age ;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
}

JsonUtils类：

 

public class JsonUtils {

    public void parseUserFromJson(String jsonData){
        Gson gson = new Gson();
        User user = gson.fromJson(jsonData, User.class);
        System.out.println("name--->" + user.getName());
        System.out.println("age---->" + user.getAge());

    }
}

public class JsonUtils {
	
	public void parseUserFromJson(String jsonData){
		Gson gson = new Gson();
		User user = gson.fromJson(jsonData, User.class);
		System.out.println("name--->" + user.getName());
		System.out.println("age---->" + user.getAge());
		
	}
}

MainActivity.java类：

public class MainActivity extends Activity {
    private Button button = null;
    private String jsonData = "{\"name\":\"Michael\",\"age\":20}";
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button = (Button)findViewById(R.id.buttonId);
        button.setOnClickListener(new ButtonListener());
    }

    private class ButtonListener implements OnClickListener{

        public void onClick(View v) {
            JsonUtils jsonUtils = new JsonUtils();
            jsonUtils.parseUserFromJson(jsonData);
        }

    }
}

public class MainActivity extends Activity {
	private Button button = null;
	private String jsonData = "{\"name\":\"Michael\",\"age\":20}";
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button = (Button)findViewById(R.id.buttonId);
        button.setOnClickListener(new ButtonListener());
    }
    
    private class ButtonListener implements OnClickListener{

		public void onClick(View v) {
			JsonUtils jsonUtils = new JsonUtils();
			jsonUtils.parseUserFromJson(jsonData);
		}
    	
    } 
}

JsonUtils类：

public class JsonUtils {

    public void parseUserFromJson(String jsonData){
        /*
         *  This is the main class for using Gson.
         *  Gson is typically used by first constructing a Gson instance
         *  and then invoking toJson(Object) or fromJson(String, Class) methods on it
         */
        Gson gson = new Gson();

        /*public <T> T fromJson(String json,
                 *            Type typeOfT)
                 *        throws JsonSyntaxException
         * This method deserializes the specified Json into an object of the specified type
         *  json - the string from which the object is to be deserialized
                 *  typeOfT - The specific genericized type of src. You can obtain this type by using the TypeToken class. For example, to get the type for Collection<Foo>, you should use:
                 *  Type typeOfT = new TypeToken<Collection<Foo>>(){}.getType();
         */
        User user = gson.fromJson(jsonData, User.class);
        System.out.println("name--->" + user.getName());
        System.out.println("age---->" + user.getAge());

    }
}

public class JsonUtils {
	
	public void parseUserFromJson(String jsonData){
		/*
		 * 	This is the main class for using Gson.
		 *  Gson is typically used by first constructing a Gson instance 
		 * 	and then invoking toJson(Object) or fromJson(String, Class) methods on it
		 */
		Gson gson = new Gson();
		
		/*public <T> T fromJson(String json,
                 *            Type typeOfT)
                 * 	      throws JsonSyntaxException
		 * This method deserializes the specified Json into an object of the specified type
		 *  json - the string from which the object is to be deserialized
    	         *	typeOfT - The specific genericized type of src. You can obtain this type by using the TypeToken class. For example, to get the type for Collection<Foo>, you should use:
    	         *	Type typeOfT = new TypeToken<Collection<Foo>>(){}.getType();
		 */
		User user = gson.fromJson(jsonData, User.class);
		System.out.println("name--->" + user.getName());
		System.out.println("age---->" + user.getAge());
		
	}
}

在往下看这个例子：

MainActivity.java和User.java同上,JsonUtils.java代码如下：

 

public class JsonUtils {

    public void parseUserFromJson(String jsonData){
        Type listType = new TypeToken<LinkedList<User>>(){}.getType();
        Gson gson = new Gson();
        LinkedList<User> users = gson.fromJson(jsonData, listType);
        for (Iterator iterator = users.iterator(); iterator.hasNext();) {
            User user = (User) iterator.next();
            System.out.println("name--->" + user.getName());
            System.out.println("age---->" + user.getAge());
        }

    }
}

public class JsonUtils {
	
	public void parseUserFromJson(String jsonData){
		Type listType = new TypeToken<LinkedList<User>>(){}.getType();
		Gson gson = new Gson();
		LinkedList<User> users = gson.fromJson(jsonData, listType);
		for (Iterator iterator = users.iterator(); iterator.hasNext();) {
			User user = (User) iterator.next();
			System.out.println("name--->" + user.getName());
			System.out.println("age---->" + user.getAge());
		}
		
	}
}

上面的代码让你一步一步深入学习JSON各种操作方法！