读取Java文件到byte数组的三种方式（转载）

来源：互联网发布：鱼鹰软件编辑：程序博客网时间：2024/06/11 14:50
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();            }        }    }}
阅读全文
0 0