基于Predictive Parsing的ABNF语法分析器（五）——AbnfParser文法解析器之单字符的情形（如HTAB、LF、CR、SP）
先来看看AbnfParser类如何对ABNF文法中最简单的一些单字节符号如何进行解析，这些单字节符号包括跳格、换行、回车和空格：
/*
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/>.
*/
// HTAB = %x09
protected String HTAB() throws IOException, MatchException {
// 断言下一个字符为0x09（否则抛出MatchException异常）
assertMatch(is.peek(), 0x09);
int value = is.read();
// 返回HTAB的字符串值
return String.valueOf((char)value);
}
// LF = %x0A
protected String LF() throws IOException, MatchException {
// 断言下一个字符为0x0A（否则抛出MatchException异常）
assertMatch(is.peek(), 0x0A);
int value = is.read();
// 返回换行的字符串值
return String.valueOf((char)value);
}
// CR = %x0D
protected String CR() throws IOException, MatchException {
// 断言下一个字符为0x0D（否则抛出MatchException异常）
assertMatch(is.peek(), 0x0D);
int value = is.read();
// 返回回车的字符串值
return String.valueOf((char)value);
}
// SP = %x20
protected String SP() throws IOException, MatchException {
// 断言下一个字符为0x20（否则抛出MatchException异常）
assertMatch(is.peek(), 0x20);
int value = is.read();
// 返回空格的字符串值
return String.valueOf((char)value);
}
这些单字符的解析函数不需要向前看（预测），因为当他们一旦被调用，就意味着必须是相应的字符，否则就是抛出异常了。
接下来看看上面各个函数对应的单元测试函数。
/*
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/>.
*/
// HTAB = %x09
@Test
public void testHTAB() throws Exception {
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
// 测试器负责调用被测函数AbnfParser.HTAB()
return parser.HTAB();
}
};
// 测试用例1:一个0x09字符输入的情形
Assert.assertEquals(String.valueOf((char)0x09), AbnfParserFactory.newInstance(new char[] {0x09}).HTAB());
// 测试用例2:两个0x09字符输入的情形
Assert.assertEquals(String.valueOf((char) 0x09), AbnfParserFactory.newInstance(new char[]{0x09, 0x09}).HTAB());
// 测试用例3:一个0x0D字符输入的情形（异常）
Assertion.assertMatchException("" + (char) 0x0D, tester, 1, 1);
// 测试用例3:空字符输入的情形（异常）
Assertion.assertMatchException("", tester, 1, 1);
}
// LF = %x0A
@Test
public void testLF() throws Exception {
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
// 测试器负责调用被测函数AbnfParser.LF()
return parser.LF();
}
};
// 测试用例1:一个0x0A字符输入的情形
Assert.assertEquals(String.valueOf((char)0x0A), AbnfParserFactory.newInstance(new char[] {0x0A}).LF());
// 测试用例2:两个0x0A字符输入的情形
Assert.assertEquals(String.valueOf((char) 0x0A), AbnfParserFactory.newInstance(new char[]{0x0A, 0x0A}).LF());
// 测试用例3:一个0x0D字符输入的情形（异常）
Assertion.assertMatchException("", tester, 1, 1);
// 测试用例3:空字符输入的情形（异常）
Assertion.assertMatchException("" + (char)0x0D, tester, 1, 1);
}
// CR = %x0D
@Test
public void testCR() throws Exception {
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
return parser.CR();
}
};
Assert.assertEquals(String.valueOf((char) 0x0D), AbnfParserFactory.newInstance(new char[]{0x0D, 0x0D}).CR());
Assertion.assertMatchException("", tester, 1, 1);
Assertion.assertMatchException("" + (char)0x0A, tester, 1, 1);
}
// SP = %x20
@Test
public void testSP() throws Exception {
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
return parser.SP();
}
};
Assert.assertEquals(String.valueOf((char)0x20), AbnfParserFactory.newInstance(new char[] {0x20, 0x20}).SP());
Assertion.assertMatchException("", tester, 1, 1);
Assertion.assertMatchException("" + (char)0x0D, tester, 1, 1);
}