Java ASCII输出到文件

Question

当我试图将ASCII值输出到文件时，它会返回错误的值。例如：

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.PrintWriter;

    public class test {
    public static void main(String args[]){
                                  //Supposed to:
        writeFile("./test.txt"); //write ASCII 147
        readFile("./test.txt"); //read ASCII 147
    }

    public static boolean writeFile(String path){
        try{
            PrintWriter fo = new PrintWriter(new FileOutputStream(new File(path)));
            fo.print((char) 147); //WRITES "?" TO FILE (ASCII 63, NOT 147)
            fo.close();
        }catch(Exception e){
            return true;
        }
        return false;
    }

    public static boolean readFile(String path){
        try {
            BufferedReader fi = new BufferedReader(new FileReader(path));
            char c[] = fi.readLine().toCharArray();
            System.out.println((int) c[0]); //OBVIOUSLY PRINTS 63 INSTEAD OF 147
            fi.close();
            return true;
        } catch (Exception e){
            e.printStackTrace();
            return false;
        }
    }
}

我做错了什么？任何帮助都会很好。谢谢

Answer 1

ASCII中没有“字符147”这样的东西

你应该给出一个能代表你感兴趣的字符的特定编码——UTF-8通常是一个不错的选择——并在读写时使用相同的编码

不幸的是FileWriter和FileReader不允许您指定编码，因此需要FileOutputStream和FileInputStream包装在OutputStreamWriter和InputStreamReader中：

import java.io.*;
import java.nio.charset.*;

public class Test {

    private static Charset UTF8 = Charset.forName("UTF-8");

    public static void main(String args[]) throws IOException {
        writeFile("./test.txt");
        readFile("./test.txt");
    }

    public static void writeFile(String path) throws IOException {
        Writer writer = new OutputStreamWriter(new FileOutputStream(path), UTF8);
        try {
            writer.write((char) 147);
        } finally {
            writer.close();
        }
    }

    public static void readFile(String path) throws IOException {
        Reader reader = new InputStreamReader(new FileInputStream(path), UTF8);
        try {
            int c = reader.read();
            System.out.println(c);
        } finally {
            reader.close();
        }
    }
}

Answer 2

有些语言将字符和八位字节类型相混淆（C和C++是显著的例子）。Java char类型隐式地是UTF-16，ASCII必须使用byte类型来表示。请参见here进行比较。有关Java编码指南，请参见here