在Java 中高效檢索文字檔案的最後一行
讀取大型文字檔案的最後一行可能是一項具有挑戰性的任務，尤其是在嘗試避免載入時整個檔案進入記憶體。本文探討了兩種無需遍歷整個文件即可完成此任務的有效方法。
方法1：拖尾檔案
第一種方法，稱為「拖曳」 ,」涉及定位到檔案結尾並逐字元向後迭代，記錄字元直到遇到換行符。 >
public String tail(File file) {
try (RandomAccessFile fileHandler = new RandomAccessFile(file, "r")) {
long fileLength = fileHandler.length() - 1;
StringBuilder sb = new StringBuilder();
for (long filePointer = fileLength; filePointer != -1; filePointer--) {
fileHandler.seek(filePointer);
int readByte = fileHandler.readByte();
if (readByte == 0xA) { // line break (LF)
if (filePointer == fileLength) {
continue;
}
break;
} else if (readByte == 0xD) { // carriage return (CR)
if (filePointer == fileLength - 1) {
continue;
}
break;
}
sb.append((char) readByte);
}
String lastLine = sb.reverse().toString();
return lastLine;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}用法
public String tail2(File file, int lines) {
try (RandomAccessFile fileHandler = new RandomAccessFile(file, "r")) {
long fileLength = fileHandler.length() - 1;
StringBuilder sb = new StringBuilder();
int lineCount = 0;
for (long filePointer = fileLength; filePointer != -1; filePointer--) {
fileHandler.seek(filePointer);
int readByte = fileHandler.readByte();
if (readByte == 0xA) { // line break (LF)
if (filePointer < fileLength) {
lineCount++;
}
} else if (readByte == 0xD) { // carriage return (CR)
if (filePointer < fileLength - 1) {
lineCount++;
}
}
if (lineCount >= lines) {
break;
}
sb.append((char) readByte);
}
String lastLines = sb.reverse().toString();
return lastLines;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}注意
File file = new File("D:\stuff\huge.log");
System.out.println(tail(file));
System.out.println(tail2(file, 10));以上是如何在 Java 中有效率地檢索文字檔案的最後一行？的詳細內容。更多資訊請關注PHP中文網其他相關文章！
