File processing (IO)

1.File Use of objects

1.1File Object description

1. File class It is the abstract representation of files or folders in the current system  
2. Generally speaking   Is the use of File object To operate the files or folders in our computer system
3. Study File class It's really just through file Object to file in the system / Add, delete, change and check the folder
4. All in all :File: File object , Used to represent folders or data files on disk

   Method or constant	type	describe
   public File(String filename)	Construction method	establish File Class object and pass in the full path
   public boolean createNewFile()	Method	Create a new file
   public boolean delete()	Method	Delete file
   public boolean exists()	Method	Judge whether the file exists
   public boolean isDirectory()	Method	Determine whether the given path is a directory
   public long length()	Method	Returns the size of the file
   public String[] list()	Method	List all the contents of the specified directory , List only names
   public File[] listFiles()	Method	List all of the specified directories File object
   public boolean mkdir()	Method	Create directory
   public boolean renameTo(File dest)	Method	Rename the existing file

 1.2 The basic operation of the file

1.2.1 Three basic operations for creating files

		File file = new File("D:/AAA");
        file.mkdir();// Create directory 
        /* Three ways to create */
        // The first one is 
        File file01 = new File("D:\\AAA\\aaa.txt");
        file01.createNewFile();// create a file 
        /*
           \\ Directory level    stay window The lower level separator of the system is \   But in linux and mac The separator on the system is  /
            We have to java Code is a cross platform language .  We have to develop in window   But our project has to be deployed in linux.
            We make our code usable on any system .  We have two solutions */
		// The second kind ( The first solution )---- because window  compatible  /  and  \
        File file02 = new File("D:/AAA/bbb.txt");
        file02.createNewFile();
		// The third kind of ( The second solution )----File.separator The corresponding delimiter is automatically obtained according to the system where the current code is located  
        File file03 = new File("D:"+File.separator+"AAA"+File.separator+"ccc.txt");
        file03.createNewFile();// create a file 
        File file04 = new File("D:/AAA/CCC/DDD");
        file04.mkdirs();// Create multi-level directory 

1.2.2 Delete operation

 		/* Delete operation */
        file03.delete();// Delete file 
        file02.deleteOnExit();// Delete after the program exits 
        file04.delete();// Delete empty directory   When there is content, it cannot be deleted 

1.2.3 Modify the operating

		file01.setReadable(false);// Others cannot be read   But you can read it yourself   Set the permission of this file to unreadable 
        file02.setWritable(false);// Set that the file cannot be written 
        file03.setReadOnly();// Set read-only permission 

        file04.renameTo(new File("D:/AAA/CCC/EEE"));// rename 

1.2.4 Query operation

		File file = new File("D:/AAA/BBB/CCC/a.txt");
        file.createNewFile();

        // Get the name of the file 
        String name = file.getName();
        System.out.println(" Name of file ====>"+name);
        String parent = file.getParent();// Get the parent path 
        System.out.println(" Parent path ====>"+parent);
        String path = file.getPath(); // Get the file path 
        System.out.println(" File path ====>"+path);

        boolean file1 = file.isFile();// Determine whether the file object is a file type 
        System.out.println(file1);
        boolean directory = file.isDirectory();// Determine whether the file object is a directory 
        System.out.println(directory);

        File file2 = new File("D:/AAA");
        String[] list = file2.list();// List AAA Names of all sub files in the directory 
        System.out.println(Arrays.toString(list));

1.2.5 File traversal

		File[] files = file2.listFiles();
        for (File f:files){
            System.out.println(f);
        }

1.2.6  File recursive traversal ( classic )

 public static void main(String[] args) {
        String path = "D:/BBB";
        showAllFiles(path);
    }

    public static void showAllFiles(String path){
        File file = new File(path);
        // Determine whether the file exists or is a directory 
        if(!(file.exists())||!(file.isDirectory())){
            return; // Exit of procedure   Exit only when it does not exist or is not a directory   If it is a directory, continue to call recursively ( Exit if it is a file )
        }

        File[] files = file.listFiles(); // List all file objects 
        int c = 0;
        for (File f:files){
            if(f.isDirectory()){
                showAllFiles(f.getPath());
            }else{
                c++;
                System.out.println(" file "+c+" by :"+f.getName());
            }
        }

    }

2.IO flow

2.1IO The use of data streams

flow : Flow ( There is a direction , There are basic constituent units : Water drop ), Traffic ( There is a direction , Basic unit : vehicle )

Data flow : Data flow is formed by transmitting in a specific direction in bytes or characters .



 2.1.1 Character output stream

// Character output stream  --- Specify which file （ route ） Write operation 
        //true: Indicates that content is allowed to be appended to the file 
        FileWriter fileWriter = new FileWriter("D:/AAA/aaa.txt");
        String str = " Hello world ！";
        fileWriter.write(str);
        fileWriter.flush();// Refresh stream 
        fileWriter.close();// Closed flow 

2.1.2 Character input stream

		// This way is to read only one character at a time 
		// Create character input stream object .  effect ： It's reading aaaa.txt Contents of Li 
        Reader reader = new FileReader("D:/AAA/aaa.txt");
        /*int read = reader.read();
        System.out.println((char)read);// Read the first character 
        int read1 = reader.read();
        System.out.println((char)read1);// Read the second character */
        int r=0;
        /* Cycle through all characters */
        while ((r = reader.read())!=-1){
            System.out.print((char)r);
        }
    }
	// But this efficiency will be slow   Because only one character is read at a time .
	// We can use the character array to read several characters at a time 
		char[] chars = new char[10];// Custom array length 
        int c = reader.read(chars);// The two characters read each time are stored in the array and the number of reads is returned 
        String s = new String(chars, 0, c);// Convert the read array into a string 
        System.out.println(s);
       
  // Then you can cycle through and read all the characters 
  // You can read all the characters circularly   When the data cannot be read, this time c==-1, Program exit 
       char[] chars = new char[10];
       int readC=0;// Record the number of read characters 
        while ((readC=reader.read(chars))!=-1){
            String s = new String(chars, 0, readC);
            System.out.print(s);
        }
	

2.1.3 Use the character stream to copy the contents of the file

【 The code here uses junit Write the test unit ( Easy to write )】
requirement : take  D:/AAA/aaa.txt  Copy the contents of to  D:/BBB/b.txt

     

 	@Test
   	 public void test1() throws Exception {
        // Create a character input stream 
        FileReader fr = new FileReader("D:/AAA/aaa.txt");
        // Create a character output stream 
        FileWriter fw = new FileWriter("D:/BBB/b.txt");

        int c=0;// Number of read characters 
        
        char[] chars = new char[10];// Save the data 
        /* When the content is not read, it returns -1*/
        while ((c=fr.read(chars))!=-1){
            fw.write(chars,0,c); // Write about D:/BBB/b.txt in 
            fw.flush();
        }

        fr.close();
        fw.close();
    }

notes : But the character stream above can't operate on pictures, movies or compressed files . Because the movie 、 music 、 Picture isochronous binary , The character stream can only operate on text .

2.2.1 Byte output stream (OutputStream)

OutputStream You can operate on any file , Output the file . In bytes . It is the parent of all byte output streams ,

// Write data to a file 
@Test
    public void outPutStreamTest() throws IOException {
        FileOutputStream fos = new FileOutputStream("D:/AAA/aaa.txt");
        String str=" Life is simple , After today is tomorrow ";
        byte[] bytes = str.getBytes();// Convert string to array 
        fos.write(bytes);// write in 
        fos.close();// close resource 
    }

2.2.2 Byte input stream (InputStream)

It can read any file , In bytes , It is the parent of all byte input streams , Subclasses have FileInputStream

	// Read one at a time 
    @Test
    // The input stream must exist in a file   Otherwise you cannot read 
    public void inPutStreamTest() throws IOException{
        InputStream fis = new FileInputStream("D:/AAA/aaa.txt");
        byte[] bytes = new byte[3];
        int c=0;// Record the number of reads 
        // Read the data for the first time 
        c = fis.read(bytes); // Store the read content in byte Array 
        System.out.println(bytes+"=====> Number of first reads :"+c);

        //d Read the data for the second time 
        c = fis.read(bytes); // Store the read content in byte Array 
        System.out.print(bytes+"=====> The number of the second reading :"+c);
    }

	// Read all 
	 @Test
    // The input stream must exist in a file   Otherwise you cannot read 
    // If the content in the file is very large    Use a loop to read 
    public void inPutStreamTestMore() throws IOException{
        InputStream fis = new FileInputStream("D:/AAA/aaa.txt");
        byte[] bytes = new byte[3];// The size of the array depends on the actual demand   variable 
        int c=0;// Record the number of reads 
        while ((c=fis.read(bytes))!=-1){
            // take byte Array to string 
            String s = new String(bytes, 0, c);
            System.out.print(s);
        }
        fis.close();// close resource 
    }

2.2.3  Use byte input stream and output stream to copy files

explain :InputStream and OutputStream Binary and character files can be copied ( The universal )

 // Copy the picture  ( Text can also change the path   Take the picture for example )
    @Test
    public void fileCopyTest() throws IOException{
        //1. Create input stream 
        FileInputStream fis = new FileInputStream("D:/AAA/1.jpg");
        //2. Create output stream 
        FileOutputStream fos = new FileOutputStream("D:/BBB/2.jpg");

        //3. Define an array   Save read content   Any length 
        byte[] bytes = new byte[20];

        int c=0;// Record the number of read contents 

        //4. Copy content 
        while ((c=fis.read(bytes))!=-1){
            //5. Write the contents saved in the array to the output stream 
            fos.write(bytes,0,c);
        }
        fis.close();
        fos.close();

    }

2.2.4 Buffer flow

The buffer stream is in the basic stream [InputStream OutputStream Reader Writer] above Added a cache pool function      can .
BufferInutStream  BufferOutputStream BufferReader  BufferWriter Improve IO The efficiency of , Reduce     IO The number of times .
 

  @Test
    public void BufferTest() throws IOException {
        OutputStream os = new FileOutputStream("D:/AAA/e.txt");
        BufferedOutputStream bf = new BufferedOutputStream(os);// Buffer flow should act on basic flow 
        String s="aaaaa";
        byte[] bytes = s.getBytes();
        bf.write(bytes);// The written things are temporarily put into the cache pool , Not directly put into the file , So the file has no content 
        //bf.flush();// When refreshing, it will display   But this one can also be skipped   Because there will be an automatic refresh operation when closing the stream ( That is, refresh first and then close the stream )
        bf.close();// close ---> Refresh the cache pool first and then close the resource 
    }

  @Test
    public void BufferInputTest() throws IOException{
        FileInputStream fis = new FileInputStream("D:/AAA/e.txt");
        BufferedInputStream bf = new BufferedInputStream(fis);
        byte[] bytes = new byte[2];
        int read = bf.read(bytes);
        String s = new String(bytes, 0, read);
        System.out.println(s);
        bf.close();
    }

2.2.4 Object flow

Why do I need object flow ？
  We now operate IO When it's flowing , Both are string read and write operations , Can you put java Objects are read and written in files ？ 
  Tolerable Student st=new Student();  take java Object for read and write operations The point is to persist information for example ： Game archive . Because when it's running All data is in the running memory   Persistence The data in memory will be run Save to hard disk     The archive （ Write ）   Reading ( read )

//public ObjectOutputStream(OutputStream out) throws IOException
    @Test // The archive ：---- serialize :
    public void testObjectStream() throws Exception{
        OutputStream out=new FileOutputStream("D:/AAA/a.txt");
        // Object output stream 
        ObjectOutputStream oos=new ObjectOutputStream(out);

        // Use the object output stream to call the output method   Output class object   This class must implement Serializable  Serialization interface 
        Role r=new Role(" Lyu3 bu4 ","7 level ",1," Patricide ");
        oos.writeObject(r);
        oos.close();
    }
    // test   Reading : ---- Deserialization :
    @Test
    public void testObjectStream2()throws Exception{
        InputStream input=new FileInputStream("D:/AAA/a.txt");
        ObjectInputStream ois=new ObjectInputStream(input);
        Object o = ois.readObject();

        System.out.println(o);
        ois.close();
    }

1.   Copy the file through the character stream ----> It can only copy text files
2.   Byte stream :--- Byte input stream and byte output stream .
3.   Byte stream We can also copy files --- It can copy any type of file .
4.   Cache stream ---> It is based on the basic flow Added a cache pool  
5.   Object flow : ObjectInputStream  ObjectOutputStream
6. serialize : Put... In memory java Objects are stored on disk [ Network disk ] The process of .
     ---java The class to which the object belongs must implement the serialization interface .implements Serializable 
7. Deserialization : Read the contents of the disk to java Process in object memory .