如何 show/write 导致日志文件？

Question

我应该 write/show 我的“结果”（计算器）输入到日志文件...例如：results.txt 但是，如果我做的计算多于 1 次……只有最后一个会打印在 results.txt.

中

public class Calculator {
    public static void main(String[] args) throws FileNotFoundException {
        String filename = "results.txt";
        //PrintWriter output = new PrintWriter(filename);
        int number1;
        int number2;
        char mathchoice;
        int result;
        char userchoice;
        do {
            PrintWriter output = new PrintWriter(filename);

            Scanner choice = new Scanner(System.in);
            System.out.println("Enter first number...");
            number1 = choice.nextInt();
            System.out.println("Math choice...");
            mathchoice = choice.next().charAt(0);
            System.out.println("Enter second number...");
            number2 = choice.nextInt();

            if (mathchoice == '+') {
                result = number1 + number2;
                System.out.println("Result is: " + result);
                output.print("Result is: " + result);
            } else if (mathchoice == '-') {
                result = number1 - number2;
                System.out.println("Result is: " + result);
                output.print("Result is: " + result);
            } else if (mathchoice == '*') {
                result = number1 * number2;
                output.print("Result is: " + result);
                System.out.println("Result is: " + result);
            } else if (mathchoice == '/') {
                if (number2 == 0) {
                    throw new java.lang.ArithmeticException("Devided by zero not aloud");
                } else {
                    result = number1 / number2;
                    output.print("Result is: " + result);
                    System.out.println("Result is: " + result);

                }

            } else if (mathchoice == '%') {
                result = number1 % number2;
                output.print("Result is: " + result);
                System.out.println("Result is: " + result);
            } else if (mathchoice == '^') {
                result = (int) Math.pow(number1, number2);
                output.print("Result is: " + result);
                System.out.println("Result is: " + result);
            } else {
                System.out.println("Wrong choice");

            }
            output.close();
            System.out.println("Again?");
            userchoice = choice.next().charAt(0);

        }while (userchoice == 'j');
    }
    
}

我在 lus 的末尾添加了 output.close()。但是我只得到最后一个计算。

Answer 1

您可以创建一个文件并直接写入它，参见“java.io”类，例如OutputStream、FileWriter等。您基本上需要创建对文件的引用并使用“write”方法写入它。

// on Windows use "c:\temp\my-file.log"
FileOutputStream fos = new FileOutputStream("/tmp/my-file.log");
fos.write("My log message".getBytes());

但如果可能的话，不要重新发明轮子，使用LOG4J来记录你的日志。 LOG4J 是一个广泛使用的库，它使日志记录工作变得更加容易。

要管理项目的依赖项，请使用 Maven。创建一个maven项目并添加POM.XML中的依赖，这将大大简化你的生活。

Answer 2

如果您想获得与控制台中打印的完全相同的输出，那么 System.out + System.in，一种解决方法是创建一个自定义 InputStreamReader 以提供给扫描仪，以及将 System.out 设置为的自定义 PrintStream。这些自定义实现可以在 read/write 数据时写入文件。

这是一个例子：

import java.io.*;
import java.nio.file.Paths;
import java.util.Scanner;

public class ScannerTest {

    static boolean alive = true;

    public static void main(String[] args){

        int number1;
        int number2;
        char mathchoice;
        int result;
        char userchoice;

        final File file = Paths.get("result.txt").toFile();

        FileOutputStream fileOutputStream = null;
        try {
            fileOutputStream = new FileOutputStream(file);
            file.createNewFile();
            System.setOut(new PrintStreamFileForwarder(System.out, fileOutputStream));
        } catch (IOException e) {
            e.printStackTrace();
        }

        Scanner choice = new Scanner(new InputStreamFileForwarder(System.in, fileOutputStream));

        do {

            System.out.println("Enter first number...");
            number1 = choice.nextInt();
            System.out.println("Math choice...");
            mathchoice = choice.next().charAt(0);
            System.out.println("Enter second number...");
            number2 = choice.nextInt();

            if (mathchoice == '+') {
                result = number1 + number2;
                System.out.println("Result is: " + result);
            } else if (mathchoice == '-') {
                result = number1 - number2;
                System.out.println("Result is: " + result);
            } else if (mathchoice == '*') {
                result = number1 * number2;
                System.out.println("Result is: " + result);
            } else if (mathchoice == '/') {
                if (number2 == 0) {
                    throw new java.lang.ArithmeticException("Devided by zero not aloud");
                } else {
                    result = number1 / number2;
                    System.out.println("Result is: " + result);
                }

            } else if (mathchoice == '%') {
                result = number1 % number2;
                System.out.println("Result is: " + result);
            } else if (mathchoice == '^') {
                result = (int) Math.pow(number1, number2);
                System.out.println("Result is: " + result);
            } else {
                System.out.println("Wrong choice");

            }
            System.out.println("Again?");
            userchoice = choice.next().charAt(0);

        } while (userchoice == 'j');
        alive = false;
    }

    public static class InputStreamFileForwarder extends InputStreamReader {

        private final FileOutputStream fileOutputStream;

        public InputStreamFileForwarder(InputStream console, FileOutputStream fileOutputStream) {
            super(console);
            this.fileOutputStream = fileOutputStream;
        }

        @Override
        public int read(char[] cbuf, int offset, int length) throws IOException {
            int read = super.read(cbuf, offset, length);
            if(read > 0) {
                char[] allRead = new char[read];
                System.arraycopy(cbuf, offset, allRead, 0, read);
                fileOutputStream.write(new String(allRead).getBytes());
            }
            return read;
        }
    }

    public static class PrintStreamFileForwarder extends PrintStream {

        private final FileOutputStream fileOutputStream;

        public PrintStreamFileForwarder(PrintStream console, FileOutputStream fileOutputStream) {
            super(console);
            this.fileOutputStream = fileOutputStream;
        }

        @Override
        public void write(byte[] buf, int off, int len) {
            super.write(buf, off, len);
            try {
                fileOutputStream.write(buf, off, len);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

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