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();
			}
		}
	}
}

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