[转Java读取文件]各种流

[Java]读取文件方法大全 
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); 
    } 
}