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Java ofereix dues biblioteques molt potents per treballar amb dades JSON, és a dir, JACKSON i Gson biblioteques. Sovint hem de convertir les respostes JSON en un mapa per treballar fàcilment amb les dades JSON retornades.

Podem convertir fàcilment les dades JSON en un mapa perquè el format JSON és essencialment una agrupació de parells clau-valor i el mapa també emmagatzema dades en parells clau-valor.

Entendrem com podem utilitzar les biblioteques JACKSON i Gson per convertir dades JSON en un mapa. També entenem com podem utilitzar les dues biblioteques per convertir les dades del mapa a JSON.

pyspark

Suposem que tenim un fitxer Sample.json al sistema que conté les dades següents:

 { 'Name' : 'Donal', 'Mobile' : '89346724', 'Designation' : 'Sr. Salesforce Developer', 'Pet' : 'Dog', 'Address' : 'AMERICA' } 

Biblioteca JACKSON

Per convertir les dades JSON en Java Map, utilitzem l'ajuda de la biblioteca JACKSON. Afegim la següent dependència al fitxer POM.xml per treballar amb la biblioteca JACKSON.

 com.fasterxml.jackson.core jackson-databind 2.5.3 

Implementem la lògica de convertir dades JSON en un mapa mitjançant les classes ObjectMapper, File i TypeReference.

JacksonConvertJSONToMap.java

convertint int a cadena

 // import required classes and packages package javaTpoint.JavaExample; import java.io.File; // for reading file data import java.util.Map; import com.fasterxml.jackson.core.type.TypeReference; import com.fasterxml.jackson.databind.ObjectMapper; // create JacksonConvertJSONToMap class to convert JSON data into Java Map public class JacksonConvertJSONToMap { // main() method start public static void main(String args[]) { // create instance of the ObjectMapper class to map JSON data ObjectMapper mapper = new ObjectMapper(); // create instance of the File class File fileObj = new File(&apos;C:\Users\rastogi ji\OneDrive\Desktop\Sample.json&apos;); // use try-catch block to convert JSON data into Map try { // read JSON data from file using fileObj and map it using ObjectMapper and TypeReference classes Map userData = mapper.readValue( fileObj, new TypeReference<map>() { }); // print all key-value pairs System.out.println(&apos;Name : &apos; + userData.get(&apos;Name&apos;)); System.out.println(&apos;Mobile : &apos; + userData.get(&apos;Mobile&apos;)); System.out.println(&apos;Designation : &apos; + userData.get(&apos;Designation&apos;)); System.out.println(&apos;Pet : &apos; + userData.get(&apos;Pet&apos;)); System.out.println(&apos;Address : &apos; + userData.get(&apos;Address&apos;)); } catch (Exception e) { // show error message e.printStackTrace(); } } } </map>

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Prenguem un altre exemple de la biblioteca Jackson per entendre com podem convertir un mapa Java en JSON perquè sovint necessitem passar dades del mapa a l'API com a JSON. Per tant, en aquest exemple, convertim les dades del mapa a JSON i les emmagatzemem en un fitxer.

JacksonConvertMapToJson.java

 // import required classes and packages package javaTpoint.JavaExample; import java.io.File; import java.util.HashMap; import java.util.Map; import java.util.Scanner; import com.fasterxml.jackson.databind.ObjectMapper; //create JacksonConvertMapToJSON class to convert Map data into JSON public class JacksonConvertMapToJSON { // main() method start public static void main(String args[]) { // create instance of the ObjectMapper class ObjectMapper mapper = new ObjectMapper(); // declare and initialize map (key is of type String and value is of type Object) Map userData = new HashMap(); // declare variables and array to store user entered data String name, price, model; String colors[]; // create an instance of the Scanner class Scanner sc = new Scanner(System.in); // take inputs from the user and store them to the variables System.out.println('Enter the name of the car: '); name = sc.nextLine(); System.out.println('Enter the modal number of the car: '); model = sc.nextLine(); System.out.println('Enter the price of the car: '); price = sc.nextLine(); colors = new String[3]; colors[0] = 'Red'; colors[1] = 'Black'; colors[2] = 'White'; // close Scanner class object sc.close(); // fill userData map userData.put('Car', name); userData.put('Price', price); userData.put('Model', model); userData.put('Colors', colors); // use try-catch block to convert Java map into JSON try { // use ObjectMapper class to convert Map data into JSON and write it into Sample.json file mapper.writeValue(new File('C:\Users\rastogi ji\OneDrive\Desktop\Sample.json'), userData); System.out.println('Map data successfully written to the Sample.json file.'); } catch (Exception e) { // handle exception e.printStackTrace(); } } } 

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formes normals

Biblioteca Gson

Gson biblioteca és una altra biblioteca que podem utilitzar per convertir dades JSON en mapes o dades de mapes en JSON. Per utilitzar la biblioteca Gson, hem d'afegir la següent dependència al nostre fitxer POM.xml.

 com.google.code.gson gson 2.8.3 

GsonConvertJSONToMap.java

 //import required classes and packages package javaTpoint.JavaExample; import java.util.HashMap; import java.util.Map; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; //create GsonConvertJSONToMap class to convert JSON data into Java Map public class GsonConvertJSONToMap { // main() method start public static void main(String args[]) { // create variable loc that store location of the Sample.json file String loc = &apos;C:\Users\rastogi ji\OneDrive\Desktop\Sample.json&apos;; String result; try { // read byte data from the Sample.json file and convert it into String result = new String(Files.readAllBytes(Paths.get(loc))); // store string data into Map by using TypeToken class Map userData = new Gson().fromJson(result, new TypeToken<hashmap>() { }.getType()); // print all key-value pairs System.out.println(&apos;Name : &apos; + userData.get(&apos;Name&apos;)); System.out.println(&apos;Mobile : &apos; + userData.get(&apos;Mobile&apos;)); System.out.println(&apos;Designation : &apos; + userData.get(&apos;Designation&apos;)); System.out.println(&apos;Pet : &apos; + userData.get(&apos;Pet&apos;)); System.out.println(&apos;Address : &apos; + userData.get(&apos;Address&apos;)); } catch (IOException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } } } </hashmap>

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Prenguem un altre exemple de la biblioteca Gson per entendre com convertir un mapa Java a JSON. L'ús de la biblioteca Gson és una mica diferent de la biblioteca Jackson.

java agitant a int

GsonConvertMapToJson.java

 //import required classes and packages package javaTpoint.JavaExample; import java.io.File; import java.io.FileWriter; import java.io.IOException; import java.util.HashMap; import java.util.Map; import java.util.Scanner; import com.google.gson.Gson; //create GsonConvertMapToJson class to convert Map data into JSON public class GsonConvertMapToJson { // main() method start public static void main(String args[]) { // declare and initialize map(key is of type String and value is of type Object) Map userData = new HashMap(); // declare variables and array to store user entered data String name, price, model; String colors[]; // create an instance of the Scanner class Scanner sc = new Scanner(System.in); // take inputs from the user and store them to the variables System.out.println('Enter the name of the car: '); name = sc.nextLine(); System.out.println('Enter the modal number of the car: '); model = sc.nextLine(); System.out.println('Enter the price of the car: '); price = sc.nextLine(); colors = new String[3]; colors[0] = 'Red'; colors[1] = 'Black'; colors[2] = 'White'; // close Scanner class object sc.close(); // fill userData map userData.put('Car', name); userData.put('Price', price); userData.put('Model', model); userData.put('Colors', colors); // use try-catch block to convert Java map into JSON try (FileWriter file = new FileWriter('C:\Users\rastogi ji\OneDrive\Desktop\Sample.json')) { // create instance of the Gson Gson gsonObj = new Gson(); // convert userData map to json string String jsonStr = gsonObj.toJson(userData); // use write() of File to write json string into file file.write(jsonStr); // use flush() method to flushes stream file.flush(); System.out.println('Map data successfully written to the Sample.json file.'); } catch (IOException e) { // error handling and exceptions e.printStackTrace(); } } } 

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