Java 中将 JSON 转换为 Map

2025年9月4日 | 阅读5分钟

Java 提供了两个非常强大的库来处理 JSON 数据，即 **JACKSON** 和 **Gson** 库。为了方便处理返回的 JSON 数据，我们经常需要将 JSON 响应转换为 Map。

由于 JSON 格式本质上是键值对的集合，而 Map 也以键值对的形式存储数据，因此我们可以轻松地将 JSON 数据转换为 Map。

让我们了解如何使用 JACKSON 和 Gson 库将 JSON 数据转换为 Map。我们还将了解如何使用这两个库将 Map 数据转换为 JSON。

假设系统中有一个 Sample.json 文件，其中包含以下数据：

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

JACKSON 库

为了将 JSON 数据转换为 Java Map，我们借助了 JACKSON 库。我们在 POM.xml 文件中添加以下依赖项来使用 JACKSON 库。

<dependencies>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.5.3</version>
    </dependency>
</dependencies>

让我们使用 ObjectMapper、File 和 TypeReference 类来实现使用 Jackson 库将 JSON 数据转换为 Map 的逻辑。

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<String, Object> userData = mapper.readValue(
            		fileObj, new TypeReference<Map<String, Object>>() {
            }); 
            // 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();
        } 
    }
}

输出

让我们以 Jackson 库的另一个示例来理解如何将 Java Map 转换为 JSON，因为我们经常需要将 Map 数据作为 JSON 传递给 API。因此，在本例中，我们将 Map 数据转换为 JSON 并将其存储在文件中。

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<String, Object> userData = new HashMap<String, Object>();
        
        // 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();
        } 
    }
}

输出

Gson 库

**Gson** 库是另一个我们可以用来将 JSON 数据转换为 Map 或将 Map 数据转换为 JSON 的库。为了使用 Gson 库，我们需要在 POM.xml 文件中添加以下依赖项。

<dependencies>
 	<dependency>
 		<groupId>com.google.code.gson</groupId>
 		<artifactId>gson</artifactId>
 		<version>2.8.3</version>
 	</dependency>
</dependencies>

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<String, Object> userData = new Gson().fromJson(result, new TypeToken<HashMap<String, Object>>() {
	    		        }.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();
		}
	}
}

输出

让我们以 Gson 库的另一个示例来理解如何将 Java Map 转换为 JSON。使用 Gson 库与 Jackson 库略有不同。

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<String, Object> userData = new HashMap<String, Object>();
	     	// 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();
      		}
  	}
}

输出