Java gir to veldig sterke biblioteker for å jobbe med JSON-data, dvs. JACKSON og Gson biblioteker. Vi trenger ofte å konvertere JSON-svar til et kart for å fungere enkelt med de returnerte JSON-dataene.
Vi kan enkelt konvertere JSON-data til et kart fordi JSON-formatet i hovedsak er en nøkkelverdi-pargruppering, og kartet lagrer også data i nøkkelverdi-par.
La oss forstå hvordan vi kan bruke både JACKSON- og Gson-biblioteker til å konvertere JSON-data til et kart. Vi forstår også hvordan vi kan bruke begge bibliotekene til å konvertere kartdata til JSON.
Anta at vi har en Sample.json-fil i systemet som inneholder følgende data:
{ 'Name' : 'Donal', 'Mobile' : '89346724', 'Designation' : 'Sr. Salesforce Developer', 'Pet' : 'Dog', 'Address' : 'AMERICA' } JACKSON bibliotek
For å konvertere JSON-data til Java Map, tar vi hjelp av JACKSON-biblioteket. Vi legger til følgende avhengighet i POM.xml-filen for å fungere med JACKSON-biblioteket.
com.fasterxml.jackson.core jackson-databind 2.5.3
La oss implementere logikken med å konvertere JSON-data til et kart ved å bruke ObjectMapper, File og TypeReference-klasser.
JacksonConvertJSONToMap.java
// 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('C:\Users\rastogi ji\OneDrive\Desktop\Sample.json'); // 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('Name : ' + userData.get('Name')); System.out.println('Mobile : ' + userData.get('Mobile')); System.out.println('Designation : ' + userData.get('Designation')); System.out.println('Pet : ' + userData.get('Pet')); System.out.println('Address : ' + userData.get('Address')); } catch (Exception e) { // show error message e.printStackTrace(); } } } </map> Produksjon:
La oss ta et annet eksempel på Jackson-biblioteket for å forstå hvordan vi kan konvertere et Java-kart til JSON fordi vi ofte trenger å sende kartdata til API som JSON. Så i dette eksemplet konverterer vi kartdata til JSON og lagrer dem i en fil.
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(); } } } Produksjon:
Gson bibliotek
Gson bibliotek er et annet bibliotek som vi kan bruke til å konvertere JSON-data til kart eller kartdata til JSON. For å bruke Gson-biblioteket må vi legge til følgende avhengighet i POM.xml-filen vår.
k nærmeste nabo
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 = 'C:\Users\rastogi ji\OneDrive\Desktop\Sample.json'; 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('Name : ' + userData.get('Name')); System.out.println('Mobile : ' + userData.get('Mobile')); System.out.println('Designation : ' + userData.get('Designation')); System.out.println('Pet : ' + userData.get('Pet')); System.out.println('Address : ' + userData.get('Address')); } catch (IOException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } } } </hashmap> Produksjon:
La oss ta et annet eksempel på Gson-biblioteket for å forstå hvordan du konverterer et Java-kart til JSON. Å bruke Gson-biblioteket er litt annerledes enn Jackson-biblioteket.
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(); } } } Produksjon:
