我想从结束到开始我的文件的相反方向读取文件,
[1322110800] LOG ROTATION: DAILY
[1322110800] LOG VERSION: 2.0
[1322110800] CURRENT HOST STATE:arsalan.hussain;DOWN;HARD;1;CRITICAL - Host Unreachable (192.168.1.107)
[1322110800] CURRENT HOST STATE: localhost;UP;HARD;1;PING OK - Packet loss = 0%, RTA = 0.06 ms
[1322110800] CURRENT HOST STATE: musewerx-72c7b0;UP;HARD;1;PING OK - Packet loss = 0%, RTA = 0.27 ms
我用代码以这种方式阅读它,
String strpath="/var/nagios.log";
FileReader fr = new FileReader(strpath);
BufferedReader br = new BufferedReader(fr);
String ch;
int time=0;
String Conversion="";
do {
ch = br.readLine();
out.print(ch+"<br/>");
} while (ch != null);
fr.close();
我更喜欢使用缓冲读取器以相反的顺序读取
Mar*_*hue 57
我遇到了和此处描述的问题相同的问题.我想以相反的顺序查看文件中的行,从结尾返回到开始(unix tac命令将执行此操作).
但是我的输入文件相当大,所以将整个文件读入内存,因为在其他示例中对我来说并不是一个可行的选项.
下面是我提出的类,它确实使用RandomAccessFile,但不需要任何缓冲区,因为它只保留指向文件本身的指针,并使用标准InputStream方法.
它适用于我的案例,空文件和我尝试过的其他一些东西.现在我没有Unicode字符或任何花哨的东西,但只要这些行由LF分隔,即使它们有LF + CR也应该有效.
基本用法是:
in = new BufferedReader (new InputStreamReader (new ReverseLineInputStream(file)));
while(true) {
String line = in.readLine();
if (line == null) {
break;
}
System.out.println("X:" + line);
}
这是主要来源:
package www.kosoft.util;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
public class ReverseLineInputStream extends InputStream {
RandomAccessFile in;
long currentLineStart = -1;
long currentLineEnd = -1;
long currentPos = -1;
long lastPosInFile = -1;
public ReverseLineInputStream(File file) throws FileNotFoundException {
in = new RandomAccessFile(file, "r");
currentLineStart = file.length();
currentLineEnd = file.length();
lastPosInFile = file.length() -1;
currentPos = currentLineEnd;
}
public void findPrevLine() throws IOException {
currentLineEnd = currentLineStart;
// There are no more lines, since we are at the beginning of the file and no lines.
if (currentLineEnd == 0) {
currentLineEnd = -1;
currentLineStart = -1;
currentPos = -1;
return;
}
long filePointer = currentLineStart -1;
while ( true) {
filePointer--;
// we are at start of file so this is the first line in the file.
if (filePointer < 0) {
break;
}
in.seek(filePointer);
int readByte = in.readByte();
// We ignore last LF in file. search back to find the previous LF.
if (readByte == 0xA && filePointer != lastPosInFile ) {
break;
}
}
// we want to start at pointer +1 so we are after the LF we found or at 0 the start of the file.
currentLineStart = filePointer + 1;
currentPos = currentLineStart;
}
public int read() throws IOException {
if (currentPos < currentLineEnd ) {
in.seek(currentPos++);
int readByte = in.readByte();
return readByte;
}
else if (currentPos < 0) {
return -1;
}
else {
findPrevLine();
return read();
}
}
}
nes*_*.gp 21
Apache Commons IO现在有了ReversedLinesFileReader类(从版本2.2开始).
所以你的代码可能是:
String strpath="/var/nagios.log";
ReversedLinesFileReader fr = new ReversedLinesFileReader(new File(strpath));
String ch;
int time=0;
String Conversion="";
do {
ch = fr.readLine();
out.print(ch+"<br/>");
} while (ch != null);
fr.close();
Tim*_*lee 10
上面发布的ReverseLineInputStream正是我想要的.我正在阅读的文件很大,无法缓冲.
有几个错误:
这是更正后的代码:
package www.kosoft.util;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
public class ReverseLineInputStream extends InputStream {
RandomAccessFile in;
long currentLineStart = -1;
long currentLineEnd = -1;
long currentPos = -1;
long lastPosInFile = -1;
int lastChar = -1;
public ReverseLineInputStream(File file) throws FileNotFoundException {
in = new RandomAccessFile(file, "r");
currentLineStart = file.length();
currentLineEnd = file.length();
lastPosInFile = file.length() -1;
currentPos = currentLineEnd;
}
private void findPrevLine() throws IOException {
if (lastChar == -1) {
in.seek(lastPosInFile);
lastChar = in.readByte();
}
currentLineEnd = currentLineStart;
// There are no more lines, since we are at the beginning of the file and no lines.
if (currentLineEnd == 0) {
currentLineEnd = -1;
currentLineStart = -1;
currentPos = -1;
return;
}
long filePointer = currentLineStart -1;
while ( true) {
filePointer--;
// we are at start of file so this is the first line in the file.
if (filePointer < 0) {
break;
}
in.seek(filePointer);
int readByte = in.readByte();
// We ignore last LF in file. search back to find the previous LF.
if (readByte == 0xA && filePointer != lastPosInFile ) {
break;
}
}
// we want to start at pointer +1 so we are after the LF we found or at 0 the start of the file.
currentLineStart = filePointer + 1;
currentPos = currentLineStart;
}
public int read() throws IOException {
if (currentPos < currentLineEnd ) {
in.seek(currentPos++);
int readByte = in.readByte();
return readByte;
} else if (currentPos > lastPosInFile && currentLineStart < currentLineEnd) {
// last line in file (first returned)
findPrevLine();
if (lastChar != '\n' && lastChar != '\r') {
// last line is not terminated
return '\n';
} else {
return read();
}
} else if (currentPos < 0) {
return -1;
} else {
findPrevLine();
return read();
}
}
@Override
public void close() throws IOException {
if (in != null) {
in.close();
in = null;
}
}
}
当您尝试读取数千行时,建议的ReverseLineInputStream工作得非常慢.在我的PC上,英特尔酷睿i7在SSD驱动器上,它在80秒内大约有6万行.这是带有缓冲读取的灵感优化版本(与ReverseLineInputStream中的一次一字节读取相反).在400毫秒内读取60k行日志文件:
public class FastReverseLineInputStream extends InputStream {
private static final int MAX_LINE_BYTES = 1024 * 1024;
private static final int DEFAULT_BUFFER_SIZE = 1024 * 1024;
private RandomAccessFile in;
private long currentFilePos;
private int bufferSize;
private byte[] buffer;
private int currentBufferPos;
private int maxLineBytes;
private byte[] currentLine;
private int currentLineWritePos = 0;
private int currentLineReadPos = 0;
private boolean lineBuffered = false;
public ReverseLineInputStream(File file) throws IOException {
this(file, DEFAULT_BUFFER_SIZE, MAX_LINE_BYTES);
}
public ReverseLineInputStream(File file, int bufferSize, int maxLineBytes) throws IOException {
this.maxLineBytes = maxLineBytes;
in = new RandomAccessFile(file, "r");
currentFilePos = file.length() - 1;
in.seek(currentFilePos);
if (in.readByte() == 0xA) {
currentFilePos--;
}
currentLine = new byte[maxLineBytes];
currentLine[0] = 0xA;
this.bufferSize = bufferSize;
buffer = new byte[bufferSize];
fillBuffer();
fillLineBuffer();
}
@Override
public int read() throws IOException {
if (currentFilePos <= 0 && currentBufferPos < 0 && currentLineReadPos < 0) {
return -1;
}
if (!lineBuffered) {
fillLineBuffer();
}
if (lineBuffered) {
if (currentLineReadPos == 0) {
lineBuffered = false;
}
return currentLine[currentLineReadPos--];
}
return 0;
}
private void fillBuffer() throws IOException {
if (currentFilePos < 0) {
return;
}
if (currentFilePos < bufferSize) {
in.seek(0);
in.read(buffer);
currentBufferPos = (int) currentFilePos;
currentFilePos = -1;
} else {
in.seek(currentFilePos);
in.read(buffer);
currentBufferPos = bufferSize - 1;
currentFilePos = currentFilePos - bufferSize;
}
}
private void fillLineBuffer() throws IOException {
currentLineWritePos = 1;
while (true) {
// we've read all the buffer - need to fill it again
if (currentBufferPos < 0) {
fillBuffer();
// nothing was buffered - we reached the beginning of a file
if (currentBufferPos < 0) {
currentLineReadPos = currentLineWritePos - 1;
lineBuffered = true;
return;
}
}
byte b = buffer[currentBufferPos--];
// \n is found - line fully buffered
if (b == 0xA) {
currentLineReadPos = currentLineWritePos - 1;
lineBuffered = true;
break;
// just ignore \r for now
} else if (b == 0xD) {
continue;
} else {
if (currentLineWritePos == maxLineBytes) {
throw new IOException("file has a line exceeding " + maxLineBytes
+ " bytes; use constructor to pickup bigger line buffer");
}
// write the current line bytes in reverse order - reading from
// the end will produce the correct line
currentLine[currentLineWritePos++] = b;
}
}
}}
据我了解，您尝试逐行向后阅读。假设这是您尝试读取的文件：
线路1
线路2
线路3
并且您希望将其写入 servlet 的输出流，如下所示：
线路3
线路2
线路1
在这种情况下，以下代码可能会有所帮助：
List<String> tmp = new ArrayList<String>();
do {
ch = br.readLine();
tmp.add(ch);
out.print(ch+"<br/>");
} while (ch != null);
for(int i=tmp.size()-1;i>=0;i--) {
out.print(tmp.get(i)+"<br/>");
}
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