在ANTLR4中处理自定义异常

Question

I have a grammar that parses URIs in the lexer and then constructs a java.net.URL from them in a grammar action. The lexer can accept strings that might not be legal URLs so I'd like to intelligently handle URISyntaxExceptions if they get thrown.

I'm new to ANTLR 4 (but spent some time with ANTLR 3) and just want to know the best practice for handling such exceptions in 4.

Here's a code snippet from the grammar:

iri returns [IRI term] :
    IRIREF 
    { $term = spt.getIRI($IRIREF.text); } |
    prefixedName
    ;

'spt' is a support object I set with a parameter to the start rule. The method 'getIRI' can throw the java.net.URISyntaxException . I would like a graceful way to handle this locally in the rule, terminate the parse (or do something else), but don't know where to attach a catch block.

Answer 1

The documentation covers the basics of catching errors and the implementation of error strategies. The Definitive ANTLR 4 Reference covers both topics in much more detail.

Update:

The actual grammar specification (from ANTLRv4Parser.g4) for a 'rule' is

parserRuleSpec
  : DOC_COMMENT?
    ruleModifiers? RULE_REF ARG_ACTION?
    ruleReturns? throwsSpec? localsSpec?
    rulePrequel*
    COLON
    ruleBlock
    SEMI
    exceptionGroup
  ;

(In relevant part, this is the same as the 'rule' spec in ANTLRParser.g, which is the actual grammar used to build compiler tool present in the Antlr v4 jar.)