MappingJackson2MessageConverter doesn't check if payload assignable to target type

[tdorzhi]

spring-framework/spring-messaging/src/main/java/org/springframework/messaging/converter/MappingJackson2MessageConverter.java

Line 229 in 7cde283

return this.objectMapper.readValue(payload.toString(), javaType);

Given object with usual toString implementation (for example Foo(field1=SomeString) and sending it to messageChannel using MessageBuilder#withPayload factory method results in above mentioned line to be executed, which predictably throws

[rstoyanchev]

Yes we could check if the payload is already an instance of the target class and skip the conversion.