如果将在SpringWebFlux中使用的Entity类的成员设为final，会出现错误

这已经完全是我自己的备忘录了。虽然可以在Twitter上留下，但为了保留，这里留一份。

如果随意创建Spring Data MongoDB中使用的实体类，会出现一些错误。
会出现一些要求提供Setter方法的错误。
试着加上Setter方法确实能成功运行。
但只是执行findOne然后返回结果，为什么会出现这种情况？？？

This application has no configured error view, so you are seeing this as a fallback.

Mon Feb 18 06:27:46 JST 2019
There was an unexpected error (type=Internal Server Error, status=500).
No accessor to set property @org.springframework.data.annotation.Id()private final java.lang.Integer com.example.demo.Flower.id!
java.lang.UnsupportedOperationException: No accessor to set property @org.springframework.data.annotation.Id()private final java.lang.Integer com.example.demo.Flower.id!
    at com.example.demo.Flower_Accessor_jjo0e1.setProperty(Unknown Source)
    at org.springframework.data.mapping.model.ConvertingPropertyAccessor.setProperty(ConvertingPropertyAccessor.java:61)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.readAndPopulateIdentifier(MappingMongoConverter.java:326)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.populateProperties(MappingMongoConverter.java:289)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:275)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:245)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:194)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:190)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:78)
    at org.springframework.data.mongodb.core.ReactiveMongoTemplate$ReadDocumentCallback.doWith(ReactiveMongoTemplate.java:2910)
    at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:107)
    at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onNext(FluxOnAssembly.java:353)
    at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:76)
    at com.mongodb.reactivestreams.client.internal.ObservableToPublisher$1.onNext(ObservableToPublisher.java:68)
...

稍微改动一下代码，再仔细读读错误信息…
啊，原来如果把它设为final，在转换这一部分会有问题。我大概了解了。

没有setter，只要把final去掉就可以工作了。背后有很多事情呢。

@Document
public class Flower {
    @Id
    private Integer id;
    private String name;
    private String color;

    Flower(){
        id = null;
        name = "";
        color = "";
    }
    Flower(int id, String name, String color){
        this.id = id;
        this.name = name;
        this.color = color;
    }

    public Integer getId() {
        return this.id;
    }
    public String getName() {
        return this.name;
    }
    public String getColor() {
        return this.color;
    }
}