java 四種方式讀取文件

在學習java讀取文件之間，應該先了解一下java讀寫文件常用的幾種流，具體看本人博客http://www.cnblogs.com/Zchaowu/p/7353348.html

讀取文件的四種方式：按字節讀取、按字符讀取、按行讀取、隨機讀取

 

一、按字節讀取

//1.按字節讀寫文件，用FileInputStream、FileOutputStream
        String path = "D:\\iotest.txt";
        File file = new File(path);
        InputStream in;
        //每次只讀一個字節
        try {
            System.out.println("以字節為單位，每次讀取一個字節");
            in = new FileInputStream(file);
            int c;
            while((c=in.read())!=-1){
                if(c!=13&&c!=10){    // \n回車的Ascall碼是10 ，\r換行是Ascall碼是13，不現實揮着換行
                    System.out.println((char)c);
                }
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        
        //每次讀多個字節
        try {
            System.out.println("以字節為單位，每次讀取多個字節");
            in = new FileInputStream(file);
            byte[] bytes = new byte[10];   //每次讀是個字節，放到數組里
            int c;
            while((c=in.read(bytes))!=-1){
                System.out.println(Arrays.toString(bytes));
            }
        } catch (Exception e) {
            // TODO: handle exception
        }

 

二、按字符讀取

//2.按字符讀取文件，用InputStreamReader,OutputStreamReader
        Reader reader = null;
        try {//每次讀取一個字符
            System.out.println("以字符為單位讀取文件，每次讀取一個字符");
            in = new FileInputStream(file);
            reader = new InputStreamReader(in);
            int c;
            while((c=reader.read())!=-1){
                if(c!=13&&c!=10){    // \n回車的Ascall碼是10 ，\r換行是Ascall碼是13，不現實揮着換行
                    System.out.println((char)c);
                }                
            }
        } catch (Exception e) {
            // TODO: handle exception
        }
        
        try {//每次讀取多個字符
            System.out.println("以字符為單位讀取文件，每次讀取一個字符");
            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、按行讀取

//3.按行讀取文件
        try {
            System.out.println("按行讀取文件內容");
            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、隨機讀取

//4.隨機讀取
        try {
            System.out.println("隨機讀取文件");
            //以只讀的方式打開文件
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
            //獲取文件長度，單位為字節
            long len = randomAccessFile.length();
            //文件起始位置
            int beginIndex = (len>4)?4:0;
            //將文件光標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
        }