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Reading and writing of file content - data flow

2022-07-27 06:15:00 【Envy only mandarin ducks, not immortals】

Catalog

One 、 The reading and writing of content

1、 About reading

2、InputStream summary

3、FileInputStream summary

4、 Specific introduction of the method

5、 utilize Scanner Read characters

6、OutputStream summary

Two 、 Related codes

One 、 The reading and writing of content

1、 About reading

① Direct reading （ Read as binary data , Expressed in code with byte In units of ）
② Text reading

2、InputStream summary

InputStream Is from java.io.InputStream package , That is, the meaning of input stream , This class itself is an abstract class , The real use depends on the concrete implementation subclasses of this abstract class , such as FileInputStream, It's about the input stream of the file , Input stream can be abstracted as a tap to understand

3、FileInputStream summary

package data_flow;

import java.io.FileInputStream;
import java.io.InputStream;
import java.util.Arrays;

public class FileRead {
    public static void main(String[] args) throws Exception {
        //f1 It's the faucet 
        InputStream f1=new FileInputStream("D:\\ Desktop files \\java Course \\ Course materials \\javaweb\\a.txt");
        // Prepare a bucket ,1024 Indicates the capacity of the barrel 
        byte[] bucket=new byte[1024];
        // Use a bucket to catch water , Here n Indicates the actual water quantity received 
        int n=f1.read(bucket);
        // When the reading is finished , Remember to turn off the tap （ Is to close the data flow ）
        System.out.println(n);
        // View the data ( Decimal data )
        byte[] bytes= Arrays.copyOf(bucket,n);
        for (byte b : bytes) {
            System.out.println(b);
        }
        f1.close();
    }
}

4、 Specific introduction of the method

Take only a drop of water , What is returned is the data of the next byte , When the return value is -1 when , It means that there will never be water in the future

/**
     *  A drop of water reading 
     * @param f1
     * @throws IOException
     */
    public static void read1(InputStream f1) throws IOException {
        while(true){
            int data=f1.read();
            if (data==-1){
                // At this point, the data has been read 
                break;
            }
            // otherwise ,data Is the data stream 
            byte b=(byte) data;
            System.out.println(b);
            f1.close();
        }
    }

Connect a lot of water at one time , It can be stored in byte In an array , The return value is how much water we received this time , When n=-1 when , It means there will never be water in the future

 /**
     *  Take a lot of water at one time 
     * @param f1
     * @throws Exception
     */
    public static void readbyte(InputStream f1) throws Exception{
        byte[] bytes=new byte[5];
        while (true){
            int n=f1.read(bytes);
            if (n==-1){
                // It means that the data has been read 
                break;
            }
            for (int i = 0; i <n ; i++) {
                byte b=bytes[i];
                System.out.println(b);
            }
        }
        f1.close();
    }

5、 utilize Scanner Read characters

6、OutputStream summary

import java.io.FileOutputStream;
import java.io.OutputStream;

public class OutputStream1 {
    public static void main(String[] args) throws Exception {
        // If the file does not exist before , It will be created 
        // If the file existed before , The previous content will be cleared and rewritten 
        try (OutputStream os = new FileOutputStream("D:\\ Desktop files \\java Course \\ Course materials \\javaweb\\a.txt")) {
            //" I " Of UTF-8 code 
            os.write(0xe6);
            os.write(0x88);
            os.write(0x91);
            // Make sure to write all the possible remaining data in the buffer to Output in 
            os.flush();
        }
    }
}

Use PrintWriter Method

import java.io.*;

public class PrintWritertest {
    public static void main(String[] args) throws Exception {
        try(OutputStream os=new FileOutputStream("D:\\ Desktop files \\java Course \\ Course materials \\javaweb\\a.txt")){
            try(Writer writer=new OutputStreamWriter(os,"UTF-8")){
                try(PrintWriter p1=new PrintWriter(writer)){
                    p1.println(1+1);
                    p1.print(3);
                    p1.printf("%s"+"%d"," I ",3);

                    p1.flush();
                }
            }
        }
    }
}