Java Tutorial/File/FileInputStream
Содержание
- 1 Constructing FileInputStream to read from a Text File
- 2 Copy a file with read(byte[] data) and write(byte[] data)
- 3 Create FileInputStream and read, display data
- 4 Creating FileInputStream from File object
- 5 Creating File Input Streams from file name
- 6 Display file contents in hexadecimal
- 7 FileInputStream
- 8 Getting FileChannel from FileInputStream
- 9 Read bytes and display their hexadecimal values.
- 10 Read file character by character
- 11 Reading a Binary File
- 12 Reading a File into a Byte Array: reads the entire contents of a file into a byte array
- 13 Reading into a Large Buffer through FileChannel
- 14 Reading Mixed Data from a File
- 15 Reading UTF-8 Encoded Data
- 16 Read one byte from a file
- 17 Skip n bytes while reading the file using FileInputStream
- 18 Using a FileDescriptor from getFD() and creating a FileInputStream from FileDescriptor
Constructing FileInputStream to read from a Text File
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.nio.channels.FileChannel; public class MainClass {
public static void main(String[] a) {
File aFile = new File("charData.txt");
FileInputStream inFile = null;
try {
inFile = new FileInputStream(aFile);
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
}
FileChannel inChannel = inFile.getChannel();
}
}</source>
Copy a file with read(byte[] data) and write(byte[] data)
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; public class Main {
public static void main(String[] args) throws Exception {
FileInputStream fin = null;
FileOutputStream fout = null;
File file = new File("C:/myfile1.txt");
fin = new FileInputStream(file);
fout = new FileOutputStream("C:/myfile2.txt");
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = fin.read(buffer)) > 0) {
fout.write(buffer, 0, bytesRead);
}
fin.close();
fout.close();
}
}</source>
Create FileInputStream and read, display data
<source lang="java">
import java.io.FileInputStream; class FileInputStreamDemo {
public static void main(String args[]) throws Exception {
FileInputStream fis = new FileInputStream(args[0]);
// Read and display data
int i;
while ((i = fis.read()) != -1) {
System.out.println(i);
}
fis.close();
}
}</source>
Creating FileInputStream from File object
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; public class MainClass {
public static void main(String[] a) {
File aFile = new File("C:/myFile.txt");
FileInputStream inputFile = null;
try {
inputFile = new FileInputStream(aFile);
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
}
}
}</source>
Creating File Input Streams from file name
<source lang="java">
import java.io.FileInputStream; import java.io.FileNotFoundException; public class MainClass {
public static void main(String[] a) {
FileInputStream inputFile = null;
try {
inputFile = new FileInputStream("C:/myFile.txt");
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
}
}
}</source>
Display file contents in hexadecimal
<source lang="java">
import java.io.FileInputStream; public class Main {
public static void main(String[] args) throws Exception {
FileInputStream fis = new FileInputStream("/home/username/data.txt");
int i = 0;
int count = 0;
while ((i = fis.read()) != -1) {
if (i != -1) {
System.out.printf("%02X ", i);
count++;
}
if (count == 16) {
System.out.println("");
count = 0;
}
}
fis.close();
}
}</source>
FileInputStream
- The FileInputStream class is a subclass of InputStream.
- The FileInputStream class allows you to read binary data sequentially from a file.
- The FileInputStream class"s constructors allow you to pass either a File object or a path to a file.
<source lang="java">
public FileInputStream (String path) public FileInputStream (File file)</source>
Getting FileChannel from FileInputStream
<source lang="java">
import java.io.FileInputStream; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; public class MainClass {
private static final int BSIZE = 1024;
public static void main(String[] args) throws Exception {
FileChannel fc = new FileInputStream("data.txt").getChannel();
ByteBuffer buff = ByteBuffer.allocate(BSIZE);
fc.read(buff);
buff.flip();
while (buff.hasRemaining())
System.out.print((char) buff.get());
}
}</source>
Read bytes and display their hexadecimal values.
<source lang="java">
import java.io.FileInputStream; public class Main {
public static void main(String[] argv) throws Exception {
FileInputStream fin = new FileInputStream("text.txt");
int len;
byte data[] = new byte[16];
// Read bytes until EOF is encountered.
do {
len = fin.read(data);
for (int j = 0; j < len; j++)
System.out.printf("%02X ", data[j]);
} while (len != -1);
}
}</source>
Read file character by character
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.IOException; public class Main {
public static void main(String[] args) {
File file = new File(args[0]);
if (!file.exists()) {
System.out.println(args[0] + " does not exist.");
return;
}
if (!(file.isFile() && file.canRead())) {
System.out.println(file.getName() + " cannot be read from.");
return;
}
try {
FileInputStream fis = new FileInputStream(file);
char current;
while (fis.available() > 0) {
current = (char) fis.read();
System.out.print(current);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}</source>
Reading a Binary File
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; public class MainClass {
public static void main(String[] args) {
File aFile = new File("C:/test.bin");
FileInputStream inFile = null;
try {
inFile = new FileInputStream(aFile);
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
}
FileChannel inChannel = inFile.getChannel();
final int PRIMECOUNT = 6;
ByteBuffer buf = ByteBuffer.allocate(8 * PRIMECOUNT);
long[] primes = new long[PRIMECOUNT];
try {
while (inChannel.read(buf) != -1) {
((ByteBuffer) (buf.flip())).asLongBuffer().get(primes);
for (long prime : primes) {
System.out.printf("%10d", prime);
}
buf.clear();
}
inFile.close();
} catch (IOException e) {
e.printStackTrace(System.err);
}
}
}</source>
Reading a File into a Byte Array: reads the entire contents of a file into a byte array
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; public class Main {
public static void main(String[] argv) throws Exception {
File file = new File("c:\\a.bat");
InputStream is = new FileInputStream(file);
long length = file.length();
if (length > Integer.MAX_VALUE) {
System.out.println("File is too large");
}
byte[] bytes = new byte[(int) length];
int offset = 0;
int numRead = 0;
while (numRead >= 0) {
numRead = is.read(bytes, offset, bytes.length - offset);
offset += numRead;
}
if (offset < bytes.length) {
throw new IOException("Could not completely read file " + file.getName());
}
is.close();
System.out.println(new String(bytes));
}
}</source>
Reading into a Large Buffer through FileChannel
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; public class MainClass {
public static void main(String[] args) {
try {
test();
} catch (Exception e) {
e.printStackTrace();
}
}
private static void test() throws Exception {
File aFile = new File("primes.txt");
FileInputStream inFile = new FileInputStream(aFile);
FileChannel inChannel = inFile.getChannel();
ByteBuffer buf = ByteBuffer.allocateDirect(1024);
buf.position(buf.limit());
while (true) {
if (buf.remaining() < 8) {
if (inChannel.read(buf.rupact()) == -1){
break;
}
buf.flip();
}
int strLength = (int) buf.getDouble();
if (buf.remaining() < 2 * strLength) {
if (inChannel.read(buf.rupact()) == -1){
break;
}
buf.flip();
}
byte[] strChars = new byte[2 * strLength];
buf.get(strChars);
if (buf.remaining() < 8) {
if (inChannel.read(buf.rupact()) == -1){
break;
}
buf.flip();
}
System.out.println(strLength);
System.out.println(ByteBuffer.wrap(strChars).asCharBuffer());
System.out.println(buf.getLong());
}
inFile.close();
}
}</source>
Reading Mixed Data from a File
<source lang="java">
import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; public class MainClass {
public static void main(String[] args) {
File aFile = new File("primes.txt");
FileInputStream inFile = null;
try {
inFile = new FileInputStream(aFile);
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
}
FileChannel inChannel = inFile.getChannel();
try {
ByteBuffer lengthBuf = ByteBuffer.allocate(8);
while (true) {
if (inChannel.read(lengthBuf) == -1){
break;
}
lengthBuf.flip();
int strLength = (int) lengthBuf.getDouble();
ByteBuffer buf = ByteBuffer.allocate(2 * strLength + 8);
if (inChannel.read(buf) == -1) {
break;
}
buf.flip();
byte[] strChars = new byte[2 * strLength];
buf.get(strChars);
System.out.println(strLength);
System.out.println(ByteBuffer.wrap(strChars).asCharBuffer());
System.out.println(buf.getLong());
lengthBuf.clear();
}
inFile.close();
} catch (IOException e) {
e.printStackTrace(System.err);
}
}
}</source>
Reading UTF-8 Encoded Data
<source lang="java">
import java.io.BufferedReader; import java.io.FileInputStream; import java.io.InputStreamReader; public class Main {
public static void main(String[] argv) throws Exception {
BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream("infilename"),
"UTF8"));
String str = in.readLine();
System.out.println(str);
}
}</source>
Read one byte from a file
<source lang="java">
import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; public class Main {
public void readOneByte() throws FileNotFoundException {
FileInputStream file = null;
byte x = -1;
try {
file = new FileInputStream("fileName");
x = (byte) file.read();
} catch (FileNotFoundException f) {
throw f;
} catch (IOException i) {
i.printStackTrace();
} finally {
try {
if (file != null) {
file.close();
}
} catch (IOException e) {
}
}
}
}</source>
Skip n bytes while reading the file using FileInputStream
<source lang="java">
import java.io.File; import java.io.FileInputStream; public class Main {
public static void main(String[] args) throws Exception {
File file = new File("C:/String.txt");
FileInputStream fin = new FileInputStream(file);
int ch;
// skip first 10 bytes
fin.skip(10);
while ((ch = fin.read()) != -1){
System.out.print((char) ch);
}
}
}</source>
Using a FileDescriptor from getFD() and creating a FileInputStream from FileDescriptor
<source lang="java">
import java.io.File; import java.io.FileDescriptor; import java.io.FileInputStream; import java.io.IOException; public class MainClass {
public static void main(String[] a) {
File aFile = new File("C:/myFile.text");
FileInputStream inputFile1 = null;
FileDescriptor fd = null;
try {
inputFile1 = new FileInputStream(aFile);
fd = inputFile1.getFD();
} catch (IOException e) {
e.printStackTrace(System.err);
System.exit(1);
}
FileInputStream inputFile2 = new FileInputStream(fd);
}
}</source>
