基于Predictive Parsing的ABNF语法分析器（六）——AbnfParser文法解析器之多个符号连接的情形（如rule和CRLF）
基于预测的文法分析器，一个明显的特点就是将非终结符定义为解析函数（方法），当非终结符号可以派生为其他非终结符号时，在解析函数中递归调用即可。这种方法的一个缺点，是难以处理需要回溯的情形，后面我们再详细分析。上次我们研究了诸如CR、LF、HTAB等单个字符的解析，这一篇来看看稍微复杂一点的多个符号连接的情形，包括CRLF和RULE两个符号。
/*
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/>.
*/
// CRLF = CR LF
protected String CRLF() throws IOException, MatchException {
// 回车和换行符号，直接调用相应的CR、LF方法来进行解析就OK。
return CR() + LF();
}
// CRLF = CR LF
@Test
// 测试CRLF方法的单元测试方法
public void testCRLF() throws Exception {
// 创建一个测试器，在测试器的test方法中调用被测方法CRLF()
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
return parser.CRLF();
}
};
// 对于字符串0x0D + 0x0A，断言解析成功
Assert.assertEquals(String.valueOf((char)0x0D) + String.valueOf((char)0x0A), AbnfParserFactory.newInstance(new char[] {0x0D, 0x0A}).CRLF());
// 对于字符串0x0D + 0x0A + 0x0C，断言解析成功，但最后面的0x0C不应该被解析。
Assert.assertEquals(String.valueOf((char)0x0D) + String.valueOf((char)0x0A), AbnfParserFactory.newInstance(new char[] {0x0D, 0x0A, 0x0C}).CRLF());
// 对于字符串0x0D + 0x0A + 0x0D，断言解析成功，但最后面的0x0D不应该被解析。
Assert.assertEquals(String.valueOf((char)0x0D) + String.valueOf((char)0x0A), AbnfParserFactory.newInstance(new char[] {0x0D, 0x0A, 0x0D}).CRLF());
// 对于字符串0x0D + 0x0A + 0x0A，断言解析成功，但最后面的0x0A不应该被解析。
Assert.assertEquals(String.valueOf((char)0x0D) + String.valueOf((char)0x0A), AbnfParserFactory.newInstance(new char[] {0x0D, 0x0A, 0x0A}).CRLF());
// 对于空字符串0x0D + 0x0A + 0x0C，断言解析异常
Assertion.assertMatchException("", tester, 1, 1);
// 对于字符串0x0D，断言解析异常
Assertion.assertMatchException("" + (char)0x0D, tester, 1, 1);
// 对于字符串0x0A，断言解析异常
Assertion.assertMatchException("" + (char)0x0A, tester, 1, 1);
}
// rule = rulename defined-as elements c-nl
// 解析rule的方法
protected Rule rule() throws IOException, MatchException {
// rule的第一个元素是rulename，首先调用rulename()方法，并记录解析到的规则名
RuleName rulename = rulename();
// rulename后面紧接着defined-as元素，调用相应的方法
String definedAs = defined_as();
// defined-as后面接着elements元素，调用elements()
Elements elements = elements();
// elements后面接着c-nl元素，调用之。
c_nl();
// 返回解析到的规则
return new Rule(rulename, definedAs, elements);
}
// rule = rulename defined-as elements c-nl
@Test
public void testRule() throws Exception {
// 创建测试器
Tester<Rule> tester = new Tester<Rule>() {
@Override
public Rule test(AbnfParser parser) throws MatchException, IOException {
return parser.rule();
}
};
String input;
Elements elements;
elements = AbnfParserFactory.newInstance("b").elements();
// a=b是一条符合文法的规则
Assertion.assertMatch("a=b" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=", elements), 1, 2);
// a=/b是一条符合文法的规则
Assertion.assertMatch("a=/b" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=/", elements), 1, 2);
elements = AbnfParserFactory.newInstance("b/c").elements();
Assertion.assertMatch("a=b/c" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=", elements), 1, 2);
Assertion.assertMatch("a=/b/c" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=/", elements), 1, 2);
elements = AbnfParserFactory.newInstance("b c d").elements();
// a=b c d是一条符合文法的规则
Assertion.assertMatch("a=b c d" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=", elements), 1, 2);
// a=/b c d是一条符合文法的规则
Assertion.assertMatch("a=/b c d" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=/", elements), 1, 2);
elements = AbnfParserFactory.newInstance("[b]").elements();
// a=[b]是一条符合文法的规则
Assertion.assertMatch("a=[b]" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=", elements), 1, 2);
// a=/[b]是一条符合文法的规则
Assertion.assertMatch("a=/[b]" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=/", elements), 1, 2);
elements = AbnfParserFactory.newInstance("*b").elements();
// a=*b是一条符合文法的规则
Assertion.assertMatch("a=*b" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=", elements), 1, 2);
// a=/*b是一条符合文法的规则
Assertion.assertMatch("a=/*b" + (char)0x0D + (char)0x0A, tester, new Rule(new RuleName("a"), "=/", elements), 1, 2);
}
下一篇我们将分析更复杂的文法。