三分鐘帶你讀懂RandomAccessFile

RandomAccessFile(File file, String mode)
RandomAccessFile(String fileName, String mode)
void  close()
synchronized final FileChannel  getChannel()
final FileDescriptor  getFD()
long  getFilePointer()
long  length()
int  read(byte[] buffer, int byteOffset, int byteCount)
int  read(byte[] buffer)
int  read()
final boolean  readBoolean()
final byte  readByte()
final char  readChar()
final double  readDouble()
final float  readFloat()
final void  readFully(byte[] dst)
final void  readFully(byte[] dst, int offset, int byteCount)
final int  readInt()
final String  readLine()
final long  readLong()
final short  readShort()
final String  readUTF()
final int  readUnsignedByte()
final int  readUnsignedShort()
void  seek(long offset)
void  setLength(long newLength)
int  skipBytes(int count)
void  write(int oneByte)
void  write(byte[] buffer, int byteOffset, int byteCount)
void  write(byte[] buffer)
final void  writeBoolean(boolean val)
final void  writeByte(int val)
final void  writeBytes(String str)
final void  writeChar(int val)
final void  writeChars(String str)
final void  writeDouble(double val)
final void  writeFloat(float val)
final void  writeInt(int val)
final void  writeLong(long val)
final void  writeShort(int val)
final void  writeUTF(String str)

 import java.io.File;
 import java.io.FileDescriptor;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
 import java.io.PrintStream;;
 import java.io.RandomAccessFile;
 import java.io.IOException;
 /**
 * RandomAccessFile 測試程序
 *
 * 運(yùn)行結(jié)果(輸出如下)：
 * c1=a
 * c2=b
 * buf=
 * 
 * 此外,
 * (01) 在源文件所在目錄生成了file.txt。
 * (02) 注意RandomAccessFile寫入boolean, byte, char, int,所占的字符個(gè)數(shù)。
 *
 * 
 */
 public class RandomAccessFileTest {
  private static final String FileName = "file.txt";
  public static void main(String[] args) {
   // 若文件“file.txt”存在，則刪除該文件。
   File file = new File(FileName);
   if (file.exists())
    file.delete();
   testCreateWrite();
   testAppendWrite();
   testRead();
  }
  /**
  * 若“file.txt”不存在的話，則新建文件，并向文件中寫入內(nèi)容
  */
  private static void testCreateWrite() {
   try {
    // 創(chuàng)建文件“file.txt”對應(yīng)File對象
    File file = new File(FileName);
    // 創(chuàng)建文件“file.txt”對應(yīng)的RandomAccessFile對象
    RandomAccessFile raf = new RandomAccessFile(file, "rw");
    // 向“文件中”寫入個(gè)字母+回車
    raf.writeChars("abcdefghijklmnopqrstuvwxyz\n");
    // 向“文件中”寫入""+回車
    raf.writeChars("\n");
    raf.close();
   } catch(IOException e) {
    e.printStackTrace();
   }
  }
  /**
  * 向文件末尾追加內(nèi)容
  */
  private static void testAppendWrite() {
   try {
    // 創(chuàng)建文件“file.txt”對應(yīng)File對象
    File file = new File(FileName);
    // 創(chuàng)建文件“file.txt”對應(yīng)的RandomAccessFile對象
    RandomAccessFile raf = new RandomAccessFile(file, "rw");
    // 獲取文件長度
    long fileLen = raf.length();
    // 將位置定位到“文件末尾”
    raf.seek(fileLen);
    // 以下向raf文件中寫數(shù)據(jù) 
    raf.writeBoolean(true); // 占個(gè)字節(jié) 
    raf.writeByte(x); // 占個(gè)字節(jié) 
    raf.writeChar('a');  // 占個(gè)字節(jié) 
    raf.writeShort(xcc); // 占個(gè)字節(jié) 
    raf.writeInt(x);  // 占個(gè)字節(jié) 
    raf.writeLong(xL); // 占個(gè)字節(jié) 
    raf.writeFloat(.f); // 占個(gè)字節(jié) 
    raf.writeDouble(.);// 占個(gè)字節(jié) 
    raf.writeUTF("UTF嚴(yán)"); // UTF-格式寫入
    raf.writeChar('\n'); // 占個(gè)字符。“換行符”
    raf.close();
   } catch(IOException e) {
    e.printStackTrace();
   }
  }
  /**
  * 通過RandomAccessFile讀取文件
  */
  private static void testRead() {
   try {
    // 創(chuàng)建文件“file.txt”對應(yīng)File對象
    File file = new File(FileName);
    // 創(chuàng)建文件“file.txt”對應(yīng)的RandomAccessFile對象，以只讀方式打開
    RandomAccessFile raf = new RandomAccessFile(file, "r");
    // 讀取一個(gè)字符
    char c1 = raf.readChar();
   System.out.println("c1="+c1);
   // 讀取一個(gè)字符
   char c2 = raf.readChar();
   System.out.println("c2="+c2);
    // 跳過54個(gè)字節(jié)。
   raf.seek(54);
   // 測試read(byte[] buffer, int byteOffset, int byteCount)
   byte[] buf = new byte[20];
    raf.read(buf, , buf.length);
    System.out.println("buf="+(new String(buf)));
    raf.close();
   } catch(IOException e) {
    e.printStackTrace();
   }
  }
 }

c1=a
c2=b
buf=9876543210