Java_io体系之RandomAccessFile简介、走进源码及示例――20(三)
))
imode |= O_SYNC;
else if (mode.equals("rwd"))
imode |= O_DSYNC;
else
imode = -1;
}
}
if (imode < 0)
throw new IllegalArgumentException("Illegal mode \"" + mode
+ "\" must be one of "
+ "\"r\", \"rw\", \"rws\","
+ " or \"rwd\"");
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkRead(name);
if (rw) {
security.checkWrite(name);
}
}
if (name == null) {
throw new NullPointerException();
}
fd = new FileDescriptor();
open(name, imode);
}
/**
* 返回指定文件的“文件描述符”
*/
public final FileDescriptor getFD() throws IOException {
if (fd != null) return fd;
throw new IOException();
}
/**
* 打开唯一与此流有关的FileChannel
*/
public final FileChannel getChannel() {
synchronized (this) {
if (channel == null)
channel = FileChannelImpl.open(fd, true, rw, this);
return channel;
}
}
/**
* 以指定模式打开指定文件
*/
private native void open(String name, int mode)
throws FileNotFoundException;
// 'Read' primitives
/**
* 读取下一个字节并以整数形式返回
*/
public native int read() throws IOException;
/**
* 将一组字节读取到b中
*/
private native int readBytes(byte b[], int off, int len) throws IOException;
/**
* 将一组字节读取到b中、调用上面的方法
*/
public int read(byte b[], int off, int len) throws IOException {
return readBytes(b, off, len);
}
/**
* 将一组字节读取到b中
*/
public int read(byte b[]) throws IOException {
return readBytes(b, 0, b.length);
}
/**
* 读取字节放入到b中、直到存满b或者文件结尾、或者异常才结束
* 与read(byte[] b)的区别是返回值。
*/
public final void readFully(byte b[]) throws IOException {
readFully(b, 0, b.length);
}
/**
* 读取字节放入到下标从off开始的后len个位置的字节数组b中、直到存满b或者文件结尾、或者异常才结束
* 与read(byte[] b, int off, int len)的区别是返回值。
*/
public final void readFully(byte b[], int off, int len) throws IOException {
int n = 0;
do {
int count = this.read(b, off + n, len - n);
if (count < 0)
throw new EOFException();
n += count;
} while (n < len);
}
/**
* 跳过n个字节、返回实际跳过的字节、他是通过从定位“文件指针”来实现跨过要跳过的字节
*/
public int skipBytes(int n) throws IOException {
long pos;
long len;
long newpos;
if (n <= 0) {
return 0;
}
pos = getFilePointer();
len = length();
newpos = pos + n;
if (newpos > len) {
newpos = len;
}
seek(newpos);
/* return the actual number of bytes skipped */
return (int) (newpos - pos);
}
// 'Write' primitives
/**
* 在当前“文件指针”标示的地方写入一个字节
*/
public native void write(int b) throws IOException;
/**
* 将b的一部分写入到文件中
*/
private native void writeBytes(byte b[], int off, int len) throws IOException;
/**
* 将b写入到文件中
*/
public void write(byte b[]) throws IOException {
writeBytes(b, 0, b.length);
}
/**
* 将b的一部分写入到文件中
*/
public void write(byte b[], int off, int len) throws IOException {
writeBytes(b, off, len);
}
// 'Random access' stuff
/**
* 返回当前文件的偏移量、即“文件描述符”的位置
*/
public native long getFilePointer() throws IOException;
/**
* 设置“文件指针”的偏移量、从文件的开头开始计数、如果pos大于文件的长度、也不会改变文件的大小、
* 文件的大小只有在当“文件指针”指向文件最后的时候、再向文件中写入字节才会扩展。
*/
public native void seek(long pos) throws IOException;
/**
* 返回文件的字节数
*/
public native long length() throws IOException;
/**
* 设置文件长度：
* if(newLength > originalLength)
* 扩展文件长度、新增加的长度使用默认值填充;
* else
* 截取源文件的前originalLength字节、如果源文件的偏移量大于newLength、则将源文件的偏移量设为newLength;
*/
public native void setLength(long newLength) throws IOException;
/**
* 关闭此流、释放与此流有关的所有资源
*/
public void close() throws IOException {
if (channel != null)
channel.close();
close0();
}
// 一些方法是从DataInputStream/DataOutputStream中剽窃来的。。。
/**
* 读取一个boolean型数据
*/
public final boolean readBoolean() throws IOException {
int ch = this.read();
if (ch < 0)
throw new EOFException();
return (ch != 0);
}
/**
* 从此文件读取一个有符号的八位值。
*/
public final byte readByte() throws IOException {
int ch = this.read();
if (ch < 0)
throw new EOFException();
return (byte)(ch);
}
/**
* 从此文件读取一个无符号的八位数。
*/
public final int readUnsignedByte() throws IOException {
int ch = this.read();
if (ch < 0)
throw new EOFException();
return ch;
}
/**
* 从此文件读取一个有符号的 16 位数。
*/
public final short readShort() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (short)((ch1 << 8) + (ch2 << 0));
}
/**
* 从此文件读取一个无符号的 16 位数。
*/
public final int readUnsignedShort() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (ch1 << 8) + (ch2 << 0);
}
/**
* 从此文件读取一个字符。
*/
public final char readChar() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (char)((ch1 << 8) + (ch2 << 0));
}
/**
* 从此文件读取一个有符号的 32 位整数。
*/
public final int readInt() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
int ch3 = this.read();
int ch4 = this.read();
if ((ch1 | ch2 | ch3 | ch4) < 0)
throw new EOFException();
return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
}
/**
* 从此文件读取一个有符号的 64 位整数。
*/
public final long readLong() throws IOException {
return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
}
/**
* 从此文件读取一个 float。
*/
public final float readFloat() throws IOException {
return Float.intBitsToFloat(readInt());
}
/**
* 从此文件读取一个 double。
*/
public final double readDouble() throws IOException {
return Double.longBitsToDouble(readLong());
}
/**
* 从此文件读取文本的下一行。
*/
public final String readLine() throws IOException {
StringBuffer input = new StringBuffer();
int c = -1;
boolean eol = false;
while (!eol) {
switch (c = read()) {
case -1:
case '\n':
eol = true;
break;
case '\r':
eol = true;
long cur = getFilePointer();
if ((read()) != '\n') {
seek(cur);
}
break;
default:
input.append((char)c);
break;
}
}
if ((c == -1) && (input.length() == 0)) {
return null;
}
return input.toString();
}
/**
* 从此文件读取一个字符串。
*/
public final String readUTF() throws IOException {
return DataInputStream.readUTF(this);
}
/**
* 将一boolean型数据写入文件中
*/
public final void writeBoolean(boolean v) throws IOException {
write(v 1 : 0);
//written++;
}
/**
* 将一个字节写入文件中
*/
public final void writeByte(int v) throws IOException {
write(v);
//written++;
}
/**
* 将一个short写入文件
*/
public final void writeShort(int v) throws IOException {
write((v >
>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 2;
}
/**
* 将一个char写入文件
*/
public final void writeChar(int v) throws IOException {
write((v >>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 2;
}
/**
* 将一个int写入文件
*/
public final void writeInt(int v) throws IOException {
write((v >>> 24) & 0xFF);
write((v >>> 16) & 0xFF);
write((v >>> 8) & 0xFF);
write((v >>> 0) & 0xFF);
//written += 4;
}
/**
* 将一个long写入文件
*/
public final void writeLong(long v) throws IOException {
write((int)(v >>> 56) & 0xFF);
write((int)(v >>> 48) & 0xFF);
write((int)(v >>> 40) & 0xFF);
write((int)(v >>> 32) & 0xFF);
write((int)(v >>> 24) & 0xFF);
write((int)(v >>> 16) & 0xFF);
write((int)(v >>> 8) & 0xFF);
write((int)(v >>> 0) & 0xFF);
//written += 8;
}
/**
* 将一个long写入文件
*/
public final void writeFloat(float v) throws IOException {
writeInt(Float.floatToIntBits(v));
}
/**
* 将一个double写入文件。
*/
public final void writeDouble(double v) throws IOException {
writeLong(Double.doubleToLongBits(v));
}
/**
* 将一个字符串转换成一串有序字节写入
*/
public final void writeBytes(String s) throws IOException {
int len = s.length();
byte[] b = new byte[len];
s.getBytes(0, len, b, 0);
writeBytes(b, 0, len);
}
/**
* 将一个字符串以一串有序字符写入文件中
*/
public final void writeChars(String s) throws IOException {
int clen = s.length();
int blen = 2*clen;
byte[] b = new byte[blen];
char[] c = new char[clen];
s.getChars(0, clen, c, 0);
for (int i = 0, j = 0; i < clen; i++) {
b[j++] = (byte)(c[i] >>> 8);
b[j++] = (byte)(c[i] >>> 0);
}
writeBytes(b, 0, blen);
}
/**
* 调用DataOutputStream的 writeUTF(String str, DataOutput out) 将一个字符串写入文件。
*/
public final void writeUTF(String str) throws IOException {
DataOutputStream.writeUTF(str, this);
}
private static native void initIDs();
private native void close0() throws IOException;
static {
init