本章介绍DataOutputStream。我们先对DataOutputStream有个大致认识，然后再深入学习它的源码，最后通过示例加深对它的了解。
转载请注明出处：http://www.cnblogs.com/skywang12345/p/io_15.html
DataOutputStream 介绍
DataOutputStream 是数据输出流。它继承于FilterOutputStream。
DataOutputStream 是用来装饰其它输出流，将DataOutputStream和DataInputStream输入流配合使用，“允许应用程序以与机器无关方式从底层输入流中读写基本 Java 数据类型”。
DataOutputStream 源码分析(基于jdk1.7.40)
package java.io;
public class DataOutputStream extends FilterOutputStream implements DataOutput {
// “数据输出流”的字节数
protected int written;
// “数据输出流”对应的字节数组
private byte[] bytearr = null;
// 构造函数
public DataOutputStream(OutputStream out) {
super(out);
}
// 增加“输出值”
private void incCount(int value) {
int temp = written + value;
if (temp < 0) {
temp = Integer.MAX_VALUE;
}
written = temp;
}
// 将int类型的值写入到“数据输出流”中
public synchronized void write(int b) throws IOException {
out.write(b);
incCount(1);
}
// 将字节数组b从off开始的len个字节，都写入到“数据输出流”中
public synchronized void write(byte b[], int off, int len)
throws IOException
{
out.write(b, off, len);
incCount(len);
}
// 清空缓冲，即将缓冲中的数据都写入到输出流中
public void flush() throws IOException {
out.flush();
}
// 将boolean类型的值写入到“数据输出流”中
public final void writeBoolean(boolean v) throws IOException {
out.write(v ? 1 : 0);
incCount(1);
}
// 将byte类型的值写入到“数据输出流”中
public final void writeByte(int v) throws IOException {
out.write(v);
incCount(1);
}
// 将short类型的值写入到“数据输出流”中
// 注意：short占2个字节
public final void writeShort(int v) throws IOException {
// 写入 short高8位 对应的字节
out.write((v >>> 8) & 0xFF);
// 写入 short低8位 对应的字节
out.write((v >>> 0) & 0xFF);
incCount(2);
}
// 将char类型的值写入到“数据输出流”中
// 注意：char占2个字节
public final void writeChar(int v) throws IOException {
// 写入 char高8位 对应的字节
out.write((v >>> 8) & 0xFF);
// 写入 char低8位 对应的字节
out.write((v >>> 0) & 0xFF);
incCount(2);
}
// 将int类型的值写入到“数据输出流”中
// 注意：int占4个字节
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);
}
private byte writeBuffer[] = new byte[8];
// 将long类型的值写入到“数据输出流”中
// 注意：long占8个字节
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);
}
// 将float类型的值写入到“数据输出流”中
public final void writeFloat(float v) throws IOException {
writeInt(Float.floatToIntBits(v));
}
// 将double类型的值写入到“数据输出流”中
public final void writeDouble(double v) throws IOException {
writeLong(Double.doubleToLongBits(v));
}
// 将String类型的值写入到“数据输出流”中
// 实际写入时，是将String对应的每个字符转换成byte数据后写入输出流中。
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);
}
// 将String类型的值写入到“数据输出流”中
// 实际写入时，是将String对应的每个字符转换成char数据后写入输出流中。
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);
}
// 将UTF-8类型的值写入到“数据输出流”中
public final void writeUTF(String str) throws IOException {
writeUTF(str, this);
}
// 将String数据以UTF-8类型的形式写入到“输出流out”中
static int writeUTF(String str, DataOutput out) throws IOException {
//获取String的长度
int strlen = str.length();
int utflen = 0;
int c, count = 0;
// 由于UTF-8是1～4个字节不等；
// 这里，根据UTF-8首字节的范围，判断UTF-8是几个字节的。
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");
// 新建“字节数组bytearr”
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];
}
// “字节数组”的前2个字节保存的是“UTF-8数据的长度”
bytearr[count++] = (byte) ((utflen >>> 8) & 0xFF);
bytearr[count++] = (byte) ((utflen >>> 0) & 0xFF);
// 对UTF-8中的单字节数据进行预处理
int i=0;
for (i=0; i<strlen; i++) {
c = str.charAt(i);
if (!((c >= 0x0001) && (c <= 0x007F))) break;
bytearr[count++] = (byte) c;
}
// 对预处理后的数据，接着进行处理
for (;i < strlen; i++){
c = str.charAt(i);
// UTF-8数据是1个字节的情况
if ((c >= 0x0001) && (c <= 0x007F)) {
bytearr[count++] = (byte) c;
} else if (c > 0x07FF) {
// UTF-8数据是3个字节的情况
bytearr[count++] = (byte) (0xE0 | ((c >> 12) & 0x0F));
bytearr[count++] = (byte) (0x80 | ((c >> 6) & 0x3F));
bytearr[count++] = (byte) (0x80 | ((c >> 0) & 0x3F));
} else {
// UTF-8数据是2个字节的情况
bytearr[count++] = (byte) (0xC0 | ((c >> 6) & 0x1F));
bytearr[count++] = (byte) (0x80 | ((c >> 0) & 0x3F));
}
}
// 将字节数组写入到“数据输出流”中
out.write(bytearr, 0, utflen+2);
return utflen + 2;
}
public final int size() {
return written;
}
}
示例代码
关于DataOutStream中API的详细用法，参考示例代码(DataInputStreamTest.java)：
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.InputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.lang.SecurityException; /**
* DataInputStream 和 DataOutputStream测试程序
*
* @author skywang
*/
public class DataInputStreamTest { private static final int LEN = 5; public static void main(String[] args) {
// 测试DataOutputStream，将数据写入到输出流中。
testDataOutputStream() ;
// 测试DataInputStream，从上面的输出流结果中读取数据。
testDataInputStream() ;
} /**
* DataOutputStream的API测试函数
*/
private static void testDataOutputStream() { try {
File file = new File("file.txt");
DataOutputStream out =
new DataOutputStream(
new FileOutputStream(file)); out.writeBoolean(true);
out.writeByte((byte)0x41);
out.writeChar((char)0x4243);
out.writeShort((short)0x4445);
out.writeInt(0x12345678);
out.writeLong(0x0FEDCBA987654321L); out.writeUTF("abcdefghijklmnopqrstuvwxyz严12"); out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* DataInputStream的API测试函数
*/
private static void testDataInputStream() { try {
File file = new File("file.txt");
DataInputStream in =
new DataInputStream(
new FileInputStream(file)); System.out.printf("byteToHexString(0x8F):0x%s\n", byteToHexString((byte)0x8F));
System.out.printf("charToHexString(0x8FCF):0x%s\n", charToHexString((char)0x8FCF)); System.out.printf("readBoolean():%s\n", in.readBoolean());
System.out.printf("readByte():0x%s\n", byteToHexString(in.readByte()));
System.out.printf("readChar():0x%s\n", charToHexString(in.readChar()));
System.out.printf("readShort():0x%s\n", shortToHexString(in.readShort()));
System.out.printf("readInt():0x%s\n", Integer.toHexString(in.readInt()));
System.out.printf("readLong():0x%s\n", Long.toHexString(in.readLong()));
System.out.printf("readUTF():%s\n", in.readUTF()); in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
} // 打印byte对应的16进制的字符串
private static String byteToHexString(byte val) {
return Integer.toHexString(val & 0xff);
} // 打印char对应的16进制的字符串
private static String charToHexString(char val) {
return Integer.toHexString(val);
} // 打印short对应的16进制的字符串
private static String shortToHexString(short val) {
return Integer.toHexString(val & 0xffff);
}
}
运行结果：
byteToHexString(0x8F):0x8f
charToHexString(0x8FCF):0x8fcf
readBoolean():true
readByte():0x41
readChar():0x4243
readShort():0x4445
readInt():0x12345678
readLong():0xfedcba987654321
readUTF():abcdefghijklmnopqrstuvwxyz严12
结果说明：