在ANTLR 3中,如何在运行时而不是提前生成词法分析器(和解析器)？

Question

我想在运行时生成一个antlr词法分析器 - 也就是说,生成语法并从语法生成lexer类,并在运行时生成它的支持位.我很乐意将它提供给java编译器,它可以在运行时访问.

Answer 1

这是一个快速而肮脏的方式:

1. 生成一个组合的(!)ANTLR语法.g文件,给定一个String作为语法源,
2. 并从此.g文件创建一个Parser&Lexer ,
3. 编译这些Parser和Lexer .java文件,
4. 创建Parser和Lexer类的实例并调用解析器的入口点.

Main.java

import java.io.*;
import javax.tools.*;
import java.lang.reflect.*;
import org.antlr.runtime.*;
import org.antlr.Tool;

public class Main {

    public static void main(String[] args) throws Exception {

        // The grammar which echos the parsed characters to theconsole,
        // skipping any white space chars.
        final String grammar =
                "grammar T;                                                  \n" +
                "                                                            \n" +
                "parse                                                       \n" +
                "  :  (ANY {System.out.println(\"ANY=\" + $ANY.text);})* EOF \n" +
                "  ;                                                         \n" +
                "                                                            \n" +
                "SPACE                                                       \n" +
                "  :  (' ' | '\\t' | '\\r' | '\\n') {skip();}                \n" +
                "  ;                                                         \n" +
                "                                                            \n" +
                "ANY                                                         \n" +
                "  :  .                                                      \n" +
                "  ;                                                           ";
        final String grammarName = "T";
        final String entryPoint = "parse";

        // 1 - Write the `.g` grammar file to disk.
        Writer out = new BufferedWriter(new FileWriter(new File(grammarName + ".g")));
        out.write(grammar);
        out.close();

        // 2 - Generate the lexer and parser.
        Tool tool = new Tool(new String[]{grammarName + ".g"});
        tool.process();

        // 3 - Compile the lexer and parser.
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        compiler.run(null, System.out, System.err, "-sourcepath", "", grammarName + "Lexer.java");
        compiler.run(null, System.out, System.err, "-sourcepath", "", grammarName + "Parser.java");

        // 4 - Parse the command line parameter using the dynamically created lexer and 
        //     parser with a bit of reflection Voodoo :)
        Lexer lexer = (Lexer)Class.forName(grammarName + "Lexer").newInstance();
        lexer.setCharStream(new ANTLRStringStream(args[0]));
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        Class<?> parserClass = Class.forName(grammarName + "Parser");
        Constructor parserCTor = parserClass.getConstructor(TokenStream.class);
        Parser parser = (Parser)parserCTor.newInstance(tokens);
        Method entryPointMethod = parserClass.getMethod(entryPoint);
        entryPointMethod.invoke(parser);
    }
}

在编译和运行之后(在*nix上):

java -cp .:antlr-3.2.jar Main "a b    c"

或在Windows上

java -cp .;antlr-3.2.jar Main "a b    c"

,产生以下输出:

ANY=a
ANY=b
ANY=c