java - 跳转到 .txt 文件中的特定行，其中所有行在 Java 中的长度相同

Question

我有一个包含大约 100 万行信息的文本文件。鉴于我知道我想要哪条线，并且所有线的长度相等，我正在寻找一种跳转到特定线的方法。

我读到，鉴于所有行都相等，因此不必阅读每一行就可以这样做。如果是这样，任何人都可以提供如何执行此操作的示例代码吗？还是我最好简单地阅读每一行并循环它？

Answer 1

我猜你正在寻找随机文件访问

File file = ...;
RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
int lineNumber = ...; // first line number is 0
int lineWidth = ...;  // your fixed line width
long beginIndexOfLine = lineWidth * lineNumber;
randomAccessFile.seek(beginIndexOfLine);

byte[] line = new byte[lineWidth];
randomAccessFile.read(line);

Answer 2

您是否正在寻找这个：

String line = FileUtils.readLines(file).get(lineNumber);

或者您可以尝试像这样使用迭代器：-

LineIterator l= IOUtils.lineIterator(new BufferedReader(new FileReader("file.txt")));
 for (int lineNumber = 0; l.hasNext(); lineNumber++) {
    String line = (String) l.next();
    if (lineNumber == desiredLineNumber) {
        return line;
    }
 }

编辑：-

从这里：-

int sizeofrecordinbytes = 290;
 // for this example this is 1 based, not zero based 
int recordIWantToStartAt = 12400;
int totalRecordsIWant = 1000;

File myfile = new File("someGiantFile.txt");


// where to seek to
long seekToByte =  (recordIWantToStartAt == 1 ? 0 : ((recordIWantToStartAt-1) * sizeofrecordinbytes));

// byte the reader will jump to once we know where to go
long startAtByte = 0;

// seek to that position using a RandomAccessFile
try {
        // NOTE since we are using fixed length records, you could actually skip this 
        // and just use our seekToByte as the value for the BufferedReader.skip() call below

    RandomAccessFile rand = new RandomAccessFile(myfile,"r");
    rand.seek(seekToByte);
    startAtByte = rand.getFilePointer();
    rand.close();

} catch(IOException e) {
    // do something
}

// Do it using the BufferedReader 
BufferedReader reader = null;
try {
    // lets fire up a buffered reader and skip right to that spot.
    reader = new BufferedReader(new FileReader(myfile));
    reader.skip(startAtByte);

    String line;
    long totalRead = 0;
    char[] buffer = new char[sizeofrecordinbytes];
    while(totalRead < totalRecordsIWant && (-1 != reader.read(buffer, 0, sizeofrecordinbytes))) {
        System.out.println(new String(buffer));
        totalRead++;
    }
} catch(Exception e) {
    // handle this

} finally {
    if (reader != null) {
        try {reader.close();} catch(Exception ignore) {}
    }
}