一、DataInputStream和DataOutputStream函数
DataInputStream和DataOutputStream函数是文件输入/输出二进制流函数。
DataInputStream函数主要实现数据输入流允许应用程序以独立于机器的方式从底层输入流中读取原始 Java 数据类型。应用程序使用数据输出流写入稍后可由数据输入流读取的数据。
DataOutputStream函数主要实现数据输出流允许应用程序以可移植的方式将原始 Java 数据类型写入输出流。然后,应用程序可以使用数据输入流将数据读回。
二、DataInputStream源码介绍
DataInputStream继承于FilterInputStream类,他连接了DataInput接口
public
class DataInputStream extends FilterInputStream implements DataInput {
}
创建一个使用指定的底层 InputStream 的 DataInputStream。
public DataInputStream(InputStream in) {
super(in);
}
创建了byte数组和char数组,默认大小为80;
private byte bytearr[] = new byte[80];
private char chararr[] = new char[80];
定义了一个读取数组,将读取的放置在byte数组里
public final int read(byte b[]) throws IOException {
return in.read(b, 0, b.length);
}
读取数组中部分数据
public final int read(byte b[], int off, int len) throws IOException {
return in.read(b, off, len);
}
读取完整的byte数组
public final void readFully(byte b[]) throws IOException {
readFully(b, 0, b.length);
}
此操作的字节是从包含的输入流中读取的。
public final void readFully(byte b[], int off, int len) throws IOException {
if (len < 0)
throw new IndexOutOfBoundsException();
int n = 0;
while (n < len) {
int count = in.read(b, off + n, len - n);
if (count < 0)
throw new EOFException();
n += count;
}
}
跳过读取某一字段
public final int skipBytes(int n) throws IOException {
int total = 0;
int cur = 0;
while ((total<n) && ((cur = (int) in.skip(n-total)) > 0)) {
total += cur;
}
return total;
}
此操作的字节是从包含的输入流中读取的。
public final boolean readBoolean() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return (ch != 0);
}
定义读取一个byte的方法
public final byte readByte() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return (byte)(ch);
}
定义了读取一个无符号byte的方法
public final int readUnsignedByte() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return ch;
}
定义了读取short类型的方法
public final short readShort() throws IOException {
int ch1 = in.read();
int ch2 = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (short)((ch1 << 8) + (ch2 << 0));
}
定义了读取无符号整型的方法
public final int readUnsignedShort() throws IOException {
int ch1 = in.read();
int ch2 = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (ch1 << 8) + (ch2 << 0);
}
定义了读取char类型的方法
public final char readChar() throws IOException {
int ch1 = in.read();
int ch2 = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (char)((ch1 << 8) + (ch2 << 0));
}
定义了读取整型的方法
public final int readInt() throws IOException {
int ch1 = in.read();
int ch2 = in.read();
int ch3 = in.read();
int ch4 = in.read();
if ((ch1 | ch2 | ch3 | ch4) < 0)
throw new EOFException();
return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
}
定义了一个读取缓冲池,8个byte
private byte readBuffer[] = new byte[8];
定义了读取long类型的方法
public final long readLong() throws IOException {
readFully(readBuffer, 0, 8);
return (((long)readBuffer[0] << 56) +
((long)(readBuffer[1] & 255) << 48) +
((long)(readBuffer[2] & 255) << 40) +
((long)(readBuffer[3] & 255) << 32) +
((long)(readBuffer[4] & 255) << 24) +
((readBuffer[5] & 255) << 16) +
((readBuffer[6] & 255) << 8) +
((readBuffer[7] & 255) << 0));
}
定义了读取浮点型float的方法
public final float readFloat() throws IOException {
return Float.intBitsToFloat(readInt());
}
定义了读取双精度double类型的方法
public final double readDouble() throws IOException {
return Double.longBitsToDouble(readLong());
}
定义一个行行缓冲区
private char lineBuffer[];
下面函数实现了一个读行操作
public final String readLine() throws IOException {
char buf[] = lineBuffer;
if (buf == null) {
buf = lineBuffer = new char[128];
}
int room = buf.length;
int offset = 0;
int c;
loop: while (true) {
switch (c = in.read()) {
case -1:
case '\n':
break loop;
case '\r':
int c2 = in.read();
if ((c2 != '\n') && (c2 != -1)) {
if (!(in instanceof PushbackInputStream)) {
this.in = new PushbackInputStream(in);
}
((PushbackInputStream)in).unread(c2);
}
break loop;
default:
if (--room < 0) {
buf = new char[offset + 128];
room = buf.length - offset - 1;
System.arraycopy(lineBuffer, 0, buf, 0, offset);
lineBuffer = buf;
}
buf[offset++] = (char) c;
break;
}
}
if ((c == -1) && (offset == 0)) {
return null;
}
return String.copyValueOf(buf, 0, offset);
}
参见DataInput的readUTF方法的通用约定。
public final String readUTF() throws IOException {
return readUTF(this);
}
从以修改的 UTF-8 格式编码的 Unicode 字符串表示形式的流中读取;这个字符串然后作为一个字符串返回。
public final static String readUTF(DataInput in) throws IOException {
int utflen = in.readUnsignedShort();
byte[] bytearr = null;
char[] chararr = null;
if (in instanceof DataInputStream) {
DataInputStream dis = (DataInputStream)in;
if (dis.bytearr.length < utflen){
dis.bytearr = new byte[utflen*2];
dis.chararr = new char[utflen*2];
}
chararr = dis.chararr;
bytearr = dis.bytearr;
} else {
bytearr = new byte[utflen];
chararr = new char[utflen];
}
int c, char2, char3;
int count = 0;
int chararr_count=0;
in.readFully(bytearr, 0, utflen);
while (count < utflen) {
c = (int) bytearr[count] & 0xff;
if (c > 127) break;
count++;
chararr[chararr_count++]=(char)c;
}
while (count < utflen) {
c = (int) bytearr[count] & 0xff;
switch (c >> 4) {
case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
/* 0xxxxxxx*/
count++;
chararr[chararr_count++]=(char)c;
break;
case 12: case 13:
/* 110x xxxx 10xx xxxx*/
count += 2;
if (count > utflen)
throw new UTFDataFormatException(
"malformed input: partial character at end");
char2 = (int) bytearr[count-1];
if ((char2 & 0xC0) != 0x80)
throw new UTFDataFormatException(
"malformed input around byte " + count);
chararr[chararr_count++]=(char)(((c & 0x1F) << 6) |
(char2 & 0x3F));
break;
case 14:
/* 1110 xxxx 10xx xxxx 10xx xxxx */
count += 3;
if (count > utflen)
throw new UTFDataFormatException(
"malformed input: partial character at end");
char2 = (int) bytearr[count-2];
char3 = (int) bytearr[count-1];
if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
throw new UTFDataFormatException(
"malformed input around byte " + (count-1));
chararr[chararr_count++]=(char)(((c & 0x0F) << 12) |
((char2 & 0x3F) << 6) |
((char3 & 0x3F) << 0));
break;
default:
/* 10xx xxxx, 1111 xxxx */
throw new UTFDataFormatException(
"malformed input around byte " + count);
}
}
// The number of chars produced may be less than utflen
return new String(chararr, 0, chararr_count);
}
三、DataOutputStream源码介绍
DataOutputStream继承了 FilterOutputStream 连接了DataOutput接口
public
class DataOutputStream extends FilterOutputStream implements DataOutput {
定义了到目前为止写入数据输出流的字节数。
protected int written;
定义了一个byte数组
private byte[] bytearr = null;
创建新的数据输出流以将数据写入指定的底层输出流
public DataOutputStream(OutputStream out) {
super(out);
}
定义统计传入字符数的计数器
private void incCount(int value) {
int temp = written + value;
if (temp < 0) {
temp = Integer.MAX_VALUE;
}
written = temp;
}
定义一个写入一个字符的函数
public synchronized void write(int b) throws IOException {
out.write(b);
incCount(1);
}
下面函数定义了写入字符数组
public synchronized void write(byte b[], int off, int len)
throws IOException
{
out.write(b, off, len);
incCount(len);
}
定义了一个刷新输出函数
public void flush() throws IOException {
out.flush();
}
用于判断是否可以写入
public final void writeBoolean(boolean v) throws IOException {
out.write(v ? 1 : 0);
incCount(1);
}
定义一个写入byte方法
public final void writeByte(int v) throws IOException {
out.write(v);
incCount(1);
}
下面函数是实现了写入一个short类型
public final void writeShort(int v) throws IOException {
out.write((v >>> 8) & 0xFF);
out.write((v >>> 0) & 0xFF);
incCount(2);
}
下面方法定义了写入一个char字节
public final void writeChar(int v) throws IOException {
out.write((v >>> 8) & 0xFF);
out.write((v >>> 0) & 0xFF);
incCount(2);
}
下面定义了实现写入一个int的方法
public final void writeInt(int v) throws IOException {
out.write((v >>> 24) & 0xFF);
out.write((v >>> 16) & 0xFF);
out.write((v >>> 8) & 0xFF);
out.write((v >>> 0) & 0xFF);
incCount(4);
}
定义一个八字节的写缓冲区
private byte writeBuffer[] = new byte[8];
下面方法定义了一个写long类型的方法
public final void writeLong(long v) throws IOException {
writeBuffer[0] = (byte)(v >>> 56);
writeBuffer[1] = (byte)(v >>> 48);
writeBuffer[2] = (byte)(v >>> 40);
writeBuffer[3] = (byte)(v >>> 32);
writeBuffer[4] = (byte)(v >>> 24);
writeBuffer[5] = (byte)(v >>> 16);
writeBuffer[6] = (byte)(v >>> 8);
writeBuffer[7] = (byte)(v >>> 0);
out.write(writeBuffer, 0, 8);
incCount(8);
}
下面方法定义了写入浮点型float方法
public final void writeFloat(float v) throws IOException {
writeInt(Float.floatToIntBits(v));
}
下面定义写入双精度double方法
public final void writeDouble(double v) throws IOException {
writeLong(Double.doubleToLongBits(v));
}
下面定义了写入字符串的方法
public final void writeBytes(String s) throws IOException {
int len = s.length();
for (int i = 0 ; i < len ; i++) {
out.write((byte)s.charAt(i));
}
incCount(len);
}
下面方法定义了写入一个字节char的方法
public final void writeChars(String s) throws IOException {
int len = s.length();
for (int i = 0 ; i < len ; i++) {
int v = s.charAt(i);
out.write((v >>> 8) & 0xFF);
out.write((v >>> 0) & 0xFF);
}
incCount(len * 2);
}
下面方法实现写入UTF编码的字符
public final void writeUTF(String str) throws IOException {
writeUTF(str, this);
}
下面实现写UTF编码字符的实现类
static int writeUTF(String str, DataOutput out) throws IOException {
int strlen = str.length();
int utflen = 0;
int c, count = 0;
/* use charAt instead of copying String to char array */
for (int i = 0; i < strlen; i++) {
c = str.charAt(i);
if ((c >= 0x0001) && (c <= 0x007F)) {
utflen++;
} else if (c > 0x07FF) {
utflen += 3;
} else {
utflen += 2;
}
}
if (utflen > 65535)
throw new UTFDataFormatException(
"encoded string too long: " + utflen + " bytes");
byte[] bytearr = null;
if (out instanceof DataOutputStream) {
DataOutputStream dos = (DataOutputStream)out;
if(dos.bytearr == null || (dos.bytearr.length < (utflen+2)))
dos.bytearr = new byte[(utflen*2) + 2];
bytearr = dos.bytearr;
} else {
bytearr = new byte[utflen+2];
}
bytearr[count++] = (byte) ((utflen >>> 8) & 0xFF);
bytearr[count++] = (byte) ((utflen >>> 0) & 0xFF);
int i=0;
for (i=0; i<strlen; i++) {
c = str.charAt(i);
if (!((c >= 0x0001) && (c <= 0x007F))) break;
bytearr[count++] = (byte) c;
}
for (;i < strlen; i++){
c = str.charAt(i);
if ((c >= 0x0001) && (c <= 0x007F)) {
bytearr[count++] = (byte) c;
} else if (c > 0x07FF) {
bytearr[count++] = (byte) (0xE0 | ((c >> 12) & 0x0F));
bytearr[count++] = (byte) (0x80 | ((c >> 6) & 0x3F));
bytearr[count++] = (byte) (0x80 | ((c >> 0) & 0x3F));
} else {
bytearr[count++] = (byte) (0xC0 | ((c >> 6) & 0x1F));
bytearr[count++] = (byte) (0x80 | ((c >> 0) & 0x3F));
}
}
out.write(bytearr, 0, utflen+2);
return utflen + 2;
}
返回写入的计数器的当前值,到目前为止写入此数据输出流的字节数
public final int size() {
return written;
}