Question

这是一个代码片段，但基本上我想要做的是从名为'listings.txt'的文件中读取并写入名为'overview.txt'的文件。我想从'listings.txt'中取出信息并将它们按原样放入'overview.txt'中（稍后我会弄清楚其余部分）。

创建文件'overview.txt'并显示循环遍历文件'listings.txt'并写入'overview.txt'。但是，一旦我打开文件'overview.txt'，它就是空的。
有人可以快速浏览我的代码并发现错误的内容吗？

package yesOverview;

import java.io.BufferedReader;
import java.io.*;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;


public class yesOverview {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String strInput = "foo.bar";
        System.out.print("Please enter the listings file (the full path to the file): ");
        strInput = input.next();

        //This makes sure that the inputed file is listings.txt as required for KET1 task 2
        while (strInput.contains("listings.txt") == false) {
            System.out.print("Incorrect file. Please enter listings file(the full path to the file): ");
            strInput = input.next();
        }

        infos(strInput);
        input.close();
    }

    public static void infos(String strInput) {
        Scanner input2 = new Scanner(System.in);
        System.out.print("Please enter the overview.txt file (the full path to the file): ");
        String strInput2 = "foo.bar";
        strInput2 = input2.next();

        //This also makes sure that the overview.txt file is provided. 
        while (strInput2.contains("overview.txt") == false) {
            System.out.print("Incorrect file. Please enter overview file(the full path to the file): ");
            strInput2 = input2.next();
        }

        //Creates the file f then places it in the specified directory.
        File f = new File(strInput2);

        try {
            //Creates a printerwriter out that writes to the output file. 
            PrintWriter out = new PrintWriter(strInput2);
        } catch (FileNotFoundException ex) {
            Logger.getLogger(KETTask2Overview.class.getName()).log(Level.SEVERE, null, ex);
        }

        //String that holds the value of the next line. 
        String inputLine = "";

        //Creates the Buffered file reader / writer.  
        try {
            BufferedReader in = new BufferedReader(new FileReader(strInput));
            FileWriter fstream = new FileWriter(strInput2);
            BufferedWriter out = new BufferedWriter(fstream);
            while (in.readLine() != null) {
                out.write(in.read());
            }
            in.close();
        } catch (IOException e) {
            System.err.println("Error: " + e.getMessage());
        }

    }
}

Answer 1

试试这个

关闭BufferedWriter流（即out.close（））

尝试使用nextLine（）而不是next（），因为next（）只接受一个单词，但是对于一个完整的行使用nextLine（），虽然这似乎不是这里的问题。

当我必须阅读和写入文件时，我通常按照这些步骤进行操作

从文件中读取

File f = new File("my.txt");
FileReader fr = new FileReader(f);
BufferedReader br  = new BufferedReader(fr);

String s = null;

while ((br.readLine())!=null) {

// Do whatever u want to do with the content of the file,eg print it on console using SysOut...etc

}

br.close();

写入文件：

Boolean isDone = true;
Scanner scan = new Scanner(System.in);
File f = new File("my.txt");
FileWriter fr = new FileWriter(f);
BufferedWriter br  = new BufferedWriter(fr);

while (isDone) {

   if (!isDone) {

 br.write(new Scanner(System.in).nextLine());

 }


}

Answer 2

public static long copy (Reader input, Writer output) throws IOException {

    char[] buffer = new char[8192];
    long count = 0;
    int n;
    while ((n = input.read( buffer )) != -1) {
        output.write( buffer, 0, n );
        count += n;
    }
    return count;
}

用法示例：

 copy( reader, new FileWriter( file ) );

Answer 3

你还没结束。 writeList方法的finally块清除然后关闭BufferedWriter。

finally {
    if (out != null) { 
        System.out.println("Closing BufferedWriter");
        out.close(); 
    } else { 
        System.out.println("BufferedWriter not open");
    } 
}

Java读/写文件 - BufferedReader BufferedWriter

3 个答案: