What is JSON

JSON: JavaScript Object Notation

JSON is a grammar for storing and exchanging text information. Similar to XML.

JSON adopts a text format completely independent of any programming language, making JSON an ideal data exchange language S

Why do you need JSON

When it comes to JSON, we should compare it with XML. XML is also a means of storing and exchanging text information. So what's good about JSON?

JSON is smaller, faster and easier to parse than XML.

• javaScript natively supports JSON and parses quickly
• When XML is parsed into DOM objects, browsers [IE and fireFox] differ.
• It's simpler to use JSON

 

 

Easier to create JavaScript objects

var p = {'city':['Beijing','Shanghai','Guangzhou','Shenzhen']};
for(var i=0;i<p.city.length;i++){
	document.write(p.city[i]+"<br/>");
}

JSON syntax

There are two kinds of interactive data between client and server.

• array
• object

So the data represented by JSON is either object or data.

JSON grammar is a subset of javaScript grammar, javaScript uses parentheses in [] to represent arrays, and {} braces to represent objects, and so does JSON.

JSON array:

	var employees = [
	{ "firstName":"Bill" , "lastName":"Gates" },
	{ "firstName":"George" , "lastName":"Bush" },
	{ "firstName":"Thomas" , "lastName": "Carter" }
	];

JSON object

        var obj = {

            age: 20,
            str: "zhongfucheng",
            method: function () {
                alert("I love learning.");
            }

        };

Of course, arrays can contain objects and arrays in objects.

Parsing JSON

JavaScript natively supports JSON. We can use eval() function to parse JSON and convert JSON text data into a JavaScript object.

        function test() {
			//When writing JOSN, remember to put a comma on it.
            var txt = "{a:123," +
                    "b:'zhongfucheng'}";

            //Using eval to parse JSON strings, you need to add ()
            var aa = eval("(" + txt + ")");
            alert(aa);

        }

 

Effect

 

 

Converting JavaBean s to JSON without frameworks

• When using Struts 2, Struts 2 comes with components that can turn JavaBean objects and collections into JSON without splicing them together by ourselves.. This is very convenient.
• When using Spring MVC, Spring MVC also supports converting JavaBean s to JSON

But we don't necessarily use frameworks for development. Therefore, we also have to learn how to use third-party libraries to convert JavaBean objects and collections into JSON.

Import Development Package

• commons-io-2.0.1.jar
• commons-lang-2.5.jar
• commons-collections-3.1.jar
• commons-beanutils-1.7.0.jar
• ezmorph-1.0.3.jar
• json-lib-2.1-jdk15.jar

Case code

package cn.itcast.javaee.js.bean2json;

import net.sf.json.JSONArray;

import java.util.*;

/**
 * Converting JavaBean objects / List or Set or Map objects to JSON using third-party tools 
 * @author AdminTC
 */
public class TestBean2Json {
	private static void javabean2json() {
		City city = new City(1,"Guangzhou");
		JSONArray jSONArray = JSONArray.fromObject(city);
		String jsonJAVA = jSONArray.toString();
		System.out.println(jsonJAVA);
		//[{id":1,"name":"Guangzhou"}]
	}
	private static void list2json() {
		List<City> cityList = new ArrayList<City>();
		cityList.add(new City(1,"Guangzhou"));
		cityList.add(new City(2,"Zhuhai"));
		JSONArray jSONArray = JSONArray.fromObject(cityList);
		String jsonJAVA = jSONArray.toString();
		System.out.println(jsonJAVA);
		//[{id":1,"name":"Guangzhou"}, {id":2,"name": "Zhuhai"}]
	}
	private static void set2json() {
		Set<City> citySet = new LinkedHashSet<City>();
		citySet.add(new City(1,"Guangzhou"));
		citySet.add(new City(2,"Zhuhai"));
		JSONArray jSONArray = JSONArray.fromObject(citySet);
		String jsonJAVA = jSONArray.toString();
		System.out.println(jsonJAVA);
		//[{id":1,"name":"Guangzhou"}, {id":2,"name": "Zhuhai"}]
	}
	private static void javabeanlist2json() {
		List<City> cityList = new ArrayList<City>();
		cityList.add(new City(1,"Zhongshan"));
		cityList.add(new City(2,"Foshan"));
		Province province = new Province(1,"Guangdong",cityList);
		
		JSONArray jSONArray = JSONArray.fromObject(province);
		String jsonJAVA = jSONArray.toString();
		System.out.println(jsonJAVA);
		/*
		  [
			 {
			  "id":1,
			  "name":"Guangdong "
			  "cityList":[{"id":1,"name":"Zhongshan"}, {id":2,"name": "Foshan"},
		     }
		  ]
		  */
	}
	private static void map2json() {
		
		List<City> cityList = new ArrayList<City>();
		cityList.add(new City(1,"Zhongshan"));
		cityList.add(new City(2,"Foshan"));
		
		Map<String,Object> map = new LinkedHashMap<String,Object>();
		map.put("total",cityList.size());//Represents the length of a collection
		map.put("rows",cityList);//rows represents a set
		
		JSONArray jSONArray = JSONArray.fromObject(map);
		String jsonJAVA = jSONArray.toString();
		System.out.println(jsonJAVA);
		//[{total": 2,"rows": [{id": 1, "name": "Zhongshan"}, {id":2,"name":"Foshan"}]
		
		jsonJAVA = jsonJAVA.substring(1,jsonJAVA.length()-1);
		System.out.println(jsonJAVA);
	}
	
}

Put the javaBena objects and collections to be parsed into JSON into the following code!

		JSONArray jSONArray = JSONArray.fromObject(map);

Whatever you put in, you return arrays.

summary