java IO包学习（一）——inputStream outputStream Reader Writer

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java中的io主要由四个抽象类组成：

inputStream outputStream Reader Writer

这四个抽象类分别对应了输入和输出，字节流和字符流。

一般使用的时候是这样的 inputStream和outputStream对应的子类用来进行图片，视频等文件的处理，Reader和Writer用来进行字符流文件的处理，比如文本文件，尤其是文件中带有中文的。由于中文是占2个字节，如果使用inputStream读取的时候可能遇到读取乱码的情况，所以建议使用Reader和Writer。

下面是我写的两个例子，用来理解一下这四个抽象类。

例子1：使用Reader和Writer实现copy文本文件，同时读取除文本文件的内容。

package com.xueyou.demo.ioandnio;

import java.io.*;

public class IoReadWriterDemo {
    private static final String FILE_NAME = "src/main/resources/abc.txt";
    private static final String FILE_NAME2 = "src/main/resources/abc-copy.txt";
    //    private static final String FILE_NAME = "src/main/resources/aa.gif";
//    private static final String FILE_NAME2 = "src/main/resources/aa-copy.gif";
    private static final int BUFFER_SIZE = 2048;

    public static void main(String[] args) throws IOException {
        File f = new File(FILE_NAME);
        File f2 = new File(FILE_NAME2);
        FileReader fileReader = null;
        FileWriter fileWriter = null;
        char[] chars = new char[BUFFER_SIZE];
        try {
            fileReader = new FileReader(f);
            fileWriter = new FileWriter(f2);
            int len = 0;
            StringBuffer sb = new StringBuffer();
            while ((len = fileReader.read(chars)) != -1) {
                fileWriter.write(chars, 0, len);
                sb.append(chars, 0, len);
            }
            System.out.println(sb.toString());
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            if (fileReader != null) {
                fileReader.close();
            }
            if (fileWriter != null) {
                fileWriter.close();
            }
        }
    }
}

例子2：使用inputStream和outputStream来实现一个copy文件的功能。

package com.xueyou.demo.ioandnio;

import java.io.*;

public class IoStreamDemo {
    private static final String FILE_NAME = "src/main/resources/abc.txt";
    private static final String FILE_NAME2 = "src/main/resources/abc-copy.txt";
    //    private static final String FILE_NAME = "src/main/resources/aa.gif";
//    private static final String FILE_NAME2 = "src/main/resources/aa-copy.gif";
//    private static final String FILE_NAME = "http://static3.j.cn/img/dailySign/180907/2258/739558a6b2ae11e8.png";
//    private static final String FILE_NAME2 = "src/main/resources/net-copy.png";
    private static final int BUFFER_SIZE = 2048;

    public static void main(String[] args) throws IOException {
        File f = new File(FILE_NAME);
        File f2 = new File(FILE_NAME2);
        byte[] bytes = new byte[BUFFER_SIZE];
        FileInputStream fileInputStream = null;
        FileOutputStream fileOutputStream = null;
        try {
            fileInputStream = new FileInputStream(f);
            fileOutputStream = new FileOutputStream(f2);
            int len = 0;
            int a = 0;
            while ((len = fileInputStream.read(bytes)) != -1) {
                System.out.println(++a);
                fileOutputStream.write(bytes, 0, len);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            if (fileInputStream != null) {
                fileInputStream.close();
            }
            if (fileOutputStream != null) {
                fileOutputStream.close();
            }
        }
    }
}