java 四种方式读取文件

Zchaowu 2021-09-07 原文

在学习java读取文件之间，应该先了解一下java读写文件常用的几种流，具体看本人博客http://www.cnblogs.com/Zchaowu/p/7353348.html

读取文件的四种方式：按字节读取、按字符读取、按行读取、随机读取

一、按字节读取

//1.按字节读写文件，用FileInputStream、FileOutputStream
        String path = "D:\\iotest.txt";
        File file = new File(path);
        InputStream in;
        //每次只读一个字节
        try {
            System.out.println("以字节为单位，每次读取一个字节");
            in = new FileInputStream(file);
            int c;
            while((c=in.read())!=-1){
                if(c!=13&&c!=10){    // \n回车的Ascall码是10 ，\r换行是Ascall码是13，不现实挥着换行
                    System.out.println((char)c);
                }
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        
        //每次读多个字节
        try {
            System.out.println("以字节为单位，每次读取多个字节");
            in = new FileInputStream(file);
            byte[] bytes = new byte[10];   //每次读是个字节，放到数组里
            int c;
            while((c=in.read(bytes))!=-1){
                System.out.println(Arrays.toString(bytes));
            }
        } catch (Exception e) {
            // TODO: handle exception
        }

二、按字符读取

//2.按字符读取文件，用InputStreamReader,OutputStreamReader
        Reader reader = null;
        try {//每次读取一个字符
            System.out.println("以字符为单位读取文件，每次读取一个字符");
            in = new FileInputStream(file);
            reader = new InputStreamReader(in);
            int c;
            while((c=reader.read())!=-1){
                if(c!=13&&c!=10){    // \n回车的Ascall码是10 ，\r换行是Ascall码是13，不现实挥着换行
                    System.out.println((char)c);
                }                
            }
        } catch (Exception e) {
            // TODO: handle exception
        }
        
        try {//每次读取多个字符
            System.out.println("以字符为单位读取文件，每次读取一个字符");
            in = new FileInputStream(file);
            reader = new InputStreamReader(in);
            int c;
            char[] chars = new char[5];
            while((c=reader.read(chars))!=-1){
                System.out.println(Arrays.toString(chars));
            }
        } catch (Exception e) {
            // TODO: handle exception
        }

三、按行读取

//3.按行读取文件
        try {
            System.out.println("按行读取文件内容");
            in = new FileInputStream(file);
            Reader reader2 = new InputStreamReader(in);
            BufferedReader bufferedReader = new BufferedReader(reader2);
            String line;
            while((line=bufferedReader.readLine())!=null){
                System.out.println(line);
            }
            bufferedReader.close();
        } catch (Exception e) {
            // TODO: handle exception
        }

四、随机读取

//4.随机读取
        try {
            System.out.println("随机读取文件");
            //以只读的方式打开文件
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
            //获取文件长度，单位为字节
            long len = randomAccessFile.length();
            //文件起始位置
            int beginIndex = (len>4)?4:0;
            //将文件光标定位到文件起始位置
            randomAccessFile.seek(beginIndex);
            byte[] bytes = new byte[5];
            int c;
            while((c=randomAccessFile.read(bytes))!=-1){
                System.out.println(Arrays.toString(bytes));
            }
        } catch (Exception e) {
            // TODO: handle exception
        }