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14.2 byte stream learning

2022-07-26 12:17:00 【Wang Xiaoya】

1.IO flow

1.1 IO Flow overview and classification 【 understand 】

  • IO Stream Introduction

    • IO： Input / Output (Input/Output)

    • flow ： It's an abstract concept , It's a general term for data transmission . In other words, the transmission of data between devices is called a stream , What is the essence of flow The data transfer

    • IO Stream is used to deal with data transmission between devices .

    •   Common applications ： File replication ; Upload files ; File download

  • IO Classification of flows

    • according to The flow of data

      • Input stream ： Reading data

      • Output stream ： Writing data

    • according to data type Come to share （ Default category ）

      • Byte stream

        • Byte input stream

        • Byte output stream

      • Character stream

        • Character input stream

        • Character output stream

  • IO Stream usage scenarios

    • If the operation is Plain text file （ Can read ）, priority of use Character stream

    • If it's a picture 、 video 、 Audio etc. Binary . priority of use Byte stream

    • If Not sure file type , priority of use Byte stream . Byte stream is a universal stream

1.2 Byte stream writes data 【 application 】

  • Byte stream abstract base class

    • InputStream： This abstract class is a superclass of all classes representing the byte input stream

    • OutputStream： This abstract class is the superclass of all classes representing the byte output stream

    • Subclass name characteristics ： Subclass names are suffixes of subclass names with their parent class names

  • Byte output stream

    • FileOutputStream(String name)： Create a file output stream to write to the file with the specified name

  • Steps to write data using byte output stream

    • Create byte output stream object ( Call the system function to create a file , Create byte output stream object , Let the byte output stream object point to the file )

    • Call the write data method of the byte output stream object

    • Release resources ( Close this file output stream and free any system resources associated with this stream )

  • Sample code 

    public class FileOutputStreamDemo01 {
    public static void main(String[] args) throws IOException {
        // Create byte output stream object 
        //FileOutputStream(String name)： Create a file output stream to write to the file with the specified name 
        FileOutputStream fos = new FileOutputStream("myByteStream\\fos.txt");
        /*
             Did three things ：
                A: Call the system function to create a file 
                B: Created byte output stream object 
                C: Let the byte output stream object point to the created file 
         */
​
        //void write(int b)： Writes the specified bytes to the output stream of this file 
        fos.write(97);
//        fos.write(57);
//        fos.write(55);
​
        // In the end, we need to release resources 
        //void close()： Close this file output stream and free any system resources associated with this stream .
        fos.close();
    }
}

1.3 There are three ways to write data by byte stream 【 application 】

  • How to write data

    Method name explain
    void write(int b) Writes the specified bytes to the output stream of this file Write one byte of data at a time
    void write(byte[] b) take b.length Byte writes the output stream of this file from the specified byte array Write array data one byte at a time
    void write(byte[] b, int off, int len) take len Bytes start with the specified byte array , From the offset off Start writing this file output stream Write part of a byte array at a time

  • Sample code 

    public class FileOutputStreamDemo02 {
    public static void main(String[] args) throws IOException {
        //FileOutputStream(String name)： Create a file output stream to write to the file with the specified name 
        FileOutputStream fos = new FileOutputStream("myByteStream\\fos.txt");
        //new File(name)
//        FileOutputStream fos = new FileOutputStream(new File("myByteStream\\fos.txt"));
​
        //FileOutputStream(File file)： Creates a file output stream to write to the  File File represented by object 
//        File file = new File("myByteStream\\fos.txt");
//        FileOutputStream fos2 = new FileOutputStream(file);
//        FileOutputStream fos2 = new FileOutputStream(new File("myByteStream\\fos.txt"));
​
        //void write(int b)： Writes the specified bytes to the output stream of this file 
//        fos.write(97);
//        fos.write(98);
//        fos.write(99);
//        fos.write(100);
//        fos.write(101);
​
//        void write(byte[] b)： take  b.length Byte writes the output stream of this file from the specified byte array 
//        byte[] bys = {97, 98, 99, 100, 101};
        //byte[] getBytes()： Returns the byte array corresponding to the string 
        byte[] bys = "abcde".getBytes();
//        fos.write(bys);
​
        //void write(byte[] b, int off, int len)： take  len Bytes start with the specified byte array , From the offset off Start writing this file output stream 
//        fos.write(bys,0,bys.length);
        fos.write(bys,1,3);
​
        // Release resources 
        fos.close();
    }
}

1.4 The problem of writing two small bytes of data stream 【 application 】

  • How to implement line feed for byte stream write data

    • windows:\r\n

    • linux:\n

    • mac:\r

  • How to realize additional writing of byte stream write data

    • public FileOutputStream(String name,boolean append)

    • Create a file output stream to write to the file with the specified name . If the second parameter is true , Write the beginning of the byte to the end of the file instead of

  • Sample code 

    public class FileOutputStreamDemo03 {
    public static void main(String[] args) throws IOException {
        // Create byte output stream object 
//        FileOutputStream fos = new FileOutputStream("myByteStream\\fos.txt");
        FileOutputStream fos = new FileOutputStream("myByteStream\\fos.txt",true);
​
        // Writing data 
        for (int i = 0; i < 10; i++) {
            fos.write("hello".getBytes());
            fos.write("\r\n".getBytes());
        }
​
        // Release resources 
        fos.close();
    }
}

1.5 Byte stream write data and exception handling 【 application 】

  • Exception handling format

    • try-catch-finally

      try{
     Code with possible exception ;
}catch( Exception class name   Variable name ){
     Exception handling code ;
}finally{
     Perform all cleanup operations ;
}

    • finally characteristic

finally: Provide... In exception handling finally Block to perform all cleanup operations . for instance IO Free resources in the stream
By finally The control statement must be executed , Unless JVM sign out

  • Sample code 

    public class FileOutputStreamDemo04 {
    public static void main(String[] args) {
        // Join in finally To release resources 
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream("myByteStream\\fos.txt");// Create byte output stream object 
            fos.write("hello".getBytes());// call write Method , Write a byte array data 
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos != null) {
                try {
                    fos.close();// Released resources 
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

1.6 Byte stream read data ( Read one byte of data at a time )【 application 】

  • Byte input stream

    • FileInputStream(String name)： Create a... By opening a connection to the actual file FileInputStream , This file is made up of pathnames in the file system name name

  • The steps of reading data from byte input stream

    • Create byte input stream object

    • Call the read data method of byte input stream object

    • Release resources

  • Sample code 

    public class FileInputStreamDemo01 {
    public static void main(String[] args) throws IOException {
        // Create byte input stream object 
        //FileInputStream(String name)
        FileInputStream fis = new FileInputStream("myByteStream\\fos.txt");
​
        int by;
        /*
            fis.read()： Reading data 
            by=fis.read()： Assign the read data to by
            by != -1： Judge whether the data read is -1
         */
        while ((by=fis.read())!=-1) {
            System.out.print((char)by);
        }
​
        // Release resources 
        fis.close();
    }
}

1.7 Byte stream copy text file 【 application 】

  • Case needs

    hold “E:\itcast\ Inside and outside the window .txt” Copy to... In the module directory “ Inside and outside the window .txt”

  • Implementation steps

    • Copy text file , In fact, the content of a text file is read out from a file ( data source ), And then write it to another file ( Destination )

    • data source ：

      E:\itcast\ Inside and outside the window .txt --- Reading data --- InputStream --- FileInputStream

    • Destination ：

      myByteStream\ Inside and outside the window .txt --- Writing data --- OutputStream --- FileOutputStream

  • Code implementation 

    public class CopyTxtDemo {
    public static void main(String[] args) throws IOException {
        // Create a byte input stream object from the data source 
        FileInputStream fis = new FileInputStream("E:\\itcast\\ Inside and outside the window .txt");
        // Create a byte output stream object based on the destination 
        FileOutputStream fos = new FileOutputStream("myByteStream\\ Inside and outside the window .txt");
​
        // Read and write data , Copy text file ( Read one byte at a time , Write one byte at a time )
        int by;
        while ((by=fis.read())!=-1) {
            fos.write(by);
        }
​
        // Release resources 
        fos.close();
        fis.close();
    }
}

1.8 Byte stream read data ( Read array data one byte at a time )【 application 】

  • A way to read an array of bytes at a time

    • public int read(byte[] b)： Read most from input stream b.length Bytes of data

    • Returns the total number of bytes read into the buffer , That is, the actual number of bytes read

  • Sample code 

    public class FileInputStreamDemo02 {
    public static void main(String[] args) throws IOException {
        // Create byte input stream object 
        FileInputStream fis = new FileInputStream("myByteStream\\fos.txt");
​
        /*
            hello\r\n
            world\r\n
​
             for the first time ：hello
             The second time ：\r\nwor
             third time ：ld\r\nr
​
         */
​
        byte[] bys = new byte[1024]; //1024 And its integral multiples 
        int len;
        while ((len=fis.read(bys))!=-1) {
            System.out.print(new String(bys,0,len));
        }
​
        // Release resources 
        fis.close();
    }
}

1.9 Byte stream copy image 【 application 】

  • Case needs

    hold “E:\itcast\mn.jpg” Copy to... In the module directory “mn.jpg”

  • Implementation steps

    • Create a byte input stream object from the data source

    • Create a byte output stream object based on the destination

    • Read and write data , Copy the picture ( Read one byte array at a time , Write one byte array at a time )

    • Release resources

  • Code implementation 

    public class CopyJpgDemo {
    public static void main(String[] args) throws IOException {
        // Create a byte input stream object from the data source 
        FileInputStream fis = new FileInputStream("E:\\itcast\\mn.jpg");
        // Create a byte output stream object based on the destination 
        FileOutputStream fos = new FileOutputStream("myByteStream\\mn.jpg");

        // Read and write data , Copy the picture ( Read one byte array at a time , Write one byte array at a time )
        byte[] bys = new byte[1024];
        int len;
        while ((len=fis.read(bys))!=-1) {
            fos.write(bys,0,len);
        }

        // Release resources 
        fos.close();
        fis.close();
    }
}

2. Byte buffer stream

2.1 Byte buffer stream construction method 【 application 】

  • Byte buffer stream introduction

    • BufferOutputStream： This class implements buffered output streams . By setting such an output stream , Applications can write bytes to the underlying output stream , Instead of causing the underlying system to call for every byte written

    • BufferedInputStream： establish BufferedInputStream An internal buffer array will be created . When reading or skipping bytes from the stream , The internal buffer will be refilled from the contained input stream as needed , Many bytes at a time

  • Construction method ：

    Method name explain
    BufferedOutputStream(OutputStream out) Create a byte buffered output stream object
    BufferedInputStream(InputStream in) Create a byte buffered input stream object
  • Why a constructor needs a byte stream , Not a specific file or path ?
    Byte buffer stream only Provide buffer , The real reading and writing data also depends on the basic byte stream object
     

  • Sample code 

    public class BufferStreamDemo {
    public static void main(String[] args) throws IOException {
        // Byte buffered output stream ：BufferedOutputStream(OutputStream out)
 
        BufferedOutputStream bos = new BufferedOutputStream(new 				                                       FileOutputStream("myByteStream\\bos.txt"));
        // Writing data 
        bos.write("hello\r\n".getBytes());
        bos.write("world\r\n".getBytes());
        // Release resources 
        bos.close();
    

        // Byte buffered input stream ：BufferedInputStream(InputStream in)
        BufferedInputStream bis = new BufferedInputStream(new                                                          FileInputStream("myByteStream\\bos.txt"));

        // Read one byte of data at a time 
//        int by;
//        while ((by=bis.read())!=-1) {
//            System.out.print((char)by);
//        }

        // Read one byte array at a time 
        byte[] bys = new byte[1024];
        int len;
        while ((len=bis.read(bys))!=-1) {
            System.out.print(new String(bys,0,len));
        }

        // Release resources 
        bis.close();
    }
}

2.2 Byte stream copy video 【 application 】

  • Case needs

    hold “E:\itcast\ Byte stream copy image .avi” Copy to... In the module directory “ Byte stream copy image .avi”

  • Implementation steps

    • Create a byte input stream object from the data source

    • Create a byte output stream object based on the destination

    • Read and write data , Copy video

    • Release resources

  • Code implementation 

    public class CopyAviDemo {
    public static void main(String[] args) throws IOException {
        // Record the start time 
        long startTime = System.currentTimeMillis();

        // Copy video 
//        method1();
//        method2();
//        method3();
        method4();

        // Record the end time 
        long endTime = System.currentTimeMillis();
        System.out.println(" Total time consuming ：" + (endTime - startTime) + " millisecond ");
    }

    // The byte buffer stream reads and writes one byte array at a time 
    public static void method4() throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream("E:\\itcast\\ Byte stream copy image .avi"));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("myByteStream\\ Byte stream copy image .avi"));

        byte[] bys = new byte[1024];
        int len;
        while ((len=bis.read(bys))!=-1) {
            bos.write(bys,0,len);
        }

        bos.close();
        bis.close();
    }

    // The byte buffer stream reads and writes one byte at a time 
    public static void method3() throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream("E:\\itcast\\ Byte stream copy image .avi"));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("myByteStream\\ Byte stream copy image .avi"));

        int by;
        while ((by=bis.read())!=-1) {
            bos.write(by);
        }

        bos.close();
        bis.close();
    }


    // The basic byte stream reads and writes one byte array at a time 
    public static void method2() throws IOException {
        //E:\\itcast\\ Byte stream copy image .avi
        // Module directory   Byte stream copy image .avi
        FileInputStream fis = new FileInputStream("E:\\itcast\\ Byte stream copy image .avi");
        FileOutputStream fos = new FileOutputStream("myByteStream\\ Byte stream copy image .avi");

        byte[] bys = new byte[1024];
        int len;
        while ((len=fis.read(bys))!=-1) {
            fos.write(bys,0,len);
        }

        fos.close();
        fis.close();
    }

    // The basic byte stream reads and writes one byte at a time 
    public static void method1() throws IOException {
        //E:\\itcast\\ Byte stream copy image .avi
        // Module directory   Byte stream copy image .avi
        FileInputStream fis = new FileInputStream("E:\\itcast\\ Byte stream copy image .avi");
        FileOutputStream fos = new FileOutputStream("myByteStream\\ Byte stream copy image .avi");

        int by;
        while ((by=fis.read())!=-1) {
            fos.write(by);
        }

        fos.close();
        fis.close();
    }
}
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