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Learn how to build a REST API in Spring Boot using @PutMapping and ResponseEntity. This article walks through:

• Creating a PUT endpoint to update a resource
• Using ResponseEntity to return HTTP 200 or 404
• Handling request data and in-memory persistence
• Returning JSON responses for successful and failed updates

Perfect for developers building RESTful services with proper status handling.

🔧 Scenario: Update an Item via PUT Request

Let’s say we’re managing items using a REST API. You want to:

• Accept an updated Item via a PUT request
• Return 200 OK if updated successfully
• Return 404 Not Found if the item doesn't exist

✅ Step 1: Create the Item Class

java

public class Item {
    private Long id;
    private String name;

    // Getters & Setters
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

✅ Step 2: Create the Service Layer

java

import org.springframework.stereotype.Service;
import java.util.*;

@Service
public class ItemService {
    private Map<Long, Item> itemRepository = new HashMap<>();

    public ItemService() {
        // Seed data
        itemRepository.put(1L, new Item() {{ setId(1L); setName("Item1"); }});
        itemRepository.put(2L, new Item() {{ setId(2L); setName("Item2"); }});
    }

    public Item updateItem(Long id, Item item) {
        if (itemRepository.containsKey(id)) {
            item.setId(id); // Ensure consistent ID
            itemRepository.put(id, item);
            return item;
        }
        return null;
    }
}

✅ Step 3: Create the REST Controller

java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.*;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api/items")
public class ItemController {

    @Autowired
    private ItemService itemService;

    @PutMapping("/{id}")
    public ResponseEntity<Item> updateItem(@PathVariable Long id, @RequestBody Item item) {
        Item updated = itemService.updateItem(id, item);
        if (updated != null) {
            return new ResponseEntity<>(updated, HttpStatus.OK);
        } else {
            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
        }
    }
}

📡 Example API Request

PUT Request to Update Item with ID 1

• URL: http://localhost:8080/api/items/1
• Method: PUT
• Body:

json

{
  "name": "Updated Item Name"
}

🟢 If Item Exists

Response:

json

{
  "id": 1,
  "name": "Updated Item Name"
}

Status Code: 200 OK

🔴 If Item Does Not Exist

Response:

css

(empty body)

Status Code: 404 Not Found

📌 Summary Table

ComponentDescription@PutMappingHandles PUT request to update dataResponseEntity<T>Controls HTTP status and response bodyHttpStatus.OKReturned if update is successfulHttpStatus.NOT_FOUNDReturned if the resource does not exist