J2EE Week 7

1. What is JSON?

JSON is a data structure that replaces XML. Compared with xml, it is smaller but the description ability is not bad. Because of its small size, the network transmission data will reduce more traffic and speed up.

JSON is just a string of strings except that elements are marked with specific symbols.

{} Double brackets denote objects

[] Brackets indicate an array

"" Inside double quotes is an attribute or value

: The colon indicates that the latter is the value of the former (this value can be a string, a number, or another array or object)

So {"name": "Michael"} can be understood as an object containing the name Michael

And [{"name": "Michael"},{"name": "Jerry"}] represents an array containing two objects

Of course, you can also use {"name":["Michael","Jerry"]} to simplify the above one, which is an object with an array of names

2. Traditional JSON parsing of JSON parsing

1. Generate a json string

public static String createJsonString(String key, Object value) {
        JSONObject jsonObject = new JSONObject(); jsonObject.put(key, value);
        return jsonObject.toString(); }

2. Parse the JSON string

Divided into the following three cases, a Java Bean, a List array, a List array of nested Map:

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.json.JSONArray;
import org.json.JSONObject;

import com.android.myjson.domain.Person;

/**
 * Complete the parsing of json data
 *
 */ public class JsonTools { public static Person getPerson(String key, String jsonString) { Person person = new Person(); try { JSONObject jsonObject = new JSONObject(jsonString); JSONObject personObject = jsonObject.getJSONObject("person"); person.setId(personObject.getInt("id")); person.setName(personObject.getString("name")); person.setAddress(personObject.getString("address")); } catch (Exception e) { // TODO: handle exception  } return person; } public static List getPersons(String key, String jsonString) { List list = new ArrayList(); try { JSONObject jsonObject = new JSONObject(jsonString); // 返回json的数组 JSONArray jsonArray = jsonObject.getJSONArray(key); for (int i = 0; i < jsonArray.length(); i++) { JSONObject jsonObject2 = jsonArray.getJSONObject(i); Person person = new Person(); person.setId(jsonObject2.getInt("id")); person.setName(jsonObject2.getString("name")); person.setAddress(jsonObject2.getString("address")); list.add(person); } } catch (Exception e) { // TODO: handle exception  } return list; } public static List getList(String key, String jsonString) { List list = new ArrayList(); try { JSONObject jsonObject = new JSONObject(jsonString); JSONArray jsonArray = jsonObject.getJSONArray(key); for (int i = 0; i < jsonArray.length(); i++) { String msg = jsonArray.getString(i); list.add(msg); } } catch (Exception e) { // TODO: handle exception  } return list; } public static List> listKeyMaps(String key, String jsonString) { List> list = new ArrayList>(); try { JSONObject jsonObject = new JSONObject(jsonString); JSONArray jsonArray = jsonObject.getJSONArray(key); for (int i = 0; i < jsonArray.length(); i++) { JSONObject jsonObject2 = jsonArray.getJSONObject(i); Map map = new HashMap(); Iterator iterator = jsonObject2.keys(); while (iterator.hasNext()) { String json_key = iterator.next(); Object json_value = jsonObject2.get(json_key); if (json_value == null) { json_value = ""; } map.put(json_key, json_value); } list.add(map); } } catch (Exception e) { // TODO: handle exception  } return list; } }

3. GSON for JSON parsing

1. Generate JSON string

import com.google.gson.Gson;

public class JsonUtils {

    public static String createJsonObject(Object obj) { Gson gson = new Gson(); String str = gson.toJson(obj); return str; } } 二、解析JSON import java.util.ArrayList; import java.util.List; import java.util.Map; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; ; public class GsonTools { public GsonTools() { // TODO Auto-generated constructor stub  } /** * @param * @param jsonString * @param cls * @return */ public static T getPerson(String jsonString, Class cls) { T t = null; try { Gson gson = new Gson(); t = gson.fromJson(jsonString, cls); } catch (Exception e) { // TODO: handle exception  } return t; } /** * 使用Gson进行解析 List * * @param * @param jsonString * @param cls * @return */ public static List getPersons(String jsonString, Class cls) { List list = new ArrayList(); try { Gson gson = new Gson(); list = gson.fromJson(jsonString, new TypeToken>() { }.getType()); } catch (Exception e) { } return list; } /** * @param jsonString * @return */ public static List getList(String jsonString) { List list = new ArrayList(); try { Gson gson = new Gson(); list = gson.fromJson(jsonString, new TypeToken>() { }.getType()); } catch (Exception e) { // TODO: handle exception  } return list; } public static List> listKeyMaps(String jsonString) { List> list = new ArrayList>(); try { Gson gson = new Gson(); list = gson.fromJson(jsonString, new TypeToken>>() { }.getType()); } catch (Exception e) { // TODO: handle exception  } return list; } }

3. FastJSON for JSON parsing

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;

public class JsonTool {

    public static T getPerson(String jsonstring, Class cls) { T t = null; try { t = JSON.parseObject(jsonstring, cls); } catch (Exception e) { // TODO: handle exception  } return t; } public static List getPersonList(String jsonstring, Class cls) { List list = new ArrayList(); try { list = JSON.parseArray(jsonstring, cls); } catch (Exception e) { // TODO: handle exception  } return list; } public static List> getPersonListMap1( String jsonstring) { List> list = new ArrayList>(); try { list = JSON.parseObject(jsonstring, new TypeReference>>() { }.getType()); } catch (Exception e) { // TODO: handle exception  } return list; } }

Source address: https://www.cnblogs.com/zhujiabin/p/5498272.html

Summarize:

For mobile devices, especially in the case of poor network environment and limited traffic, JSON will save more traffic and be more efficient than data transmission in XML format. Among the three parsing methods, FastJson is the most efficient and recommended.