org.apache.commons.io.input

Class ReversedLinesFileReader

java.lang.Object

org.apache.commons.io.input.ReversedLinesFileReader

All Implemented Interfaces:

Closeable, AutoCloseable

public class ReversedLinesFileReader
extends Object
implements Closeable

Reads lines in a file reversely (similar to a BufferedReader, but starting at the last line). Useful for e.g. searching in log files.

Since:

2.2

Constructor Summary

Constructors

Constructor and Description
ReversedLinesFileReader(File file) Deprecated. 2.5 use ReversedLinesFileReader(File, Charset) instead
ReversedLinesFileReader(File file, Charset charset) Creates a ReversedLinesFileReader with default block size of 4KB and the specified encoding.
ReversedLinesFileReader(File file, int blockSize, Charset charset) Creates a ReversedLinesFileReader with the given block size and encoding.
ReversedLinesFileReader(File file, int blockSize, String charsetName) Creates a ReversedLinesFileReader with the given block size and encoding.
ReversedLinesFileReader(Path file, Charset charset) Creates a ReversedLinesFileReader with default block size of 4KB and the specified encoding.
ReversedLinesFileReader(Path file, int blockSize, Charset charset) Creates a ReversedLinesFileReader with the given block size and encoding.
ReversedLinesFileReader(Path file, int blockSize, String charsetName) Creates a ReversedLinesFileReader with the given block size and encoding.

Method Summary

Modifier and Type	Method and Description
void	close() Closes underlying resources.
String	readLine() Returns the lines of the file from bottom to top.
List<String>	readLines(int lineCount) Returns lineCount lines of the file from bottom to top.
String	toString(int lineCount) Returns the last lineCount lines of the file.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(File file)
                                    throws IOException

Deprecated. 2.5 use ReversedLinesFileReader(File, Charset) instead

Creates a ReversedLinesFileReader with default block size of 4KB and the platform's default encoding.

Parameters:

file - the file to be read

Throws:

IOException - if an I/O error occurs.

ReversedLinesFileReader

public ReversedLinesFileReader(File file,
                               Charset charset)
                        throws IOException

Creates a ReversedLinesFileReader with default block size of 4KB and the specified encoding.

Parameters:

file - the file to be read

charset - the charset to use, null uses the default Charset.

Throws:

IOException - if an I/O error occurs.

Since:

2.5

ReversedLinesFileReader

public ReversedLinesFileReader(File file,
                               int blockSize,
                               Charset charset)
                        throws IOException

Creates a ReversedLinesFileReader with the given block size and encoding.

Parameters:

file - the file to be read

blockSize - size of the internal buffer (for ideal performance this should match with the block size of the underlying file system).

charset - the encoding of the file, null uses the default Charset.

Throws:

IOException - if an I/O error occurs.

Since:

2.3

ReversedLinesFileReader

public ReversedLinesFileReader(File file,
                               int blockSize,
                               String charsetName)
                        throws IOException

Creates a ReversedLinesFileReader with the given block size and encoding.

Parameters:

file - the file to be read

blockSize - size of the internal buffer (for ideal performance this should match with the block size of the underlying file system).

charsetName - the encoding of the file, null uses the default Charset.

Throws:

IOException - if an I/O error occurs

UnsupportedCharsetException - thrown instead of UnsupportedEncodingException in version 2.2 if the encoding is not supported.

ReversedLinesFileReader

public ReversedLinesFileReader(Path file,
                               Charset charset)
                        throws IOException

Creates a ReversedLinesFileReader with default block size of 4KB and the specified encoding.

Parameters:

file - the file to be read

charset - the charset to use, null uses the default Charset.

Throws:

IOException - if an I/O error occurs.

Since:

2.7

ReversedLinesFileReader

public ReversedLinesFileReader(Path file,
                               int blockSize,
                               Charset charset)
                        throws IOException

Creates a ReversedLinesFileReader with the given block size and encoding.

Parameters:

file - the file to be read

blockSize - size of the internal buffer (for ideal performance this should match with the block size of the underlying file system).

charset - the encoding of the file, null uses the default Charset.

Throws:

IOException - if an I/O error occurs.

Since:

2.7

ReversedLinesFileReader

public ReversedLinesFileReader(Path file,
                               int blockSize,
                               String charsetName)
                        throws IOException

Creates a ReversedLinesFileReader with the given block size and encoding.

Parameters:

file - the file to be read

blockSize - size of the internal buffer (for ideal performance this should match with the block size of the underlying file system).

charsetName - the encoding of the file, null uses the default Charset.

Throws:

IOException - if an I/O error occurs

UnsupportedCharsetException - thrown instead of UnsupportedEncodingException in version 2.2 if the encoding is not supported.

Since:

2.7

Method Detail

close

public void close()
           throws IOException

Closes underlying resources.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException - if an I/O error occurs.

readLine

public String readLine()
                throws IOException

Returns the lines of the file from bottom to top.

Returns:

the next line or null if the start of the file is reached

Throws:

IOException - if an I/O error occurs.

readLines

public List<String> readLines(int lineCount)
                       throws IOException

Returns lineCount lines of the file from bottom to top.

If there are less than lineCount lines in the file, then that's what you get.

Note: You can easily flip the result with Collections.reverse(List).

Parameters:

lineCount - How many lines to read.

Returns:

A new list

Throws:

IOException - if an I/O error occurs.

Since:

2.8.0

toString

public String toString(int lineCount)
                throws IOException

Returns the last lineCount lines of the file.

If there are less than lineCount lines in the file, then that's what you get.

Parameters:

lineCount - How many lines to read.

Returns:

A String.

Throws:

IOException - if an I/O error occurs.

Since:

2.8.0