Java(11) file operations

Java(11) file operations

1. Basic concepts

1.1. Data persistence

1. Store only the attributes of the class
2. Storage object-object serialization

1.2. The data structure of the file

1.Frame

2. File organization

• Record-record
  • Area-field
    • Byte-byte
    • Bit

1.3. Buffer

Temporary storage location

1.4. Stream

1. Concept

Data sequence

2. Different levels of flow

3. Read and write

1. Sequential file
2. random document

4. Attention

Exception handling must be set for all streams

1.5. Common flow

1. Input stream

1. Byte input stream
   InputStream
2. Character input stream
   Reader

2. Output stream

1. Byte output stream
   OutputStream
2. Character output stream

Writer

3. File operations

1. File class
   File
2. Random access file
   RandomAccessFile

4. Summary

2. Examples

2.1. Byte read and write

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



public class FileStream {
    
    
	public Boolean StreamWriter(byte[] message,String path) {
    
    
		FileOutputStream outputStream;
		try {
    
    
			outputStream = new FileOutputStream(path);
			outputStream.write(message);
			outputStream.close();
		}catch (FileNotFoundException e) {
    
    
			// TODO: handle exception
			e.printStackTrace();
		}
		catch (IOException e) {
    
    
			// TODO: handle exception
			e.printStackTrace();
		}
		return true;
	}
	public Boolean StreamReader(String path) {
    
    
		FileInputStream inputStream;
		byte[] message = new byte[50];
		try {
    
    
			inputStream = new FileInputStream(path);
			inputStream.read(message);
			inputStream.close();
		}catch (FileNotFoundException e) {
    
    
			// TODO: handle exception
			e.printStackTrace();
		}
		catch (IOException e) {
    
    
			// TODO: handle exception
			e.printStackTrace();
		}
		return true;
	}
	public static void main(String[] args) {
    
    
		byte[] message  = "中南大".getBytes();
		String path = "./text.txt";
		FileStream fileStream = new FileStream();
		fileStream.StreamWriter(message, path);
		System.out.println(fileStream.StreamReader(path));
	}
}

2.2. Character reading and writing

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;



public class FileIo {
    
    

	public static void main(String[] args) {
    
    
		// TODO Auto-generated method stub
		char[] message = "中南大".toCharArray();
		String path = "./File_IO.txt";
		CharIO io = new CharIO();
		try {
    
    
			io.charWrite(path,message);
		} catch (IOException e) {
    
    
			// TODO: handle exception
			System.out.println(e);
		}
		char[] text = io.charRead(path);
		String text1 = new String(text);
		System.out.println(text1);
	}
	

}
class CharIO{
    
    
	public boolean charWrite(String name,char[] message) throws IOException  {
    
    
		File file = new File(name);
		FileWriter fileWriter = new FileWriter(file);
		fileWriter.write(message);
		fileWriter.close();
		System.out.println("文件读写成功"+String.valueOf(message));
		return true;
	}
	public char[] charRead(String name) {
    
    
		char[] text = new char[20];
		FileReader fileReader;
		try {
    
    
			fileReader = new FileReader(name);
			fileReader.read(text);
			fileReader.close();
		} catch (IOException e) {
    
    
			// TODO: handle exception
			e.printStackTrace();
		}
		return text;
		
	}
}

2.3. Random read and write

import java.io.File;
import java.io.RandomAccessFile;


public class RandomIO {
    
    
	public static void main(String[] args) {
    
    
		Student[] studentArray = {
    
    new Student("关于","123"),
				new Student("郭德纲", "456"),
				new Student("叶蕴屏", "789")};
		RandomAccessFile randomWriter = null;
		RandomAccessFile randomReader = null;
		try {
    
    
			File file = new File("Student.txt");
			randomWriter = new RandomAccessFile(file, "rw");
			for(int i=0;i<studentArray.length;i++) {
    
    
				randomWriter.write(studentArray[i].getName().getBytes());
				randomWriter.write(studentArray[i].getNumber().getBytes());
			}
			randomWriter.close();
			int len = 0;
			String str = null;
			int length = (int)file.length()/studentArray.length;
			byte[] buf = new byte[length];
			randomReader = new RandomAccessFile(file, "r");
			//跳过前面字符
			randomReader.skipBytes(length);
			System.out.println("指针位置是"+randomReader.getFilePointer());
			len = randomReader.read(buf);
			
			//转到字符串
			str = new String(buf,0,len);
			System.out.println("第二个记录"+str);
			
			randomReader.seek(0);
			System.out.println("指针位置"+randomReader.getFilePointer());
			len = randomReader.read(buf);
			str = new String(buf,0,len);
			System.out.println("第一个记录"+str);
			
			randomReader.skipBytes(length);
			System.out.println("指针位置"+randomReader.getFilePointer());
			len = randomReader.read(buf);
			str = new String(buf,0,len);
			System.out.println("第三个记录"+str);
			randomReader.close();

		} catch (Exception e) {
    
    
			// TODO: handle exception
			System.out.println(e);
		}
		
	}
}
class Student{
    
    
	private String name;
	private String number;
	public Student(String name,String number) {
    
    
		this.name = name;
		this.number = number;
	}
	public String getName() {
    
    
		return this.name;
	}
	public String getNumber() {
    
    
		return this.number;
	}
}