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Byte stream & character stream of IO stream

2022-07-23 15:05:00 【Red bean ice 746】

Catalog
Preface
One 、 understand IO flow
1.IO The characteristics of flow
2. Three classification methods of flow
3. The hierarchy of flows
Two 、 Byte stream
1. What is a byte stream
2. Use byte stream to copy files
3. Use try - catch - finally Optimize resource release
4. Use try - catch - resource Further optimize resource release
3、 ... and 、 Character stream
1. What is a character stream
2. File character input stream - Read a single character at a time
3. File character input stream - Read one character array at a time
4. Character output stream
summary

Preface

Most applications need to realize data transmission with devices , For example, the keyboard can enter data , The display can display the running results of the program . stay Java in , Pass this through different input and output devices （ keyboard , Memory , Monitor , Network, etc ） The abstract expression of data transmission between is “ flow ”, The program allows data transmission with input and output devices through streaming .Java Medium “ flow ” All in Java.io In bag , be called IO（ Input and output ） flow . IO flow ： namely InputOutput Abbreviation .

One 、 understand IO flow

1.IO The characteristics of flow

IO Streams are used to handle data transfer between devices .

Java The operation of data is by means of flow .

Java The objects used to manipulate the flow are all in IO In bag .

Streams are divided into two types by operation data ： Byte stream and character stream .

The flow is divided into ： Input and output streams

2. Three classification methods of flow

Divide into... According to the direction of the flow ： Input and output streams

It can be divided into ： Byte stream and character stream

It can be divided into : Node flow and processing flow

3. The hierarchy of flows

IO Common base classes for streams ：

Abstract base stream of byte stream ：InputStream and OutputStream
Abstract base stream of character stream ：Reader and Writer

Two 、 Byte stream

1. What is a byte stream

All file data is stored , It's all about Binary system Save in the form of numbers , One byte at a time , So it's the same when it's transmitted . therefore , Byte stream can transfer any file data . When operating the flow , We need to be clear at all times , No matter what kind of flow object is used , The underlying transmission is always binary data .

2. Use byte stream to copy files

The bottom layer of both audio and video files and text files is composed of bytes , So you can use byte input streams & Byte output stream completes any form of file copy （ As long as the file format before and after is guaranteed 、 There is no problem with consistent coding ）

Be careful ： Byte stream is not suitable for reading Chinese content output ,（ stay UTF-8 In the encoding , A Chinese character is 3 Bytes ） It is easy to cause garbled code due to truncation

public static void main(String[] args)  {
        try {
            // Create byte input stream pipeline 
            InputStream is = new FileInputStream("E:\\Pictures\\wx_camera_1654694320902.mp4");
            // Create byte input stream pipeline 
            OutputStream os = new FileOutputStream("C:\\Users\\ Xiaoyin \\Desktop\\lhy.mp4");

            // Define a 1024 Size byte array , Used to transfer data 
            byte[] buffer = new byte[1024];
            int len;
            while((len = is.read(buffer)) != -1){
                os.write(buffer,0,len);
            }
            System.out.println(" Copy complete ！~~~~~");
            // Closed flow 
            os.close();
            is.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

3. Use try - catch - finally Optimize resource release

finall Code blocks are bound to be executed in the end , You can finally release resources here

    public static void main(String[] args)  {
        InputStream is = null;
        OutputStream os = null;
        try {
            // Create byte input stream pipeline 
            is = new FileInputStream("E:\\Pictures\\wx_camera_1654694320902.mp4");
            // Create byte input stream pipeline 
            os = new FileOutputStream("C:\\Users\\ Xiaoyin \\Desktop\\lhy.mp4");

            // Define a 1024 Size byte array , Used to transfer data 
            byte[] buffer = new byte[1024];
            int len;
            while((len = is.read(buffer)) != -1){
                os.write(buffer,0,len);
            }
            System.out.println(" Copy complete ！~~~~~");


        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            // Whether the code ends normally or there is an exception, you should execute here 
            try {
                // First judge that it is not empty , Then close the flow 
                if (os != null)os.close();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            try {
                if (is != null)is.close();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

4. Use try - catch - resource Further optimize resource release

    public static void main(String[] args)  {
        try (
                // Only resource objects can be placed here , After use, even if there is an exception, the resource object will be automatically called close Method to close the resource 
                // Create byte input stream pipeline 
                InputStream is = new FileInputStream("E:\\Pictures\\wx_camera_1654694320902.mp4");
                // Create byte input stream pipeline 
                OutputStream os = new FileOutputStream("C:\\Users\\ Xiaoyin \\Desktop\\lhy.mp4");
                ){
            // Define a 1024 Size byte array , Used to transfer data 
            byte[] buffer = new byte[1024];
            int len;
            while((len = is.read(buffer)) != -1){
                os.write(buffer,0,len);
            }
            System.out.println(" Copy complete ！~~~~~");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

3、 ... and 、 Character stream

1. What is a character stream

Because the byte stream reading Chinese may be truncated, resulting in garbled code , therefore ,java It provides the conversion flow . Character stream = Byte stream + Encoding table .

Encoding table ： A table of characters and their corresponding values

2. File character input stream - Read a single character at a time

There will be no garbled code when reading Chinese characters

But the performance is slow

 public static void main(String[] args) throws IOException {
        Reader fr = new FileReader("D:\\IDEA\\untitled1\\ Exercise draft \\Test1\\src\\data.txt");
        int code;
        while ((code = fr.read()) != -1){
            System.out.print((char) code);
        }
    }

3. File character input stream - Read one character array at a time

Performance is improved relative to reading a single character

public static void main(String[] args) throws IOException {
        Reader fr = new FileReader("D:\\IDEA\\untitled1\\ Exercise draft \\Test1\\src\\data.txt");
        char[] buffer = new char[1024];
        int len;
        while ((len = fr.read(buffer)) != -1){
            String rs = new String(buffer,0,len);
            System.out.print(rs);
        }
    }

4. Character output stream

public static void main(String[] args) throws IOException {
        // Create a character output stream pipeline to connect with the target file 
        Writer fw = new FileWriter("D:\\IDEA\\untitled1\\ Exercise draft \\Test1\\src\\data.txt");
        // Write a character out 
        fw.write(1);
        fw.write('a');
        fw.write(' Ha ');
        // Write a string out 
        fw.write(" Ha ha ha ha ha ha ha ");
        // Write a character array out 
        char[] chars = "abcdef".toCharArray();
        fw.write(chars);
        // Write only a part of the character array 、 character string 
        fw.write(chars,0,3);
        fw.write(" Ha ha ha ha ha ha ha ",0,3);
        // close 
        fw.close();
    }