In ANTLR 3, how do I generate a lexer (and parser) at runtime instead of ahead of time?

问题:

I want to generate an antlr lexer at runtime -- that is, generate the grammar and from the grammar generate the lexer class, and its supporting bits at runtime. I am happy to feed it into the the java compiler, which is accessible at runtime.

回答1:

Here's a quick and dirty way to:

1. generate a combined (!) ANTLR grammar .g file given a String as grammar-source,
2. and create a Parser & Lexer from this .g file,
3. compile the these Parser & Lexer .java files,
4. create instances of the Parser & Lexer classes and invoke the entry point of the parser.

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);     } } 

Which, after compiling and running it like this (on *nix):

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

or on Windows

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

, produces the following output:

 ANY=a ANY=b ANY=c 

回答2:

You'll have to use org.antlr.Tool() class to get it working.

You can check ANTLRWorks source code on github to have an idea how to use it, specifically the generate() method here:

ErrorListener el = ErrorListener.getThreadInstance(); ErrorManager.setErrorListener(el);  String[] params; if(debug)     params = new String[] { "-debug", "-o", getOutputPath(), "-lib", window.getFileFolder(), window.getFilePath() }; else     params = new String[] { "-o", getOutputPath(), "-lib", window.getFileFolder(), window.getFilePath() };  new File(getOutputPath()).mkdirs();  Tool antlr = new Tool(Utils.concat(params, AWPrefs.getANTLR3Options())); antlr.process();  boolean success = !el.hasErrors(); if(success) {     dateOfModificationOnDisk = window.getDocument().getDateOfModificationOnDisk(); } lastError = el.getFirstErrorMessage(); el.clear(); ErrorManager.removeErrorListener(); return success; 

回答3:

Have you tried calling org.antlr.Tool.main(String[]) with an appropriate String[] argument?

If that's too cumbersome, you could reverse engineer the Tool class (source code) to figure out how it works, and how to do the specific tasks you need to do.

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