未注释的参数覆盖@NonNullApi 参数

Question

我一直在寻找其他问题，但我仍然不明白这里发生了什么。我有这个 class:

package com.test.service.database.converter;

import com.test.service.database.dao.DocumentType;
import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;

import java.util.Optional;

@Component
public class DocumentStringConverter implements Converter<DocumentType, String> {

    @Override
    public String convert(DocumentType documentType) {
        return Optional.ofNullable(documentType).map(DocumentType::type).orElse(null);
    }
}

它实现了这个 Spring 接口：

package org.springframework.core.convert.converter;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

@FunctionalInterface
public interface Converter<S, T> {

    @Nullable
    T convert(S source);

    default <U> Converter<S, U> andThen(Converter<? super T, ? extends U> after) {
        Assert.notNull(after, "After Converter must not be null");
        return (S s) -> {
            T initialResult = convert(s);
            return (initialResult != null ? after.convert(initialResult) : null);
        };
    }
}

并且 IntelliJ 对

中的参数发出警告

public String convert(DocumentType documentType) {

表示

Not annotated parameter overrides @NonNullApi parameter

documentType – the source object to convert, which must be an instance of S (never null)

这是为什么？这是什么意思，因为 Converter 被注释为 @Nullable？我该如何解决这个警告？

Answer 1

https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/lang/NonNullApi.html:

A common Spring annotation to declare that parameters and return values are to be considered as non-nullable by default for a given package.

这是org/springframework/core/convert/converter/package-info.java：

/**
 * SPI to implement Converters for the type conversion system.
 */
@NonNullApi       // !!!!!!!!!!!!
@NonNullFields
package org.springframework.core.convert.converter;

@NonNullApi 可以在方法级别使用 @Nullable 注释覆盖，以防止对可能 return 为空的方法发出警告，这就是您在 [=15 中看到的=]:

@FunctionalInterface
public interface Converter<S, T> {

    /**
     * Convert the source object of type {@code S} to target type {@code T}.
     * @param source the source object to convert, which must be an instance of {@code S} (never {@code null})
     * @return the converted object, which must be an instance of {@code T} (potentially {@code null})
     * @throws IllegalArgumentException if the source cannot be converted to the desired target type
     */
    @Nullable            // !!!!!!!!!!
    T convert(S source);

在覆盖方法时，您没有指定 @Nullable 注释，因此没有指定警告。

未注释的参数覆盖@NonNullApi 参数

Not annotated parameter overrides @NonNullApi parameter

java

spring-boot

intellij-idea

nullable