124.数据流(DataOutputStream、DataInputStream)

数据流用于操作基本数据类型和字符串

写和读必须成对出现，简单说就是必须先写出再读入

DataOutputStream

This class is the superclass of all classes that filter output streams. These streams sit on top of an already existing output stream (the underlying output stream) which it uses as its basic sink of data, but possibly transforming the data along the way or providing additional functionality.

The class FilterOutputStream itself simply overrides all methods of OutputStream with versions that pass all requests to the underlying output stream. Subclasses of FilterOutputStream may further override some of these methods as well as provide additional methods and fields.

继承关系

Constructor Summary

Constructor	Description
DataOutputStream(OutputStream out)	Creates a new data output stream to write data to the specified underlying output stream.

Method Summary

Method Modifier and Type	Description
void flush()	Flushes this data output stream.
int size()	Returns the current value of the counter written, the number of bytes written to this data output stream so far.
void write(byte[] b, int off, int len)	Writes len bytes from the specified byte array starting at offset off to the underlying output stream.
void write(int b)	Writes the specified byte (the low eight bits of the argument b) to the underlying output stream.
void writeBoolean(boolean v)	Writes a boolean to the underlying output stream as a 1-byte value.
void writeByte(int v)	Writes out a byte to the underlying output stream as a 1-byte value.
void writeBytes(String s)	Writes out the string to the underlying output stream as a sequence of bytes.
void writeChar(int v)	Writes a char to the underlying output stream as a 2-byte value, high byte first.
void writeChars(String s)	Writes a string to the underlying output stream as a sequence of characters.
void writeDouble(double v)	Converts the double argument to a long using the doubleToLongBits method in class Double, and then writes that long value to the underlying output stream as an 8-byte quantity,
void writeFloat(float v)	Converts the float argument to an int using the floatToIntBits method in class Float, and then writes that int value to the underlying output stream as a 4-byte quantity, high
void writeInt(int v)	Writes an int to the underlying output stream as four bytes, high byte first.
void writeLong(long v)	Writes a long to the underlying output stream as eight bytes, high byte first.
void writeShort(int v)	Writes a short to the underlying output stream as two bytes, high byte first.
void writeUTF(String str)	Writes a string to the underlying output stream using modified UTF-8 encoding in a machine-independent manner.

DatainputStream

A data input stream lets an application read primitive Java data types from an underlying input stream in a machine-independent way. An application uses a data output stream to write data that can later be read by a data input stream.

DataInputStream is not necessarily safe for multithreaded access. Thread safety is optional and is the responsibility of users of methods in this class.

继承关系

Constructor Summary

Constructor	Description
DataInputStream(InputStream in)

Creates a DataInputStream that uses the specified underlying InputStream.

Method Summary

Method Modifier and Type	Description
int read(byte[] b)	Reads some number of bytes from the contained input stream and stores them into the buffer array b.
int read(byte[] b, int off, int len)	Reads up to len bytes of data from the contained input stream into an array of bytes.
boolean readBoolean()	See the general contract of the readBoolean method of DataInput.
byte readByte()	See the general contract of the readByte method of DataInput.
char readChar()	See the general contract of the readChar method of DataInput.
double readDouble()	See the general contract of the readDouble method of DataInput.
float readFloat()	See the general contract of the readFloat method of DataInput.
void readFully(byte[] b)	See the general contract of the readFully method of DataInput.
void readFully(byte[] b, int off, int len)	See the general contract of the readFully method of DataInput.
int readInt()	See the general contract of the readInt method of DataInput.
String readLine()	Deprecated.This method does not properly convert bytes to characters.
long readLong()	See the general contract of the readLong method of DataInput.
short readShort()	See the general contract of the readShort method of DataInput.
int readUnsignedByte()	See the general contract of the readUnsignedByte method of DataInput.
int readUnsignedShort()	See the general contract of the readUnsignedShort method of DataInput.
String readUTF()	See the general contract of the readUTF method of DataInput.
static String readUTF(DataInput in)	Reads from the stream in a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a String.
int skipBytes(int n)	See the general contract of the skipBytes method of DataInput.

利用数据流对基本类型进行读写

package cn.yzy.io;import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;/** DataOutputStream* DataInputStream* 数据流* 1.写出后读取* 2.读取的顺序与写出保持一致*/
public class dataTest {public static void main(String[] args) throws IOException {/*DataOutputStream dos = new DataOutputStream(new ByteArrayOutputStream());* 要使用ByteArrayOutputStream的toArray方法，因此不能使用匿名对象*///写出ByteArrayOutputStream baos = new ByteArrayOutputStream();DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(baos));//操作数据（类型）dos.writeUTF("编码辛酸史");dos.writeInt(18);dos.writeBoolean(false);dos.writeChar('b');dos.flush();byte[] datas = baos.toByteArray();//读取DataInputStream dis = new DataInputStream(new BufferedInputStream(new ByteArrayInputStream(datas))); String msgString = dis.readUTF();int integer = dis.readInt();Boolean bool = dis.readBoolean();char c = dis.readChar();System.out.println(bool);}
}

数据流关系图