Jackson failed to convert request element - spring

Question

I'm using Spring to craft a REST API which exposes a POST endpoint. I'm able to reach the endpoint, but I'm having trouble reading the request body.
The following code works: payload contains the object sent.
#RestController
public class RestController {
#RequestMapping(value = "/endpoint")
public ResponseEntity endpoint(#RequestParam("payload") String str) throws IOException {
ObjectMapper objectMapper = new ObjectMapper();
Payload payload = objectMapper.readValue(str, Payload.class);
return ResponseEntity.status(HttpStatus.OK).build();
}
}
However, the following code DOES NOT works: it throws an exception.
#RestController
public class RestController {
#RequestMapping(value = "/endpoint")
public ResponseEntity endpoint(#RequestParam("payload") Payload payload) throws IOException {
return ResponseEntity.status(HttpStatus.OK).build();
}
}
The exception:
Failed to convert request element: org.springframework.web.method.annotation.MethodArgumentConversionNotSupportedException: Failed to convert value of type 'java.lang.String' to required type 'beans.Payload'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'beans.Payload': no matching editors or conversion strategy found
Why the latter doesn't work? I thought Spring decode request parameters in the same way...
UPDATE: my Payload class:
#JsonIgnoreProperties(ignoreUnknown = true)
public class Payload {
#JsonProperty("type")
private String type;
#JsonProperty("callback_id")
private String callbackId;
#JsonProperty("message_ts")
private String message_ts;
#JsonProperty("response_url")
private String responseUrl;
protected Payload() {}
public String getType() {
return type;
}
public String getCallbackId() {
return callbackId;
}
public String getMessage_ts() {
return message_ts;
}
public String getResponseUrl() {
return responseUrl;
}
}
UPDATE: I'm testing the endpoint with Postman. This is what I'm sending:
KEY VALUE
payload { "type": "test" }
and this is the error I got:
{
"timestamp": "2018-08-28T10:38:33.133+0000",
"status": 415,
"error": "Unsupported Media Type",
"message": "Content type 'multipart/form-data;boundary=--------------------------586093407866564427326096;charset=UTF-8' not supported",
"path": "/endpoint"
}

Answer 1

Payload constructor should not be protected. It should be public.
Change it to
Public PayLoad(){}
Otherwise, controllers cant create a payload object when mapping is done.

Answer 2

Use #RequestBody instead of #RequestParam. Your Payload is in post body and #RequestBody annotation will deserialize it to payload.

Answer 3

Just get rid of protected Payload() {} . As you don't have any parameterized constructer you are fine, Java compiler will take care of adding the default constructer to the compiled byte code.
And you need to change this
Controller method
#RestController
public class RestController {
#RequestMapping(value = "/endpoint")
public ResponseEntity endpoint(#RequestParam("payload") Payload payload) throws IOException {
return ResponseEntity.status(HttpStatus.OK).build();
}
}
Changes
a. Change HTTP request method to POST it, instead of GET . (method = RequestMethod.POST) .
b. Change Payload to a message body insteda of request param (#RequestParam("payload") Payload payload --> #RequestBody Payload payload ).
Change it as
#RequestMapping(value = "/endpoint", method = RequestMethod.POST)
public ResponseEntity endpoint(#RequestBody Payload payload) throws IOException {
return ResponseEntity.status(HttpStatus.OK).build();
}

Answer 4

Your URL patterns are mal-configured. Try,
#RestController
#RequestMapping(value = "/")
public class PayLoadController {
#RequestMapping(value = "endpoint/",method = RequestMethod.POST)
public ResponseEntity endpoint(#RequestBody Payload payload) throws IOException {
return ResponseEntity.status(HttpStatus.OK).build();
}}
Just copy paste this code and rename controller file name.
Then post your data to,
localhost:8080/endpoint/