org.apache.commons.io.input

Class ReversedLinesFileReader

java.lang.Object

org.apache.commons.io.input.ReversedLinesFileReader

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, IOIterable<java.lang.String>

public class ReversedLinesFileReader
extends java.lang.Object
implements java.io.Closeable, IOIterable<java.lang.String>

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

To build an instance, use ReversedLinesFileReader.Builder.

For example:

 
 try (ReversedLinesFileReader reader = ReversedLinesFileReader.builder()
   .setPath(path)
   .setBufferSize(4096)
   .setCharset(StandardCharsets.UTF_8)
   .get()) {
      reader.forEach(line -> System.out.println(line));
 }
 
 

Since:

2.2

See Also:

ReversedLinesFileReader.Builder

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ReversedLinesFileReader.Builder Builds a new ReversedLinesFileReader.

Constructor Summary

Constructors

Constructor and Description
ReversedLinesFileReader(java.io.File file) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()
ReversedLinesFileReader(java.io.File file, java.nio.charset.Charset charset) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()
ReversedLinesFileReader(java.io.File file, int blockSize, java.nio.charset.Charset charset) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()
ReversedLinesFileReader(java.io.File file, int blockSize, java.lang.String charsetName) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()
ReversedLinesFileReader(java.nio.file.Path file, java.nio.charset.Charset charset) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()
ReversedLinesFileReader(java.nio.file.Path file, int blockSize, java.nio.charset.Charset charset) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()
ReversedLinesFileReader(java.nio.file.Path file, int blockSize, java.lang.String charsetName) Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Method Summary

Modifier and Type	Method and Description
static ReversedLinesFileReader.Builder	builder() Constructs a new ReversedLinesFileReader.Builder.
void	close() Closes underlying resources.
IOIterator<java.lang.String>	iterator() Like Iterable.iterator().
java.lang.String	readLine() Returns the lines of the file from bottom to top.
java.util.List<java.lang.String>	readLines(int lineCount) Returns lineCount lines of the file from bottom to top.
java.lang.String	toString(int lineCount) Returns the last lineCount lines of the file.
java.lang.Iterable<java.lang.String>	unwrap() Unwraps this instance and returns the underlying Iterable.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.commons.io.function.IOIterable

forEach, spliterator

Constructor Detail

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.io.File file)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs a ReversedLinesFileReader with default block size of 4KB and the virtual machine's default charset.

Parameters:

file - the file to be read

Throws:

java.io.IOException - if an I/O error occurs.

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.io.File file,
                                           java.nio.charset.Charset charset)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs 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:

java.io.IOException - if an I/O error occurs.

Since:

2.5

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.io.File file,
                                           int blockSize,
                                           java.nio.charset.Charset charset)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs 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:

java.io.IOException - if an I/O error occurs.

Since:

2.3

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.io.File file,
                                           int blockSize,
                                           java.lang.String charsetName)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs 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:

java.io.IOException - if an I/O error occurs

java.nio.charset.UnsupportedCharsetException - if the encoding is not supported

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.nio.file.Path file,
                                           java.nio.charset.Charset charset)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs 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:

java.io.IOException - if an I/O error occurs.

Since:

2.7

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.nio.file.Path file,
                                           int blockSize,
                                           java.nio.charset.Charset charset)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs 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:

java.io.IOException - if an I/O error occurs.

Since:

2.7

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(java.nio.file.Path file,
                                           int blockSize,
                                           java.lang.String charsetName)
                                    throws java.io.IOException

Deprecated. Use builder(), ReversedLinesFileReader.Builder, and ReversedLinesFileReader.Builder.get()

Constructs 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:

java.io.IOException - if an I/O error occurs

java.nio.charset.UnsupportedCharsetException - if the encoding is not supported

Since:

2.7

Method Detail

builder

public static ReversedLinesFileReader.Builder builder()

Constructs a new ReversedLinesFileReader.Builder.

Returns:

a new ReversedLinesFileReader.Builder.

Since:

2.12.0

close

public void close()
           throws java.io.IOException

Closes underlying resources.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Throws:

java.io.IOException - if an I/O error occurs.

iterator

public IOIterator<java.lang.String> iterator()

Description copied from interface: IOIterable

Like Iterable.iterator().

Specified by:

iterator in interface IOIterable<java.lang.String>

Returns:

See delegate.

See Also:

Iterable.iterator()

readLine

public java.lang.String readLine()
                          throws java.io.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:

java.io.IOException - if an I/O error occurs.

readLines

public java.util.List<java.lang.String> readLines(int lineCount)
                                           throws java.io.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:

java.io.IOException - if an I/O error occurs.

Since:

2.8.0

toString

public java.lang.String toString(int lineCount)
                          throws java.io.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:

java.io.IOException - if an I/O error occurs.

Since:

2.8.0

unwrap

public java.lang.Iterable<java.lang.String> unwrap()

Description copied from interface: IOIterable

Unwraps this instance and returns the underlying Iterable.

Implementations may not have anything to unwrap and that behavior is undefined for now.

Specified by:

unwrap in interface IOIterable<java.lang.String>

Returns:

the underlying Iterable.