java txt文件读写操作

男娘i 2024-04-19 14:27 74阅读 0赞

**  最近接到了文件上传和下载的小需求，故整理了下java文件操作的一些方法。**

**1、往指定路径的文件写入110万行**字符串

/**
         * 写入TXT文件
         */
        public static void writeFile() {
            try {
                File writeName = new File("E:\\home\\mobile.txt"); //文件路径
                writeName.createNewFile(); // 创建新文件,有同名的文件的话直接覆盖
    
                FileWriter writer = new FileWriter(writeName);
                BufferedWriter out = new BufferedWriter(writer);
                for (int i = 1; i <= 1100000; i++) {
                    out.write("qwertyuioplmknjbhvgcfxdzsa\r\n"); // \r\n即为换行
                    if (i % 10000 == 0) ;
                    out.flush(); // 把缓存区内容压入文件
                }
                out.flush(); // 把缓存区内容压入文件
    
            } catch (IOException e) {
                e.printStackTrace();
    
            }
        }

2、上传和下载文件，一次性读取到内存和一次性写入

public static void main(String[] args) throws IOException {
             //读文件到内存
            InputStream in = new FileInputStream("F:\\mobileSmall1.txt");
            byte[] buffer = new byte[in.available()];
            in.read(buffer); //一次性将文件二进制流读入
    
            //从内存到硬盘
    
            OutputStream out = new FileOutputStream("D:\\destination.txt");
            out.write(buffer);
            out.close();
            in.close();
        }

3、每次读取固定大小的文件到内存并写入文件

public static void main(String[] args) throws IOException {
            //读文件到内存
            InputStream in = new FileInputStream("F:\\mobileSmall1.txt");
            byte[] buffer = new byte[1024 * 1024 * 10];//每次10M
    
            OutputStream out = new FileOutputStream("D:\\destination.txt");
            while (in.read(buffer) != -1) {
                out.write(buffer);
                out.flush();
            }
            //从内存到硬盘
            out.close();
            in.close();
        }

4、按行读取文件

public static void upload() throws IOException {
            InputStream in = new FileInputStream("f:\\lys455558.txt");
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(in));
            String lines;
            long rows=0l; //统计文件行数
            OutputStream out = new FileOutputStream("D:\\destination.txt");
            while ((lines = bufferedReader.readLine()) != null) {
                rows++;
                if (lines.startsWith("")) {  //取出空行
                    System.out.println(lines);
                    out.write(lines.getBytes() );
                    out.flush();
                }
            }
            System.out.println("文件行数："+rows);
        }

6、统计文件行数

public static void count() throws IOException {
            long rows=0;
            InputStream in = new FileInputStream("F:\\mobileSmall1.txt");
            if(in.available()>0){
                LineNumberReader lineNumberReader = new LineNumberReader(new InputStreamReader(in));
                lineNumberReader.skip(in.available());//跳到行末
                rows = lineNumberReader.getLineNumber() + 1; //取当前行号并加1
            }
            System.out.println("文件行数："+rows);
        }

7、字符串转输入流（String   to  inputstream）

String Result="今天不下雨！";
    InputStream  inputStream = new ByteArrayInputStream(Result.getBytes(Charset.forName("UTF-8")));