How to Trace Spring RestTemplate Requests and Responses: A Comprehensive Guide

Tracing Spring RestTemplate Requests and Responses: A Comprehensive Guide

Debugging Spring RestTemplate requests and responses can be a perplexing task. This article explores an effective solution to overcome this challenge, providing a comprehensive approach to enable full logging and debugging capabilities.

The Need for Enhanced Logging

In contrast to using curl with the "verbose" option, the Spring RestTemplate often provides limited insights into request and response details. This lack of visibility hinders efficient debugging and troubleshooting.

Customization with ClientHttpRequestInterceptor

To address this issue, Spring Web Client and RestTemplate offer the ClientHttpRequestInterceptor interface. By implementing this interface, developers can customize the behavior of the RestTemplate instance, including the ability to trace both outgoing requests and incoming responses.

A Practical Implementation

To implement the ClientHttpRequestInterceptor, consider the following example:

import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class LoggingRequestInterceptor implements ClientHttpRequestInterceptor {

    final static Logger log = LoggerFactory.getLogger(LoggingRequestInterceptor.class);

    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        traceRequest(request, body);
        ClientHttpResponse response = execution.execute(request, body);
        traceResponse(response);
        return response;
    }

    private void traceRequest(HttpRequest request, byte[] body) throws IOException {
        log.info("===========================request begin================================================");
        log.debug("URI         : {}", request.getURI());
        log.debug("Method      : {}", request.getMethod());
        log.debug("Headers     : {}", request.getHeaders() );
        log.debug("Request body: {}", new String(body, "UTF-8"));
        log.info("==========================request end================================================");
    }

    private void traceResponse(ClientHttpResponse response) throws IOException {
        StringBuilder inputStringBuilder = new StringBuilder();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(response.getBody(), "UTF-8"));
        String line = bufferedReader.readLine();
        while (line != null) {
            inputStringBuilder.append(line);
            inputStringBuilder.append('\n');
            line = bufferedReader.readLine();
        }
        log.info("============================response begin==========================================");
        log.debug("Status code  : {}", response.getStatusCode());
        log.debug("Status text  : {}", response.getStatusText());
        log.debug("Headers      : {}", response.getHeaders());
        log.debug("Response body: {}", inputStringBuilder.toString());
        log.info("=======================response end=================================================");
    }

}

Using the Interceptor and Buffering

To utilize the interceptor, instantiate the RestTemplate using a BufferingClientHttpRequestFactory and register the LoggingRequestInterceptor as follows:

RestTemplate restTemplate = new RestTemplate(new BufferingClientHttpRequestFactory(new SimpleClientHttpRequestFactory()));
List<ClientHttpRequestInterceptor> interceptors = new ArrayList<>();
interceptors.add(new LoggingRequestInterceptor());
restTemplate.setInterceptors(interceptors);

The BufferingClientHttpRequestFactory is necessary to enable multiple readings of the response body.

Conclusion

By implementing the ClientHttpRequestInterceptor, you can enhance the debugging capabilities of Spring RestTemplate. The example provided in this article demonstrates how to trace both requests and responses, providing comprehensive insights into the communication process. This approach simplifies troubleshooting and improves the efficiency of development and maintenance tasks.

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