几种读取文件方式的性能测试

这些天一直在对文件进行读写操作，为了性能，换了好几种方式，我下面贴出来：

/**
* 随机读取文件内容
* 
* @param fileName
*/
public static String readFileByRandomAccess(String path) {
	StringBuffer sb = new StringBuffer();
	RandomAccessFile randomFile = null;
	try {
		// 打开一个随机访问文件流，按只读方式
		randomFile = new RandomAccessFile(path, "rw");
		byte[] bytes = new byte[1024];
		int byteread = 0;
		while ((byteread = randomFile.read(bytes)) != -1) {
			// System.out.write(bytes, 0, byteread);
			sb.append(new String(bytes, 0, byteread));
		}
	} catch (IOException e) {
		e.printStackTrace();
	} finally {
		if (randomFile != null) {
			try {
				randomFile.close();
			} catch (IOException e1) {
			}
		}
	}
	return sb.toString();
}

/**
* 以行为单位读取文件，常用于读面向行的格式化文件
* 
* @param fileName
*/
public static String readFileByLines(String path) {
	StringBuffer sb = new StringBuffer();
	BufferedReader reader = null;
	try {
		reader = new BufferedReader(new FileReader(path));
		String tempString = null;
		while ((tempString = reader.readLine()) != null) {
		sb.append(tempString).append(System.getProperty("line.separator"));// 显示行号
		}
	} catch (IOException e) {
		e.printStackTrace();
	} finally {
		try {
			if (reader != null) {
				reader.close();
			}
		} catch (IOException e) {
			System.err.println("流关闭失败");
		}
	}
	return sb.toString();
}

/**
* 使用Java.nio ByteBuffer字节将一个文件输出
* 
* @param filePath
*/
public static String readFileByBybeBuffer(String path) {
	StringBuffer sb = new StringBuffer();
	FileInputStream in = null;
	FileOutputStream out = null;
	try {
		// 获取源文件和目标文件的输入输出流
		in = new FileInputStream(path);
		// 获取输入输出通道
		FileChannel fcIn = in.getChannel();
		ByteBuffer buffer = ByteBuffer.allocate(1024);
		CharBuffer charBuffer = null;
		Charset charset = Charset.forName("UTF-8");
		CharsetDecoder decoder = charset.newDecoder();
		while (true) {
			// clear方法重设缓冲区，使它可以接受读入的数据
			buffer.clear();
			// 从输入通道中将数据读到缓冲区
			int r = fcIn.read(buffer);
			if (r == -1) {
				break;
			}
			charBuffer = decoder.decode(buffer);
			// flip方法让缓冲区可以将新读入的数据写入另一个通道
			buffer.flip();
			sb.append(charBuffer.toString());
		}
	} catch (Exception e) {
		e.printStackTrace();
	} finally {
		try {
			if (in != null && out != null) {
				in.close();
				out.close();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	//System.out.println(sb.toString());
	return sb.toString();
}

/**
* 通过scanner的方式读取文件
* 
* @param fileName
* @return
*/
public static String readByScanner(String path) {
	StringBuffer sb = new StringBuffer();
	Scanner s = null;
	try {
		File f = new File(path);
			s = new Scanner(f);
			while (s.hasNext()) {
			sb.append(s.next());
		}
	} catch (FileNotFoundException e) {
		e.printStackTrace();
	} finally {
		if(s!=null)s.close();
	}
	return sb.toString();
}

我们来测试下：

String fileName="Z:\\flume\\flume\\conf\\ErrLog";
long t1=OperateUtil.getTime();
OperateUtil.readByScanner(fileName);
long t2=OperateUtil.getTime();
OperateUtil.readFileByBybeBuffer(fileName);
long t3=OperateUtil.getTime();
OperateUtil.readFileByLines(fileName);
long t4=OperateUtil.getTime();
OperateUtil.readFileByRandomAccess(fileName);
long t5=OperateUtil.getTime();
		
System.out.println("readByScanner:"+(t2-t1));
System.out.println("readFileByBybeBuffer:"+(t3-t2));
System.out.println("readFileByLines:"+(t4-t3));
System.out.println("readFileByRandomAccess:"+(t5-t4));
ErrLog的文件大小是65M。

下面看下测试结果：

readByScanner:6180
readFileByBybeBuffer:171
readFileByLines:468
readFileByRandomAccess:531

经过多次测试，依旧发现readFileByBybeBuffer这个方式的效率更好，使用的是NIO