IO flow review

Catalog

BufferedReader And BufferWriter：

Introduce ：

Example ： Array by array reading ：

The code problem ：

Copy file （ Similar to file download ）

SpringMvc Packaged transferto() Method ：

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BufferedReader And BufferWriter：

Introduce ：

It is conducive to improving the reading and writing efficiency of character stream , Buffer mechanism is introduced ;

BufferedReader And BufferedWriter Each has 8192 A character buffer ：—> When BufferedReader When reading external resources , The buffer will be filled with resources first , Then if you call read（）, It is also read from the buffer first ;

and BufferedWriter, When we use it to introduce resources or write files , The written data will not be delivered to the destination first , But now in the buffer ;

Example ： Array by array reading ：

package Demo;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

/**
 * @author diao 2022/2/14
 */
public class demo7 {
    public static void main(String[] args) throws IOException {
        String filePath = null;
        BufferedReader reader = new BufferedReader(new FileReader(filePath));
//         Judge 
        if(!reader.ready()){
            System.out.println(" The file is temporarily unreadable ");
            return;
        }
        int size=0;
        char[] chars = new char[20];
        // call Reader Of read Method to read （ Array , The offset , length ）
        while((size=reader.read(chars,0,chars.length))!=-1){
            // An array of reading resources 
            System.out.println(new String(chars,0,size));
        }
        reader.close();
    }
}

Line by line reading ：

package Demo;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

/**
 * @author diao 2022/2/14
 */
public class demo7 {
    public static void main(String[] args) throws IOException {
        String filePath=null;
        BufferedReader reader = new BufferedReader(new FileReader(filePath));
        
        if(!reader.ready()){
            System.out.println(" The file stream is temporarily unreadable ");
            return;
        }
        int size=0;
        String line;
        // Read line by line 
        while((line=reader.readLine())!=null){
            System.out.println(line+"\n");
        }
        reader.close();
    }
}

When reading line breaks , You need to add newline symbols yourself ;

BufferedReader Than FileReader Advanced place ：BufferedReader In addition to one character reading and one array array reading , It can also be read line by line , And it also has a faster buffer speed ;

The code problem ：

Handle ： Used packaging InputStreamReader Of BufferedReader To read the file ;

package Demo;

import java.io.*;

/**
 * @author diao 2022/2/14
 */
public class demo8 {
    public static void main(String[] args) throws IOException {
        String file=null;
        BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file), "utf-8"));
        char[] chars = new char[20];
        String line;// That's ok 
        int size;
        while((size=reader.read(chars,0,chars.length))!=-1){
            System.out.println(new String(chars,0,chars.length));
        }
    }
}

Copy file （ Similar to file download ）

Two steps ： First, read external resources （ It can be understood as on an external hard disk ）, Then put the external resources into memory at this time , Finally, transfer the resource to the local hard disk and save it ;

  some demo：

Read one by one , Reading while writing —> Copy file

static void copyByChar(String srcFile, String destFile) throws IOException
{
    BufferedReader reader = new BufferedReader(new FileReader(srcFile));
    BufferedWriter writer = new BufferedWriter(new FileWriter(destFile));
    int ch=0;
// Reading while writing 
    // Read a character 
    while ((ch = reader.read()) != -1)
    {
        // Write a character 
        writer.write(ch);
    }
    reader.close();
    writer.close();
}

Array form —> Read as much as you write

static void copyByCharArray(String srcFile, String destFile) throws IOException
{
    BufferedReader reader = new BufferedReader(new FileReader(srcFile));
    BufferedWriter writer = new BufferedWriter(new FileWriter(destFile));
    int size=0;
    char[] cbuf=new char[20];
    // Read an array of characters 
    while ((size = reader.read(cbuf)) != -1)
    {
        // How much to read and how much to write 
        writer.write(cbuf,0,size);
    }
    reader.close();
    writer.close();
}

Copy... By line ：

static void copyByLine(String srcFile,String destFile) throws IOException
{
    BufferedReader reader=new BufferedReader(new FileReader(srcFile));
    BufferedWriter writer=new BufferedWriter(new FileWriter(destFile));
    String line;
    //BufferedReader When reading a line, the returned string does not include line breaks 
    // If there is a line of characters, the string of that line is returned , Return on no null
    while((line=reader.readLine())!=null)
    {
        writer.write(line);
        writer.newLine();// Write line breaks 
    }
    reader.close();
    writer.close();
}

test ：

public static void main(String[] args) throws IOException
{
    String from = "gbk.txt";
    String to = "gbk_copy.txt";
    String to1 = "gbk_copy1.txt";
    String to2 = "gbk_copy2.txt";
    copyByChar(from, to);
    copyByCharArray(from, to1);
    copyByLine(from, to2);
}

Line break problem ：

Add a first line to judge ： Write in the first line if you have resources , Write the line separator without ;

static void copyByLine(String srcFile,String destFile) throws IOException
{
    BufferedReader reader=new BufferedReader(new FileReader(srcFile));
    BufferedWriter writer=new BufferedWriter(new FileWriter(destFile));
    String line;
    //BufferedReader When reading a line, the returned string does not include line breaks 
    // If there is a line of characters, the string of that line is returned , Return on no null
    boolean flag=false;
    while((line=reader.readLine())!=null)
    {
        if(!flag)
        {
            flag=true;
            writer.write(line);
        }
        else
        {
            writer.newLine();// Write line breaks 
            writer.write(line);
        }

    }
    reader.close();
    writer.close();
}

SpringMvc Packaged transferto() Method ：

One time direct reading

// To upload pictures 
				//1 Image storage path 
				String pic_path="";
				//2 old name 
				String originalFilename = items_pic.getOriginalFilename();
				//3 New name (uuid Random number plus suffix )
			    String newfileName=UUID.randomUUID()+originalFilename.substring(originalFilename.lastIndexOf("."));
			     // New pictures 
			    File newfile=new File(pic_path+newfileName);
			    // Write memory pictures to disk 
			    items_pic.transferTo(newfile);
			    // Write the new picture into the object , Easy to update in the database 
			    itemsCustom.setPic(newfileName);
			//  call service Update product information , The page needs to pass the product information to this method 
			itemsService.updateItems(id, itemsCustom);