国标GB2312编码自学教程 - v3.13, by 杨和荣
从Unicode到GB2312转换表制作程式
本章介绍了UnicodeGB2312.java源程序。它可以用来制作Unicode编码到GB2312编码转换 表。
在我发表了GB2312到Unicode的转换表以后，收到了许多读者信件，寻求Unicode到GB2312 的转换表。
下面的程式便可以用来制作这样的转换表。程式的输出结果收入下一章之中。
/* UnicodeGB2312.java
- Copyright (c) 2016, HerongYang.com, All Rights Reserved.
*/
import java.io.*;
import java.nio.*;
import java.nio.charset.*;
class UnicodeGB2312 {
static OutputStream out = null;
static char hexDigit[] = {'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
static int b_out[] = {201,267,279,293,484,587,625,657,734,782,827,
874,901,980,1001,5590,8801};
static int e_out[] = {216,268,280,294,494,594,632,694,748,794,836,
894,903,994,1594,5594,9494};
public static void main(String[] a) {
try {
out = new FileOutputStream("unicode_gb2312.gb");
writeCode();
out.close();
} catch (IOException e) {
System.out.println(e.toString());
}
}
public static void writeCode() throws IOException {
CharsetEncoder gbec = Charset.forName("GBK").newEncoder();
char[] ca = new char[1];
CharBuffer cb = null;
ByteBuffer gbbb = null;
writeHeader();
int count = 0;
for (int i=0; i<0x010000; i++) {
ca[0] = (char) i;
cb = CharBuffer.wrap(ca);
try {
gbbb = gbec.encode(cb);
} catch (CharacterCodingException e) {
gbbb = null;
}
if (validGB(gbbb)) {
count++;
writeHex((byte) (ca[0] >>> 8));
writeHex((byte) (ca[0] & 0xff));
writeString(" ");
writeByteBuffer(gbbb,2);
writeString(" ");
writeByte(gbbb.get(0));
writeByte(gbbb.get(1));
if (count%5 == 0) writeln();
else writeString(" ");
}
}
if (count%5 != 0) writeln();
writeFooter();
System.out.println("Number of GB characters wrote: "+count);
}
public static boolean validGB(ByteBuffer gbbb) {
if (gbbb==null) return false;
else if (gbbb.limit()!=2) return false;
else {
byte hi = gbbb.get(0);
byte lo = gbbb.get(1);
if ((hi&0xFF)<0xA0) return false;
if ((lo&0xFF)<0xA0) return false;
int i = (hi&0xFF) - 0xA0;
int j = (lo&0xFF) - 0xA0;
if (i<1 || i>94) return false;
if (j<1 || j>94) return false;
for (int l=0; l<b_out.length; l++) {
if (i*100+j>=b_out[l] && i*100+j<=e_out[l]) return false;
}
}
return true;
}
public static void writeHeader() throws IOException {
writeString("<pre>");
writeln();
writeString("Uni. GB ");
writeGBSpace();
writeString(" ");
writeString("Uni. GB ");
writeGBSpace();
writeString(" ");
writeString("Uni. GB ");
writeGBSpace();
writeString(" ");
writeString("Uni. GB ");
writeGBSpace();
writeString(" ");
writeString("Uni. GB ");
writeGBSpace();
writeln();
writeln();
}
public static void writeFooter() throws IOException {
writeString("</pre>");
writeln();
}
public static void writeln() throws IOException {
out.write(0x0D);
out.write(0x0A);
}
public static void writeGBSpace() throws IOException {
out.write(0xA1);
out.write(0xA1);
}
public static void writeByteBuffer(ByteBuffer b, int l)
throws IOException {
int i = 0;
if (b==null) {
writeString("null");
i = 2;
} else {
for (i=0; i<b.limit(); i++) writeHex(b.get(i));
}
for (int j=i; j<l; j++) writeString(" ");
}
public static void writeString(String s) throws IOException {
if (s!=null) {
for (int i=0; i<s.length(); i++) {
out.write((int) (s.charAt(i) & 0xFF));
}
}
}
public static void writeHex(byte b) throws IOException {
out.write((int) hexDigit[(b >> 4) & 0x0F]);
out.write((int) hexDigit[b & 0x0F]);
}
public static void writeByte(byte b) throws IOException {
out.write(b & 0xFF);
}
}
上面的程式发表后，又有许多读者来信要求对程式加以说明，以便理解。其实这个程式的 逻辑很简单，阅读时仅需注意以下几点：
一， Unicode字符集的全体编码都在0x0000和0xFFFF之间，所以子程式writeCode()使用 了一个循环复句，以变量i走遍了Unicode的全体可能编码。
二，把单个Unicode编码转换成GB2312编码的关键语句是：gbec.encode(cb)，它使用了 JDK中CharsetEncoder的中文编码功能。注意，GBK是由GB2312扩张而成。JDK只提供GBK编 码功能。
三，由于Unicode字符集比GB2312大，gbec.encode(cb)输出的编码有许多是废码，或者是 GBK的扩张码，所以要用子程式validGB()进行验证。
四，程式的其它部分主要是用于输出的列表制作。
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