一、工具

（1）GSON
Google Gson是一个简单的基于Java的库，用于将Java对象序列化为JSON，反之亦然。 它是由Google开发的一个开源库。
以下几点说明为什么应该使用这个库 -
  • 标准化 - Gson是一个由Google管理的标准化库。
  • 高效 - 这是对Java标准库的可靠，快速和高效的扩展。
  • 优化 - Gson库经过高度优化。
  • 支持泛型 - 它为泛型提供了广泛的支持。
  • 支持复杂的内部类 - 它支持具有深度继承层次结构的复杂对象。
（2）OGNL表达式
OGNL表达式是Object-Graph Navigation Language的缩写，是一种功能强大的表达式语言，通过
简单一致的表达式语法，可以存取对象的任意属性，调用对象的方法，遍历整个对象的结构图，实现字段类型转换。
二、mavan所需引入的依赖
<dependency>

  <groupId>ognl</groupId>

  <artifactId>ognl</artifactId>

  <version>3.1.1</version>

</dependency>

<dependency>

  <groupId>com.google.code.gson</groupId> 
  <artifactId>gson</artifactId>

  <version>2.9.0</version>

</dependency>

<dependency>

  <groupId>junit</groupId>

  <artifactId>junit</artifactId>

  <version>4.13.2</version>

</dependency>

三、工具类

public class JsonUtils { 

/**

* 将指定JSON转为Map对象，Key固定为String，对应JSONkey

* Value分情况：

* 1. Value是字符串，自动转为字符串,例如:{"a","b"} 6 * 2. Value是其他JSON对象，自动转为Map，例如：{"a":{"b":"2"}}}

* 3. Value是数组，自动转为List<Map>，例如：{"a":[{"b":"2"},"c":"3"]}

* @param json 输入的JSON对象

* @return 动态的Map集合

*/

public static Map<String,Object> transferToMap(String json) {

    Gson gson = new Gson();

    Map<String, Object> map = gson.fromJson(json,

    new TypeToken<Map<String, Object>>() {}.getType());

    return map;

}

/**

* 简化方法

* @param json 原始的JSON数据

* @param path OGNL规则表达式

* @param clazz Value对应的目标类

* @return clazz对应数据

*/

public static <T> T getValue(String json, String path, Class<T> clazz) {

  try {

    Map map = transferToMap(json);

    OgnlContext context = new OgnlContext();

    context.setRoot(map);

    T value = (T) Ognl.getValue(path, context, context.getRoot());

     return value;

    } catch (Exception e) {

     throw new RuntimeException(e);

   }

}

public static <T> T getValueFromMap(Map map, String path, Class<T> clazz) {

  try {

   OgnlContext context = new OgnlContext();

    context.setRoot(map);

    T value = (T) Ognl.getValue(path, context, context.getRoot());

     return value;

    } catch (Exception e) {

     throw new RuntimeException(e);

   }

  }

 }

四、测试用例

import com.itlaoqi.JsonUtils;
import org.junit.Test;
import java.util.List;
import java.util.Map;
public class JsonCase {
/**
* {
* "a": {
* "b": {
* "c": {
* "d": {
* "e": "nothing"
* }
* }
* }
* }
* }
*/
/**
* 超多层级JSON嵌套的快速提取
*/
@Test
public void case0(){
String text = "{\n" +
" \"a\": {\n" +
" \"b\": {\n" +
" \"c\": {\n" +
" \"d\": {\n" +
" \"e\": \"nothing\"\n" +
" }\n" +
" }\n" +
" }\n" +
" }\n" +
"}";
Map<String, Object> jsonMap = JsonUtils.transferToMap(json);
String e = JsonUtils.getValue(text, "a.b.c.d.e", String.class);
System.out.println(e);
}

/**
* {
* "showapi_res_error": "",
* "showapi_res_id": "628cc9850de3769f06edbb49",
* "showapi_res_code": 0,
* "showapi_fee_num": 1,
* "showapi_res_body": {"ret_code":0,"area":"南 安","areaid":"101230506","areaCode":"350583","hourList":
[{"weather_code":"07","time":"202205242000","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"20"},
{"weather_code":"07","time":"202205242100","area":"南安","wind_direction":"东 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"20"},
{"weather_code":"07","time":"202205242200","area":"南安","wind_direction":"东 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"20"},
{"weather_code":"07","time":"202205242300","area":"南安","wind_direction":"东 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"20"},
{"weather_code":"07","time":"202205250000","area":"南安","wind_direction":"南 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"21"},
{"weather_code":"07","time":"202205250100","area":"南安","wind_direction":"西 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"21"},
{"weather_code":"07","time":"202205250200","area":"南安","wind_direction":"西北
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"21"},
{"weather_code":"02","time":"202205250300","area":"南安","wind_direction":"西北
风","wind_power":"0-3级 微风
<5.4m/s","weather":"阴","areaid":"101230506","temperature":"21"},
{"weather_code":"02","time":"202205250400","area":"南安","wind_direction":"西北
风","wind_power":"0-3级 微风
<5.4m/s","weather":"阴","areaid":"101230506","temperature":"21"},
{"weather_code":"02","time":"202205250500","area":"南安","wind_direction":"西 风","wind_power":"0-3级 微风
<5.4m/s","weather":"阴","areaid":"101230506","temperature":"21"},
{"weather_code":"07","time":"202205250600","area":"南安","wind_direction":"西北
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"21"},
{"weather_code":"07","time":"202205250700","area":"南安","wind_direction":"西北
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"21"},
{"weather_code":"07","time":"202205250800","area":"南安","wind_direction":"西北
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"21"},
{"weather_code":"07","time":"202205250900","area":"南安","wind_direction":"西南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"22"},
{"weather_code":"07","time":"202205251000","area":"南安","wind_direction":"南 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"23"},
{"weather_code":"07","time":"202205251100","area":"南安","wind_direction":"东 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"24"},
{"weather_code":"07","time":"202205251200","area":"南安","wind_direction":"东 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"24"},
{"weather_code":"07","time":"202205251300","area":"南安","wind_direction":"东 风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"25"},
{"weather_code":"07","time":"202205251400","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"25"},
{"weather_code":"07","time":"202205251500","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"25"},
{"weather_code":"07","time":"202205251600","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"24"},
{"weather_code":"07","time":"202205251700","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"23"},
{"weather_code":"07","time":"202205251800","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"23"},
{"weather_code":"07","time":"202205251900","area":"南安","wind_direction":"东南
风","wind_power":"0-3级 微风 <5.4m/s","weather":"小 雨","areaid":"101230506","temperature":"23"}]}
* }
*/
private String json = "{\n" +
"\"showapi_res_error\": \"\",\n" +
"\"showapi_res_id\": \"628cc9850de3769f06edbb49\",\n" +
"\"showapi_res_code\": 0,\n" +
"\"showapi_fee_num\": 1,\n" +
"\"showapi_res_body\": {\"ret_code\":0,\"area\":\"南安
\",\"areaid\":\"101230506\",\"areaCode\":\"350583\",\"hourList\":
[{\"weather_code\":\"07\",\"time\":\"202205242000\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"20\"},
{\"weather_code\":\"07\",\"time\":\"202205242100\",\"area\":\"南安
\",\"wind_direction\":\"东风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"20\"},
{\"weather_code\":\"07\",\"time\":\"202205242200\",\"area\":\"南安
\",\"wind_direction\":\"东风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"20\"},
{\"weather_code\":\"07\",\"time\":\"202205242300\",\"area\":\"南安
\",\"wind_direction\":\"东风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"20\"},
{\"weather_code\":\"07\",\"time\":\"202205250000\",\"area\":\"南安
\",\"wind_direction\":\"南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"07\",\"time\":\"202205250100\",\"area\":\"南安
\",\"wind_direction\":\"西风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"07\",\"time\":\"202205250200\",\"area\":\"南安
\",\"wind_direction\":\"西北风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"02\",\"time\":\"202205250300\",\"area\":\"南安
\",\"wind_direction\":\"西北风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"阴
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"02\",\"time\":\"202205250400\",\"area\":\"南安
\",\"wind_direction\":\"西北风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"阴
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"02\",\"time\":\"202205250500\",\"area\":\"南安
\",\"wind_direction\":\"西风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"阴
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"07\",\"time\":\"202205250600\",\"area\":\"南安
\",\"wind_direction\":\"西北风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"07\",\"time\":\"202205250700\",\"area\":\"南安
\",\"wind_direction\":\"西北风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"07\",\"time\":\"202205250800\",\"area\":\"南安
\",\"wind_direction\":\"西北风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"21\"},
{\"weather_code\":\"07\",\"time\":\"202205250900\",\"area\":\"南安
\",\"wind_direction\":\"西南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"22\"},
{\"weather_code\":\"07\",\"time\":\"202205251000\",\"area\":\"南安
\",\"wind_direction\":\"南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"23\"},
{\"weather_code\":\"07\",\"time\":\"202205251100\",\"area\":\"南安
\",\"wind_direction\":\"东风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"24\"},
{\"weather_code\":\"07\",\"time\":\"202205251200\",\"area\":\"南安
\",\"wind_direction\":\"东风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"24\"},
{\"weather_code\":\"07\",\"time\":\"202205251300\",\"area\":\"南安
\",\"wind_direction\":\"东风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"25\"},
{\"weather_code\":\"07\",\"time\":\"202205251400\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"25\"},
{\"weather_code\":\"07\",\"time\":\"202205251500\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"25\"},
{\"weather_code\":\"07\",\"time\":\"202205251600\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"24\"},
{\"weather_code\":\"07\",\"time\":\"202205251700\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"23\"},
{\"weather_code\":\"07\",\"time\":\"202205251800\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"23\"},
{\"weather_code\":\"07\",\"time\":\"202205251900\",\"area\":\"南安
\",\"wind_direction\":\"东南风\",\"wind_power\":\"0-3级 微风 <5.4m/s\",\"weather\":\"小雨
\",\"areaid\":\"101230506\",\"temperature\":\"23\"}]}\n" +
"}";

//将JSON转为标准Map结构
@Test
public void case1(){
Map<String, Object> jsonMap = JsonUtils.transferToMap(json);
System.out.println(jsonMap);
}
/**
* OGNL直接提取数据，Value为子JSON对象的情况
*/
@Test
public void case2(){
Map<String, Object> jsonMap = JsonUtils.transferToMap(json);
Map resBody = JsonUtils.getValue(json, "showapi_res_body", Map.class);
System.out.println(resBody);
}

/**
* OGNL直接提取数据，Value为标准字符串的情况
*/
@Test
public void case3(){
Map<String, Object> jsonMap = JsonUtils.transferToMap(json);
String value = JsonUtils.getValue(json, "showapi_res_body.area", String.class);
System.out.println(value);
}

/**
* OGNL直接提取数据，Value为标准字符串的情况，Value为数组的情况
*/
@Test
public void case4(){
Map<String, Object> jsonMap = JsonUtils.transferToMap(json);
List<Map> hourList = JsonUtils.getValue(json, "showapi_res_body.hourList",st.class);
System.out.println(hourList);
// 每一个集合对象都是List
for(Map hour : hourList){
System.out.println(hour);
}
}

/**
* 利用List语法获取第6个时点天气预报
*/
@Test
public void case5(){
Map<String, Object> jsonMap = JsonUtils.transferToMap(json);
String area = JsonUtils.getValue(json,"showapi_res_body.hourList[5].weather_code", String.class);
System.out.println(area);
}
}

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