以下教學演示了如何使用Apache HttpClient 4.5從資源伺服器獲取證書。 證書用於通過使用SSL / TLS的HTTPS保護用戶端和伺服器之間的連線。 當您需要有關證書的詳細資訊時，例如:證書何時到期？誰頒發證書？等等。或者在某些情況下需要讀取伺服器證書。 在下面的例子中，我們將詳細解釋如何實現。
我們使用maven來管理依賴關係，並使用Apache HttpClient 4.5版本。 將以下依賴項新增到您的專案中，以便建立HTTP DELETE請求方法。
pom.xml 檔案的內容如下 -
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.yiibai.httpclient.httmethods</groupId>
<artifactId>http-get</artifactId>
<version>1.0.0-SNAPSHOT</version>
<url>https://memorynotfound.com</url>
<name>httpclient - ${project.artifactId}</name>
<dependencies>
<!-- Apache Commons IO -->
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<version>4.5.2</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
在以下範例中，我們向https://www.baidu.com發出請求以獲取伺服器證書。 首先，我們建立一個HttpResponseInterceptor，它將從SSLSession中讀取證書(如果存在)，並將證書新增到HttpContext中，以便稍後用於處理。
接下來，建立一個自定義的HttpClient並使用addInterceptorLast()工廠方法新增攔截器。
最後，向資源伺服器發出一個HttpGet請求，並從HttpContext獲取伺服器證書，我們之前將它們放在這裡。 現在擁有了證書，然後遍歷集合併將一些資料列印到控制台。
檔案:HttpClientGetServerCertificate.java -
package com.yiibai.httpdemo;
import org.apache.http.HttpResponseInterceptor;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.DateUtils;
import org.apache.http.conn.ManagedHttpClientConnection;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.apache.http.protocol.HttpCoreContext;
import javax.net.ssl.SSLSession;
import java.io.IOException;
import java.security.cert.Certificate;
import java.security.cert.X509Certificate;
/**
* This example demonstrates how to obtain server certificates {@link X509Certificate}.
*/
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();
}
}
}
執行上面範例程式碼，得到以下結果 -
Executing request GET https://www.baidu.com HTTP/1.1
----------------------------------------
Type: X.509
Signing Algorithm: SHA256withRSA
IssuerDN Principal: CN=Symantec Class 3 Secure Server CA - G4, OU=Symantec Trust Network, O=Symantec Corporation, C=US
SubjectDN Principal: CN=baidu.com, OU=service operation department., O="BeiJing Baidu Netcom Science Technology Co., Ltd", L=beijing, ST=beijing, C=CN
Not After: 17-08-2018
Not Before: 29-06-2017
----------------------------------------
Type: X.509
Signing Algorithm: SHA256withRSA
IssuerDN Principal: CN=VeriSign Class 3 Public Primary Certification Authority - G5, OU="(c) 2006 VeriSign, Inc. - For authorized use only", OU=VeriSign Trust Network, O="VeriSign, Inc.", C=US
SubjectDN Principal: CN=Symantec Class 3 Secure Server CA - G4, OU=Symantec Trust Network, O=Symantec Corporation, C=US
Not After: 30-10-2023
Not Before: 31-10-2013
----------------------------------------
Type: X.509
Signing Algorithm: SHA1withRSA
IssuerDN Principal: OU=Class 3 Public Primary Certification Authority, O="VeriSign, Inc.", C=US
SubjectDN Principal: CN=VeriSign Class 3 Public Primary Certification Authority - G5, OU="(c) 2006 VeriSign, Inc. - For authorized use only", OU=VeriSign Trust Network, O="VeriSign, Inc.", C=US
Not After: 07-11-2021
Not Before: 08-11-2006