Spring RestTemplate - how to enable full debugging/logging of requests/responses?

java

logging

debugging

rest-template

byAlex Kataev·Oct 18, 2024

Enable in-depth logging for Spring's RestTemplate with a ClientHttpRequestInterceptor. Here is an efficient interceptor for logging request/response details:

public class LoggingInterceptor implements ClientHttpRequestInterceptor {
    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        // Alerting the headquarters about the coming request
        log("Request status", request.getMethod(), request.getURI(), new String(body, StandardCharsets.UTF_8));
        
        // Carry on with the execution; keep calm and carry on!
        ClientHttpResponse response = execution.execute(request, body);

        // Response received, let the world know about it!
        log("Response status", response.getStatusCode(), response.getStatusText(), StreamUtils.copyToString(response.getBody(), StandardCharsets.UTF_8));
        return response;
    }
    
    private void log(String prefix, Object... payloads) {
        // Let's sekritly collect the logs
        System.out.println(prefix + Arrays.stream(payloads).map(Object::toString).collect(Collectors.joining(" | ")));
    }
}

// Debugging, RestTemplate's style!
RestTemplate restTemplate = new RestTemplate();
restTemplate.getInterceptors().add(new LoggingInterceptor());

This compact piece of code outlines an interceptor logging HTTP method, URI, body for requests, status for responses, and glues it onto RestTemplate.

Advanced: In-depth debugging

While the Fast answer provides you with a head start, let's venture further to Advanced: logging techniques. These come only second to your coffee when it comes to easing your debugging mornings.

Buffering: Catch 'em all

Use BufferingClientHttpRequestFactory to read the response body multiple times. It’s like a Pokémon master, catching all info circulating in and out:

restTemplate.setRequestFactory(new BufferingClientHttpRequestFactory(new SimpleClientHttpRequestFactory()));

Log settings: Dial M for Monitoring

application.properties is your go-to place to Set. Debug. Go!:

logging.level.org.springframework.web.client.RestTemplate=DEBUG

Take it up a notch, log like a pro using log4j:

log4j.logger.httpclient.wire.header=DEBUG
log4j.logger.httpclient.wire.content=DEBUG

Logging Inception: Library within libraries

In the world of libraries, spring-rest-template-logger is The One. Grapple it tight (add the dependency) and whisper the logging command (edit the properties):

<dependency>
    <groupId>com.github</groupId>
    <artifactId>spring-rest-template-logger</artifactId>
    <version>1.0.0</version>
</dependency>

logging.level.spring-rest-template-logger=DEBUG

Refining the edges

Creating a masterpiece requires attention to detail. Let's brush up on some key attributes that will put us on the debugging pedestal.

Encoding: lost in translation

Without proper encoding identification, the log messages may seem like they're directed by Christopher Nolan:

new String(body, StandardCharsets.UTF_8)

Exception Handling: We'll Always Have Errors

Exception handling in your interceptors is as inevitable as encountering Ross' "We were on a break!" in every FRIENDS series. Try, catch, continue:

try {
    // Fingers crossed
} catch (Exception e) {
    // Well, that happened
    throw e;
}

Interplay: SLF4J & The Loggers

Master the art of managing SLF4J, Logback, and Log4j. Make them work together like The Avengers of logging.

curl-in-the-headlights

Extracting curl's verbose mode goodness for connection lifecycle and data exchange is a gamechanger:

logging.level.org.apache.http=DEBUG
logging.level.org.apache.http.wire=DEBUG

Early riser: StringBuilder

For early risers (read: better memory management and performance), let the StringBuilder do the logging.

Plot Twists: Different scenarios

Different HTTP methods and content types have their plot twists, like a Shyamalan movie. Adapt your strategy; don't let POST and JSON surprise you.

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