Java——读取和写入txt文件

package com.java.test.a;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

public class ReadAndWriteTXT {
    public static String resolveCode(String path) throws Exception {
        InputStream inputStream = new FileInputStream(path);    
        byte[] head = new byte[3];    
        inputStream.read(head);      
        String code = "gb2312";  //或GBK  
        if (head[0] == -1 && head[1] == -2 )    
            code = "UTF-16";    
        else if (head[0] == -2 && head[1] == -1 )    
            code = "Unicode";    
        else if(head[0]==-17 && head[1]==-69 && head[2] ==-65)    
            code = "UTF-8";    
            
        inputStream.close();   
        return code;  
    } 

    public static void main(String[] args) {
    
            /**读取txt文件*/
            String pathname = "D:/test.txt"; // 绝对路径或相对路径都可以，这里是绝对路径 
            String code = "";
            try {
                code = resolveCode(pathname);//获取txt文档编码
            } catch (Exception e1) {
                e1.printStackTrace();
            }
            File filename = new File(pathname); //读取文件
            InputStreamReader reader = null;
            BufferedReader br = null;
            try {
                try {
                    reader = new InputStreamReader(new FileInputStream(filename),code);
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                } //输入流
                br = new BufferedReader(reader); // 建立一个对象，它把文件内容转成计算机能读懂的语言  
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
            try {
                String line = "";
                while ((line = br.readLine()) != null) {
//                    line = br.readLine(); // 一次读入一行数据  
                    System.out.println(line);
                } 
            } catch (IOException e) {
                System.out.println("文件读取错误");
            }  
            
             //在写入文件时，若没有找到目标文件，则会创建一个
            /**写入txt文件*/
            File writename = new File(".\\file\\output.txt"); //相对路径,以项目文件为根路径：Test/file/output.txt
            BufferedWriter out = null;
            try {
                writename.createNewFile(); // 创建新文件  
                out = new BufferedWriter(new FileWriter(writename));
                out.write("写入文件测试\r\n第二行\r\n第三行\r\nnqwertyuiop\r\n1234567890"); // \r\n即为换行  
                out.flush(); // 把缓存区内容压入文件  
                out.close(); // 关闭输出
            } catch (IOException e) {
                System.out.println("文件输入错误");
                 e.printStackTrace();
            }  
            
    }

}

 相对路径：

在使用相对路径读取和写入文件时，相对项目根目录Test进行读取，例如：./file/output.txt，完整路径为D:/workspace/Test/file/output.txt