Creating an abstract syntax tree for Java source code using ANTLR

Question

How can I create an AST from java src code using ANTLR?
any help?

Answer 1

Installations for generating java src AST using antlr4:

• Install antlr4, you can use this link for this.
• After installation, download the JAVA grammar here .

• Now create Java8Lexer and Java8Parser using the command:

  antlr4 -visitor Java8.g4

• This will lead to the creation of several files such as Java8BaseListener.java Java8BaseVisitor.java Java8Lexer.java Java8Lexer.tokens Java8Listener.java Java8Parser.java Java8.tokens Java8Visitor.java

Use this code to generate the AST:

 import java.io.File; import java.io.IOException; import java.nio.charset.Charset; import java.nio.file.Files; import org.antlr.v4.runtime.ANTLRInputStream; import org.antlr.v4.runtime.CommonTokenStream; import org.antlr.v4.runtime.ParserRuleContext; import org.antlr.v4.runtime.RuleContext; import org.antlr.v4.runtime.tree.ParseTree; public class ASTGenerator { public static String readFile() throws IOException { File file = new File("path/to/the/test/file.java"); byte[] encoded = Files.readAllBytes(file.toPath()); return new String(encoded, Charset.forName("UTF-8")); } public static void main(String args[]) throws IOException { String inputString = readFile(); ANTLRInputStream input = new ANTLRInputStream(inputString); Java8Lexer lexer = new Java8Lexer(input); CommonTokenStream tokens = new CommonTokenStream(lexer); Java8Parser parser = new Java8Parser(tokens); ParserRuleContext ctx = parser.classDeclaration(); printAST(ctx, false, 0); } private static void printAST(RuleContext ctx, boolean verbose, int indentation) { boolean toBeIgnored = !verbose && ctx.getChildCount() == 1 && ctx.getChild(0) instanceof ParserRuleContext; if (!toBeIgnored) { String ruleName = Java8Parser.ruleNames[ctx.getRuleIndex()]; for (int i = 0; i < indentation; i++) { System.out.print(" "); } System.out.println(ruleName + " -> " + ctx.getText()); } for (int i = 0; i < ctx.getChildCount(); i++) { ParseTree element = ctx.getChild(i); if (element instanceof RuleContext) { printAST((RuleContext) element, verbose, indentation + (toBeIgnored ? 0 : 1)); } } } } 

After you finish coding, you can use gradle to create your project, or you can download antlr-4.7.1-complete.jar to the project directory and start compiling.

If you want to get the result in a DOT file so that u can render the AST, you can refer to this QnA post or directly access this repository in which I used gradle to create the project.

Hope this helps. :)

Answer 2

OK, follow these steps:

• go to ANTLR Site and download the latest version now 4.7
• Download the Java.g and JavaTreeParser.g from here .

• Run the following commands:

   java -jar antlrTool Java.g java -jar antlrTool JavaTreeParser.g 

• 5 files will be created:

  • Java.tokens
  • JavaLexer.java
  • JavaParser.java
  • JavaTreeParser.g
  • JavaTreeParser.tokens

use this java code to generate an abstract syntax tree and print it:

  String input = "public class HelloWord {"+ "public void print(String r){" + "for(int i = 0;true;i+=2)" + "System.out.println(r);" + "}" + "}"; CharStream cs = new ANTLRStringStream(input); JavaLexer jl = new JavaLexer(cs); CommonTokenStream tokens = new CommonTokenStream(); tokens.setTokenSource(jl); JavaParser jp = new JavaParser(tokens); RuleReturnScope result = jp.compilationUnit(); CommonTree t = (CommonTree) result.getTree(); CommonTreeNodeStream nodes = new CommonTreeNodeStream(t); nodes.setTokenStream(tokens); JavaTreeParser walker = new JavaTreeParser(nodes); System.out.println("\nWalk tree:\n"); printTree(t,0); System.out.println(tokens.toString()); } public static void printTree(CommonTree t, int indent) { if ( t != null ) { StringBuffer sb = new StringBuffer(indent); for ( int i = 0; i < indent; i++ ) sb = sb.append(" "); for ( int i = 0; i < t.getChildCount(); i++ ) { System.out.println(sb.toString() + t.getChild(i).toString()); printTree((CommonTree)t.getChild(i), indent+1); } } }