IO

File

file: 
	Abstract paths and files
 1. Objects are created without paying attention to the current path or the existence of files.
2. Platform-independent path separators
	File.pathSeparator path Terminator
	File.separator path splitter
 Common methods:
	File  f  = new File();
	f.canExecute() to see if executable f.canRead() is readable
	f.createNewFile() Create a file successfully
	f.getAbsolutePath() Gets the absolute path; f.getPath () Gets the relative path
	f.getName() Gets the filename f.getTotalSpace() Gets the total size
	getusableSpace() Gets the available size
 The difference between mkdir and mkdirs:
	The former can only create a first-level directory, while the latter can create a multi-level directory.

io

Why do I need io?
	1. The file class itself can only operate on the metadata of the file or directory (except the content itself), and can not do anything about the content of the file.
	2. Up to now, our means of storage are very limited and problematic.
		Learned storage means:
			Variables, objects, arrays, and storage are in memory. Data exists after the program starts; data is lost when the program is destroyed
		But during the whole coding and project process, we must store the data permanently, which is convenient for later use and update.
	3. Data cannot be persisted
 Solution:
	Through the knowledge of IO flow, the data can be written to the file or read the data information in the file. Files are stored on disk. After the computer shuts down, the data is still there.

io(input/output):

Classification of IO Flows

1. According to the type of data output:
	Byte streams: Byte input and output streams
	Character Stream: Character Input and Output Streams
 2. According to the direction of flow:
	Input stream and output stream
 3. According to the processing function:
	Node flow
	Processing flow

Node Flow and Processing Flow

/// Writer out = new Output Stream Writer (os); for processing flow
//	OutputStream os = new FileOutputStream("a.txt"); and
//  BufferedWriter bw = new BufferedWriter(out); for node flow


public class Test05 {
	public static void main(String[] args) throws IOException {
		
		//create object
		OutputStream os = new FileOutputStream("a.txt");
		
		Writer out = new OutputStreamWriter(os);
		
		BufferedWriter bw = new BufferedWriter(out);
		
		
		//write
		bw.write("I laughed at the sky with my knife");
		bw.newLine();
		bw.write("Two Kunlun Mountains of Liver and Gallbladder");
		
		
		bw.flush();
		
		bw.close();
		out.close();
		os.close();
	}
}

InputStream

FileInputStream

Read data:
	Byte streams: InputStream is the parent of all byte streams
	Input:
	Subclass:
		FileInputStream file byte input stream, data source in the file, read by word section, flow direction input

Loop read:
	Each time data is read, only one byte can be read. When read through the read method, if read to the end of the file, return - 1. FileInputStream ensures that the file exists during cyclic reading
	

public static void main(String[] args) throws IOException { //1: Create objects 
InputStream is = new FileInputStream("C:\\Users\\wawjy\\Desktop\\cc.txt");
    int num = 0;
//2: Read data
while((num=is.read())!=-1) {
//3: Analytical data
System.out.println("Read data:"+num);
}
//4: Closing resources
is.close();
}

Read multiple bytes

Read an array of bytes at once
	public static void main(String[] args) throws IOException { 
	//Declare objects
    InputStream is = new FileInputStream("C:\\Users\\wawjy\\Desktop\\cc.txt");
    //Read data 
    //Declare a byte array 
    byte[] buf = new byte[1024]; 
    //Reading the length of a byte array returns the length of the byte array read
    int len = is.read(buf);
    //Read the data into buf 
    //Analytical data 
    String msg = new String(buf,0,len); System.out.println(msg); 
    //close resource 
    is.close(); 
    }

Handling exceptions

package com.mage.Io;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

public class Test {
	public static void main(String[] args) {
		InputStream is=null;
		try {
			is = new FileInputStream("C:\\aa.txt");
			byte[] buf = new byte[1024];
			int len = is.read(buf);
			String msg = new String(buf,0,len);
			System.out.println(msg);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}finally {
			try {
				is.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}

ObjectInputStream

package com.mage.Io;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.ObjectInputStream;

public class Test01 {
	public static void main(String[] args) throws FileNotFoundException, IOException {
		//create object
		ObjectInputStream ois = new ObjectInputStream(new FileInputStream("a.txt"));
		//Read data
		int num = ois.readInt();
		//output data
		System.out.println(num);
		//Read data
		double d = ois.readDouble();
		//output data
		System.out.println(d);
		//Read data
		String s = ois.readUTF();
		//output data
		System.out.println(s);
		//Close
		ois.close();
	}
}

OutputStream

FileOutputStream

Byte output stream:
	The parent class of all byte output streams
	The subclass is FileOutputStream, the destination of output is file, and the type of output is byte.
	When output, if the file does not exist, the file will be created, but no non-existent directory will be created.

Write multiple characters

When creating a FileOutputStream object, the second parameter is boolean, which indicates whether to append content after the file. By default, false does not append.

public static void main(String[] args) throws IOException { 
//create object 
OutputStream os = new FileOutputStream("aaa.a",true); 
//Declarations Written Data
String msg = "laoxuezhideniyongyou"; 
//write
os.write(msg.getBytes(),0,10); //10 Represents Length
//close resource 
os.close();
}

serialization and deserialization

(Object Input Stream, Object Output Stream)
The process that the output stream of the object writes the specified object to the file is the process of serializing the object. The process that the input stream of the object reads the specified serialized file is the process of deserializing the object.

Serialization of objects

package com.mage.Io.outputstream;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class Test {
	public static void main(String[] args) throws FileNotFoundException, ClassNotFoundException, IOException {
		write();
		read();
		
	}
	
	public static void write() throws FileNotFoundException, IOException {
		//create object
		User u =new User("linzhengaugn",1,22);
		ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("aa.txt"));
		
		//Write data
		oos.writeObject(u);
		
		
		//Refresh and close resources
		oos.flush();
		oos.close();
	}
	public static void read() throws FileNotFoundException, IOException, ClassNotFoundException {
		ObjectInputStream ois = new ObjectInputStream(new FileInputStream("aa.txt"));
		Object obj = ois.readObject();
		System.out.println(obj);
		ois.close();
	}
	
	
}
class User implements Serializable{
	private String name;
	private int gender;
	private int age;
	public User() {
		
		
	}
	public User(String name,int gender,int age) {
		super();
		this.name = name;
		this.gender=gender;
		this.age = age;
		
		
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getGender() {
		return gender;
	}
	public void setGender(int gender) {
		this.gender = gender;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	
	@Override
	public String toString() {
		return "User [name=" + name + ", gender=" + gender + ", age=" + age + "]";
	}
	
	
}

Results (output of console and file aa.txt)

If transient is added to the above code (the value corresponding to the current property is not serialized when serialized, and the value is changed to the default value)

class User implements Serializable{
	private transient String name;
	private int gender;
	private transient int age;
	public User() {
		
		
	}

Result

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Serialized id

When serializing, remember to add the serialized version number to ensure that after the output is modified, the reader will not report errors.
	class User implements Serializable{
	// serialized id
	private static final long serialversionUID = 1L;
	private String name;
	private int gender;
	private int age;

The impact on singletons

The readResolve method in the class is invoked by default when the program is serialized. If this method is not overridden, a copy of the object of the current class is returned each time. This copy is a new object, leading to the destruction of the singleton pattern.

package com.mage.Io;

import java.io.Serializable;

public class Lazy implements Serializable{
	private static Lazy lazy = null;
	private Lazy() {
		
	}
	public static Lazy getInstance() {
		if(lazy==null) {
			new Lazy();
		}
		return lazy;
	}
	public Object readResolve() {
		
		return lazy;
	}
}

Copy and paste

public static void CtrlCV(String srcFile,String destFile) throws IOException{
    /*
    //1:Declare copy and paste file objects 
    String srcFile = "C:\\Users\\wawjy\\Desktop\\1.jpg"; 
    String destFile = "123.jpg";
    */
    //2: Declare objects
    InputStream is = new FileInputStream(srcFile); 		       OutputStream os = new FileOutputStream(destFile); 
    //3: Read files 
    int len = 0; while((len=is.read())!=-1) {
        //Write out 
        os.write(len); 
    }
    os.close();
    is.close();
}

Reader

InputStreamReader

public class Test03 {
	public static void main(String[] args) throws FileNotFoundException,IOException{
		//create object
		InputStream is = new FileInputStream("a.txt");
		Reader r = new InputStreamReader(is);
		//Specified Character Set
		//Reader reader = new InputStreamReader(new FileInputStream("c.txt"),"utf-8");
		//read
		char[] chs = new char[1024];
		int count = r.read(chs);
		//Analysis results
		System.out.print(new String(chs,0,count));
		//close resource
		r.close();
		is.close();
	}
}

Buffered Reader

StringBuilder is used to create objects in the same way as Reader

public class Test02 {
	public static void main(String[] args) throws IOException {
	
		//Create objects in the same way as Reader
		BufferedReader reader = new BufferedReader(
				new InputStreamReader(
				new FileInputStream("a.txt")));
		
		//read
		String str = null;
		StringBuilder sb = new StringBuilder();
		while((str=reader.readLine())!=null) {
			sb.append(str);
			sb.append("\r\n");
			
		}
		System.out.println(sb.toString());
		//close resource
		reader.close();
	}
}

Writer

public class Test02 {
	public static void main(String[] args) throws IOException {
		
		//create object
		Writer out = new OutputStreamWriter(new FileOutputStream("a.txt"));
		
		//Declare output data
		String str = "you a good a";
		
		//output
		//out.write(str.toCharArray());
		out.write(str);
		
		//Refresh
		out.flush();
		
		//Close
		out.close();
		
	}
}

BufferedWriter

public class Test05 {
	public static void main(String[] args) throws IOException {
		
		//create object
		OutputStream os = new FileOutputStream("a.txt");
		
		Writer out = new OutputStreamWriter(os);
		
		BufferedWriter bw = new BufferedWriter(out);
		
		
		//write
		bw.write("I laughed at the sky with my knife");
		bw.newLine();
		bw.write("Two Kunlun Mountains of Liver and Gallbladder");
		
		
		bw.flush();
		
		bw.close();
		out.close();
		os.close();
	}
}