public Map<String,Integer> load() {
		Map<String,Integer> tokens = new LinkedHashMap<String,Integer>();
		int maxTokenType = -1;
		File fullFile = getImportedVocabFile();
		FileInputStream fis = null;
		BufferedReader br = null;
		Tool tool = g.tool;
		String vocabName = g.getOptionString("tokenVocab");
		try {
			Pattern tokenDefPattern = Pattern.compile("([^\n]+?)[ \\t]*?=[ \\t]*?([0-9]+)");
			fis = new FileInputStream(fullFile);
			InputStreamReader isr;
			if (tool.grammarEncoding != null) {
				isr = new InputStreamReader(fis, tool.grammarEncoding);
			}
			else {
				isr = new InputStreamReader(fis);
			}

			br = new BufferedReader(isr);
			String tokenDef = br.readLine();
			int lineNum = 1;
			while ( tokenDef!=null ) {
				Matcher matcher = tokenDefPattern.matcher(tokenDef);
				if ( matcher.find() ) {
					String tokenID = matcher.group(1);
					String tokenTypeS = matcher.group(2);
					int tokenType;
					try {
						tokenType = Integer.valueOf(tokenTypeS);
					}
					catch (NumberFormatException nfe) {
						tool.errMgr.toolError(ErrorType.TOKENS_FILE_SYNTAX_ERROR,
											  vocabName + CodeGenerator.VOCAB_FILE_EXTENSION,
											  " bad token type: "+tokenTypeS,
											  lineNum);
						tokenType = Token.INVALID_TOKEN_TYPE;
					}
					tool.log("grammar", "import "+tokenID+"="+tokenType);
					tokens.put(tokenID, tokenType);
					maxTokenType = Math.max(maxTokenType,tokenType);
					lineNum++;
				}
				else {
					if ( tokenDef.length()>0 ) { // ignore blank lines
						tool.errMgr.toolError(ErrorType.TOKENS_FILE_SYNTAX_ERROR,
											  vocabName + CodeGenerator.VOCAB_FILE_EXTENSION,
											  " bad token def: " + tokenDef,
											  lineNum);
					}
				}
				tokenDef = br.readLine();
			}
		}
		catch (FileNotFoundException fnfe) {
			GrammarAST inTree = g.ast.getOptionAST("tokenVocab");
			String inTreeValue = inTree.getToken().getText();
			if ( vocabName.equals(inTreeValue) ) {
				tool.errMgr.grammarError(ErrorType.CANNOT_FIND_TOKENS_FILE_REFD_IN_GRAMMAR,
										 g.fileName,
										 inTree.getToken(),
										 fullFile);
			}
			else { // must be from -D option on cmd-line not token in tree
				tool.errMgr.toolError(ErrorType.CANNOT_FIND_TOKENS_FILE_GIVEN_ON_CMDLINE,
									  fullFile,
									  g.name);
			}
		}
		catch (Exception e) {
			tool.errMgr.toolError(ErrorType.ERROR_READING_TOKENS_FILE,
								  e,
								  fullFile,
								  e.getMessage());
		}
		finally {
			try {
				if ( br!=null ) br.close();
			}
			catch (IOException ioe) {
				tool.errMgr.toolError(ErrorType.ERROR_READING_TOKENS_FILE,
									  ioe,
									  fullFile,
									  ioe.getMessage());
			}
		}
		return tokens;
	}
Load a vocab file {@code <vocabName>.tokens} and return mapping.
tool/src/org/antlr/v4/parse/TokenVocabParser.java