读取Java文件到byte数组的三种方法(总结)

读取Java文件到byte数组的三种方法(总结)

package zs;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;

public class FileUtils {
public byte[] getContent(String filePath) throws IOException {
File file = new File(filePath);
long fileSize = file.length();
if (fileSize > Integer.MAX_VALUE) {
System.out.println("file too big...");
return null;
}
FileInputStream fi = new FileInputStream(file);
byte[] buffer = new byte[(int) fileSize];
int offset = 0;
int numRead = 0;
while (offset < buffer.length
&& (numRead = fi.read(buffer, offset, buffer.length - offset)) >= 0) {
offset += numRead;
}
// 确保所有数据均被读取
if (offset != buffer.length) {
throw new IOException("Could not completely read file "
+ file.getName());
}
fi.close();
return buffer;
}

/**
* the traditional io way
*
* @param filename
* @return
* @throws IOException
*/
public static byte[] toByteArray(String filename) throws IOException {

File f = new File(filename);
if (!f.exists()) {
throw new FileNotFoundException(filename);
}

ByteArrayOutputStream bos = new ByteArrayOutputStream((int) f.length());
BufferedInputStream in = null;
try {
in = new BufferedInputStream(new FileInputStream(f));
int buf_size = 1024;
byte[] buffer = new byte[buf_size];
int len = 0;
while (-1 != (len = in.read(buffer, 0, buf_size))) {
bos.write(buffer, 0, len);
}
return bos.toByteArray();
} catch (IOException e) {
e.printStackTrace();
throw e;
} finally {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
bos.close();
}
}

/**
* NIO way
*
* @param filename
* @return
* @throws IOException
*/
public static byte[] toByteArray2(String filename) throws IOException {

File f = new File(filename);
if (!f.exists()) {
throw new FileNotFoundException(filename);
}

FileChannel channel = null;
FileInputStream fs = null;
try {
fs = new FileInputStream(f);
channel = fs.getChannel();
ByteBuffer byteBuffer = ByteBuffer.allocate((int) channel.size());
while ((channel.read(byteBuffer)) > 0) {
// do nothing
// System.out.println("reading");
}
return byteBuffer.array();
} catch (IOException e) {
e.printStackTrace();
throw e;
} finally {
try {
channel.close();
} catch (IOException e) {
e.printStackTrace();
}
try {
fs.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

/**
* Mapped File way MappedByteBuffer 可以在处理大文件时，提升性能
*
* @param filename
* @return
* @throws IOException
*/
public static byte[] toByteArray3(String filename) throws IOException {

FileChannel fc = null;
try {
fc = new RandomAccessFile(filename, "r").getChannel();
MappedByteBuffer byteBuffer = fc.map(MapMode.READ_ONLY, 0,
fc.size()).load();
System.out.println(byteBuffer.isLoaded());
byte[] result = new byte[(int) fc.size()];
if (byteBuffer.remaining() > 0) {
// System.out.println("remain");
byteBuffer.get(result, 0, byteBuffer.remaining());
}
return result;
} catch (IOException e) {
e.printStackTrace();
throw e;
} finally {
try {
fc.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}