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JavaInterviewPoint

Java Development Tutorials

How to Convert JSON to / from Java Map using JACKSON

November 14, 2016 by javainterviewpoint Leave a Comment

In this Jackson example we will learn how to convert JSON to Java Map and vice versa (Convert Java Map to JSON) using Jackson API. Since JSON will be in the form of Key Value pairs it can be easily converted to Java map.

Folder Structure:

Convert JSON to Java

  1. Create a new Java Project  “JacksonJSONTutorial” and create a package for our src files “com.javainterviewpoint“
  2. Add the required libraries to the build path. Java Build Path ->Libraries ->Add External JARs and add the below jars.

jackson-core.jar
jackson-annotations.jar
jackson-databind.2.8.4.jar

if you are running on maven add the below dependency to your pom.xml

 <dependencies>
  <dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-databind</artifactId>
   <version>2.8.4</version>
 </dependency>
</dependencies>
  1. Create the Java classes JSONFileToMap.java, JSONToMap.java,MapToJSON.java and MapToJSONFile.java under  com.javainterviewpoint folder.

Other Posts which you may like …

  • Jackson 2 JSON Parser – Convert JSON to/from Java Object
  • How to Convert JSON to / from Java Map using JACKSON
  • Jackson Tree Model Example – JsonNode
  • Jackson Streaming API Example | Read and Write JSON
  • Jackson JSON Example | ObjectMapper and @JSONView
  • How to Parse JSON to/from Java Object using Boon JSON Parser
  • How to Read and Write JSON using GSON
  • How to write JSON object to File in Java?
  • How to read JSON file in Java – JSONObject and JSONArray
  • Jersey Jackson JSON Tutorial
  • Spring REST Hello World Example – JSON and XML responses
  • How to Convert Java Object to JSON using JAXB
  • JAX-RS REST @Consumes both XML and JSON Example
  • JAX-RS REST @Produces both XML and JSON Example

Convert JSON to Java Map

Read JSON String and convert JSON String to Java Map

package com.javainterviewpoint;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JSONToMap
{
    public static void main(String args[])
    {
        try
        {
            ObjectMapper mapper = new ObjectMapper();
            String jsonString = "{\"name\":\"JavaInterviewPoint\", \"department\":\"blogging\"}";
            
            Map<String, Object> jsonMap = new HashMap<String, Object>();
            
            // convert JSON string to Map
            jsonMap = mapper.readValue(jsonString,
                    new TypeReference<Map<String, String>>(){});
            
            System.out.println(jsonMap);
        }
        catch(IOException ie)
        {
            ie.printStackTrace();
        }

    }
}

Output :

{name=JavaInterviewPoint, department=blogging}

Convert Java Map to JSON String

package com.javainterviewpoint;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.databind.ObjectMapper;

public class MapToJSON
{
    public static void main(String args[])
    {
        try
        {
            ObjectMapper mapper = new ObjectMapper();
            String jsonString = "";
            
            Map<String, Object> jsonMap = new HashMap<String, Object>();
            jsonMap.put("name","JavaInterviewPoint");
            jsonMap.put("department","IT");
           
            // convert Map to JSON String
            jsonString = mapper.writeValueAsString(jsonMap);
            
            System.out.println(jsonString);
        }
        catch(IOException ie)
        {
            ie.printStackTrace();
        }

    }
}

Output:

{"name":"JavaInterviewPoint","department":"IT"}

Convert JSON File to Java Map

package com.javainterviewpoint;

import java.io.File;
import java.io.IOException;
import java.util.Map;

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JSONFileToMap
{
    public static void main(String args[])
    {
        try
        {
            ObjectMapper mapper = new ObjectMapper();

            // read JSON from a file
            Map<String, Object> jsonMap = mapper.readValue(new File(
                    "D:\\test.json"),
                    new TypeReference<Map<String, Object>>(){});
            
            System.out.println("*** JSON File Contents ***");
            System.out.println("Name : "+jsonMap.get("name"));
            System.out.println("Name : "+jsonMap.get("department"));
            System.out.println("Name : "+jsonMap.get("age"));
            
        } catch (IOException ie)
        {
            ie.printStackTrace();
        }

    }
}

Output:

*** JSON File Contents ***
Name : JavaInterviewPoint
Name : IT
Name : 22

Convert Java Map to JSON File

package com.javainterviewpoint;

import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.databind.ObjectMapper;

public class MapToJSONFile
{
    public static void main(String args[])
    {
        try
        {
            ObjectMapper mapper = new ObjectMapper();
            
            Map<String, Object> jsonMap = new HashMap<String, Object>();
            jsonMap.put("name","JavaInterviewPoint");
            jsonMap.put("department","IT");
            jsonMap.put("age",22);
            
            // convert map to JSON File
            mapper.writeValue(new File("D:\\test.json"),jsonMap);
            
            System.out.println("File Write Completed");
        }
        catch(IOException ie)
        {
            ie.printStackTrace();
        }
    }
}

Output :
After execution of the above class, we will be having a test.json created with the below content

{"name":"JavaInterviewPoint","department":"IT","age":22}

asdf

Filed Under: J2EE, Java, JSON Tagged With: Convert JSON to Java

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