Java BufferedReader 在循环之前检查循环的下一行

发布于 2025-01-03 21:34:18 字数 597 浏览 0 评论 0 原文

我正在解析 .cvs 文件。对于 cvs 的每一行，我使用解析的值创建一个对象，并将它们放入一个集合中。

在将对象放入地图并循环到下一个之前，我需要检查下一个 cvs 行是否与实际对象相同，但特定属性值不同。

为此，我需要检查缓冲区的下一行，但将循环缓冲区保持在同一位置。

例如：

BufferedReader input  = new BufferedReader(new InputStreamReader(new FileInputStream(file),"ISO-8859-1"));
String line = null;

while ((line = input.readLine()) != null) {
    do something

    while ((nextline = input.readLine()) != null) { //now I have to check the next lines
       //I do something with the next lines. and then break.
    }
    do something else and continue the first loop.
}

原文

I'm parsing a .cvs file.
For each line of the cvs, I create an object with the parsed values, and put them into a set.

Before putting the object in the map and looping to the next, I need to check if the next cvs's line is the same object as the actual, but with a particular property value different.

For that, I need check the next lines of the buffer, but keep the loop's buffer in the same position.

For example:

BufferedReader input  = new BufferedReader(new InputStreamReader(new FileInputStream(file),"ISO-8859-1"));
String line = null;

while ((line = input.readLine()) != null) {
    do something

    while ((nextline = input.readLine()) != null) { //now I have to check the next lines
       //I do something with the next lines. and then break.
    }
    do something else and continue the first loop.
}

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老娘不死你永远是小三 2025-01-10 21:34:19

您可以使用 BufferedReader.mark(int)。要返回到调用 BufferedReader.reset() 的位置。 mark 的参数是“预读限制”；如果您在读取超过限制后尝试reset()，您可能会收到 IOException。

或者您可以使用RandomAccessFile改为：


//获取当前位置
长 pos = raf.getFilePointer();
// 读取更多行...
// 返回旧位置
raf.seek(pos);

或者您可以使用 PushbackReader 允许您取消读取个字符。但有一个缺点： PushbackReader 不提供 readLine 方法。

You can mark the current position using BufferedReader.mark(int). To return to the position you call BufferedReader.reset(). The parameter to mark is the "read ahead limit"; if you try to reset() after reading more than the limit you may get an IOException.

Or you could use RandomAccessFile instead:

// Get current position
long pos = raf.getFilePointer();
// read more lines...
// Return to old position
raf.seek(pos);

Or you could use PushbackReader which allows you to unread characters. But there's the drawback: PushbackReader does not provide a readLine method.

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守不住的情 2025-01-10 21:34:19

您还可以使用嵌套的 do...while 循环来执行此操作，而无需重新读取流中的任何内容：

public void process(File file) throws Exception {
    BufferedReader input = new BufferedReader(new InputStreamReader(new FileInputStream(file), "ISO-8859-1"));
    String batchParent = input.readLine(); // read the first line in the file, this is a new batch
    String batchChild;
    do {
        currentBatch = new Batch(batchParent);
        do {
            batchChild = input.readLine();
        } while (addToBatchIfKeysMatch(batchParent, batchChild));
        // if we break out of the inner loop, that means batchChild is a new parent
        // assign it to batchParent and continue the outer loop
        batchParent = batchChild;
    } while (batchParent != null);
}

private boolean addToBatchIfKeysMatch(final String batchParent, final String batchChild) {
    if (batchChild != null && keysMatch(batchParent, batchChild)) {
        currentBatch.add(batchChild);
        return true;
    } else {
        return false;
    }
}

关键是只读取每个文件并将其作为内部循环中的子行处理，或者将parentLine 设置为新读取的值并继续外循环。

You can also do this with nested do…while loops, without re-reading anything from your stream:

public void process(File file) throws Exception {
    BufferedReader input = new BufferedReader(new InputStreamReader(new FileInputStream(file), "ISO-8859-1"));
    String batchParent = input.readLine(); // read the first line in the file, this is a new batch
    String batchChild;
    do {
        currentBatch = new Batch(batchParent);
        do {
            batchChild = input.readLine();
        } while (addToBatchIfKeysMatch(batchParent, batchChild));
        // if we break out of the inner loop, that means batchChild is a new parent
        // assign it to batchParent and continue the outer loop
        batchParent = batchChild;
    } while (batchParent != null);
}

private boolean addToBatchIfKeysMatch(final String batchParent, final String batchChild) {
    if (batchChild != null && keysMatch(batchParent, batchChild)) {
        currentBatch.add(batchChild);
        return true;
    } else {
        return false;
    }
}

The key is to just read each file and either process it as a child line in the inner loop, or set the parentLine to the newly read value and continue the outer loop.

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