Spring RestTemplate Request/Response 日志记录

1. 概述

一份详细的日志对于我们程序 debug 非常重要，特别是涉及跨服务器之间的调用。本教程我们将学习如何有效的记录 RestTemplate HTTP 请求和响应日志。

遗憾的是，Spring Boot 并没有提供一种简单的方法来记录 HTTP 请求。下面我们将探索几种方法来记录 HTTP header、HTTP body。

提示: Spring RestTemplate 将会被废弃（deprecated），取而代之的是 WebClient。想学习如何使用 WebClient 记录日志，请阅读这篇文章 Logging Spring WebClient Calls。

2. RestTemplate - 基础日志记录

Let's start configuring the RestTemplate logger in the application.properties file:

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

As a result, we can see only basic information like the request URL, method, body, and response status:

o.s.w.c.RestTemplate - HTTP POST http://localhost:8082/spring-rest/persons
o.s.w.c.RestTemplate - Accept=[text/plain, application/json, application/*+json, */*]
o.s.w.c.RestTemplate - Writing [my request body] with org.springframework.http.converter.StringHttpMessageConverter
o.s.w.c.RestTemplate - Response 200 OK

However, the response body isn't logged here, which is unfortunate because it's the most interesting part.

To solve this, we'll choose either Apache HttpClient or a Spring interceptor.

3. 使用 Apache HttpClient 记录 Http Header 和 Body

First, we have to make RestTemplate use the Apache HttpClient implementation.

We'll need the Maven dependency:

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.12</version>
</dependency>

When creating the RestTemplate instance, we should tell it we're using Apache HttpClient:

RestTemplate restTemplate = new RestTemplate();
restTemplate.setRequestFactory(new HttpComponentsClientHttpRequestFactory());

Then, let's configure the client logger in the application.properties file:

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

Now we can see both request/response headers and body:

    o.a.http.headers - http-outgoing-0 >> POST /spring-rest/persons HTTP/1.1
    o.a.http.headers - http-outgoing-0 >> Accept: text/plain, application/json, application/*+json, */*
// ... more request headers
    o.a.http.headers - http-outgoing-0 >> User-Agent: Apache-HttpClient/4.5.9 (Java/1.8.0_171)
    o.a.http.headers - http-outgoing-0 >> Accept-Encoding: gzip,deflate
org.apache.http.wire - http-outgoing-0 >> "POST /spring-rest/persons HTTP/1.1[\r][\n]"
org.apache.http.wire - http-outgoing-0 >> "Accept: text/plain, application/json, application/*+json, */*[\r][\n]"
org.apache.http.wire - http-outgoing-0 >> "Content-Type: text/plain;charset=ISO-8859-1[\r][\n]"
// ... more request headers
org.apache.http.wire - http-outgoing-0 >> "[\r][\n]"
org.apache.http.wire - http-outgoing-0 >> "my request body"
org.apache.http.wire - http-outgoing-0 << "HTTP/1.1 200 [\r][\n]"
org.apache.http.wire - http-outgoing-0 << "Content-Type: application/json[\r][\n]"
// ... more response headers
org.apache.http.wire - http-outgoing-0 << "Connection: keep-alive[\r][\n]"
org.apache.http.wire - http-outgoing-0 << "[\r][\n]"
org.apache.http.wire - http-outgoing-0 << "21[\r][\n]"
org.apache.http.wire - http-outgoing-0 << "["Lucie","Jackie","Danesh","Tao"][\r][\n]"

However, these logs are verbose and not handy to debug.

We'll see how to solve this in the following chapter.

4. 使用 RestTemplate Interceptor 拦截器记录日志

As another solution, we can configure interceptors for RestTemplate.

4.1. Logging Interceptor Implementation

First, let's create a new LoggingInterceptor to customize our logs. This interceptor logs the request body as a simple byte array. However, for the response, we have to read the entire body stream:

public class LoggingInterceptor implements ClientHttpRequestInterceptor {

    static Logger LOGGER = LoggerFactory.getLogger(LoggingInterceptor.class);

    @Override
    public ClientHttpResponse intercept(
      HttpRequest req, byte[] reqBody, ClientHttpRequestExecution ex) throws IOException {
        LOGGER.debug("Request body: {}", new String(reqBody, StandardCharsets.UTF_8));
        ClientHttpResponse response = ex.execute(req, reqBody);
        InputStreamReader isr = new InputStreamReader(
          response.getBody(), StandardCharsets.UTF_8);
        String body = new BufferedReader(isr).lines()
            .collect(Collectors.joining("\n"));
        LOGGER.debug("Response body: {}", body);
        return response;
    }
}

Beware, this interceptor has an impact on the response content itself, as we'll discover in the next chapter.

4.2. Using Interceptor With RestTemplate

Now, we must deal with a streaming problem: As the interceptor consumes the response stream, our client application will see an empty response body.

To avoid that, we should use BufferingClientHttpRequestFactory: it buffers stream content into memory. This way, it can be read twice: once by our interceptor, and a second time by our client application:

ClientHttpRequestFactory factory = 
        new BufferingClientHttpRequestFactory(new SimpleClientHttpRequestFactory());
        RestTemplate restTemplate = new RestTemplate(factory);

However, the use of this factory involves a performance drawback, which we'll describe in the next subsection.

Then we can add our logging interceptor to the RestTemplate instance — we'll append it after the existing interceptors, if any:

List<ClientHttpRequestInterceptor> interceptors = restTemplate.getInterceptors();
if (CollectionUtils.isEmpty(interceptors)) {
    interceptors = new ArrayList<>();
}
interceptors.add(new LoggingInterceptor());
restTemplate.setInterceptors(interceptors);

As a result, only the necessary information is present in the logs:

c.b.r.l.LoggingInterceptor - Request body: my request body
c.b.r.l.LoggingInterceptor - Response body: ["Lucie","Jackie","Danesh","Tao"]

4.3. RestTemplate Interceptor Drawback

A mentioned before, the use of BufferingClientHttpRequestFactory has a serious drawback: it undoes the benefits of streaming. As a consequence, loading the entire body data into memory could expose our application to performance issues. Worse, it can lead to OutOfMemoryError.

To prevent this, one possible option is to assume that these verbose logs would be turned off when the data volume scales up, which typically happens in production. For example, we can use a buffered RestTemplate instance only if DEBUG level is enabled on our logger:

RestTemplate restTemplate = null;
if (LOGGER.isDebugEnabled()) {
    ClientHttpRequestFactory factory 
    = new BufferingClientHttpRequestFactory(new SimpleClientHttpRequestFactory());
    restTemplate = new RestTemplate(factory);
} else {
    restTemplate = new RestTemplate();
}

Similarly, we'll ensure that our interceptor only reads the response when DEBUG logging is enabled:

if (LOGGER.isDebugEnabled()) {
    InputStreamReader isr = new InputStreamReader(response.getBody(), StandardCharsets.UTF_8);
    String body = new BufferedReader(isr)
        .lines()
        .collect(Collectors.joining("\n"));
    LOGGER.debug("Response body: {}", body);
}

5. 总结

RestTemplate request/response logging is not a straightforward matter, as Spring Boot doesn't include it out-of-the-box.

Fortunately, we've seen that we can use the Apache HttpClient logger to get a verbose trace of exchanged data.

Or, we can implement a custom interceptor to get more human-readable logs. However, this can induce performance drawbacks for large data volumes.

As always, the source code for this article is available over on GitHub in the test folder. The example uses the RestTemplate in a live test for the REST endpoint defined in the same project.

Persistence

REST

Security