本文共33个字，预计阅读时间需要1分钟。

Java
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package com.java.file;
 
import jdk.nashorn.internal.ir.WhileNode;
 
import java.io.*;
 
/**
* @author iBoy
* @date 2019-07-11-22:37
*/
//文件读取的一般步骤是
    //1-创建文件的输入流fis,参数是文件对象
    //2-创建文件输入流的reader
    //3-创建带有缓冲的输出reader
public class ReadWriteFile {
    public static void main(String[] args) {
        File file=new File("test.txt");
        if(file.exists()){
            System.out.println("文件存在");
            try {//文件输入的三个流
                FileInputStream fis=new FileInputStream(file);//获取文件输入流,是字节流
                InputStreamReader isr=new InputStreamReader(fis,"UTF-8");//是字符流，要制定编码，不然会乱码
                BufferedReader br=new BufferedReader(isr);//带有缓冲的reader，可直接读取一行reader
                String line;
                try {
                    while ((line=br.readLine())!=null){//如果这行数据不为空，输出文件内容
                        System.out.println(line);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
                //文件读取完成之后需要关闭输入流
                //先打开的先关闭，后打开的后关闭
                try {
                    br.close();
                    isr.close();
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
        File newfile=new File("txt.txt");//
        if(newfile.exists()){
            System.err.println("文件存在");
        }
        else{
            System.err.println("文件不存在");
            try {
                newfile.createNewFile();
                System.out.println("文件不存在但是文件创建成功");
            } catch (IOException e) {
                e.printStackTrace();
                System.err.println("文件创建失败");
            }
        }
        try {
            FileOutputStream fos=new FileOutputStream(newfile);//如果不存在，会自动创建文件
            OutputStreamWriter osw=new OutputStreamWriter(fos,"UTF-8");
            BufferedWriter bw= new BufferedWriter(osw);
            try {//文件的写入具有覆盖性
                bw.write("额额\n");
                bw.write("2额额\n");
                bw.write("1212\n");
                bw.close();
                osw.close();
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
 
 
    }
}
 

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