How Can I Generate Java Classes from JSON Data Using the jsonschema2pojo Maven Plugin?

Can You Generate Java Classes from JSON?

As a Java developer, you may encounter situations where you need to generate Java source files from JSON data. This can be a valuable technique for creating data transfer objects (DTOs) or POJOs (Plain Old Java Objects) that mirror JSON structures.

Here's how to accomplish this using the jsonschema2pojo Maven plugin:

Maven Plugin Configuration

1. Add the following plugin configuration to your pom.xml file:

<plugin>
    <groupId>org.jsonschema2pojo</groupId>
    <artifactId>jsonschema2pojo-maven-plugin</artifactId>
    <version>1.0.2</version>
    <configuration>
        <sourceDirectory>${basedir}/src/main/resources/schemas</sourceDirectory>
        <targetPackage>com.myproject.jsonschemas</targetPackage>
        <sourceType>json</sourceType>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>generate</goal>
            </goals>
        </execution>
    </executions>
</plugin>

• sourceDirectory: Specifies the location of your JSON schema files.
• targetPackage: Defines the package name for your generated classes.
• sourceType: Indicates that the source is JSON (remove this line if using JSON schemas).

Example JSON Data

Consider the following JSON data:

{
  "firstName": "John",  
  "lastName": "Smith",  
  "address": {  
    "streetAddress": "21 2nd Street",  
     "city": "New York"
  }
}

Generated Java Classes

Upon running the Maven plugin, the following Java classes will be generated:

class Address  {
    JSONObject mInternalJSONObject;
     
    Address (JSONObject json){
        mInternalJSONObject = json;
    }
     
    String  getStreetAddress () {
        return mInternalJSONObject.getString("streetAddress");
    }
    
    String  getCity (){
        return mInternalJSONObject.getString("city");
    }
}

class Person {        
    JSONObject mInternalJSONObject;
    
    Person (JSONObject json){
        mInternalJSONObject = json;
    }
    
    String  getFirstName () {
        return mInternalJSONObject.getString("firstName");
    }
    
    String  getLastName (){
        return mInternalJSONObject.getString("lastName");
    }
    
    Address getAddress (){
        return Address(mInternalJSONObject.getString("address"));
    }
}

These generated classes provide easy access to the data in the JSON structure, enabling you to work with the data in a convenient and object-oriented manner.

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