Java IO Stream (byte stream, character stream)

Io Stream and Propertiesio stream

An IO stream is an interface between a computer and the outside world or between a program and the rest of the computer. It is critical for any computer system,
Thus the body of all I/O is actually built into the operating system. Separate programs generally allow the system to do most of the work for them.
In Java programming, I/O is always done using streams. All I/O are treated as a single byte of movement,
Moves one byte at a time through an object called Stream. Flow I/O is used to contact the outside world. It is also used internally,
Used to convert an object to a byte and then back to the object. Input is also called read data, output is also called contrived to write data.

Overview

• The IO stream is the transmission of data between devices.
  
• IO stream input and output (based on the program's angle, not the file-based angle)

Classification of IO Streams

Data flow:

• Input stream: File to Program
• Output stream: Program to File

Data types (data stores within a computer are stored in bytes):

• BYTE stream: All files can be manipulated using a byte stream
• Character stream: When a text file is read, we need to convert the bytes to characters.

How many bytes represent a character? Not necessarily.

Base class

Data flow:

• Input stream:
• Output stream:

Data type:

• BYTE stream:
  1. byte input stream (InputStream): Outputs data in memory to a specified device
  2. Byte output stream (OutputStream): Output data on the device to the device
• Character Stream:
  1. Character output stream
  2. Character input stream

FileOutputStream

The construction method (if the specified file does not exist, the object is created; exists, and the data in the file is emptied (unless you use the latter two construction methods, the character stream is the same)):

• Public FileOutputStream: Creates a file output stream to write files represented by the specified file object.
• Public FileOutputStream (String name): Creates a file output stream to write to the file with the specified name (name indicates the path to the action file).
• FileOutputStream (File File, Boolean append): Creates a file output stream to write the file represented by the specified file object, and the Boolean type indicates whether the content is appended.
• FileOutputStream (String name, Boolean append): Creates a file output stream that writes to a file with the specified name, and a Boolean type that indicates whether the content is appended.

Common methods:

• void write (int b): Writes the specified bytes out to the file (a).
• void Write (byte[] b): Writes the bytes in the byte array to the file.
• void Write (byte[] b, int off, int len): Off indicates the index position of the start of the byte array, the output Len bytes length to the file
• void Close (): Closes this file output stream and frees any system resources associated with this stream.

Steps to use:

1. Create a Stream
2. Write stream

3. Close the stream

    public static void main(String[] args) throws Exception {     // 使用构造方法创建FileOutputStream对象     FileOutputStream fos = new FileOutputStream("F:\\bbb\\wangzhi.txt");     // FileOutputStream fos2 = new FileOutputStream(new File("F:\\bbb\\wangzhi.txt"));     // 调用write方法向文件中输出内容     // int字节,查询ASICC表     fos.write(97);     fos.write(65);     fos.write(98);     fos.write(66);     fos.write(99);     fos.write(new byte[]{67,100,68});     fos.close(); }    

FileInputStream

Construction method (file must exist, no throw exception exists):

• FileInputStream (File file): Creates a fileinputstream by opening a connection to the actual file, which is named by the file object files in the filesystem.
  
• FileInputStream (String name): Creates a fileinputstream by opening a connection to the actual file, which is named by the pathname name in the file system.

Common methods:

• int read (): reads a single byte of data from the input stream.
  
• int read (byte[] b): reads up to b.length bytes of data from the input stream into a byte array (returns the number of bytes read).
  

• void Close (): Closes this file input stream and frees any system resources associated with the stream.

    // 使用字节流复制图片  public static void main(String[] args) throws IOException {      FileInputStream fis = new FileInputStream("D:\\美女.jpg");      FileOutputStream fos = new FileOutputStream("F:\\bbb\\美女.jpg");      /*long start = System.currentTimeMillis();      byte[] arr = new byte[1024 * 4];      int len;      while((len = fis.read(arr)) != -1){          fos.write(arr,0,len);      }      long end = System.currentTimeMillis();      System.out.println(end - start);*/      byte[] arr1 = new byte[1024 * 4];      int len1;      StringBuilder sb = new StringBuilder();      while((len1 = fis.read(arr1)) != -1){          sb.append(new String(arr1,0,len1));      }      fos.write(sb.toString().getBytes());      /*System.out.println(System.currentTimeMillis() - end);*/      fos.close();      fis.close();  }

Character Stream

Using byte stream to read Chinese (a Chinese occupies 3 bytes) may be garbled.

• Writer: stream of writing data
  1. FileWriter
• Reader: stream of Read data
  1. FileReader

FileReader

Construction Method:

• FileReader (String fileName)
  Creates a new FileReader, given the name of the file to be read.
• FileReader (File file)
  Creates a new FileReader that gives the file read.

Common methods:

• int read ()
  Read a character
  
• int read (char[] cbuf)
  Reads a character into an array.
• void Close ()
  Closes the stream and frees any system resources associated with it.

FileWriter

Construction Method:

• FileWriter (File file)
  Constructs a FileWriter object for a file object.
  
• FileWriter (File File, Boolean append)
  Constructs a FileWriter object for a file object.
• FileWriter (String fileName)
  Constructs a FileWriter object for a given file name.
  
• FileWriter (String fileName, Boolean append)
  Constructs a FileWriter object that gives a file name with a Boolean value indicating whether to append the written data.

Common methods:

• void Write (char[] cbuf)
  Writes an array of characters.
  
• void write (int c)
  Write a character
  
• void write (String str)
  Write a string
  
• void Write (String str, int off, int len)
  Write a part of a string.
• void Flush ()
  Refreshes the stream.
  

• void Close ()
  Close the stream and refresh it first.

    // 复制txt文件  public static void main(String[] args) throws IOException {      // 创建字符输入流      FileReader fr = new FileReader("wangzhi.txt");      // 创建字符输出流      FileWriter fw = new FileWriter("wangzhi2.txt");      // 读取资源      char[] arr = new char[1024];      int len;      StringBuilder sb = new StringBuilder();      while((len = fr.read(arr)) != -1){          sb.append(arr);      }      fw.write(sb.toString());      // 关闭流      fw.close();      fr.close();  }

Java IO Stream (byte stream, character stream)