java io进修（十四） DataOutputStream的认知、源码和示例

副标题#e#

DataOutputStream(数据输出流)的认知、源码和示例

本章先容DataOutputStream。我们先对DataOutputStream有个大抵认识，然后再深入进修它的源码，最后通过示例加深对它的相识。

DataOutputStream 先容

DataOutputStream 是数据输出流。它担任于FilterOutputStream。

DataOutputStream 是用来装饰其它输出流，将DataOutputStream和DataInputStream输入流共同利用，“答允应用措施以与呆板无关方法从底层输入流中读写根基 Java 数据范例”。

DataOutputStream 源码阐明(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;
     
    // 结构函数
    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范例的值写入到“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范例的值写入到“数据输出流”中
    public final void writeBoolean(boolean v) throws IOException {
        out.write(v ? 1 : 0);
        incCount(1);
    }
     
    // 将byte范例的值写入到“数据输出流”中
    public final void writeByte(int v) throws IOException {
        out.write(v);
        incCount(1);
    }
     
    // 将short范例的值写入到“数据输出流”中
    // 留意：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范例的值写入到“数据输出流”中
    // 留意：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范例的值写入到“数据输出流”中
    // 留意：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范例的值写入到“数据输出流”中
    // 留意：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范例的值写入到“数据输出流”中
    public final void writeFloat(float v) throws IOException {
        writeInt(Float.floatToIntBits(v));
    }
     
    // 将double范例的值写入到“数据输出流”中
    public final void writeDouble(double v) throws IOException {
        writeLong(Double.doubleToLongBits(v));
    }
     
    // 将String范例的值写入到“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范例的值写入到“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范例的值写入到“数据输出流”中
    public final void writeUTF(String str) throws IOException {
        writeUTF(str, this);
    }
     
    // 将String数据以UTF-8范例的形式写入到“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，按照UTF-8首字节的范畴，判定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”
		// 查察本栏目
示例代码
#p#分页标题#e#
关于DataOutStream中API的具体用法，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测试措施
 *
 * @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，从上面的输出流功效中读取数据。
        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);
    }
}
运行功效：
byteToHexString(0x8F):0x8f
charToHexString(0x8FCF):0x8fcf
readBoolean():true
readByte():0x41
readChar():0x4243
readShort():0x4445
readInt():0x12345678
readLong():0xfedcba987654321
readUTF():abcdefghijklmnopqrstuvwxyz严12
来历：http://www.cnblogs.com/skywang12345/p/io_15.html