FileInputStream
java.lang.Object
|
+-java.io.InputStream
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+-java.io.FileInputStream
The FileInputStream class creates an InputStream that you can use to read bytes from a file.
Its two most common constructors:
FileInputStream(String filepath)- filepath is the full path name of a file
FileInputStream(File fileObj)- fileObj is a File object that describes the file.
Either can throw a FileNotFoundException.
The following example creates two FileInputStreams that use the same disk file and each of the two constructors:
FileInputStream f0 = new FileInputStream("/autoexec.bat")
File f = new File("/autoexec.bat");
FileInputStream f1 = new FileInputStream(f);
FileInputStream overrides six of the methods in the abstract class InputStream.
int 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.
void close()- Closes this file input stream and releases any system resources associated with the stream.
FileChannel getChannel()- Returns the unique FileChannel object associated with this file input stream.
FileDescriptor getFD()- Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream.
int read()- Reads a byte of data from this input stream.
int read(byte[] b)- Reads up to b.length bytes of data from this input stream into an array of bytes.
int read(byte[] b, int off, int len)- Reads up to len bytes of data from this input stream into an array of bytes.
long skip(long n)- Skips over and discards n bytes of data from the input stream.
Revised from Open JDK source code
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class Main {
public static void main(String args[]) throws IOException {
InputStream f = new FileInputStream("FileInputStreamDemo.java");
int size = f.available();
System.out.println("Total Available Bytes: " + size);
int n = 40;
System.out.println("First " + n + " bytes of the file one read() at a time");
for (int i = 0; i < n; i++) {
System.out.print((char) f.read());
}
byte b[] = new byte[n];
if (f.read(b) != n) {
System.err.println("couldn't read " + n + " bytes.");
}
System.out.println(new String(b, 0, n));
f.skip(30);
if (f.read(b, n / 2, n / 2) != n / 2) {
System.err.println("couldn't read " + n / 2 + " bytes.");
}
System.out.println(new String(b, 0, b.length));
f.close();
}
}
The following code reads one byte from the 'a.htm'
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class Main {
public static void main(String[] args) throws FileNotFoundException {
FileInputStream file = null;
byte x = -1;
try {
file = new FileInputStream("a.htm");
x = (byte) file.read();
} catch (FileNotFoundException f) {
throw f;
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (file != null) {
file.close();
}
} catch (IOException e) {
}
}
}
}