使用ANTLR工具、运行时、代码生成⌗ 

/** Grammars always start with a grammar header. This grammar is called
* ArrayInit and must match the filename: ArrayInit.g4
*/

grammar ArrayInit;

/** A rule called init that matches comma-separated values between {...}. */

init : '{' value (',' value)* '}' ; // must match at least one value

/** A value can be either a nested array/struct or a simple integer (INT) */
value : init
| INT
;

// parser rules start with lowercase letters, lexer rules with uppercase

INT : [0-9]+ ; // Define token INT as one or more digits
WS : [ \t\r\n]+ -> skip ; // Define whitespace rule, toss it out

默认生成Java解析器代码：

antlr ArrayInit.g4

生成的文件如下：

  • ArrayInit.tokens 每个token对应一个数字
  • ArrayInitLexer.tokens 每个token对应一个数字
  • ArrayInit.interp
  • ArrayInitLexer.interp
  • ArrayInitLexer.java 词法分析器
  • ArrayInitParser.java 语法分析器
  • ArrayInitListener.java Listener接口
  • ArrayInitBaseListener.java ArrayInitListener接口默认的空实现

生成Python解析器代码：

antlr ArrayInit.g4 -Dlanguage=Python3

将生成的解析器整合到Java程序中⌗

测试解析器⌗ 

// import ANTLR's runtime libraries
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
public class Test {
    public static void main(String[] args) throws Exception {
        // create a CharStream that reads from standard input
        ANTLRInputStream input = new ANTLRInputStream(System.in);
        // create a lexer that feeds off of input CharStream
        ArrayInitLexer lexer = new ArrayInitLexer(input);
        // create a buffer of tokens pulled from the lexer
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        // create a parser that feeds off the tokens buffer
        ArrayInitParser parser = new ArrayInitParser(tokens);
        ParseTree tree = parser.init(); // begin parsing at init rule
        System.out.println(tree.toStringTree(parser)); // print LISP-style tree
    }
}

实现翻译器⌗ 

/** Convert short array inits like {1,2,3} to "\u0001\u0002\u0003" */
public class ShortToUnicodeString extends ArrayInitBaseListener {
    /** Translate { to " */
    @Override
    public void enterInit(ArrayInitParser.InitContext ctx) {
    	System.out.print('"');
    }
    /** Translate } to " */
    @Override
    public void exitInit(ArrayInitParser.InitContext ctx) {
	    System.out.print('"');
    }
    /** Translate integers to 4-digit hexadecimal strings prefixed with \\u */
    @Override
    public void enterValue(ArrayInitParser.ValueContext ctx) {
	    // Assumes no nested array initializers
        int value = Integer.valueOf(ctx.INT().getText());
        System.out.printf("\\u%04x", value);
    }
}
  • ctx.INT()获取token
  • getText()获取token的文本

使用ShortToUnicodeString listener

// import ANTLR's runtime libraries
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
public class Translate {
    public static void main(String[] args) throws Exception {
        // create a CharStream that reads from standard input
        ANTLRInputStream input = new ANTLRInputStream(System.in);
        // create a lexer that feeds off of input CharStream
        ArrayInitLexer lexer = new ArrayInitLexer(input);
        // create a buffer of tokens pulled from the lexer
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        // create a parser that feeds off the tokens buffer
        ArrayInitParser parser = new ArrayInitParser(tokens);
        ParseTree tree = parser.init(); // begin parsing at init rule
        // Create a generic parse tree walker that can trigger callbacks
        ParseTreeWalker walker = new ParseTreeWalker();
        // Walk the tree created during the parse, trigger callbacks
        walker.walk(new ShortToUnicodeString(), tree);
        System.out.println(); // print a \n after translation
    }
}