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BufferedReader.skip() 相当于行，而不是字符

发布于 2025-01-09 19:18:16 字数 162 浏览 0 评论 0原文

Java中是否有某种相当于BufferedReader.skip()的东西，它将行数而不是字符数作为参数？

我想跳到文本文件中的特定行并从该点开始读取，而不需要遍历文件的所有行并检查行号（数以万计的行号 - 模型 obj 文件）。

我看到的所有示例都在处理行号检查，这不是我想要的。

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长途伴 2025-01-16 19:18:16

因此，解决方案是使用 FileInputStream.skip()。

更新： 在每次行迭代时手动将系统特定的新行分隔符字节长度添加到行字节长度解决了错误字节跳过的问题，所以现在它终于按预期工作了！

定义一些 Long 变量，用于存储要跳过的字节数。我在我的主应用程序类（App.class）中做到了这一点：

public static long lineByteOffset = 0;

然后，在您使用 BufferedReder 读取行的方法/函数中，使其像这样（我读取的所有文件都编码为UTF-8）：

File objFile = new File(PATH_TO_YOUR_FILE_HERE);

FileInputStream fir = null;
try {
    fir = new FileInputStream(objFile);
} catch (FileNotFoundException e) {
    System.err.println("File not found!");
}
fir.skip(App.lineByteOffset);//<--- 1ST IMPORTANT PART: SET HOW MANY BYTES TO SKIP, YOU START WITH 0 FOR THE 1ST TIME

BufferedReader reader = new BufferedReader(new InputStreamReader(fir, "UTF-8"));
int nls = System.getProperty("line.separator").getBytes().length;
String line;

try {
    while ((line = reader.readLine()) != null) {
        App.lineByteOffset += (long) (line.getBytes().length + nls);//<--- 2ND IMPORTANT PART: INCREASE NUMBER OF BYTES TO SKIP FOR NEXT TIME
        /*
        DO YOUR STUFF HERE...
        IN MY CASE IT RETURNS SPECIFIC BLOCK
        WHICH IN EFFECT EXIT THE WHILE LOOP AS NEEDED
        SO THAT THE NEXT TIME IT CONTINUE WHERE WE LEFT IT
        WITHOUT NEED TO READ THE WHOLE FILE FROM THE START ONCE AGAIN
        */
    }
    reader.close();
} catch (IOException e) {
    System.err.println("Error reading the file");
}

So, the solution is to use FileInputStream.skip().

UPDATE: manually adding system-specific new line separator bytes length to line bytes length at each line iteration solved the problem of erroneous bytes skipping, so now it finally works as expected!

Define some Long variable where you will store the number of bytes to skip. I did that in my main application class (App.class):

public static long lineByteOffset = 0;

Then, in your method/function where you read your lines with BufferedReder make it like this (all my files that I read from are encoded as UTF-8):

File objFile = new File(PATH_TO_YOUR_FILE_HERE);

FileInputStream fir = null;
try {
    fir = new FileInputStream(objFile);
} catch (FileNotFoundException e) {
    System.err.println("File not found!");
}
fir.skip(App.lineByteOffset);//<--- 1ST IMPORTANT PART: SET HOW MANY BYTES TO SKIP, YOU START WITH 0 FOR THE 1ST TIME

BufferedReader reader = new BufferedReader(new InputStreamReader(fir, "UTF-8"));
int nls = System.getProperty("line.separator").getBytes().length;
String line;

try {
    while ((line = reader.readLine()) != null) {
        App.lineByteOffset += (long) (line.getBytes().length + nls);//<--- 2ND IMPORTANT PART: INCREASE NUMBER OF BYTES TO SKIP FOR NEXT TIME
        /*
        DO YOUR STUFF HERE...
        IN MY CASE IT RETURNS SPECIFIC BLOCK
        WHICH IN EFFECT EXIT THE WHILE LOOP AS NEEDED
        SO THAT THE NEXT TIME IT CONTINUE WHERE WE LEFT IT
        WITHOUT NEED TO READ THE WHOLE FILE FROM THE START ONCE AGAIN
        */
    }
    reader.close();
} catch (IOException e) {
    System.err.println("Error reading the file");
}

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