从 Java 读取和编辑文件

Question

我正在尝试在现有文件中每 100 个字符处引入换行符。但它没有写任何东西。下面是用 Java 编写的代码，用于读取现有文件并使用临时文件写入该文件。

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class ReplaceFileContents {
   public static void main(String[] args) {
     new ReplaceFileContents().replace();
   }
   public void replace() {
      String oldFileName = "Changed1.ldif";
      String tmpFileName = "Changed2.ldif";
      BufferedReader br = null;
      BufferedWriter bw = null;
      try {
         br = new BufferedReader(new FileReader(oldFileName));
         bw = new BufferedWriter(new FileWriter(tmpFileName));
         String line;
         while ((line = br.readLine()) != null) {       
                line.replaceAll("(.{100})", "$1n");       
         }
      } catch (Exception e) {
         return;
      } finally {
         try {
            if(br != null)
               br.close();
         } catch (IOException e) {
            //
         }
         try {
            if(bw != null)
               bw.close();
         } catch (IOException e) {
            //
         }
      }
      // Once everything is complete, delete old file..
      File oldFile = new File(oldFileName);
      oldFile.delete();
      // And rename tmp file's name to old file name
      File newFile = new File(tmpFileName);
      newFile.renameTo(oldFile);
   }
}

Answer 1

while ((line = br.readLine()) != null) {       
    line.replaceAll("(.{100})", "$1n");       
}

首先，line.replaceAll 不会用结果替换行变量。由于Strings是不可变的，因此此方法返回新字符串，因此您的行应line = line.replaceAll(...。

其次，您永远不会将新String写回文件中。使用 replaceAll 不会以任何方式更改文件本身。相反，请尝试使用 bw 对象将新String写入同一行。

Answer 2

从您在此处发布的内容来看，您永远不会尝试将line写回bw。试试这个：

package hello;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class Test {
    public static void main(String[] args) {
        new Test().replace();
    }
    public void replace() {
        String oldFileName = "d:\1.txt";
        String tmpFileName = "d:\2.txt";
        BufferedReader br = null;
        BufferedWriter bw = null;
        try {
            br = new BufferedReader(new FileReader(oldFileName));
            bw = new BufferedWriter(new FileWriter(tmpFileName));
            String line;
            while ((line = br.readLine()) != null) {
                line = line.replaceAll("(.{100})", "$1n");
                bw.write(line);
            }
        } catch (Exception e) {
            return;
        } finally {
            try {
                if(br != null)
                    br.close();
            } catch (IOException e) {
                //
            }
            try {
                if(bw != null)
                    bw.close();
            } catch (IOException e) {
                //
            }
        }
        // Once everything is complete, delete old file..
        File oldFile = new File(oldFileName);
        oldFile.delete();
        // And rename tmp file's name to old file name
        File newFile = new File(tmpFileName);
        newFile.renameTo(oldFile);
    }
}

1. 您永远不会尝试将行写回bw;
2. String#replaceAll将返回源的副本而不是原始String;