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

傷城~ 2022-05-14 12:27 116阅读 0赞

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();
                }
            }
        }
    }