Java input file class

Java input file class

A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment. FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader .

Constructor Summary

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.

Creates a FileInputStream by using the file descriptor fdObj , which represents an existing connection to an actual file in the file system.

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

Method Summary

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.

Ensures that the close method of this file input stream is called when there are no more references to it.

Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream .

Methods inherited from class java.io.InputStream

Methods inherited from class java.lang.Object

Constructor Detail

FileInputStream

public FileInputStream(String name) throws FileNotFoundException

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system. A new FileDescriptor object is created to represent this file connection. First, if there is a security manager, its checkRead method is called with the name argument as its argument. If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown.

FileInputStream

public FileInputStream(File file) throws FileNotFoundException

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. A new FileDescriptor object is created to represent this file connection. First, if there is a security manager, its checkRead method is called with the path represented by the file argument as its argument. If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown.

FileInputStream

Creates a FileInputStream by using the file descriptor fdObj , which represents an existing connection to an actual file in the file system. If there is a security manager, its checkRead method is called with the file descriptor fdObj as its argument to see if it’s ok to read the file descriptor. If read access is denied to the file descriptor a SecurityException is thrown. If fdObj is null then a NullPointerException is thrown. This constructor does not throw an exception if fdObj is invalid . However, if the methods are invoked on the resulting stream to attempt I/O on the stream, an IOException is thrown.

Method Detail

read

read

Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

read

Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

skip

Skips over and discards n bytes of data from the input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0 . If n is negative, the method will try to skip backwards. In case the backing file does not support backward skip at its current position, an IOException is thrown. The actual number of bytes skipped is returned. If it skips forwards, it returns a positive value. If it skips backwards, it returns a negative value. This method may skip more bytes than what are remaining in the backing file. This produces no exception and the number of bytes skipped may include some number of bytes that were beyond the EOF of the backing file. Attempting to read from the stream after skipping past the end will result in -1 indicating the end of the file.

available

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. Returns 0 when the file position is beyond EOF. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. In some cases, a non-blocking read (or skip) may appear to be blocked when it is merely slow, for example when reading large files over slow networks.

close

Closes this file input stream and releases any system resources associated with the stream. If this stream has an associated channel then the channel is closed as well.

getFD

Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream .

getChannel

Returns the unique FileChannel object associated with this file input stream. The initial position of the returned channel will be equal to the number of bytes read from the file so far. Reading bytes from this stream will increment the channel’s position. Changing the channel’s position, either explicitly or by reading, will change this stream’s file position.

finalize

Ensures that the close method of this file input stream is called when there are no more references to it.

Источник

Class FileInputStream

A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment.

FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader .

Constructor Summary

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.

Creates a FileInputStream by using the file descriptor fdObj , which represents an existing connection to an actual file in the file system.

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

Method Summary

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.

Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream .

Methods declared in class java.io.InputStream

Methods declared in class java.lang.Object

Constructor Details

FileInputStream

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system. A new FileDescriptor object is created to represent this file connection. First, if there is a security manager, its checkRead method is called with the name argument as its argument. If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown.

FileInputStream

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. A new FileDescriptor object is created to represent this file connection. First, if there is a security manager, its checkRead method is called with the path represented by the file argument as its argument. If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown.

FileInputStream

Creates a FileInputStream by using the file descriptor fdObj , which represents an existing connection to an actual file in the file system. If there is a security manager, its checkRead method is called with the file descriptor fdObj as its argument to see if it’s ok to read the file descriptor. If read access is denied to the file descriptor a SecurityException is thrown. If fdObj is null then a NullPointerException is thrown. This constructor does not throw an exception if fdObj is invalid . However, if the methods are invoked on the resulting stream to attempt I/O on the stream, an IOException is thrown.

Method Details

read

read

Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

read

Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

skip

Skips over and discards n bytes of data from the input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0 . If n is negative, the method will try to skip backwards. In case the backing file does not support backward skip at its current position, an IOException is thrown. The actual number of bytes skipped is returned. If it skips forwards, it returns a positive value. If it skips backwards, it returns a negative value. This method may skip more bytes than what are remaining in the backing file. This produces no exception and the number of bytes skipped may include some number of bytes that were beyond the EOF of the backing file. Attempting to read from the stream after skipping past the end will result in -1 indicating the end of the file.

available

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. Returns 0 when the file position is beyond EOF. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. In some cases, a non-blocking read (or skip) may appear to be blocked when it is merely slow, for example when reading large files over slow networks.

close

Closes this file input stream and releases any system resources associated with the stream. If this stream has an associated channel then the channel is closed as well.

getFD

Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream .

getChannel

Returns the unique FileChannel object associated with this file input stream. The initial position of the returned channel will be equal to the number of bytes read from the file so far. Reading bytes from this stream will increment the channel’s position. Changing the channel’s position, either explicitly or by reading, will change this stream’s file position.

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Источник

Java input file class

Note: Before running the code, a text file named as «testout.txt» is required to be created. In this file, we are having following content:

After executing the above program, you will get a single character from the file which is 87 (in byte form). To see the text, you need to convert it into character.

Java FileInputStream example 2: read all characters

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