File read / write operation (files under the specified file directory)

File Introduction and reference of reading ： https://blog.csdn.net/whjk20/article/details/114067986

The operation of writing is similar .

stay java In the actual reading and writing operation of the project , I found that if I only read and write by file name ( Use Files class ), Only read or write java root directory The files under the .

If you need to read And write Specify the directory Under the file , You need to use   BufferedReader and BufferedWriter. The details are shown in the following code

It involves creating file directories File.mkdir /mkdirs ,    Get the files in the file directory File.listFiles, Relatively simple

Mainly 4-1 / 4-2  and 5-1 and 5-2 Function operation of . （4-2 and 5-2 Relatively flexible , You can batch operate files , And specify the directory , Easy to manage ）

package com.example.javatest.fileoperation;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

public class FileDirReadWriteTest {
    public static void main(String[] args) throws IOException {
        System.out.println("---- main ----");

        final String dirName = "InputFolder";
        final String outDirName = "OutputFolder";

        // 1.  input dir & files
        File inDir = new File(dirName);
        if (!inDir.exists()) {
            System.out.println("---- inDir not exist so create new dir ----");
            inDir.mkdir();
        } else {
            System.out.println("---- inDir already exist ----");
        }

        System.out.println("---- final dir exist? " + inDir.getAbsolutePath());

        File[] inFiles = inDir.listFiles();
        System.out.println("---- inDir file size= " + inFiles.length);

        // 2.  output dir & files
        System.out.println("----    outDir    ----");
        File outDir = new File(outDirName);
        if (!outDir.exists()) {
            System.out.println("---- outDir not exist so create new dir ----");
            outDir.mkdirs();
        } else {
            System.out.println("---- outDir already exist ----");
        }
        System.out.println("---- final outDir exist? " + outDir.getAbsolutePath());

        File[] outFiles = outDir.listFiles();
        System.out.println("---- outFiles file size= " + outFiles.length);
        // delete all output file
        for (File f : outFiles) {
            f.delete();
        }

        // 3. read input files and convert content, then write to output files
        for (File f : inFiles) {
            //List<String> texts = readLineFromFile(f.getName());
            List<String> texts = readLineFromFile(f);
            if (texts == null) {
                System.out.println("---- no text in current input file so skip it");
                continue;
            }
            List<String> convertedTexts = new ArrayList<>();
            for (String text : texts) {
                convertedTexts.add(text.toUpperCase());
            }

            //3-2 create related out file
            File tmpFile = new File(outDir, "out2-" + f.getName());
            if (!tmpFile.exists()) {
                tmpFile.createNewFile();
            }

            //writeFile(f.getName(), convertedTexts);
            writeFile(tmpFile, convertedTexts);
        }
    }

    // 4.  Read java Files in the root directory 
    private static List<String> readLineFromFile(String pathName) throws IOException {
        System.out.println("---readLineFromFile pathName=" + pathName);
        File file = new File(pathName);
        if (!file.exists()) {
            System.out.println("readLineFromFile file is not exist so return null ");
            return null;
        }
        // TODO path  It can only be read successfully under the project root directory , How to read if you want to read the specified directory ?
        List<String> strings = Files.readAllLines(Paths.get(file.getName()), StandardCharsets.UTF_8);//Paths.get(pathName);
        return strings;
    }

    //4-2  Read the specified file （ That is, in a specific directory ） The contents of the following documents 
    private static List<String> readLineFromFile(File file) throws IOException {
        System.out.println("---readLineFromFile file name=" + file.getName());

        if (!file.exists()) {
            System.out.println("readLineFromFile file is not exist so return null ");
            return null;
        }

        List<String> texts = new ArrayList<>();
        InputStream inputStream = new FileInputStream(file);

        if (inputStream == null) {
            System.out.println("readLineFromFile inputStream is not null so return null ");
        }

        InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        String line = bufferedReader.readLine();
        while (line != null) {
            texts.add(line);
            line = bufferedReader.readLine();
        }


        return texts;
    }


    // 5-1.  According to the file name , Can only write java The root directory of the project 
    private static void writeFile(String fileName, List<String> texts) throws IOException {
        System.out.println("---writeFile(String) fileName=" + fileName);
        File file = new File("out-" + fileName);
        if (!file.exists()) {
            System.out.println("writeFile file is not exist and create new ");
            file.createNewFile();
        }

        Files.write(Paths.get(file.getName()), texts, StandardCharsets.UTF_8);//Paths.get(pathName);

        System.out.println("---writeFile successfully");
    }

    // 5-2  Write to the specified file ( That is, under the specified directory )
    private static void writeFile(File file, List<String> texts) throws IOException {
        System.out.println("---writeFile(File) fileName=" + file.getName());

        if (!file.exists()) {
            System.out.println("writeFile file is not exist and create new ");
            file.createNewFile();
        }

        OutputStream outputStream = new FileOutputStream(file);
        if (outputStream == null) {
            System.out.println("writeFile outputStream is null so return ");
            return;
        }

        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
        BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);

        if (texts == null) {
            System.out.println("writeFile texts is null so write empty content ");
            bufferedWriter.write("");
            return;
        }

        StringBuilder stringBuilder = new StringBuilder();
        int lineCount = texts.size();
        for (int i = 0; i < lineCount; i++) {
            stringBuilder.append(texts.get(i));
            if (i != lineCount - 1) {
                stringBuilder.append("\n");
            }
        }
        bufferedWriter.write(stringBuilder.toString());
        // need close,  Otherwise, the write fails ( Not included )
        bufferedWriter.close();

        System.out.println("---writeFile successfully");
    }
}