java读取文件的四种方法总结

java读取文件的四种方式分别是：

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

import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.FileReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.RandomAccessFile;import java.io.Reader;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("++++++readFileByBytes:++++++\n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);            }            System.out.println();            in.close();        } catch (IOException e) {            e.printStackTrace();            return;        }        try {            System.out.print("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);            }            System.out.println("\r");        } 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("++++++readFileByChars:++++++\n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);                }            }            System.out.println();            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]);                        }                    }                }            }            System.out.println("\r");        } 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("++++++readFileByLines:++++++\n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++;            }            System.out.println();            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("++++++readFileByRandomAccess:++++++\n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:/newTemp.txt";        ReadFromFile.readFileByBytes(fileName);        ReadFromFile.readFileByChars(fileName);        ReadFromFile.readFileByLines(fileName);        ReadFromFile.readFileByRandomAccess(fileName);    }}

控制台输出结果为：

++++++readFileByBytes:++++++以字节为单位读取文件内容，一次读一个字节：Sun Yat-sen(November 12, 1866–March 12, 1925) was a Chinese revolutionary and political leader who is often referred to as the "father of modern China". Sun played an instrumental and leadership role in the eventual overthrow of the Qing Dynasty in 1911. He was the first provisional president when the Republic of China was founded in 1912. He later co-founded the Kuomintang (KMT) where he served as its first leader. 以字节为单位读取文件内容，一次读多个字节：当前字节输入流中的字节数为:421Sun Yat-sen(November 12, 1866–March 12, 1925) was a Chinese revolutionary and political leader who is often referred to as the "father of modern China". Sun played an instrumental and leadership role in the eventual overthrow of the Qing Dynasty in 1911. He was the first provisional president when the Republic of China was founded in 1912. He later co-founded the Kuomintang (KMT) where he served as its first leader. ++++++readFileByChars:++++++以字符为单位读取文件内容，一次读一个字节：Sun Yat-sen(November 12, 1866–March 12, 1925) was a Chinese revolutionary and political leader who is often referred to as the "father of modern China". Sun played an instrumental and leadership role in the eventual overthrow of the Qing Dynasty in 1911. He was the first provisional president when the Republic of China was founded in 1912. He later co-founded the Kuomintang (KMT) where he served as its first leader. 以字符为单位读取文件内容，一次读多个字节：Sun Yat-sen(November 12, 1866–March 12, 1925) was a Chinese revolutionary and political leader who is often referred to as the "father of modern China". Sun played an instrumental and leadership role in the eventual overthrow of the Qing Dynasty in 1911. He was the first provisional president when the Republic of China was founded in 1912. He later co-founded the Kuomintang (KMT) where he served as its first leader. ++++++readFileByLines:++++++以行为单位读取文件内容，一次读一整行：line 1: Sun Yat-sen(November 12, 1866–March 12, 1925) was a Chinese revolutionary and political leader who is often referred to as the "father of modern China". Sun played an instrumental and leadership role in the eventual overthrow of the Qing Dynasty in 1911. He was the first provisional president when the Republic of China was founded in 1912. He later co-founded the Kuomintang (KMT) where he served as its first leader. ++++++readFileByRandomAccess:++++++随机读取一段文件内容：Yat-sen(November 12, 1866–March 12, 1925) was a Chinese revolutionary and political leader who is often referred to as the "father of modern China". Sun played an instrumental and leadership role in the eventual overthrow of the Qing Dynasty in 1911. He was the first provisional president when the Republic of China was founded in 1912. He later co-founded the Kuomintang (KMT) where he served as its first leader.