Question

我正在以下面的方式阅读文件的每一行

BufferedReader in = new BufferedReader(new FileReader(inFile));

while (null != (line = in.readLine())) {


}

我想在第一行和最后一行进行一些验证。有没有检查它是否是while循环中的第一行和最后一行的方法

while (null != (line = in.readLine())) {    

    if(firstlineoffile) {
    }

    else if (lastlineoffile) {
    }

    else
    {
    }

}

Answer 1

很酷的问题。我玩了一下它，这是一个SSCCE，只是复制'n'paste'n'run它。

package com.stackoverflow.q2292917;

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

public class Test {

    public static void main(String... args) throws IOException {
        // Create test file.
        File file = new File("/test.txt");
        PrintWriter writer = new PrintWriter(file);
        writer.println("line 1");
        writer.println("line 2");
        writer.println("line 3");
        writer.println("line 4");
        writer.println("line 5");
        writer.close();

        // Read test file.
        BufferedReader reader = null;
        try {
            reader = new BufferedReader(new FileReader(file));
            String next, line = reader.readLine();
            for (boolean first = true, last = (line == null); !last; first = false, line = next) {
                last = ((next = reader.readLine()) == null);

                if (first) {
                    System.out.println("first line: " + line);
                } else if (last) {
                    System.out.println("last line: " + line);
                } else {
                    System.out.println("normal line: " + line);
                }
            }
        } finally {
            if (reader != null) try { reader.close(); } catch (IOException logOrIgnore) {}
        }

        // Delete test file.
        file.delete();
    }

}

输出：

first line: line 1
normal line: line 2
normal line: line 3
normal line: line 4
last line: line 5

然而，我对初学者的可读性和可解释性提出质疑...... ;)

Answer 2

如果你添加一个计数，并重新安排你的代码，这应该工作（我没有测试过，所以可能有语法错误）：

int count = 0;
String line = in.readLine();
while (line!=null) {
  String currLine = line;
  if(count==0){
     //currLine is the first line
  }

  line = in.readLine();
  if(line==null){
     //currLine is the last line
  }

  if(count>0 && line!=null){
     //do something with lines in between
     System.out.println(currLine);
  }
  count++;
}

Answer 3

String currentLine = in.readLine();
String nextLine = in.readLine();
boolean hasStarted = false;
while(null != currentLine){
    if(!hasStarted){
        //first line.
        hasStarted = true;
    }
    //all your processing here.
    if(null == nextLine){
        //last line, cause there's nothing else coming up
    }
    currentLine = nextLine;
    nextLine = in.readLine();
}

Answer 4

public class Vomitfirstline {

    public static void main(String[] args) {

        BufferedReader br = null;

        try {

            String sCurrentLine;

            br = new BufferedReader(new FileReader("Path"));
             br.readLine();

            {


                while ((sCurrentLine = br.readLine()) != null)
        System.out.println(sCurrentLine);

            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (br != null)br.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }

Answer 5

有人可能会提出比这更优雅的解决方案，但我们走了：

boolean isFirstLine = true;
do{
      String line = in.readLine();
      if(isFirstLine){
         //this is the first line
         isFirstLine = false; 
      }
      else if(line==null){ //previous line was the last line
         in.reset();
         line = in.readLine();
         //do last line specific stuff
         break;
      }
      else {
          //do stuff for lines in between
      }
      in.mark(100);

}while (line!=null);

我没有对此进行测试，因此可能会出现轻微错误。我没有在此代码中整理异常处理。 readLine()，mark()和reset()抛出IOException和mark()也可以抛出IllegalArgumentException

如何在reader.readLine（）期间检测第一行和最后一行？

5 个答案: