Package org.apache.commons.io.input

Class ReversedLinesFileReader

java.lang.Object

org.apache.commons.io.input.ReversedLinesFileReader

All Implemented Interfaces:

Closeable, AutoCloseable, IOIterable<String>

public class ReversedLinesFileReader
extends Object
implements Closeable, IOIterable<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	Description
static class	ReversedLinesFileReader.Builder	Builds a new ReversedLinesFileReader.

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method	Description
static ReversedLinesFileReader.Builder	builder()	Constructs a new ReversedLinesFileReader.Builder.
void	close()	Closes underlying resources.
IOIterator<String>	iterator()	Like Iterable.iterator().
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.
Iterable<String>	unwrap()	Unwraps this instance and returns the underlying Iterable.

Methods inherited from class java.lang.Object

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

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

forEach, spliterator

Constructor Details

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(File file)
                        throws 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:

IOException - if an I/O error occurs.

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(File file,
 Charset charset)
                        throws 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:

IOException - if an I/O error occurs.

Since:

2.5

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(File file,
 int blockSize,
 Charset charset)
                        throws 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:

IOException - if an I/O error occurs.

Since:

2.3

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(File file,
 int blockSize,
 String charsetName)
                        throws 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:

IOException - if an I/O error occurs

UnsupportedCharsetException - if the encoding is not supported

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(Path file,
 Charset charset)
                        throws 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:

IOException - if an I/O error occurs.

Since:

2.7

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(Path file,
 int blockSize,
 Charset charset)
                        throws 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:

IOException - if an I/O error occurs.

Since:

2.7

ReversedLinesFileReader

@Deprecated
public ReversedLinesFileReader(Path file,
 int blockSize,
 String charsetName)
                        throws 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:

IOException - if an I/O error occurs

UnsupportedCharsetException - if the encoding is not supported

Since:

2.7

Method Details

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 IOException

Closes underlying resources.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException - if an I/O error occurs.

iterator

public IOIterator<String> iterator()

Description copied from interface: IOIterable

Like Iterable.iterator().

Specified by:

iterator in interface IOIterable<String>

Returns:

See delegate.

See Also:

• Iterable.iterator()

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

unwrap

public Iterable<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<String>

Returns:

the underlying Iterable.