java.io.BufferedReader().map 无法推断 <T> 的类型参数 fromStream(Stream<? extends T>)

Question

场景：Spring WebFlux 触发 CommandLineRunner.run 以便将数据加载到 MongoDb 以进行测试。

目标：在本地启动微服务时，它旨在读取 json 文件并将文档加载到 MongDb。

个人知识："bufferedReader.lines().filter(l -> !l.trim().isEmpty()" 读取每个 json 节点并将其 return 作为流。然后我可以将它映射到 "l" 并访问 get 方法。我想我不必创建一个列表然后流式传输它，因为我已经通过 "new InputStreamReader(getClass().getClassLoader().getResourceAsStream()" 将它作为流加载，并且我假设我可以使用 lines() 因为它的节点将产生一个字符串行。我是在正确的方向还是我搞砸了一些想法？

这是一个 json 示例文件：

{
  "Extrato": {
    "description": "credit",
    "value": "R.000,00",
    "status": 11
  },
  "Extrato": {
    "description": "debit",  
    "value": "R.000,00",
    "status": 99
  }
}

型号

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document
public class Extrato {

    @Id
    private String id;
    private String description;
    private String value;
    private Integer status;

    public Extrato(String id, String description, String value, Integer status) {
        super();
        this.id = id;
        this.description = description;
        this.value = value;
        this.status = status;
    }
... getters and setter accordinly

存储库

import org.springframework.data.mongodb.repository.Query;
import org.springframework.data.repository.reactive.ReactiveCrudRepository;

import com.noblockingcase.demo.model.Extrato;

import reactor.core.publisher.Flux;
import org.springframework.data.domain.Pageable;

public interface ExtratoRepository extends ReactiveCrudRepository<Extrato, String> {
    @Query("{ id: { $exists: true }}")
    Flux<Extrato> retrieveAllExtratosPaged(final Pageable page);
}

从json文件上方加载的命令

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

import com.noblockingcase.demo.model.Extrato;
import com.noblockingcase.demo.repository.ExtratoRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import reactor.core.publisher.Flux;

@Component
public class TestDataLoader implements CommandLineRunner {

    private static final Logger log = LoggerFactory.getLogger(TestDataLoader.class);
    private ExtratoRepository extratoRepository;

    TestDataLoader(final ExtratoRepository extratoRepository) {
        this.extratoRepository = extratoRepository;
    }

    @Override
    public void run(final String... args) throws Exception {
        if (extratoRepository.count().block() == 0L) {
            final LongSupplier longSupplier = new LongSupplier() {
                Long l = 0L;

                @Override
                public long getAsLong() {
                    return l++;
                }
            };
            BufferedReader bufferedReader = new BufferedReader(
                    new InputStreamReader(getClass().getClassLoader().getResourceAsStream("carga-teste.txt")));

//*** THE ISSUE IS NEXT LINE
            Flux.fromStream(bufferedReader.lines().filter(l -> !l.trim().isEmpty())
                    .map(l -> extratoRepository.save(new Extrato(String.valueOf(longSupplier.getAsLong()),
                            l.getDescription(), l.getValue(), l.getStatus()))))
                    .subscribe(m -> log.info("Carga Teste: {}", m.block()));

        }
    }

}

这是 MongoDb 配置，但我认为它不相关

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.mongodb.MongoClientOptions;

@Configuration
public class MongoDbSettings {

    @Bean
    public MongoClientOptions mongoOptions() {
        return MongoClientOptions.builder().socketTimeout(2000).build();
    }

}

如果我尝试我的原始代码并调整它以读取文本文件，我可以成功读取文本文件而不是 json。显然它不符合我的需求，因为我想读取 json 文件。顺便说一句，它可以更清楚地说明我被阻止的地方。

加载-test.txt（https://github.com/jimisdrpc/webflux-worth-scenarious/blob/master/demo/src/main/resources/carga-teste.txt可用）

crédito de R.000,00
débito de R0,00

使用简单文本文件的代码片段

    BufferedReader bufferedReader = new BufferedReader(
            new InputStreamReader(getClass().getClassLoader().getResourceAsStream("carga-teste.txt")));
    Flux.fromStream(bufferedReader.lines().filter(l -> !l.trim().isEmpty())
            .map(l -> extratoRepository
                    .save(new Extrato(String.valueOf(longSupplier.getAsLong()), "Qualquer descrição", l))))
            .subscribe(m -> log.info("Carga Teste: {}", m.block()));

整个项目成功读取文本文件：https://github.com/jimisdrpc/webflux-worth-scenarious/tree/master/demo

Docker 为引导编写 MongoDb https://github.com/jimisdrpc/webflux-worth-scenarious/blob/master/docker-compose.yml

总而言之，我的问题是：在 CommandLineRunner.run()

期间，我没有弄清楚如何读取 json 文件并将数据插入 MongoDb

Answer 1

我找到了一个带有 Flux::using Flux::fromStream 的示例可以帮助实现此目的。这会将您的文件读入 Flux，然后您可以订阅并使用 .flatmap 或其他内容进行处理。来自 Javadoc

using(Callable resourceSupplier, Function> sourceSupplier, Consumer resourceCleanup) Uses a resource, generated by a supplier for each individual Subscriber, while streaming the values from a Publisher derived from the same resource and makes sure the resource is released if the sequence terminates or the Subscriber cancels.

和我放在一起的代码：

private static Flux<Account> fluxAccounts() {
    return Flux.using(() -> 
        new BufferedReader(new InputStreamReader(new ClassPathResource("data/ExportCSV.csv").getInputStream()))
            .lines()
            .map(s->{
                String[] sa = s.split(" ");
                return Account.builder()
                    .firstname(sa[0])
                    .lastname(sa[1])
                    .build();
            }),
            Flux::fromStream,
            BaseStream::close
    );
}

Answer 2

请注意您的 json 无效。文本数据与 json 不同。 Json 需要特殊处理，所以最好还是使用库。

carga-teste.json

[
  {"description": "credit", "value": "R.000,00", "status": 11},
  {"description": "debit","value": "R.000,00", "status": 99}
]

此处为文章致谢 - https://www.nurkiewicz.com/2017/09/streaming-large-json-file-with-jackson.html。

我已经开始使用 Flux。

@Override
public void run(final String... args) throws Exception {

        BufferedReader bufferedReader = new BufferedReader(
                new InputStreamReader(getClass().getClassLoader().getResourceAsStream("carga-teste.json")));

        ObjectMapper mapper = new ObjectMapper();

        Flux<Extrato> flux = Flux.generate(
                () -> parser(bufferedReader, mapper),
                this::pullOrComplete,
                jsonParser -> {
                    try {
                        jsonParser.close();
                    } catch (IOException e) {}
                });

        flux.map(l -> extratoRepository.save(l)).subscribe(m -> log.info("Carga Teste: {}", m.block()));
    }
}

private JsonParser parser(Reader reader, ObjectMapper mapper) {
    JsonParser parser = null;
    try {
        parser = mapper.getFactory().createParser(reader);
        parser.nextToken();
    } catch (IOException e) {}
    return parser;
}

private JsonParser pullOrComplete(JsonParser parser, SynchronousSink<Extrato> emitter) {
    try {
        if (parser.nextToken() != JsonToken.END_ARRAY) {
            Extrato extrato = parser.readValueAs(Extrato.class);
            emitter.next(extrato);
        } else {
            emitter.complete();
        }
    } catch (IOException e) {
        emitter.error(e);
    }
    return parser;
}

java.io.BufferedReader().map 无法推断 <T> 的类型参数 fromStream(Stream<? extends T>)

java.io.BufferedReader().map Cannot infer type argument(s) for <T> fromStream(Stream<? extends T>)

mongodb

java-io

spring-data

java-stream

spring-webflux