讀取Java文件到byte數組的三種方式

轉自：http://blog.csdn.net/z69183787/article/details/16883243

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;  
        }  
        // 確保所有數據均被讀取  
        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 可以在處理大文件時，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();  
            }  
        }  
    }  
}