NIO读取文件

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
 
public class TestJavaNIO {
 
	static void readNIO() {
		String pathname = "C:\\Users\\adew\\Desktop\\jd-gui.cfg";
		FileInputStream fin = null;
		try {
			fin = new FileInputStream(new File(pathname));
			FileChannel channel = fin.getChannel();
 
			int capacity = 100;// 字节
			ByteBuffer bf = ByteBuffer.allocate(capacity);
			System.out.println("限制是：" + bf.limit() + "容量是：" + bf.capacity()
					+ "位置是：" + bf.position());
			int length = -1;
 
			while ((length = channel.read(bf)) != -1) {
 
				/*
				 * 注意，读取后，将位置置为0，将limit置为容量, 以备下次读入到字节缓冲中，从0开始存储
				 */
				bf.clear();
				byte[] bytes = bf.array();
				System.out.write(bytes, 0, length);
				System.out.println();
 
				System.out.println("限制是：" + bf.limit() + "容量是：" + bf.capacity()
						+ "位置是：" + bf.position());
 
			}
 
			channel.close();
 
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fin != null) {
				try {
					fin.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}
 
	static void writeNIO() {
		String filename = "out.txt";
		FileOutputStream fos = null;
		try {
 
			fos = new FileOutputStream(new File(filename));
			FileChannel channel = fos.getChannel();
			ByteBuffer src = Charset.forName("utf8").encode("你好你好你好你好你好");
			// 字节缓冲的容量和limit会随着数据长度变化，不是固定不变的
			System.out.println("初始化容量和limit：" + src.capacity() + ","
					+ src.limit());
			int length = 0;
 
			while ((length = channel.write(src)) != 0) {
				/*
				 * 注意，这里不需要clear，将缓冲中的数据写入到通道中后 第二次接着上一次的顺序往下读
				 */
				System.out.println("写入长度:" + length);
			}
 
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fos != null) {
				try {
					fos.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}
 
	static void testReadAndWriteNIO() {
		String pathname = "C:\\Users\\adew\\Desktop\\test.txt";
		FileInputStream fin = null;
		
		String filename = "test-out.txt";
		FileOutputStream fos = null;
		try {
			fin = new FileInputStream(new File(pathname));
			FileChannel channel = fin.getChannel();
 
			int capacity = 100;// 字节
			ByteBuffer bf = ByteBuffer.allocate(capacity);
			System.out.println("限制是：" + bf.limit() + "容量是：" + bf.capacity()+ "位置是：" + bf.position());
			int length = -1;
 
			fos = new FileOutputStream(new File(filename));
			FileChannel outchannel = fos.getChannel();
			
			
			while ((length = channel.read(bf)) != -1) {
				
				//将当前位置置为limit，然后设置当前位置为0，也就是从0到limit这块，都写入到同道中
				bf.flip();
				
				int outlength =0;
				while((outlength=outchannel.write(bf)) != 0){
					System.out.println("读，"+length+"写,"+outlength);
				}
				
				//将当前位置置为0，然后设置limit为容量，也就是从0到limit（容量）这块，
				//都可以利用，通道读取的数据存储到
				//0到limit这块
				bf.clear();
				
			}
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fin != null) {
				try {
					fin.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if (fos != null) {
				try {
					fos.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}
 
	@SuppressWarnings("resource")
	public static void main(String[] args) {
		testReadAndWriteNIO();
	}
 
}

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