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1. Overview

In this quick article, we’re looking at differences between the HTTP PUT and PATCH verbs and at the semantics of the two operations.

We’ll use Spring to implement two REST endpoints that support these two types of operations, and to better understand the differences and the right way to use them.

2. When to use PUT and When PATCH?

Let’s start with a simple, and slightly simple statement.

When a client needs to replace an existing Resource entirely, they can use PUT. When they’re doing a partial update, they can use HTTP PATCH.

For instance, when updating a single field of the Resource, sending the complete Resource representation might be cumbersome and utilizes a lot of unnecessary bandwidth. In such cases, the semantics of PATCH make a lot more sense.

Another important aspect to consider here is idempotence; PUT is idempotent; PATCH can be, but isn’t required to. And, so – depending on the semantics of the operation we’re implementing, we can also choose one or the other based on this characteristic.

3. Implementing PUT and PATCH Logic

Let’s say we want to implement the REST API for updating a HeavyResource with multiple fields:

public class HeavyResource {
    private Integer id;
    private String name;
    private String address;
    // ...

First, we need to create the endpoint that handles a full update of the resource using PUT:

@PutMapping("/heavyresource/{id}")
public ResponseEntity<?> saveResource(@RequestBody HeavyResource heavyResource,
  @PathVariable("id") String id) {
    heavyResourceRepository.save(heavyResource, id);
    return ResponseEntity.ok("resource saved");
}

This is a standard endpoint for updating resources.

Now, let’s say that address field will often be updated by the client. In that case, we don’t want to send the whole HeavyResource object with all fields, but we do want the ability to only update the address field – via the PATCH method.

We can create a HeavyResourceAddressOnly DTO to represent a partial update of the address field:

public class HeavyResourceAddressOnly {
    private Integer id;
    private String address;
    
    // ...
}

Next, we can leverage the PATCH method to send a partial update:

@PatchMapping("/heavyresource/{id}")
public ResponseEntity<?> partialUpdateName(
  @RequestBody HeavyResourceAddressOnly partialUpdate, @PathVariable("id") String id) {
    
    heavyResourceRepository.save(partialUpdate, id);
    return ResponseEntity.ok("resource address updated");
}

With this more granular DTO, we can send the field we need to update only – without the overhead of sending whole HeavyResource.

If we have a large number of these partial update operations, we can also skip the creation of a custom DTO for each out – and only use a map:

@RequestMapping(value = "/heavyresource/{id}", method = RequestMethod.PATCH, consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> partialUpdateGeneric(
  @RequestBody Map<String, Object> updates,
  @PathVariable("id") String id) {
    
    heavyResourceRepository.save(updates, id);
    return ResponseEntity.ok("resource updated");
}

This solution will give us more flexibility in implementing API; however, we do lose a few things as well – such as validation.

4. Testing PUT and PATCH

Finally, let’s write tests for both HTTP methods. First, we want to test the update of the full resource via PUT method:

mockMvc.perform(put("/heavyresource/1")
  .contentType(MediaType.APPLICATION_JSON_VALUE)
  .content(objectMapper.writeValueAsString(
    new HeavyResource(1, "Tom", "Jackson", 12, "heaven street")))
  ).andExpect(status().isOk());

Execution of a partial update is achieved by using the PATCH method:

mockMvc.perform(patch("/heavyrecource/1")
  .contentType(MediaType.APPLICATION_JSON_VALUE)
  .content(objectMapper.writeValueAsString(
    new HeavyResourceAddressOnly(1, "5th avenue")))
  ).andExpect(status().isOk());

We can also write a test for a more generic approach:

HashMap<String, Object> updates = new HashMap<>();
updates.put("address", "5th avenue");

mockMvc.perform(patch("/heavyresource/1")
    .contentType(MediaType.APPLICATION_JSON_VALUE)
    .content(objectMapper.writeValueAsString(updates))
  ).andExpect(status().isOk());

5. Handling Partial Requests With Null Values

When we are writing an implementation for a PATCH method, we need to specify a contract of how to treat cases when we get null as a value for the address field in the HeavyResourceAddressOnly. 

Suppose that client sends the following request:

{
   "id" : 1,
   "address" : null
}

Then we can handle this as setting a value of the address field to null or just ignoring such request by treating it as no-change.

We should pick one strategy for handling null and stick to it in every PATCH method implementation.

6. Conclusion

In this quick tutorial, we focused on understanding the differences between the HTTP PATCH and PUT methods.

We implemented a simple Spring REST controller to update a Resource via PUT method and a partial update using PATCH.

The implementation of all these examples and code snippets can be found in the GitHub project – this is a Maven project, so it should be easy to import and run as it is.

Go deeper into building a REST API with Spring:

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Lakshman
Guest

Cool article. If I am using Elasticsearch, then elasticsearch can also perform partial document upserts. Would I still need to use PATCH in this scenario?. I can use PUT here?

Grzegorz Piwowarek
Guest

If you really want, you can even use GET with parameters 🙂 but if you want to stick to the idiomatic way, use PATCH

Eugen Paraschiv
Guest

Hey Lakshman,
Well, that’s an interesting and complex question.
If you’re using the Elasticsearch API directly, than you can find the exact verbs in their documentation of course, but generally, no – they don’t use PATCH.
If you’re building your own API and you’re only using ES in the back-end, then sure, you can definitely expose a PATCH operation.
Hope that helps. Cheers,
Eugen.

Grzegorz Piwowarek
Guest

Eugen is right, if you want to interact directly with the Elasticsearch, just double check their documentation. The real choice you have when building your own API

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