Spring AI PromptTemplate should configure error reporting in String Template

Expected Behavior

I would like to see details about what is wrong with my prompt template in my logs (that go to LogStash or a similar system), not in standard error.

So if I have code:

PromptTemplate.builder().template("bad {template").build().create()

there should be something like

11:12:13 org.springframework.ai.template.st.StTemplateRenderer ERROR 1:13: premature EOF

Current Behavior

org.stringtemplate.v4.misc.ErrorManager#DEFAULT_ERROR_LISTENER is used, which prints using System.err.println. So the message is unstructured message in stderr:

1:13: premature EOF

Context

I think StTemplateRenderer should pass a custom implementation of STErrorListener that uses SLF4J instead of System.err.

Comment From: sunyuhan1998

Good catch! The default STErrorListener outputs exception information through System.err.println, which can cause some critical rendering exception details to be lost.

I've submitted a PR: https://github.com/spring-projects/spring-ai/pull/3606 to try redirecting the exceptions to the log output. Thanks for reporting this issue!

Comment From: pkubowicz

Thank you for the quick reaction!