RandomAccessFile简介_动力节点Java学院整理

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 测试程序
 *
 * 运行结果(输出如下)：
 * c1=a
 * c2=b
 * buf=
 * 
 * 此外,
 * (01) 在源文件所在目录生成了file.txt。
 * (02) 注意RandomAccessFile写入boolean, byte, char, int,所占的字符个数。
 *
 * 
 */
 public class RandomAccessFileTest {
  private static final String FileName = "file.txt";
  public static void main(String[] args) {
   // 若文件“file.txt”存在，则删除该文件。
   File file = new File(FileName);
   if (file.exists())
    file.delete();
   testCreateWrite();
   testAppendWrite();
   testRead();
  }
  /**
  * 若“file.txt”不存在的话，则新建文件，并向文件中写入内容
  */
  private static void testCreateWrite() {
   try {
    // 创建文件“file.txt”对应File对象
    File file = new File(FileName);
    // 创建文件“file.txt”对应的RandomAccessFile对象
    RandomAccessFile raf = new RandomAccessFile(file, "rw");
    // 向“文件中”写入个字母+回车
    raf.writeChars("abcdefghijklmnopqrstuvwxyz\n");
    // 向“文件中”写入""+回车
    raf.writeChars("\n");
    raf.close();
   } catch(IOException e) {
    e.printStackTrace();
   }
  }
  /**
  * 向文件末尾追加内容
  */
  private static void testAppendWrite() {
   try {
    // 创建文件“file.txt”对应File对象
    File file = new File(FileName);
    // 创建文件“file.txt”对应的RandomAccessFile对象
    RandomAccessFile raf = new RandomAccessFile(file, "rw");
    // 获取文件长度
    long fileLen = raf.length();
    // 将位置定位到“文件末尾”
    raf.seek(fileLen);
    // 以下向raf文件中写数据 
    raf.writeBoolean(true); // 占个字节 
    raf.writeByte(x); // 占个字节 
    raf.writeChar('a');  // 占个字节 
    raf.writeShort(xcc); // 占个字节 
    raf.writeInt(x);  // 占个字节 
    raf.writeLong(xL); // 占个字节 
    raf.writeFloat(.f); // 占个字节 
    raf.writeDouble(.);// 占个字节 
    raf.writeUTF("UTF严"); // UTF-格式写入
    raf.writeChar('\n'); // 占个字符。“换行符”
    raf.close();
   } catch(IOException e) {
    e.printStackTrace();
   }
  }
  /**
  * 通过RandomAccessFile读取文件
  */
  private static void testRead() {
   try {
    // 创建文件“file.txt”对应File对象
    File file = new File(FileName);
    // 创建文件“file.txt”对应的RandomAccessFile对象，以只读方式打开
    RandomAccessFile raf = new RandomAccessFile(file, "r");
    // 读取一个字符
    char c1 = raf.readChar();
   System.out.println("c1="+c1);
   // 读取一个字符
   char c2 = raf.readChar();
   System.out.println("c2="+c2);
    // 跳过54个字节。
   raf.seek(54);
   // 测试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