黑马程序员之JAVAIO(一)

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一、概述

        IO流用来处理设备之间的数据传输。按操作的数据分为：字节流和字符流；按流向分为：输入流和输出流。

        在JAVA中字节流的抽象基类为：OutputStream和InputStream；字符流的抽象基类为：Reader和Writer。

二、Reader字符读取流，读取文字类文件。

        示例一：

import java.io.FileReader;
import java.io.IOException;

public class FileReaderDemo {

	public static void main(String[] args) throws IOException {

		//创建一个文件读取流对象, 并指定要读取的文件
		//要保证文件的存在, 否则会报FileNotFindExcption
		FileReader fr = new FileReader("D:/dome2.txt");
		
		//read()读取字符, 每次读取一个, 读完了返回-1
		int ch = 0;
		while (-1 != (ch = fr.read())) {
			System.out.println((char)ch);
		}
		fr.close();
	}

}

        示例二：

import java.io.FileReader;
import java.io.IOException;

/*
 * 通过字符数组进行读取
 */

public class FileReaderDemo2 {

	public static void main(String[] args) throws IOException {

		FileReader fr = new FileReader("D:/dome2.txt");

		// 定义数组, 用于存储读到的字符
		char[] buffer = new char[512];
		// int num = fr.read(buffer); 返回读取的个数

		StringBuffer sb = new StringBuffer();
		int num = 0;
		while (-1 != (num = fr.read(buffer))) {
			sb.append(new String(buffer, 0, num));
		}
		fr.close();
		System.out.println(sb.toString());
	}

}

        示例三：

//将一个.java文件读取出来, 并打印到控制台
public class FileReaderTest {

	public static void main(String[] args) throws IOException {

		
		FileReader fr = new FileReader("D:/CalendarDemo.java");
		
		char[] buffer = new char[5];
		int num =0 ;
		StringBuffer sb = new StringBuffer();
		while(-1 != (num = fr.read(buffer))){
			sb.append(new String(buffer,0,num));
		}
		System.out.println(sb.toString());
		fr.close();
	}
}

三、Writer字符输出流。

        示例一：

public class FileWriterDemo {

	public static void main(String[] args) throws IOException {

		//创建一个FileWriter对象, 该对象一被初始化就必须明确被操作的文件
		//该文件被创建在指定的目录下, 如果该目录下已经有同名的文件, 将会被覆盖
		FileWriter fw = new FileWriter("D:/dome.txt");
		
		//将数据写入到流中
		fw.write("313111");
		
		//刷新流对象换缓冲数据, 将数据刷到目的地中
		fw.flush();
		
		//刷新缓冲数据, 并且将流关闭
		fw.close();
	}

}

        示例二：

/*
 * 文件续写
 */
public class FileWriterDemo3 {

	public static void main(String[] args) {

		FileWriter fw = null;
		try {
			//传递true参数, 表示不会覆盖已有的文件, 并且在文件的后面续写数据
			fw = new FileWriter("D:/dome2.txt", true);
			//windows下换行
			fw.write("121\r\nmmmmm");
			fw.flush();
		} catch (Exception e) {
			System.out.println(e.toString());
		} finally {
			try {
				if (null != fw)
					fw.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

	}

}

四、为了提高文件输入和输出流的效率， Java提供了一个增强的功能，那就是流缓冲区， BufferedReader和BufferedWriter。

        示例一：

//字符读取流缓冲区


public class BufferedReaderDemo {

	public static void main(String[] args) throws IOException {

		//创建一个读取流对象
		FileReader fr = new FileReader("D:/buffer.txt");
		
		//将字符读取流对象作为参数传给缓冲区对象
		BufferedReader br = new BufferedReader(fr);
		
		String line = null;
		StringBuffer sb = new StringBuffer();
		
		//readLine() //读取一行文本, 只会读取回车之前的字符, 不会返回回车
		//无论是读取一行还是多个字符, 最终还是使用的read()方法, 一个一个的读取
		while (null != (line = br.readLine())) {	
			sb.append(line);
		}
		System.out.println(sb.toString());
		br.close();
	}

}

        示例二：

//缓冲区是为了提高流的操作效率
//所以在创建缓冲区之前必须要有流对象

public class BufferedWriterDemo {

	public static void main(String[] args) throws IOException {

		//创建一个字符写入流
		FileWriter fw = new FileWriter("D:/buffer.txt");
		
		//为了提高写入流的效率, 加入缓冲区
		//把流对像作为参数传给缓冲区构造函数即可
		BufferedWriter bw = new BufferedWriter(fw);
		
		bw.write("1aad");
		for(int i=0;i<3;i++){
			bw.write("adad" + i);
			bw.newLine();	//换行, 兼容各个系统
			bw.flush();
		}
		bw.flush();
		//关闭缓冲区, 就是在关闭缓冲区中的流对象
		bw.close();
		fw.close();
		
	}

}

        示例三：

/*
 * 从C盘拷贝一个文件到D盘
 * 运用BufferedReader和BufferedWriter
 */

public class CopyTextByBuffered {

	public static void main(String[] args) {

		String srcPath = "C:/FaceProv.log";
		String descPath = "D:/FaceProv.log";

		CopyTextByBuffered.copy(srcPath, descPath);

	}

	public static void copy(String srcPath, String descPath) {

		FileReader fr = null;
		FileWriter fw = null;
		BufferedReader br = null;
		BufferedWriter bw = null;

		try {

			fr = new FileReader(srcPath);
			fw = new FileWriter(descPath);
			br = new BufferedReader(fr);
			bw = new BufferedWriter(fw);

			int len = 0;
			char[] buffer = new char[20];
			while (-1 != (len = br.read(buffer))) {
				bw.write(buffer, 0, len);
				bw.flush();
			}

		} catch (Exception e) {
			throw new RuntimeException("拷贝失败 !");
		} finally {
			if (null != br)
				try {
					br.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			if (null != bw)
				try {
					bw.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
		}
	}
}

五、FileOutputStream字节输出流。

        示例：

//将一个字符串写入到D盘文件中
	public static void writer() throws IOException{
		FileOutputStream fos = new FileOutputStream("D:/fos.txt");
		fos.write("aaad".getBytes());
		fos.close();
	}

六、FileInputStream字节输入流。

        示例：

//一个一个读
	public static void reader() throws IOException{
		FileInputStream fis = new FileInputStream("D:/fos.txt");
		int ch =0;
		while(-1 != (ch = fis.read())){
			System.out.println((char)ch);
		}
		fis.close();
	}
	
	public static void reader2() throws IOException{
		FileInputStream fis = new FileInputStream("D:/fos.txt");
		byte[] b = new byte[20];
		int len = 0;
		while(-1 != (len = fis.read(b))){
			System.out.println(new String(b,0,len));
		}
		fis.close();
	}
	
	
	public static void reader3() throws IOException
	{
		FileInputStream fis = new FileInputStream("D:/fos.txt");
		int size = fis.available();		//返回文件中字节数大小
		byte[] b = new byte[size];	//定义一个刚好大小的缓冲区, 不用在循环, 此方式不适合读取大文件
		fis.read(b);
		System.out.println(new String(b));
		fis.close();
	}

七、同样的字节流也有缓冲区的，就是BufferedOutputStream和BufferedInputStream，下面的示例就是利用字节流的缓冲区拷贝一个

        mp3文件。

        示例：

//拷贝一个MP3文件
	public static void copyMp3(String srcPath, String descPath){
		
		BufferedOutputStream bos = null;
		BufferedInputStream bis = null;
		
		try {
			
			bos = new BufferedOutputStream(new FileOutputStream(descPath));
			bis = new BufferedInputStream(new FileInputStream(srcPath));
			
			int b = 0;
			while(-1 != (b = bis.read())){
				bos.write(b);
			}
			
		} catch (Exception e) {
			throw new RuntimeException("拷贝失败");
		}finally {
			if(null != bis)
				try {
					bis.close();
				} catch (IOException e) {
					throw new RuntimeException("关闭读取流失败");
				}
			if(null != bos)
				try {
					bos.close();
				} catch (IOException e) {
					throw new RuntimeException("关闭写入流失败");
				}
		}
	}

八、InputStreamReader和OutputStreamWriter转换流

        示例：

//readLine()是字符流BufferedReader类中的方法, 键盘录入的read()则是字节流InputStream类中的方法
//可以通过InputStreamReader类来转换

//需要注意的是, 只有转换流才可以指定字符的编码集

public class TransStreamDemo {

	public static void main(String[] args) throws IOException {

		toPrint2();
	}

	public static void myPrint() throws IOException {
		// 获取键盘录入对象
		InputStream in = System.in;
		// 将字节流转换成字符流, 需要使用转换流
		InputStreamReader isr = new InputStreamReader(in);
		BufferedReader br = new BufferedReader(isr);

		OutputStream os = System.out;
		OutputStreamWriter osw = new OutputStreamWriter(os);
		BufferedWriter bw = new BufferedWriter(osw);

		String line = null;
		while (null != (line = br.readLine())) {
			if ("over".equals(line))
				break;
			// System.out.println(line);
			bw.write(line);
			bw.newLine();
			bw.flush();
		}
		br.close();
		bw.close();
	}

	// 将控制台的录入, 写入到文件中
	public static void toFile() throws IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("D:/out.txt")));

		String line = null;
		while (null != (line = br.readLine())) {
			if ("over".equals(line))
				break;
			bw.write(line);
			bw.newLine();
			bw.flush();
		}
		br.close();
		bw.close();
	}

	// 将文件中的数据, 打印到控制台
	public static void toPrint() throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("D:/out.txt")));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

		String line = null;
		while (null != (line = br.readLine())) {
			if ("over".equals(line))
				break;
			bw.write(line);
			bw.newLine();
			bw.flush();
		}
		br.close();
		bw.close();
	}

	// 将文件中的数据, 打印到控制台, 通过改变源
	public static void toPrint2() throws IOException {
		
		//设置标准输入设备
		System.setIn(new FileInputStream("D:/out.txt"));
		
		//设置输出设备
		//System.setOut(new PrintStream("D:/setout.txt"));
		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

		String line = null;
		while (null != (line = br.readLine())) {
			if ("over".equals(line))
				break;
			bw.write(line);
			bw.newLine();
			bw.flush();
		}
		br.close();
		bw.close();
	}

}