The Adapter Design Pattern

The Adapter design pattern is a structural design pattern.

What is structural design pattern ?

Structural Design Patterns help in building the structure of a software system. They focus on how objects and classes work together to form a bigger system.

Adapter design pattern is one of the structural design pattern which helps two incompatible systems to work together without modifying their existing code. It acts like a bridge between them.

Example:

A system currently receives and processes data in XML format. However, a new third-party library only supports JSON. Instead of modifying the entire system, we use the Adapter Pattern to convert XML to JSON on the fly.

package DesignPatterns.structural.adapter.xmltojsonadapter;

// Existing system that processes XML
public class XMLProcessor {
    public void processXMLData(String xmlData) {
        System.out.println("Processing XML data: " + xmlData);
    }
}

package DesignPatterns.structural.adapter.xmltojsonadapter;

// New system that processes JSON
public class JSONProcessor {
    public void processJSONData(String jsonData) {
        System.out.println("Processing JSON data: " + jsonData);
    }
}

package DesignPatterns.structural.adapter.xmltojsonadapter;

// Adapter: Converts XML to JSON before processing
public class XmlToJsonAdapter {
    private JSONProcessor jsonProcessor;

    public XmlToJsonAdapter(JSONProcessor jsonProcessor) {
        this.jsonProcessor = jsonProcessor;
    }

    public void processXMLData(String xmlData) {
        System.out.println("Adapter: Converting XML to JSON...");

        // Convert XML to JSON
        String jsonData = convertXMLToJSON(xmlData);

        // Process JSON using the JSONProcessor
        jsonProcessor.processJSONData(jsonData);
    }

    private String convertXMLToJSON(String xmlData) {
        System.out.println("Converting XML to JSON...");
        // Example logic (In real cases, use a library like org.json or Jackson)
        return "{ \"converted\": \"" + xmlData + "\" }";
    }
}

package DesignPatterns.structural.adapter.xmltojsonadapter;

public class Client {
    public static void main(String[] args) {
        String xmlData = "<user><name>Nivedita</name></user>";
        JSONProcessor jsonProcessor = new JSONProcessor();

        // Use Adapter to convert and process data
        XmlToJsonAdapter adapter = new XmlToJsonAdapter(jsonProcessor);

        adapter.processXMLData(xmlData);
    }
}

Why Use Adapter Here?

1. The existing system expects XML, but the new library uses JSON.

2. We don’t modify either the XMLProcessor or JSONProcessor.

3. Adapter acts as a bridge, converting XML to JSON before processing.

Pros and Cons of the Adapter Design Pattern