Java bufferedreader с файлами

Class BufferedReader

Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.

The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.

In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders. For example,

BufferedReader in = new BufferedReader(new FileReader("foo.in"));

will buffer the input from the specified file. Without buffering, each invocation of read() or readLine() could cause bytes to be read from the file, converted into characters, and then returned, which can be very inefficient.

Programs that use DataInputStreams for textual input can be localized by replacing each DataInputStream with an appropriate BufferedReader.

Field Summary

Fields declared in class java.io.Reader

Constructor Summary

Method Summary

Methods declared in class java.io.Reader

Methods declared in class java.lang.Object

Constructor Details

BufferedReader

BufferedReader

Method Details

read

read

• The specified number of characters have been read,
• The read method of the underlying stream returns -1 , indicating end-of-file, or
• The ready method of the underlying stream returns false , indicating that further input requests would block.

Subclasses of this class are encouraged, but not required, to attempt to read as many characters as possible in the same fashion.

Ordinarily this method takes characters from this stream’s character buffer, filling it from the underlying stream as necessary. If, however, the buffer is empty, the mark is not valid, and the requested length is at least as large as the buffer, then this method will read characters directly from the underlying stream into the given array. Thus redundant BufferedReader s will not copy data unnecessarily.

readLine

Reads a line of text. A line is considered to be terminated by any one of a line feed (‘\n’), a carriage return (‘\r’), a carriage return followed immediately by a line feed, or by reaching the end-of-file (EOF).

ready

Tells whether this stream is ready to be read. A buffered character stream is ready if the buffer is not empty, or if the underlying character stream is ready.

markSupported

mark

Marks the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point.

reset

close

Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

lines

Returns a Stream , the elements of which are lines read from this BufferedReader . The Stream is lazily populated, i.e., read only occurs during the terminal stream operation. The reader must not be operated on during the execution of the terminal stream operation. Otherwise, the result of the terminal stream operation is undefined. After execution of the terminal stream operation there are no guarantees that the reader will be at a specific position from which to read the next character or line. If an IOException is thrown when accessing the underlying BufferedReader , it is wrapped in an UncheckedIOException which will be thrown from the Stream method that caused the read to take place. This method will return a Stream if invoked on a BufferedReader that is closed. Any operation on that stream that requires reading from the BufferedReader after it is closed, will cause an UncheckedIOException to be thrown.

Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples. Other versions.
Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries.
Copyright © 1993, 2023, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.
All rights reserved. Use is subject to license terms and the documentation redistribution policy.

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Class BufferedReader

Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.

The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.

In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders. For example,

BufferedReader in = new BufferedReader(new FileReader("foo.in"));

will buffer the input from the specified file. Without buffering, each invocation of read() or readLine() could cause bytes to be read from the file, converted into characters, and then returned, which can be very inefficient.

Programs that use DataInputStreams for textual input can be localized by replacing each DataInputStream with an appropriate BufferedReader.

Field Summary

Fields declared in class java.io.Reader

Constructor Summary

Method Summary

Methods declared in class java.io.Reader

Methods declared in class java.lang.Object

Constructor Details

BufferedReader

BufferedReader

Method Details

read

read

• The specified number of characters have been read,
• The read method of the underlying stream returns -1 , indicating end-of-file, or
• The ready method of the underlying stream returns false , indicating that further input requests would block.

Subclasses of this class are encouraged, but not required, to attempt to read as many characters as possible in the same fashion.

Ordinarily this method takes characters from this stream’s character buffer, filling it from the underlying stream as necessary. If, however, the buffer is empty, the mark is not valid, and the requested length is at least as large as the buffer, then this method will read characters directly from the underlying stream into the given array. Thus redundant BufferedReader s will not copy data unnecessarily.

readLine

Reads a line of text. A line is considered to be terminated by any one of a line feed (‘\n’), a carriage return (‘\r’), a carriage return followed immediately by a line feed, or by reaching the end-of-file (EOF).

ready

Tells whether this stream is ready to be read. A buffered character stream is ready if the buffer is not empty, or if the underlying character stream is ready.

markSupported

mark

Marks the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point.

reset

close

Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

lines

Returns a Stream , the elements of which are lines read from this BufferedReader . The Stream is lazily populated, i.e., read only occurs during the terminal stream operation. The reader must not be operated on during the execution of the terminal stream operation. Otherwise, the result of the terminal stream operation is undefined. After execution of the terminal stream operation there are no guarantees that the reader will be at a specific position from which to read the next character or line. If an IOException is thrown when accessing the underlying BufferedReader , it is wrapped in an UncheckedIOException which will be thrown from the Stream method that caused the read to take place. This method will return a Stream if invoked on a BufferedReader that is closed. Any operation on that stream that requires reading from the BufferedReader after it is closed, will cause an UncheckedIOException to be thrown.

Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples. Other versions.
Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries.
Copyright © 1993, 2023, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.
All rights reserved. Use is subject to license terms and the documentation redistribution policy.

Источник

BufferedReader и BufferedWriter

Java класс BufferedReader читает текст из потока ввода символов, буферизуя прочитанные символы, чтобы обеспечить эффективное считывание символов, массивов и строк. Можно указать в конструкторе вторым параметром размер буфера.

 BufferedReader(Reader in) // Создает буферный поток ввода символов, который использует размер буфера по умолчанию. BufferedReader(Reader in, int sz) // Создает буферный поток ввода символов, который использует указанный размер. 

 close() // закрыть поток mark(int readAheadLimit) // отметить позицию в потоке markSupported() // поддерживает ли отметку потока int read() // прочитать буфер int read(char[] cbuf, int off, int len) // прочитать буфер String readLine() // следующая строка boolean ready() // может ли поток читать reset() // сбросить поток skip(long n) // пропустить символы 

 import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class FileReaderExample < public static void main(String[] args) < String inputFileName = "file.txt"; try (BufferedReader reader = new BufferedReader(new FileReader(inputFileName))) < String line; while ((line = reader.readLine()) != null) < System.out.println(line + "\n"); >> catch (IOException e) < e.printStackTrace(); >> > 

Java класс BufferedWriter записывает текст в поток вывода символов, буферизуя записанные символы, чтобы обеспечить эффективную запись символов, массивов и строк. Можно указать в конструкторе вторым параметром размер буфера. Конструкторы:

 BufferedWriter(Writer out) // Создает буферный поток вывода символов, который использует размер буфера по умолчанию. BufferedWriter(Writer out, int sz) // Создает буферный поток вывода символов, который использует указанный размер. 

 close() // закрыть поток flush() // передать данные из буфера во Writer newLine() // перенос на новую строку write(char[] cbuf, int off, int len) // запись в буфер write(int c) // запись в буфер write(String s, int off, int len) // запись в буфер 

 import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class FileWritterExample < public static void main(String[] args) < String outputFileName = "file.txt"; String[] array = < "one", "two", "three", "four" >; try (BufferedWriter writter = new BufferedWriter(new FileWriter(outputFileName))) < for (String value : array) < writter.write(value + "\n"); >> catch (IOException e) < e.printStackTrace(); >> > 

FileWriter сразу записывает данные на диск и каждый раз к нему обращается, буфер работает как обертка и ускоряет работу приложения. Буфер будет записывать данные в себя, а потом большим куском файлы на диск. Считываем данные с консоли и записываем в файл:

 import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; import java.io.InputStreamReader; public class ConsoleReaderExample < public static void main(String[] args) < String outputFileName = "file.txt"; try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) < try (BufferedWriter writter = new BufferedWriter(new FileWriter(outputFileName))) < String line; while (!(line = reader.readLine()).equals("exit")) < // Прерывание цикла при написании строки exit writter.write(line); >> > catch (IOException e) < e.printStackTrace(); >> > 

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