JAva読み取りファイル大全

1、         
2、         
3、        

4、        

public class ReadFromFile {
    /**
     *           ，         ，   、  、     。
     */
    public static void readFileByBytes(String fileName) {
        File file = new File(fileName);
        InputStream in = null;
        try {
            System.out.println("            ，       ：");
            //        
            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("            ，       ：");
            //        
            byte[] tempbytes = new byte[100];
            int byteread = 0;
            in = new FileInputStream(fileName);
            ReadFromFile.showAvailableBytes(in);
            //             ，byteread         
            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) {
                }
            }
        }
    }

    /**
     *           ，      ，        
     */
    public static void readFileByChars(String fileName) {
        File file = new File(fileName);
        Reader reader = null;
        try {
            System.out.println("            ，       ：");
            //        
            reader = new InputStreamReader(new FileInputStream(file));
            int tempchar;
            while ((tempchar = reader.read()) != -1) {
                //   windows ，\r
         ，      。
                //              ，     。
                //   ，   \r，    
。  ，        。
                if (((char) tempchar) != '\r') {
                    System.out.print((char) tempchar);
                }
            }
            reader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            System.out.println("            ，       ：");
            //        
            char[] tempchars = new char[30];
            int charread = 0;
            reader = new InputStreamReader(new FileInputStream(fileName));
            //             ，charread        
            while ((charread = reader.read(tempchars)) != -1) {
                //      \r   
                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) {
                }
            }
        }
    }

    /**
     *          ，             
     */
    public static void readFileByLines(String fileName) {
        File file = new File(fileName);
        BufferedReader reader = null;
        try {
            System.out.println("           ，      ：");
            reader = new BufferedReader(new FileReader(file));
            String tempString = null;
            int line = 1;
            //       ，    null     
            while ((tempString = reader.readLine()) != null) {
                //     
                System.out.println("line " + line + ": " + tempString);
                line++;
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e1) {
                }
            }
        }
    }

    /**
     *         
     */
    public static void readFileByRandomAccess(String fileName) {
        RandomAccessFile randomFile = null;
        try {
            System.out.println("          ：");
            //            ，     
            randomFile = new RandomAccessFile(fileName, "r");
            //     ，   
            long fileLength = randomFile.length();
            //         
            int beginIndex = (fileLength > 4) ? 4 : 0;
            //            beginIndex  。
            randomFile.seek(beginIndex);
            byte[] bytes = new byte[10];
            int byteread = 0;
            //    10   ，        10   ，       。
            //            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) {
                }
            }
        }
    }

    /**
     *             
     */
    private static void showAvailableBytes(InputStream in) {
        try {
            System.out.println("             :" + 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、          

public class AppendToFile {
    /**
     * A      ：  RandomAccessFile
     */
    public static void appendMethodA(String fileName, String content) {
        try {
            //            ，     
            RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");
            //     ，   
            long fileLength = randomFile.length();
            //           。
            randomFile.seek(fileLength);
            randomFile.writeBytes(content);
            randomFile.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * B      ：  FileWriter
     */
    public static void appendMethodB(String fileName, String content) {
        try {
            //        ，           true          
            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!";
        //   A    
        AppendToFile.appendMethodA(fileName, content);
        AppendToFile.appendMethodA(fileName, "append end. 
");
        //      
        ReadFromFile.readFileByLines(fileName);
        //   B    
        AppendToFile.appendMethodB(fileName, content);
        AppendToFile.appendMethodB(fileName, "append end. 
");
        //      
        ReadFromFile.readFileByLines(fileName);
    }
}