在静态方法中使用Javasupplier/Function传递方法

Question

我有几个类:

public class TextContent {
    private String externalId;
}

public class ImageContent {
    private String externalImageId;
}

public static void validateImageInput(List<ImageContent> imageAssets, String requestId) {
    if(CollectionUtils.isEmpty(imageAssets)) {
        throw some Error;
    }

    Set<String> uniqueIds = imageAssets.stream().map(ImageContent::externalImageId).collect(Collectors.toSet());
    if(uniqueIds.size() != imageAssets().size()) {
        throw some Error;
    }

    //Do some processing
}

public static void validateTextInput(List<TextContent> textAssets, String requestId) {
    if(CollectionUtils.isEmpty(textAssets)) {
        throw some Error;
    }

    Set<String> uniqueIds = textAssets.stream().map(ImageContent::externalId).collect(Collectors.toSet());
    if(uniqueIds.size() != textAssets().size()) {
        throw some Error;
    }

    //Do some processing
}

如您所见，这两个类的验证部分是相同的。我想尝试使它成为一种通用方法。为此：

public static void validateInput(List<?> assets, String requestId, Supplier<String> mapper) {
    if(CollectionUtils.isEmpty(assets)) {
        throw some error;
    }

    Set<String> uniqueIds = assets.stream().map(x -> mapper.get()).collect(Collectors.toSet());
    if(uniqueIds.size() != assets().size()) {
        throw some Error;
    }
}

然后用 :

调用它

public static void validateAllInputs(List<ImageContent> imageAssets, List<TextContent> textAssets, String requestId) {
    validateInput(imageAssets, requestId, ImageContent::externalImageId);
    validateInput(textAssets, requestId, TextContent::externalId);
    doSomeProcessingWithText(textAssets, requestId);
    doSomeProcessingWithImage(imageAssets, requestId);
}

但我收到一条错误消息 Non static method cannot be referenced from static context.

编辑：我尝试的另一个选项是使用 Function ，即我传入 <TextContent, String> mapper 并在我的流中使用 .map(x -> mapper.apply(x)。但是，当我尝试将它传递给函数 validateInputs(textAsset, requestId, TextContent::externalId) 时，我得到了同样的错误 Non static method cannot be referenced from static context.

Answer 1

我建议让这两种类型实现相同的接口：

public interface Content {
    public String getExternalId();

    public static String externalId(Content content) {
        return content == null ? null : content.getExternalId();
    }
}

然后将 validateInput 签名更改为：

public static void validateInput(List<? extends Content> assets, String requestId) {
    if(CollectionUtils.isEmpty(assets)) {
        throw some error;
    }

    Set<String> uniqueIds = assets.stream().map(Content::externalId).collect(Collectors.toSet());
    if(uniqueIds.size() != assets.size()) {
        throw some error;
    }

    //Do some processing
}

如果你还想在这里提取一个常用的方法，你可以这样写：

public static <E> void commonValidate(List<E> assets, String requestId, Function<E, String> mapper) {
    Set<String> uniqueIds = assets.stream().map(mapper).collect(Collectors.toSet());
}

Answer 2

在泛型的帮助下完成：

public static <T> void validateInput(List<T> assets, String requestId, Function<T, String> mapper) {
    if(CollectionUtils.isEmpty(assets)) {
        throw some error;
    }

    Set<String> uniqueIds = assets.stream().map(mapper).collect(Collectors.toSet());
    if(uniqueIds.size() != assets().size()) {
        throw some Error;
    }
}

然后调用它：

validateInput(imageAssets, requestId, ImageContent::externalImageId);

在静态方法中使用Javasupplier/Function传递方法

Using Java supplier/Function to pass method in static method

java

java-8

supplier