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DataInputStream 介绍
DataInputStream 是数据输入流。它继承于FilterInputStream。
DataInputStream 是用来装饰其它输入流，它“允许应用程序以与机器无关方式从底层输入流中读取基本 Java 数据类型”。应用程序可以使用DataOutputStream(数据输出流)写入由DataInputStream(数据输入流)读取的数据。
DataInputStream 函数列表
DataInputStream(InputStream in) final int read(byte[] buffer, int offset, int length) final int read(byte[] buffer) 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 static String readUTF(DataInput in) final String readUTF() final int readUnsignedByte() final int readUnsignedShort() final int skipBytes(int count)</div>
DataInputStream.java源码分析(基于jdk1.7.40)
package java.io;
public class DataInputStream extends FilterInputStream implements DataInput {
// 构造函数。
public DataInputStream(InputStream in) {
super(in);
}
private byte bytearr[] = new byte[80];
private char chararr[] = new char[80];
// 从“数据输入流”中读取一个字节
public final int read(byte b[]) throws IOException {
return in.read(b, 0, b.length);
}
// 从“数据输入流”中读取数据并存储到字节数组b中。
// off是字节数组b中开始存储元素的起始位置。
// len是读取字节的个数。
public final int read(byte b[], int off, int len) throws IOException {
return in.read(b, off, len);
}
// 从“数据输入流”中读取数据并填满字节数组b中；没有填满数组b则一直读取，直到填满位置。
// 从字节数组b的位置0开始存储，并且读取的字节个数等于b的长度。
public final void readFully(byte b[]) throws IOException {
readFully(b, 0, b.length);
}
// 从“数据输入流”中读取数据并存储到字节数组b中；若没读取len个字节，直到一直读取直到读取完len个字节为止。
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n个字节
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;
}
// 从“数据输入流”中读取boolean类型的值
public final boolean readBoolean() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return (ch != 0);
}
// 从“数据输入流”中读取Byte类型的值
public final byte readByte() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return (byte)(ch);
}
// 从“数据输入流”中读取“无符号的Byte类型”的值，即读取值为正数的byte值
public final int readUnsignedByte() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return ch;
}
// 从“数据输入流”中读取“short类型”的值
public final short readShort() throws IOException {
int ch = in.read();
int ch = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (short)((ch1 << 8) + (ch2 << 0));
}
// 从“数据输入流”中读取“无符号的short类型”的值
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);
}
// 从“数据输入流”中读取“char类型”的值
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));
}
// 从“数据输入流”中读取“int类型”的值
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));
}
private byte readBuffer[] = new byte[8];
// 从“数据输入流”中读取“long类型”的值
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));
}
// 从“数据输入流”中读取“float类型”的值
public final float readFloat() throws IOException {
return Float.intBitsToFloat(readInt());
}
// 从“数据输入流”中读取“double类型”的值
public final double readDouble() throws IOException {
return Double.longBitsToDouble(readLong());
}
private char lineBuffer[];
@Deprecated
public final String readLine() throws IOException {
char buf[] = lineBuffer;
if (buf == null) {
buf = lineBuffer = new char[];
}
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, , offset);
}
// 从“数据输入流”中读取“UTF类型”的值
public final String readUTF() throws IOException {
return readUTF(this);
}
public final static String readUTF(DataInput in) throws IOException {
// 从“数据输入流”中读取“无符号的short类型”的值：
// 注意：UTF-8输入流的前2个字节是数据的长度
int utflen = in.readUnsignedShort();
byte[] bytearr = null;
char[] chararr = null;
// 如果in本身是“数据输入流”，
// 则，设置字节数组bytearr = "数据输入流"的成员bytearr
// 设置字符数组chararr = "数据输入流"的成员chararr
// 否则的话，新建数组bytearr和chararr
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;
// 从“数据输入流”中读取数据并存储到字节数组bytearr中；从bytearr的位置0开始存储，存储长度为utflen。
// 注意，这里是存储到字节数组！而且读取的是全部的数据。
in.readFully(bytearr, 0, utflen);
// 将“字节数组bytearr”中的数据 拷贝到 “字符数组chararr”中
// 注意：这里相当于“预处理的输入流中单字节的符号”，因为UTF-8是1-4个字节可变的。
while (count < utflen) {
// 将每个字节转换成int值
c = (int) bytearr[count] & xff;
// UTF-8的单字节数据的值都不会超过127；所以，超