Java：文件写入读取操作和工具类

package com.demo;
import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class FileUtil {
    public static void main(String[] args) throws IOException {
        // 覆盖写入
        PrintWriter writer = new PrintWriter(new FileWriter("data.txt"));
        writer.println("hello");
        writer.println("world");
        writer.close();
        // 追加写入
        PrintWriter appendWriter = new PrintWriter(new FileWriter("data.txt", true));
        appendWriter.println("hello");
        appendWriter.println("world");
        appendWriter.close();
        // 按行读取
        List<String> list = new ArrayList<>();
        Scanner scanner = new Scanner(new FileReader("data.txt"));
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            list.add(line);
        }
        scanner.close();
        System.out.println(list);
        // [hello, world, hello, world]
    }
}

package com.demo.fileutil;
import java.io.IOException;
import java.io.PrintWriter;
public class FileWriter {
    private PrintWriter writer;
    public FileWriter(String fileName) throws IOException {
        this(fileName, false);
    }
    public FileWriter(String fileName, boolean append) throws IOException {
        this.writer = new PrintWriter(new java.io.FileWriter(fileName, append));
    }
    public void println(String content){
        this.writer.println(content);
    }
    public void print(String content){
        this.writer.print(content);
    }
    public void close(){
        this.writer.close();
    }
}

package com.demo.fileutil;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class FileReader {
    private String fileName;
    public FileReader(String fileName) {
        this.fileName = fileName;
    }
    public List<String> readLines() throws FileNotFoundException {
        List<String> list = new ArrayList<>();
        Scanner scanner = new Scanner(new java.io.FileReader(this.fileName));
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            list.add(line);
        }
        scanner.close();
        return list;
    }
    public String readAll() throws IOException {
        StringBuilder sb = new StringBuilder();
        java.io.FileReader reader = new java.io.FileReader(this.fileName);
        int len = 0;
        char[] data = new char[1024];
        while ((len = reader.read(data)) != -1) {
            sb.append(data, 0, len);
        }
        reader.close();
        return sb.toString();
    }
}

package com.demo;
import com.demo.fileutil.FileReader;
import com.demo.fileutil.FileWriter;
import java.io.IOException;
import java.util.List;
public class TestFileUtil {
    public static void main(String[] args) throws IOException {
        FileWriter writer = new FileWriter("data.txt", true);
        writer.println("hello");
        writer.println("world");
        writer.close();
        FileReader reader = new FileReader("data.txt");
        String content = reader.readAll();
        System.out.print(content);
        // hello
        // world
        List<String> list = reader.readLines();
        System.out.println(list);
        // [hello, world]
    }
}