java - 为什么 printwriter 实际上不写入文件？

Question

我已经为这个问题苦苦挣扎了几个小时，我不确定如何才能最好地继续下去。

代码应该读取一个文件并使用凯撒密码对其进行编码，将其写入磁盘到一个新文件中并附加 _encoded。

它确实创建了文件，但每次都是空白的。当我查看文档时，它说要确保冲洗并关闭打印器。我已经做到了。

我还认为这可能是因为我以迂回的方式解决问题；我想知道是不是使用了FileOutputstream。

        Scanner sc=new Scanner(inFile);
        //File outFile=new File("caesar_encoded.txt");

        //FileOutputStream outFileStream=new FileOutputStream(outFile);
        PrintWriter outStream=new PrintWriter("caesar_encoded.txt");

        while(sc.hasNext())
        {
            String phrase = sc.nextLine().toUpperCase();
    for (int i = 0; i < phrase.length(); i++) {
        if (Character.isLetter(phrase.charAt(i))) {
            for (int j = 0; j < alpha.length; j++) {
                if (phrase.charAt(i) == alpha[j]) {
                    if (j == alpha.length - 1) {
                        outStream.print(alpha[0]);
                    } else {
                        outStream.print(alpha[j + 1]);
                    }
                }
            }
        } else {
            outStream.print(phrase.charAt(i));
        }
    }
    outStream.println();
        }
        outStream.flush();
        outStream.close();

        sc.close();

我尝试这样做，但结果相同:

Scanner sc=new Scanner(inFile);
 File outFile=new File("caesar_encoded.txt");
 FileOutputStream outFileStream=new FileOutputStream(outFile);
 PrintWriter outStream=new PrintWriter(outFileStream);

Answer 1

装饰它:

PrintWriter pw = new PrintWriter(new FileWriter("caesar_encoded.txt"), true);

或者这个:

PrintStream ps = new PrintStream(new FileOutputStream("caesar_encoded.txt"), true);

你当然明白Writer(字符流)和OutputStream(字节流)层次结构的区别。你通常不会跨越两者。您可以使用 OutputStreamWriter 从 OutputStream 跳转到 Writer，但您不能走另一条路。

这段代码对我来说运行完美。我相信你的方法，猜测 SHIFTED 数组。在任何情况下，我都会在 encrypted.txt 文件中获得输出。我认为问题出在您的扫描仪上。

package io;

import java.io.*;

/**
 * PrintWriterDemo
 * @author Michael
 * @link http://stackoverflow.com/questions/12849855/why-doesnt-printwriter-actually-write-to-the-file/12849867#comment17389040_12849867
 * @link http://en.wikipedia.org/wiki/Caesar_cipher
 * @since 10/11/12 7:17 PM
 */
public class PrintWriterDemo {

    public static void main(String[] args) {
        try {
            File unencrypted = new File((args.length > 0) ? args[0] : "resources/unencrypted.txt");
            File encrypted = new File((args.length > 1) ? args[1] : "resources/encrypted.txt");
            caesar(unencrypted, encrypted);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static final char [] SHIFTED = { 
            'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'A', 'B', 'C' };

    public static void caesar(File unencrypted, File encrypted) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(unencrypted));
        PrintWriter pw = new PrintWriter(encrypted);
        String line = "";
        while ((line = br.readLine()) != null) {
            String phrase =line.toUpperCase();
            for (int i = 0; i < phrase.length(); i++) {
                if (Character.isLetter(phrase.charAt(i))) {
                    for (int j = 0; j < SHIFTED.length; j++) {
                        if (phrase.charAt(i) == SHIFTED[j]) {
                            if (j == SHIFTED.length-1) {
                                pw.print(SHIFTED[0]);
                            } else {
                                pw.print(SHIFTED[j+1]);
                            }
                        }
                    }
                } else {
                    pw.print(phrase.charAt(i));
                }
            }
            pw.println();
        }
        pw.flush();
        pw.close();
        br.close();
    }
}

这是我的 unencrypted.txt 输入:

This should work out fine.
I have no idea what the problem is with the original code.
But I do know that this writes just fine.

这是我的 encrypted.txt 输出:

UIJT TIPVME XPSL PVU GJOF.
J IBWF OP JEFB XIBU UIF QSPCMFN JT XJUI UIF PSJHJOBM DPEF.
CVU J EP LOPX UIBU UIJT XSJUFT KVTU GJOF.