在Producer范例中读取文本文件 [英] Reading a text file in the Producer paradigm

问题描述

有一个任务可以在生产者范例中读取文本文件.生产者接口定义如下:

There is a task to read a text file in a producer paradigm. The producer interface is defined as the following:

public interface Producer<ITEM> {
    /**
     * Produces the next item.
     *
     * @return produced item
     */
    ITEM next();

    /**
     * Tells if there are more items available.
     *
     * @return true if there are more items, false otherwise
     */
    boolean hasNext();
}

当前读取文本文件的代码是:

Current code to read the text file is:

public static void readTextFile(File file, Charset charset, Consumer<String> consumer) {
    try (InputStreamReader isr = new InputStreamReader(new FileInputStream(file), charset);
         BufferedReader in = new BufferedReader(isr, BUFFER_SIZE)) {
        String line;

        while ((line = in.readLine()) != null) {
            consumer.accept(line);
        }
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

任务是将其转换为:

public static Producer<String> readTextFileRetProducer(File file, Charset charset) {
    // ???

    return null;
}

然后是问题列表:

1. 鉴于需要提前阅读文本行，因此如何正确支持 hasNext .
2. 如何正确管理异常?
3. 在生产者范式中不再提供方便的try-with-resources块的情况下，如何正确释放外部资源?

P.S.读取文件的最后一行后，将释放资源. (它是在之后产生的.)

P.S. Resources are to be released after the last line from the file has been read. (It is produced after).

P.P.S.如果有可以用作我的任务指南的库和/或代码引用，请共享它们.

P.P.S. If there are libraries and/or code references I could use as a guide to my task, please share them.

推荐答案

又快又脏:

public static Producer<String> readFile(File file, Charset charset) {
    Stream<String> stream;
    try {
        stream = Files.lines(file.toPath(), charset);
    } catch (IOException e) {
        throw new UncheckedIOException(e);
    }
    Iterator<String> iter = stream.iterator();
    return new Producer<String>() {
        @Override
        public boolean hasNext() {
            if (!iter.hasNext()) {
                stream.close();
                return false;
            }
            return true;
        }
        @Override
        public String next() {
            return iter.next();
        }
    };
}

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