8.5. Error Messages in Rules

JBoss BRMS provides standardized error messages. This standardization aims to help users to find and resolve problems in a easier and faster way.

8.5.1. Error Message Format

This is the standard error message format.
Error Message Format Example

Figure 8.2. Error Message Format Example

1st Block: This area identifies the error code.
2nd Block: Line and column information.
3rd Block: Some text describing the problem.
4th Block: This is the first context. Usually indicates the rule, function, template or query where the error occurred. This block is not mandatory.
5th Block: Identifies the pattern where the error occurred. This block is not mandatory.

8.5.2. Error Messages Description

Table 8.2. Error Messages

Error Message Description Example  
[ERR 101] Line 4:4 no viable alternative at input 'exits' in rule one
Indicates when the parser came to a decision point but couldn't identify an alternative. 
1: rule one
2:   when
3:     exists Foo()
4:     exits Bar()
5:   then
6: end
 
[ERR 101] Line 3:2 no viable alternative at input 'WHEN'
This message means the parser has encountered the token WHEN (a hard keyword) which is in the wrong place, since the rule name is missing. 
1: package org.drools;
2: rule
3:   when
4:     Object()
5:   then
6:     System.out.println("A RHS");
7: end
 
[ERR 101] Line 0:-1 no viable alternative at input '<eof>' in rule simple_rule in pattern [name]
Indicates an open quote, apostrophe or parentheses. 
1: rule simple_rule
2:   when
3:     Student( name == "Andy )
4:   then
5: end
 
[ERR 102] Line 0:-1 mismatched input '<eof>' expecting ')' in rule simple_rule in pattern Bar
Indicates that the parser was looking for a particular symbol that it didn't end at the current input position. 
1: rule simple_rule
2:   when
3:     foo3 : Bar(
 
[ERR 102] Line 0:-1 mismatched input '<eof>' expecting ')' in rule simple_rule in pattern [name]
This error is the result of an incomplete rule statement. Usually when you get a 0:-1 position, it means that parser reached the end of source. To fix this problem, it is necessary to complete the rule statement. 
1: package org.drools;
2:
3: rule "Avoid NPE on wrong syntax"
4:   when
5:     not( Cheese( ( type == "stilton", price == 10 ) || ( type == "brie", price == 15 ) ) from $cheeseList )
6:   then
7:     System.out.println("OK");
8: end
 
[ERR 103] Line 7:0 rule 'rule_key' failed predicate: {(validateIdentifierKey(DroolsSoftKeywords.RULE))}? in rule
A validating semantic predicate evaluated to false. Usually these semantic predicates are used to identify soft keywords. 
1: package nesting;
 2: dialect "mvel"
 3:
 4: import org.drools.Person
 5: import org.drools.Address
 6: 
 7: fdsfdsfds
 8: 
 9: rule "test something"
10:   when
11:     p: Person( name=="Michael" )
12:   then
13:     p.name = "other";
14:     System.out.println(p.name);
15: end
 
[ERR 104] Line 3:4 trailing semi-colon not allowed in rule simple_rule
This error is associated with the eval clause, where its expression may not be terminated with a semicolon. This problem is simple to fix: just remove the semi-colon. 
1: rule simple_rule
2:   when
3:     eval(abc();)
4:   then
5: end
 
[ERR 105] Line 2:2 required (...)+ loop did not match anything at input 'aa' in template test_error
The recognizer came to a subrule in the grammar that must match an alternative at least once, but the subrule did not match anything. To fix this problem it is necessary to remove the numeric value as it is neither a valid data type which might begin a new template slot nor a possible start for any other rule file construct. 
1: template test_error
2:   aa s  11;
3: end