使用 Cactoos 从 Stdin 读取行

Question

我正在寻找一种使用 Cactoos 库从标准输入读取单行的方法。我可以这样做：

System.out.println(
  new TextOf(
    new ReaderOf(
      new Stdin()
    )
  ).asString()
);

但是此代码会阻塞并读取 Stdin/System.in 直到它关闭 - 我使用 Ctrl+D 停止阅读并打印我的文本。是否有任何方法可以获得类似于 BufferedReader#readLine() 的行为？

我还想在阅读 Stdin 之前打印一些提示，例如：

System.out.println(
  new TextOf(
    new PromptedReaderOf( // desired decorator if I get Cactoos ideas right
      output,             // Output to display prompt-string to user
      "Type your text and press Enter: ",  // the prompt-string
      new ReaderOf(
        new Stdin()
      )
    )
  ).asString()
);

是否可以使用 Cactoos 或我应该围绕 Stdin 为此类交互式控制台应用程序编写自己的装饰器？

Answer 1

but this code blocks and reads Stdin/System.in until it's closed - I use Ctrl+D to stop reading

发生这种情况是因为 Reader 必须读取所有内容，包括 'newline' (\n\r) 个字符，直到没有可读取的内容为止（Ctrl+D，流变为有限).

当您按 'enter' 键输入换行符时，您等待 reader 停止读取无限流。例如，在 BufferedReader::read**Line**.

中重现了该行为

TextOf(Reader) 使用 Reader::read 代替（实际上它发生在 ReaderAsBytes::asBytes 内）。

Also I'd like to print some prompt before reading the Stdin Is it possible with Cactoos or should I write my own decorators around Stdin for such interactive console application?

所以，是的，您需要实施新的装饰器来处理您的问题。

您可能需要使用 TextOf(Input) 并创建一个 Input 装饰器，它在出现 'newline' 个字符时生成有限流。

public class ReaderReadLineInput implements Input {
    //we don't want to use 'new' in methods
    private final Scalar<InputStream> inputStreamScalar;

    private ReaderReadLineInput(BufferedReader bufferedReader) {
        this.inputStreamScalar = new ScalarOf<InputStream>(
            br -> new InputStreamOf(
                br.readLine() //produces finite InputStream
            ),
            bufferedReader
        );
    }
    
    public ReaderReadLineInput(Reader reader){
        this(new BufferedReader(reader));
    }

    @Override
    public InputStream stream() throws Exception {
        return inputStreamScalar.value();
    }
}

那么您可能希望将它与您的实际用例联系起来（通过键入从控制台获取输入）并且不失去以前代码的可重用性，因此创建另一个 Input 装饰器

public class ManualConsoleInput implements Input {
    //and you still don't like 'new' in methods
    private final Scalar<Input> iptScalar;

    public ManualConsoleInput(Text charsetName) {
        // do you like Cactoos primitives?
        // there's a some workaround
        this.iptScalar = new ScalarOf<Input>(
            charset -> {
                return new ReaderReadLineInput(
                    new InputStreamReader(
                        new Stdin().stream(), 
                        charset.asString() 
                    )
                )
            },
            charsetName
        );
    }

    @Override
    public InputStream stream() throws Exception {
        return this.iptScalar.value().stream();
    }
}

要在获取用户输入之前将提示文本打印到控制台，您可能还需要创建另一个装饰器。

public class InputPrintsToConsole implements Input {  
    private final Runnable printingRunnable;
    private final Input origin;

    public InputPrintsToConsole(Text textToConsole, Input origin) {
        this.printingRunnable = new ConsolePrinting(textToConsole);
        this.origin = origin;
    }

    @Override
    public InputStream stream() throws Exception {
        printingRunnable.run();
        return origin.stream();
    }
}

还请记住，例如，有些人在使用您的代码将标准输出通过管道传输到文件时可以使用 System::setOut。所以你不能仅仅依靠系统神对象来获取控制台输出流，只能使用它来获取对控制台输出流的引用，当你确定时：

public class ConsolePrinting extends RunnableEnvelope {
    public ConsolePrinting(Text textToPrint) {
        super(
            new OutputStreamPrinting(
                System.out, // and encapsulate somewhere 
                textToPrint
            )
        );
    }
}

// splitting responsibility of objects
// and using decorators
public class OutputStreamPrinting implements Runnable { 
    private final PrintStream printStream;
    private final Text text;

    public OutputStreamPrinting(PrintStream printStream, Text text) {
        this.printStream = printStream;
        this.text = text;
    }
    
    public OutputStreamPrinting(OutputStream outputStream, Text text) {
        this(new PrintStream(outputStream), text);
    }
    
    @Override
    public void run() {
        this.printStream.println(this.text);
    }
}

您示例中的顶级代码可能如下所示：

System.out.println(
    new TextOf(
        new InputPrintsToConsole(
            new TextOf("Type your text and press Enter:"),
            new ManualConsoleInput(new TextOf("utf-8"))
        )
    )
);

使用 Cactoos 从 Stdin 读取行

Read line from Stdin with Cactoos

java

cactoos