antlr4/java: pretty print parse tree to stdout

Question

Beginners question: how do I print a readable version of the parse tree to stdout?

CharStream input = CharStreams.fromFileName(\"testdata/test.txt\");
MyLexer le         


        

Answer 1

If you like to use regex only for what it's really for, you can always print a tree by yourself:

import org.antlr.v4.runtime.Parser;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.tree.ParseTree;
import org.antlr.v4.runtime.tree.Trees;

public static String printSyntaxTree(Parser parser, ParseTree root) {
    StringBuilder buf = new StringBuilder();
    recursive(root, buf, 0, Arrays.asList(parser.getRuleNames()));
    return buf.toString();
}

private static void recursive(ParseTree aRoot, StringBuilder buf, int offset, List ruleNames) {
    for (int i = 0; i < offset; i++) {
        buf.append("  ");
    }
    buf.append(Trees.getNodeText(aRoot, ruleNames)).append("\n");
    if (aRoot instanceof ParserRuleContext) {
        ParserRuleContext prc = (ParserRuleContext) aRoot;
        if (prc.children != null) {
            for (ParseTree child : prc.children) {
                recursive(child, buf, offset + 1, ruleNames);
            }
        }
    }
}

Usage:

ParseTree root = parser.yourOwnRule();
System.out.println(printSyntaxTree(parser, root));