How to Convert JSON Strings to HashMaps in Java

To convert a JSON string to a Java HashMap, you can use libraries such as Jackson or Google Gson. Below are examples using both:

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Using Jackson

The Jackson library provides a convenient way to convert JSON strings to Java objects, including HashMap.

1. Add the dependency:

   • For Maven:

     
     <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
       <version>2.x</version>
     </dependency>
     

   • For Gradle:

     
     implementation 'com.fasterxml.jackson.core:jackson-databind:2.x'
     

2. Code Example:

   
   import com.fasterxml.jackson.databind.ObjectMapper;
   import java.util.HashMap;
   import java.util.Map;
   
   public class JsonToHashMap {
       public static void main(String[] args) {
           String jsonString = "{\"key1\":\"value1\", \"key2\":\"value2\"}";
   
           ObjectMapper objectMapper = new ObjectMapper();
           try {
               // Convert JSON string to HashMap
               HashMap<String, String> map = objectMapper.readValue(jsonString, HashMap.class);
               System.out.println("HashMap: " + map);
           } catch (Exception e) {
               e.printStackTrace();
           }
       }
   }
   

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Using Google Gson

Google Gson is another popular library for JSON parsing in Java.

1. Add the dependency:

   • For Maven:

     
     <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
       <version>2.x</version>
     </dependency>
     

   • For Gradle:

     
     implementation 'com.google.code.gson:gson:2.x'
     

2. Code Example:

   
   import com.google.gson.Gson;
   import java.util.HashMap;
   
   public class JsonToHashMap {
       public static void main(String[] args) {
           String jsonString = "{\"key1\":\"value1\", \"key2\":\"value2\"}";
   
           Gson gson = new Gson();
           try {
               // Convert JSON string to HashMap
               HashMap<String, String> map = gson.fromJson(jsonString, HashMap.class);
               System.out.println("HashMap: " + map);
           } catch (Exception e) {
               e.printStackTrace();
           }
       }
   }
   

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Output:

For the input JSON string:

{"key1":"value1", "key2":"value2"}

The output for both approaches would be:

HashMap: {key1=value1, key2=value2}

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Choosing Between Jackson and Gson:

• Jackson offers more features and is widely used for enterprise-level applications.
• Gson is lightweight and simpler to use for basic JSON handling.