Java IO

Java IO

IO: Input And Output

java 中有IO，即输入与输出，输入input 输出output

java 有典型的IO与NIO，常说的IO指典型IO, 阻塞IO， NIO表示非阻塞IO

阻塞： 等待IO任务完成才能继续下一步的操作

非阻塞： 暂不能清晰描述，可以查看网址文章链接：http://ifeve.com/overview

这里简单介绍Java中常见的文件读写

字节流读写文件：

读文件

public static void readFile(String filePath) throws IOException {
		File file = new File(filePath);
		if (!file.exists() || !file.isFile()) {
			System.out.println("file is not exist");
		} else {
			FileInputStream fileInputStream = new FileInputStream(file); //创建文件输入流
			byte[] read = new byte[1024];
			while (fileInputStream.read(read) != -1) {
				System.out.println("read content:" + read);
			}
			fileInputStream.close(); // 关闭流 释放资源
		}

	}

写文件

public static void writeFile(byte[] content) throws IOException {
		File file = new File("D:\\writeFile.xml"); //获取写文件的位置
		if (!file.exists())
			file.createNewFile();
		FileOutputStream fileOutputStream = new FileOutputStream(file); //创建文件输出流
		fileOutputStream.write(content); // content 表示写入文件的内容 
		fileOutputStream.close();	//关闭流 释放资源
	}

拷贝文件

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class TestIO {
    
	public static void main(String[] args) throws IOException {
		String originFilePath = "D:\\Program.md";
		String aimFilePath = "D:\\aimFile.md";
		copyFile(originFilePath, aimFilePath);
//		testRandonAccessFile();
	}    
	
	/*
	 * 读文件
	 */
	public static void readFile(String filePath) throws IOException {
		File file = new File(filePath);
		if (!file.exists() || !file.isFile()) {
			System.out.println("file is not exist");
		} else {
			FileInputStream fileInputStream = new FileInputStream(file);
			byte[] read = new byte[1024];
			while (fileInputStream.read(read) != -1) {
				System.out.println("read content:" + read);
			}
			fileInputStream.close();
		}

	}
	
	/**
	 * 写文件
	 * @throws IOException
	 */
	public static void writeFile(byte[] content) throws IOException {
		File file = new File("D:\\writeFile.xml");
		if (!file.exists())
			file.createNewFile();
		FileOutputStream fileOutputStream = new FileOutputStream(file);
		fileOutputStream.write(content);
		fileOutputStream.close();
	}
    
	/*
	 * 文件复制 -> 读取一个文件复制到另一个地方
	 */
	public static void copyFile(String originFilePath, String aimPath) {
		File originFile = new File(originFilePath);
		if (!originFile.exists()) {
			System.err.println("file is not exists!");
			return;   //文件不存在
		}
		File aimFile = new File(aimPath);
		FileInputStream fi = null;
		FileOutputStream fo = null;
		try {
			byte[] content = new byte[1024];   //每次读文件内容的字节数组
			if (!aimFile.exists())
				aimFile.createNewFile();
            // 通过路径转化为 输入流 和 输出流
			fi = new FileInputStream(originFile);  //输入流
			fo = new FileOutputStream(aimFile);	//输出流
			while (fi.read(content) != -1) { //输入流将数据读取到字节数组，如果返回值为 -1 表示文件已经读完
				fo.write(content); //输出流将数组内容写入文件
			}
		} catch (IOException e) {
			System.err.println("read file exception!");
			try {
				// close resources;
				if (fo != null)
					fo.close();
				if (fi != null)
					fi.close();
			} catch (IOException es) {
				// TODO Auto-generated catch block
				es.printStackTrace();
			}
		} finally {
			try {
				if (fo != null)
					fo.close();
				if (fi != null)
					fi.close();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
    
    /*
    * java 涉及NIO的 RandomAccessFile 类
    */
	private static void testRandonAccessFile() throws IOException {
		RandomAccessFile aFile = new RandomAccessFile("D:\\settings.xml", "rw");
		FileChannel channel = aFile.getChannel();
		File file = new File("D:\\creatFile.xml");
		if (!file.getParentFile().exists())
			file.getParentFile().mkdirs();

		if (!file.isFile()) {
			System.err.println("file is not exist!");
			System.exit(0);
		}
		if (!file.exists())
			file.createNewFile();

		FileOutputStream newFile = new FileOutputStream(file);
		ByteBuffer buffer = ByteBuffer.allocate(1024);
		int i = 0;
		while (channel.read(buffer) != -1) {
			i++;
			buffer.flip();
			while (buffer.hasRemaining()) {
				newFile.write(buffer.get());
			}
			buffer.clear();
		}
		aFile.close();
		newFile.close();
		System.out.println("文件读取次数：" + i);
	}

}