帶星號*表示重複的次數，例如*A表示A可以重複0至任意多次，*3A表示A可以重複0次、1次、2次或3次，4*A表示A至少要重複4次。我們先來看最簡單的情形*A，ABNF的語法定義中char-val和prose-val都屬於這種。
/*
This file is one of the component a Context-free Grammar Parser Generator,
which accept a piece of text as the input, and generates a parser
for the inputted context-free grammar.
Copyright (C) 2013, Junbiao Pan (Email: [email protected])
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
// char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
// DQUOTE = %x22
protected CharVal char_val() throws IOException, MatchException {
String char_val = "";
// char-val是雙引號開始的
assertMatch(is.peek(), 0x22);
// 把這個雙引號消化掉 :)
is.read();
// 雙引號後面跟着的0x20-21、0x23-7E都屬於合法的字符，讀入之
while (match(is.peek(), 0x20, 0x21) || match(is.peek(), 0x23, 0x7E)) {
char_val += (char)is.read();
}
// 如果不是跟着0x20-21、0x23-7E，則必須是雙引號，否則異常
assertMatch(is.peek(), 0x22);
is.read();
// 返回這個字符串
return new CharVal(char_val);
}
// char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
// DQUOTE = %x22
@Test
public void testChar_val() throws Exception {
Tester<CharVal> tester = new Tester<CharVal>() {
@Override
public CharVal test(AbnfParser parser) throws MatchException, IOException {
return parser.char_val();
}
};
String input;
input = "";
// 用來虐待char_var()方法的各種case，自己看吧
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x20);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x21);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x23);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x7E);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x20) + String.valueOf((char)0x20);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x21) + String.valueOf((char)0x21);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x23) + String.valueOf((char)0x23);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x7E) + String.valueOf((char)0x7E);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = "AbCd1234#$%^~!@#$%^&*()`-=_+[]\\{}|,./<>?;:'";
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"A").char_val().toString());
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"\"").char_val().toString());
//
Assertion.assertMatchException("", tester, 1, 1);
Assertion.assertMatchException("" + (char)0x19, tester, 1, 1);
// 這個case可以發現我們這個解析器的缺陷，
// 例如當一個輸入流是隻有一個雙引號開頭，沒有雙引號結尾的情況下，
// char_var()方法會拋出異常（這一點是可以接受的），
// 但讀指針卻無法到雙引號之前了（也就是說這個算法不支持回溯）
Assertion.assertMatchException("\"", tester, 2, 1);
Assertion.assertMatchException("\"a", tester, 3, 1);
Assertion.assertMatchException("B", tester, 1, 1);
}
// prose-val = "<" *(%x20-3D / %x3F-7E) ">"
// prose_val()方法和char_val()方法很類似，請自行閱讀
protected ProseVal prose_val() throws IOException, MatchException {
String proseval = "";
assertMatch(is.peek(), '<');
is.read();
while (match(is.peek(), 0x20, 0x3D) || match(is.peek(), 0x3F, 0x7E)) {
proseval += (char)is.read();
}
assertMatch(is.peek(), '>');
is.read();
return new ProseVal(proseval);
}
// prose-val = "<" *(%x20-3D / %x3F-7E) ">"
@Test
public void testProse_val() throws Exception {
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
return parser.prose_val().toString();
}
};
String input;
input = String.valueOf(new char[] {'<', '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x20, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x3D, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x3F, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x7E, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x20, 0x3D, 0x3F, 0x7E, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
Assert.assertEquals("<>", AbnfParserFactory.newInstance("<>>").prose_val().toString());
Assertion.assertMatchException("<" + (char) 0x19 + ">", tester, 2, 1);
Assertion.assertMatchException("<" + (char) 0x7F + ">", tester, 2, 1);
Assertion.assertMatchException("<" + (char)0x20 + (char)0x19 + ">", tester, 3, 1);
}本系列文章索引：基於預測的ABNF文法分析器