File operation:

This is the 31st day of my participation in the August Text Challenge.More challenges in August

FIle manipulation is just a FIle class; We learned File manipulation by studying methods in the File class;

File base operation:

Part 1: Learn the basic operation of the document (check the manual first)

Here’s an example:

import java.io.File;
import java.io.IOException;

public class FIleDelCre {
    public static void main(String[] args) throws IOException {
        File file = new File("e:\\IOFileSource\\xbhog.txt");
        if(file.exists()){
            file.delete();
        }else{ System.out.println(file.createNewFile()); }}}Copy the code

CreateNewFile: True if the specified file does not exist and has been successfully created. False if the specified file already exists

Knowledge point (type on blackboard) :

Path delimiters: Solve the problem of path symbols on different operating systems (Windows -> “\”; Linux – > “/”);

File file = new File("e:"+File.separator +"IOFileSource"+File.separator+"xbhog.txt");
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Note:

/**
     * The system-dependent default name-separator character, represented as a
     * string for convenience.  This string contains a single character, namely
     * {@link #separatorChar}.
*/
public static final String separator = "" + separatorChar;
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To operate on the parent path:

import java.io.File;
import java.io.IOException;

public class FIleDelCre {
    public static void main(String[] args) throws IOException {
        File file = new File("e:"+File.separator +"IOFileSource"+File.separator+"test"+File.separator+"demo"+File.separator+"xbhog.txt");
        if(! file.getParentFile().exists()){// If the file's parent directory does not exist
            /* file.getParentFile().mkdirs(); File.getparentfile ().mkdir(); Create a parent directory */
        }
        if(file.exists()){
            file.delete();
        }else{ System.out.println(file.createNewFile()); }}}Copy the code

Note: mkdirs and mkdir difference, it is best to enter the source view

File list display:

Flow chart:

import java.io.File;
public class FilePwd {
    public static void main(String[] args) {
        File file = new File("D:" + File.separator);
		listDir(file);
    }
    public static void listDir(File file){
        if(file.isDirectory()){
            File[] Dirs = file.listFiles();
            while(Dirs ! =null) {for (int i = 0; i < Dirs.length; i++) {
                    listDir(Dirs[i]);  // recursive call} } } System.out.println(file); }}Copy the code

File batch rename:

Situation:

In the process of data collection, the suffix of all files in xbhog-log folder was.java due to an error. In order to correct this error, it is required to replace the suffix of all files in this directory with.txt. Meanwhile, the rename operation of files in multi-level directory should also be considered.

import java.io.File;
public class FIleChangeName {
    public static void main(String[] args) {
        File file = new File("D:" + File.separator + "xbhog-log");
        renameDir(file);

    }
    public static void renameDir(File file){
        if(file.isDirectory()){
            File[] dirs = file.listFiles(); 
            for (int i = 0; i < dirs.length; i++) {
                renameDir(dirs[i]);  // recursive call}}else {
            if (file.isFile()){ // The experience is a file
                String fileName = null;  // File name
                if(file.getName().endsWith(".java")) {// Check whether the.java end is used
                    fileName = file.getName().substring(0,file.getName().lastIndexOf(".")) +".txt";
                    File newfile = new File(file.getParentFile(), fileName);  // The new file name
                    file.renameTo(newfile);  / / renamed
                }
            }
        }
    }
}
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Byte stream and character stream:

Byte streams: outputStream and inputStream

Character streams: Writer and Reader

Basic steps for resource operations :(file as an example)- follow these steps exactly

1. If the resource to operate on is a File, you first need to find a path to the File to operate on through the File class object
2. Instantiate an object for byte stream or character stream by subclass of byte stream or character stream (uptransition)
3. Perform read and write operations
4. Close the resource

OutputStream Indicates a byte input stream

Common class methods:

Operations on files require a subclass of FileOutputStream to instantiate the object.

Its common construction method is:

Example:

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.charset.StandardCharsets;

public class FIleOutputStearm {
    public static void main(String[] args) throws IOException {
        File file = new File("xbhog.txt");
        if(! file.exists()){ file.createNewFile(); } OutputStream outputStearm =new FileOutputStream(file);
        String str = "Welcome to xbHOG's blog."; outputStearm.write(str.getBytes(StandardCharsets.UTF_8)); outputStearm.close(); }}Copy the code

Appending file contents:

    OutputStream stream = new FileOutputStream(file, true);
    String addStr = "----- this is an add-on ------";
    stream.write(addStr.getBytes());
    stream.close();
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InputStream byte InputStream:

Common methods for this class:

Operations on files require a subclass of FileInputStream to instantiate the object.

Common uses for reading files:

1. Create file input stream —InputStream input = new FileInputStream(file)
2. Set the read cache for data —-new byte[1024]
3. Read data, read data into the cache and put back the number of bytes read —-int len = input.read(data)
4. Bytes are converted to a stream of characters —-new String(data,0,len)
5. Close the resource

Example of reading file contents:

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class FileInputStreamTest {
    public static void main(String[] args) throws IOException {
        File file = new File("xbhog.txt"); // Output file path
        if (file.exists()) {    // File exists
            InputStream input = new FileInputStream(file);// File input stream
            byte data[] = new byte[1024]; // Data read buffer
            // Read the data into the buffer, and return the number of bytes read
            int len = input.read(data);
            System.out.println("【" + new String(data, 0, len) + "】");// Bytes are converted to strings
            input.close();    // Close the input stream}}}Copy the code

Read the entire contents of the file:

byte[] bytes = input.readAllBytes();
System.out.println(new String(bytes));
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Writer character stream:

To simplify the operation of output, Writer and Reader character streams are provided.

Common methods for this class:

When writing a file stream, you need to introduce the FileWriter subclass of Writer.

Class project structure:

• java.lang.Object
• • java.io.Writer
  • • java.io.OutputStreamWriter
    • • java.io.FileWriter

FileWriter:

Example:

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

public class FileWriterDemo {
    public static void main(String[] args) throws IOException {
        File file = new File("FileWriter.txt"); // Output file path
        if(! file.exists()){ file.createNewFile(); } Writer out =new FileWriter(file) ; // Instantiate the Writer class object
        out.write("Welcome to XBHOG");	// Outputs a string
        out.write("\n");
        out.append("Test\n");
        out.append("www.cblog.cn/xbhog");// Append the output
        out.close();// Close the output stream}}Copy the code

Reader character input stream:

Common methods of this class:

Example test:

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

public class FileReaderDemo {
    public static void main(String[] args) throws IOException {
        File file = new File("FileWriter.txt");// Output file path
        if (file.exists()) {// File exists
            Reader in = new FileReader(file);  // instantiate the input stream
            char data[] = new char[1024];  / / the buffer
            // "Welcome is gone"
            in.skip(2);// spans 2 characters
            int len = in.read(data); // Read data
            System.out.println(new String(data, 0, len));
            in.close();// Close the input stream}}}Copy the code

Transformation flows:

To implement the conversion operation of the two:

Converts a byte input stream into a character input stream

import java.io.*;
public class ConversionOperations {
    public static void main(String[] args) throws IOException {
        File file = new File("FileWriter1.txt"); 	// Output file path
        OutputStream output = new FileOutputStream(file) ;/ / byte streams
        Writer out = new OutputStreamWriter(output) ; 	// byte flow character stream
        out.write("Test the conversion between the two."); // Character stream output
        out.close();	// Close the output stream
        output.close(); 	// Close the output stream}}Copy the code

The end:

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There are mistakes, welcome to point out in the comments, the author will see the modification.