Spring REST and PATCH method

Question

I'm using SpringBoot and Spring REST. I would like to understand the HTTP PATCH method to update properties of my Model

Is there any good tutorial explaining how to make it works ?

• HTTP PATCH method and body to be Send
• Controller method and how to manage the update operation

Answer 1

I've noticed that many of the provided answers are all JSON patching or incomplete answers. Below is a full explanation and example of what you need with functioning real world code

First, PATCH is a selective PUT. You use it to update any number of fields for an object or list of objects. In a PUT you typically send the entire object with whatever updates.

PATCH /object/7

{
   "objId":7,
   "objName": "New name"
}

PUT /object/7

{
   "objId":7,
   "objName": "New name",
   "objectUpdates": true,
   "objectStatus": "ongoing",
   "scoring": null,
   "objectChildren":[
       {
          "childId": 1
       },
     ............ 
}

This allows you to update records without huge amounts of endpoints. For example, with above, to update scoring you need object/{id}/scoring, then to update name you need object/{id}/name. Literally one endpoint for every item or you require the front end to post the entire object for every update. If you have a huge object, this can take a lot of network time or mobile data that is unnecessary. The patch lets you have 1 endpoint with the minimal object property sends that a mobile platform should use.

here is an example of a real world use for patch:

@ApiOperation(value = "Patch an existing claim with partial update")
@RequestMapping(value = CLAIMS_V1 + "/{claimId}", method = RequestMethod.PATCH)
ResponseEntity<Claim> patchClaim(@PathVariable Long claimId, @RequestBody Map<String, Object> fields) {

    // Sanitize and validate the data
    if (claimId <= 0 || fields == null || fields.isEmpty() || !fields.get("claimId").equals(claimId)){
        return new ResponseEntity<>(HttpStatus.BAD_REQUEST); // 400 Invalid claim object received or invalid id or id does not match object
    }

    Claim claim = claimService.get(claimId);

    // Does the object exist?
    if( claim == null){
        return new ResponseEntity<>(HttpStatus.NOT_FOUND); // 404 Claim object does not exist
    }

    // Remove id from request, we don't ever want to change the id.
    // This is not necessary, you can just do it to save time on the reflection
    // loop used below since we checked the id above
    fields.remove("claimId");

    fields.forEach((k, v) -> {
        // use reflection to get field k on object and set it to value v
        // Change Claim.class to whatver your object is: Object.class
        Field field = ReflectionUtils.findField(Claim.class, k); // find field in the object class
        field.setAccessible(true); 
        ReflectionUtils.setField(field, claim, v); // set given field for defined object to value V
    });

    claimService.saveOrUpdate(claim);
    return new ResponseEntity<>(claim, HttpStatus.OK);
}

The above can be confusing for some people as newer devs don't normally deal with reflection like that. Basically, whatever you pass this function in the body, it will find the associated claim using the given ID, then ONLY update the fields you pass in as a key value pair.

Example body:

PATCH /claims/7

{
   "claimId":7,
   "claimTypeId": 1,
   "claimStatus": null
}

The above will update claimTypeId and claimStatus to the given values for claim 7, leaving all other values untouched.

So the return would be something like:

{
   "claimId": 7,
   "claimSrcAcctId": 12345678,
   "claimTypeId": 1,
   "claimDescription": "The vehicle is damaged beyond repair",
   "claimDateSubmitted": "2019-01-11 17:43:43",
   "claimStatus": null,
   "claimDateUpdated": "2019-04-09 13:43:07",
   "claimAcctAddress": "123 Sesame St, Charlotte, NC 28282",
   "claimContactName": "Steve Smith",
   "claimContactPhone": "777-555-1111",
   "claimContactEmail": "[email protected]",
   "claimWitness": true,
   "claimWitnessFirstName": "Stan",
   "claimWitnessLastName": "Smith",
   "claimWitnessPhone": "777-777-7777",
   "claimDate": "2019-01-11 17:43:43",
   "claimDateEnd": "2019-01-11 12:43:43",
   "claimInvestigation": null,
   "scoring": null
}

As you can see, the full object would come back without changing any data other than what you want to change. I know there is a bit of repetition in the explanation here, I just wanted to outline it clearly.