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HttpClient（二）结构

一、HttpClient结构图

下图来源于对org.apache.httpcomponents:httpclient:4.5.13的源码分析。

image-20211020112411018

二、HttpClient扩展口

1）HttpClientBuilder中有对ClientExecChain的装饰方法

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HttpClientBuilder#decorateMainExec
HttpClientBuilder#decorateProtocolExec

2）HttpClientBuilder中对ProtocolExec请求和响应拦截器的扩展

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HttpClientBuilder#addInterceptorFirst(org.apache.http.HttpRequestInterceptor)
HttpClientBuilder#addInterceptorLast(org.apache.http.HttpRequestInterceptor)

HttpClientBuilder#addInterceptorFirst(org.apache.http.HttpResponseInterceptor)
HttpClientBuilder#addInterceptorLast(org.apache.http.HttpResponseInterceptor)

3）HttpClientBuilder中对RetryExec的RetryHandler进行配置

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HttpClientBuilderBack#setRetryHandler(org.apache.http.client.HttpRequestRetryHandler)

三、示例

1）HTTP获取服务器证书 - 通过增加ProtocolExec的拦截器实现。代码来源

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public class HttpClientGetServerCertificate {
    public static final String PEER_CERTIFICATES = "PEER_CERTIFICATES";

    public static void main(String... args) throws IOException {
        // create http response certificate interceptor
        HttpResponseInterceptor certificateInterceptor = (httpResponse, context) -> {
            ManagedHttpClientConnection routedConnection = (ManagedHttpClientConnection)context.getAttribute(HttpCoreContext.HTTP_CONNECTION);
            SSLSession sslSession = routedConnection.getSSLSession();
            if (sslSession != null) {

                // get the server certificates from the {@Link SSLSession}
                Certificate[] certificates = sslSession.getPeerCertificates();

                // add the certificates to the context, where we can later grab it from
                context.setAttribute(PEER_CERTIFICATES, certificates);
            }
        };

        // create closable http client and assign the certificate interceptor
        CloseableHttpClient httpClient = HttpClients.custom().addInterceptorLast(certificateInterceptor).build();

        try {

            // make HTTP GET request to resource server
            HttpGet httpget = new HttpGet("https://www.baidu.com");
            System.out.println("Executing request " + httpget.getRequestLine());

            // create http context where the certificate will be added
            HttpContext context = new BasicHttpContext();
            httpClient.execute(httpget, context);

            // obtain the server certificates from the context
            Certificate[] peerCertificates = (Certificate[])context.getAttribute(PEER_CERTIFICATES);

            // loop over certificates and print meta-data
            for (Certificate certificate : peerCertificates){
                X509Certificate real = (X509Certificate) certificate;
                System.out.println("----------------------------------------");
                System.out.println("Type: " + real.getType());
                System.out.println("Signing Algorithm: " + real.getSigAlgName());
                System.out.println("IssuerDN Principal: " + real.getIssuerX500Principal());
                System.out.println("SubjectDN Principal: " + real.getSubjectX500Principal());
                System.out.println("Not After: " + DateUtils.formatDate(real.getNotAfter(), "dd-MM-yyyy"));
                System.out.println("Not Before: " + DateUtils.formatDate(real.getNotBefore(), "dd-MM-yyyy"));
            }

        } finally {
            // close httpclient
            httpClient.close();
        }
    }
}

2）增加异常监听逻辑

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HttpRequestRetryHandler retryHandler = (exception, executionCount, context) -> {
    // 可以在此处增加异常监听逻辑        
    return DefaultHttpRequestRetryHandler.INSTANCE.retryRequest(exception, executionCount, context);
};
 clientBuilder.setRetryHandler(retryHandler);

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