Apache HttpClientBuilder.create（）。setUserAgent（...）无效

Question

这是我创建HttpClient的方式：

    private String userAgent= "Non empty user agent";
    private HttpClient httpClient= HttpClientBuilder.create()
        .setDefaultCookieStore(new BasicCookieStore())
        .setUserAgent(userAgent)
        .setDefaultRequestConfig(RequestConfig.custom().setCookieSpec(CookieSpecs.STANDARD).build())
        .setDefaultHeaders(Arrays.asList(
                new BasicHeader("Accept-Encoding", "gzip"),
                new BasicHeader("Connection", "keep-alive"))
        )
        .build();

但是在发送请求时，用户代理是空，这是日志：

12:51:33.807 [http-nio-5010-exec-9] DEBUG org.apache.http.headers - http-outgoing-0 >> GET / HTTP/1.1
12:51:33.807 [http-nio-5010-exec-9] DEBUG org.apache.http.headers - http-outgoing-0 >> Accept- Encoding: gzip
12:51:33.807 [http-nio-5010-exec-9] DEBUG org.apache.http.headers - http-outgoing-0 >> Host: www.somehost.com
12:51:33.807 [http-nio-5010-exec-9] DEBUG org.apache.http.headers - http-outgoing-0 >> Connection: keep-alive
12:51:33.807 [http-nio-5010-exec-9] DEBUG org.apache.http.headers - http-outgoing-0 >> User-Agent: 

我试图将用户代理设置为默认标头，如下所示：

.setDefaultRequestConfig(RequestConfig.custom().setCookieSpec(CookieSpecs.STANDARD).build())
    .setDefaultHeaders(Arrays.asList(
            new BasicHeader("Accept-Encoding", "gzip"),
            new BasicHeader("Connection", "keep-alive"),
            new BasicHeader("User-Agent", userAgent)
    .build();

但结果相同（用户代理为空）。

这是我发送请求的方式：

        HttpResponse httpResponse = httpClient.execute(new HttpGet(baseUrl));

Http客户端的maven pom依赖项：

    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.10</version>
    </dependency>

Answer 1

问题是在实例化顺序中：实际上我正在使用SpringBoot，并且用户代理值是从属性文件中加载的，是这样的：

 @Value("${com.myapplication.userAgent}")
 private String userAgent;
private HttpClient httpClient= HttpClientBuilder.create()
    .setDefaultCookieStore(new BasicCookieStore())
    .setUserAgent(userAgent)
    .setDefaultRequestConfig(RequestConfig.custom().setCookieSpec(CookieSpecs.STANDARD).build())
    .setDefaultHeaders(Arrays.asList(
            new BasicHeader("Accept-Encoding", "gzip"),
            new BasicHeader("Connection", "keep-alive"))
    )
    .build();

JVM在为userAgent注入值之前实例化了httpClient，因此在实例化httpClient时，userAgent值为null。

感谢您的努力，