java读取文件大全

╰半夏微凉° 2022-07-16 14:50 156阅读 0赞

引用：[http://blog.csdn.net/Willon\_tom/archive/2010/02/08/5297973.aspx][http_blog.csdn.net_Willon_tom_archive_2010_02_08_5297973.aspx]

1、按字节读取文件内容  
2、按字符读取文件内容  
3、按行读取文件内容

4、随机读取文件内容

public class ReadFromFile \{  
    /\*\*  
     \* 以字节为单位读取文件，常用于读二进制文件，如图片、声音、影像等文件。  
     \*/  
    public static void readFileByBytes(String fileName) \{  
        File file = new File(fileName);  
        InputStream in = null;  
        try \{  
            System.out.println("以字节为单位读取文件内容，一次读一个字节：");  
            // 一次读一个字节  
            in = new FileInputStream(file);  
            int tempbyte;  
            while ((tempbyte = in.read()) != -1) \{  
                System.out.write(tempbyte);  
            \}  
            in.close();  
        \} catch (IOException e) \{  
            e.printStackTrace();  
            return;  
        \}  
        try \{  
            System.out.println("以字节为单位读取文件内容，一次读多个字节：");  
            // 一次读多个字节  
            byte\[\] tempbytes = new byte\[100\];  
            int byteread = 0;  
            in = new FileInputStream(fileName);  
            ReadFromFile.showAvailableBytes(in);  
            // 读入多个字节到字节数组中，byteread为一次读入的字节数  
            while ((byteread = in.read(tempbytes)) != -1) \{  
                System.out.write(tempbytes, 0, byteread);  
            \}  
        \} catch (Exception e1) \{  
            e1.printStackTrace();  
        \} finally \{  
            if (in != null) \{  
                try \{  
                    in.close();  
                \} catch (IOException e1) \{  
                \}  
            \}  
        \}  
    \}

/\*\*  
     \* 以字符为单位读取文件，常用于读文本，数字等类型的文件  
     \*/  
    public static void readFileByChars(String fileName) \{  
        File file = new File(fileName);  
        Reader reader = null;  
        try \{  
            System.out.println("以字符为单位读取文件内容，一次读一个字节：");  
            // 一次读一个字符  
            reader = new InputStreamReader(new FileInputStream(file));  
            int tempchar;  
            while ((tempchar = reader.read()) != -1) \{  
                // 对于windows下，/r/n这两个字符在一起时，表示一个换行。  
                // 但如果这两个字符分开显示时，会换两次行。  
                // 因此，屏蔽掉/r，或者屏蔽/n。否则，将会多出很多空行。  
                if (((char) tempchar) != '/r') \{  
                    System.out.print((char) tempchar);  
                \}  
            \}  
            reader.close();  
        \} catch (Exception e) \{  
            e.printStackTrace();  
        \}  
        try \{  
            System.out.println("以字符为单位读取文件内容，一次读多个字节：");  
            // 一次读多个字符  
            char\[\] tempchars = new char\[30\];  
            int charread = 0;  
            reader = new InputStreamReader(new FileInputStream(fileName));  
            // 读入多个字符到字符数组中，charread为一次读取字符数  
            while ((charread = reader.read(tempchars)) != -1) \{  
                // 同样屏蔽掉/r不显示  
                if ((charread == tempchars.length)  
                        && (tempchars\[tempchars.length - 1\] != '/r')) \{  
                    System.out.print(tempchars);  
                \} else \{  
                    for (int i = 0; i < charread; i++) \{  
                        if (tempchars\[i\] == '/r') \{  
                            continue;  
                        \} else \{  
                            System.out.print(tempchars\[i\]);  
                        \}  
                    \}  
                \}  
            \}

\} catch (Exception e1) \{  
            e1.printStackTrace();  
        \} finally \{  
            if (reader != null) \{  
                try \{  
                    reader.close();  
                \} catch (IOException e1) \{  
                \}  
            \}  
        \}  
    \}

/\*\*  
     \* 以行为单位读取文件，常用于读面向行的格式化文件  
     \*/  
    public static void readFileByLines(String fileName) \{  
        File file = new File(fileName);  
        BufferedReader reader = null;  
        try \{  
            System.out.println("以行为单位读取文件内容，一次读一整行：");  
            reader = new BufferedReader(new FileReader(file));  
            String tempString = null;  
            int line = 1;  
            // 一次读入一行，直到读入null为文件结束  
            while ((tempString = reader.readLine()) != null) \{  
                // 显示行号  
                System.out.println("line " + line + ": " + tempString);  
                line++;  
            \}  
            reader.close();  
        \} catch (IOException e) \{  
            e.printStackTrace();  
        \} finally \{  
            if (reader != null) \{  
                try \{  
                    reader.close();  
                \} catch (IOException e1) \{  
                \}  
            \}  
        \}  
    \}

/\*\*  
     \* 随机读取文件内容  
     \*/  
    public static void readFileByRandomAccess(String fileName) \{  
        RandomAccessFile randomFile = null;  
        try \{  
            System.out.println("随机读取一段文件内容：");  
            // 打开一个随机访问文件流，按只读方式  
            randomFile = new RandomAccessFile(fileName, "r");  
            // 文件长度，字节数  
            long fileLength = randomFile.length();  
            // 读文件的起始位置  
            int beginIndex = (fileLength > 4) ? 4 : 0;  
            // 将读文件的开始位置移到beginIndex位置。  
            randomFile.seek(beginIndex);  
            byte\[\] bytes = new byte\[10\];  
            int byteread = 0;  
            // 一次读10个字节，如果文件内容不足10个字节，则读剩下的字节。  
            // 将一次读取的字节数赋给byteread  
            while ((byteread = randomFile.read(bytes)) != -1) \{  
                System.out.write(bytes, 0, byteread);  
            \}  
        \} catch (IOException e) \{  
            e.printStackTrace();  
        \} finally \{  
            if (randomFile != null) \{  
                try \{  
                    randomFile.close();  
                \} catch (IOException e1) \{  
                \}  
            \}  
        \}  
    \}

/\*\*  
     \* 显示输入流中还剩的字节数  
     \*/  
    private static void showAvailableBytes(InputStream in) \{  
        try \{  
            System.out.println("当前字节输入流中的字节数为:" + in.available());  
        \} catch (IOException e) \{  
            e.printStackTrace();  
        \}  
    \}

public static void main(String\[\] args) \{  
        String fileName = "C:/temp/newTemp.txt";  
        ReadFromFile.readFileByBytes(fileName);  
        ReadFromFile.readFileByChars(fileName);  
        ReadFromFile.readFileByLines(fileName);  
        ReadFromFile.readFileByRandomAccess(fileName);  
    \}  
\}

5、将内容追加到文件尾部

public class AppendToFile \{  
    /\*\*  
     \* A方法追加文件：使用RandomAccessFile  
     \*/  
    public static void appendMethodA(String fileName, String content) \{  
        try \{  
            // 打开一个随机访问文件流，按读写方式  
            RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");  
            // 文件长度，字节数  
            long fileLength = randomFile.length();  
            //将写文件指针移到文件尾。  
            randomFile.seek(fileLength);  
            randomFile.writeBytes(content);  
            randomFile.close();  
        \} catch (IOException e) \{  
            e.printStackTrace();  
        \}  
    \}

/\*\*  
     \* B方法追加文件：使用FileWriter  
     \*/  
    public static void appendMethodB(String fileName, String content) \{  
        try \{  
            //打开一个写文件器，构造函数中的第二个参数true表示以追加形式写文件  
            FileWriter writer = new FileWriter(fileName, true);  
            writer.write(content);  
            writer.close();  
        \} catch (IOException e) \{  
            e.printStackTrace();  
        \}  
    \}

public static void main(String\[\] args) \{  
        String fileName = "C:/temp/newTemp.txt";  
        String content = "new append!";  
        //按方法A追加文件  
        AppendToFile.appendMethodA(fileName, content);  
        AppendToFile.appendMethodA(fileName, "append end. /n");  
        //显示文件内容  
        ReadFromFile.readFileByLines(fileName);  
        //按方法B追加文件  
        AppendToFile.appendMethodB(fileName, content);  
        AppendToFile.appendMethodB(fileName, "append end. /n");  
        //显示文件内容  
        ReadFromFile.readFileByLines(fileName);  
    \}  
\}

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[http_blog.csdn.net_Willon_tom_archive_2010_02_08_5297973.aspx]: http://blog.csdn.net/Willon_tom/archive/2010/02/08/5297973.aspx