java read file and write file method (simple example)

Java code

public class ReadFromFile { 
  /** 
   * Reading files byte by byte, commonly used for reading binary files such as images, sounds, videos, and other files. 
   */ 
  public static void readFileByBytes(String fileName) { 
    File file = new File(fileName); 
    InputStream in = null; 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("Read file content byte by byte, one byte at a time:"); 
      // Read one byte at a time 
      in = new FileInputStream(file); 
      int tempbyte; 
      while ((tempbyte = in.read()) != -1) { 
        System.out.write(tempbyte); 
      } 
      in.close(); 
    } 
      e.printStackTrace(); 
      return; 
    } 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("Read file content by byte, read multiple bytes at a time:"); 
      // Read multiple bytes at once 
      byte[] tempbytes = new byte[100]; 
      int byteread = 0; 
      in = new FileInputStream(fileName); 
      ReadFromFile.showAvailableBytes(in); 
      // Read multiple bytes into a byte array, where byteread represents the number of bytes read at a time 
      while ((byteread = in.read(tempbytes)) != -1) { 
        System.out.write(tempbytes, 0, byteread); 
      } 
    } catch (Exception e1) { 
      e1.printStackTrace(); 
    } 
      if (in != null) { 
        Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
          in.close(); 
        } catch (IOException e1) { 
        } 
      } 
    } 
  } 
  /** 
   * Read files by character, commonly used for reading text, numbers, and other types of files 
   */ 
  public static void readFileByChars(String fileName) { 
    File file = new File(fileName); 
    Reader reader = null; 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("Read file content by character, read one byte at a time:"); 
      // Read one character at a time 
      reader = new InputStreamReader(new FileInputStream(file)); 
      int tempchar; 
      while ((tempchar = reader.read()) != -1) { 
        // For Windows, the \r\n characters together represent a line break. 
        // But if these two characters are displayed separately, they will cause a line break twice. 
        // Therefore, the \r character should be masked, or the \n character should be masked. Otherwise, many blank lines will appear. 
        if (((char) tempchar) != '\r') { 
          System.out.print((char) tempchar); 
        } 
      } 
      reader.close(); 
    } catch (Exception e) { 
      e.printStackTrace(); 
    } 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("Read file content by character, read multiple bytes at a time:"); 
      // Read multiple characters at once 
      char[] tempchars = new char[30]; 
      int charread = 0; 
      reader = new InputStreamReader(new FileInputStream(fileName)); 
      // Read multiple characters into a character array, where charread represents the number of characters read at a time 
      while ((charread = reader.read(tempchars)) != -1) { 
        // Similarly, mask and do not display \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(); 
    } 
      if (reader != null) { 
        Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
          reader.close(); 
        } catch (IOException e1) { 
        } 
      } 
    } 
  } 
  /** 
   * Read file by lines, commonly used for reading formatted files oriented to lines 
   */ 
  public static void readFileByLines(String fileName) { 
    File file = new File(fileName); 
    BufferedReader reader = null; 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("Read file content by lines, read one entire line at a time:"); 
      reader = new BufferedReader(new FileReader(file)); 
      String tempString = null; 
      int line = 1; 
      // Read one line at a time until null is read as file end 
      while ((tempString = reader.readLine()) != null) { 
        // Display line number 
        System.out.println("line "); + line + : " + tempString); 
        line++; 
      } 
      reader.close(); 
    } 
      e.printStackTrace(); 
    } 
      if (reader != null) { 
        Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
          reader.close(); 
        } catch (IOException e1) { 
        } 
      } 
    } 
  } 
  /** 
   * Randomly read file content 
   */ 
  public static void readFileByRandomAccess(String fileName) { 
    RandomAccessFile randomFile = null; 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("Randomly read a segment of file content:"); 
      // Open a random access file stream in read-only mode 
      randomFile = new RandomAccessFile(fileName, "r"); 
      // File length, number of bytes 
      long fileLength = randomFile.length(); 
      // The starting position of reading the file 
      int beginIndex = (fileLength > 4) &63; 4 : 0; 
      // Move the read file start position to the beginIndex position. 
      randomFile.seek(beginIndex); 
      byte[] bytes = new byte[10]; 
      int byteread = 0; 
      // Read once10bytes, if the file content is not enough10bytes, then read the remaining bytes. 
      // Assign the number of bytes read in one read to byteread 
      while ((byteread = randomFile.read(bytes)) != -1) { 
        System.out.write(bytes, 0, byteread); 
      } 
    } 
      e.printStackTrace(); 
    } 
      if (randomFile != null) { 
        Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
          Append file using method B: using FileWriter 
        } catch (IOException e1) { 
        } 
      } 
    } 
  } 
  /** 
   * Display the number of bytes remaining in the input stream 
   */ 
  private static void showAvailableBytes(InputStream in) { 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      System.out.println("The number of bytes available in the current byte input stream is: "); + in.available()); 
    } 
      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); 
  } 
}

Java code

public class AppendToFile { 
  /** 
   * A method to append to a file: using RandomAccessFile 
   */ 
  public static void appendMethodA(String fileName, String content) { 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      // Open a random access file stream in read-write mode 
      RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw"); 
      // File length, number of bytes 
      long fileLength = randomFile.length(); 
      //Move the write file pointer to the end of the file. 
      randomFile.seek(fileLength); 
      randomFile.writeBytes(content); 
      Append file using method B: using FileWriter 
    } 
      e.printStackTrace(); 
    } 
  } 
  /** 
   * public static void appendMethodB(String fileName, String content) { 
   */ 
  try { 
    Open a FileWriter, the second parameter true in the constructor indicates that the file is written in append mode 
      //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!"; 
    //Append file using method A 
    AppendToFile.appendMethodA(fileName, content); 
    AppendToFile.appendMethodA(fileName, "append end. \n"); 
    //Display file content 
    ReadFromFile.readFileByLines(fileName); 
    //Append file using method B 
    AppendToFile.appendMethodB(fileName, content); 
    AppendToFile.appendMethodB(fileName, "append end. \n"); 
    //Display file content 
    ReadFromFile.readFileByLines(fileName); 
  } 
}

That's all for the ways of reading and writing files in Java brought to you by the editor (simple example). Hope everyone will support and cheer for the tutorial~