@Autowired
EventDrivenConsumer myrouter;
.....
((ExpressionEvaluatingRouter) myrouter.getHandler()).setPrimaryExpression(new SpelExpressionParser().doParseExpression("true"));

<int:router input-channel="catchweightExcluderChannel" expression="${rip.config.exclude_catchweight}" default-output-channel="productTransformerChannel">
    <int:mapping value="true" channel="catchWeightFilteringChannel" />
    <int:mapping value="false" channel="productTransformerChannel" />
</int:router>