public FunctionCondition contains(String substring) {
        return new FunctionCondition("contains", this, new LiteralOperand(substring));
    }
Returns a <a href=
"http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.SpecifyingConditions.html#ConditionExpressionReference.Functions"
>function condition</a> (that evaluates to true if the value of the
current attribute contains the specified substring) for building
condition expression.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/xspec/S.java