一、RestTemplate 簡介
Spring RestTemplate是Spring提供的用于訪問Rest服務的客戶端，RestTemplate 提供了多種便捷訪問遠程Http服務的方法，能夠大大提高客戶端的編寫效率.

RestTemplate包含以下幾個部分：

HttpMessageConverter 對象轉換器:將請求對象轉換為具體的數據格式輸出，例
入:Jaxb2RootElementHttpMessageConverterket提供對xml格式的輸入輸出支持

ClientHttpRequestFactory HTTP請求工廠，默認是JDK的HttpURLConnection，
可以通過使用ClientHttpRequestFactory指定不同的HTTP請求方式

ResponseErrorHandler 異常錯誤處理

ClientHttpRequestInterceptor 請求攔截器

RestTemplate通過HttpEntity添加消息headers

二、springboot 通過RestTemplate實現https訪問

import java.io.InputStream;
import java.security.KeyStore;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManager;

import org.apache.commons.lang3.StringUtils;
import org.apache.http.HttpHost;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.ssl.SSLContexts;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.http.converter.json.GsonHttpMessageConverter;
import org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter;
import org.springframework.web.client.RestTemplate;

/**
 * service相關配置
 *
 * @date 2017年3月1日
 * @since 1.0.0
 */
@Configuration
public class ServiceConfigConfiguration {

    @Autowired
    sslProperties sslProperties ;


    /**
     * 訪問SSL的Template
     *
     * @throws Exception
     */
    @Bean("sslRestTemplate")
    @Conditional(sslCondition.class)
    public RestTemplate tmsRestTemplate() throws Exception {
        //新建RestTemplate對象
        RestTemplate restTemplate = new RestTemplate();
        //判斷證書文件地址是否存在
        if (StringUtils.isNotEmpty(sslProperties.getKeyfile())) {
            //在握手期間，如果URL的主機名和服務器的標識主機名不匹配，則驗證機制可以回調此接口的實現 
              程序來確定是否應該允許此連接
            HostnameVerifier hv = new HostnameVerifier() {
                @Override
                public boolean verify(String urlHostName, SSLSession session) {
                    return true;
                }
            };
            HttpsURLConnection.setDefaultHostnameVerifier(hv);
            //構建SSL-Socket鏈接工廠
            SSLConnectionSocketFactory ssLSocketFactory = buildSSLSocketFactory("PKCS12", 
            sslProperties.getKeyfile(),sslProperties.getPassword(), 
            Lists.newArrayList("TLSv1"), true);
            //Spring提供HttpComponentsClientHttpRequestFactory指定使用HttpClient作為底層實現創建 HTTP請求
            HttpComponentsClientHttpRequestFactory httpRequestFactory = new HttpComponentsClientHttpRequestFactory(
                    HttpClients.custom().setSSLSocketFactory(ssLSocketFactory).build()
            );
            //設置傳遞數據超時時長
            httpRequestFactory.setReadTimeout(sslProperties.getTimeout());
            //設置建立連接超時時長
            httpRequestFactory.setConnectTimeout(sslProperties.getTimeout());
            //設置獲取連接超時時長
            httpRequestFactory.setConnectionRequestTimeout(tmsProperties.getTimeout());
            
            restTemplate.setRequestFactory(httpRequestFactory);

            // 返回消息頭也是text_html,消息格式是XML,添加新的message converter
            Jaxb2RootElementHttpMessageConverter messageConverter = new Jaxb2RootElementHttpMessageConverter();
            //設置message Converter支持的媒體類型
            List finalMediaTypes = new ArrayList<>();
            finalMediaTypes.addAll(messageConverter.getSupportedMediaTypes());
            finalMediaTypes.add(MediaType.TEXT_HTML);
            messageConverter.setSupportedMediaTypes(finalMediaTypes);
            restTemplate.setMessageConverters(Lists.newArrayList(messageConverter));

        }
        return restTemplate;
    }

    /**
     * 構建SSLSocketFactory
     *
     * @param keyStoreType
     * @param keyFilePath
     * @param keyPassword
     * @param sslProtocols
     * @param auth 是否需要client默認相信不安全證書
     * @return
     * @throws Exception
     */
    private SSLConnectionSocketFactory buildSSLSocketFactory(String keyStoreType, String keyFilePath,
                                                             String keyPassword, List sslProtocols, boolean auth) throws Exception {
        //證書管理器，指定證書及證書類型
        KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
        //KeyStore用于存放證書，創建對象時 指定交換數字證書的加密標準
        KeyStore keyStore = KeyStore.getInstance(keyStoreType);     
        InputStream inputStream = resourcePatternResolver.getResource(keyFilePath).getInputStream();
        try {
            //添加證書
            keyStore.load(inputStream, keyPassword.toCharArray());
        } finally {
            inputStream.close();
        }
        keyManagerFactory.init(keyStore, keyPassword.toCharArray());
        
        SSLContext sslContext = SSLContext.getInstance("SSL");
        if (auth) {
            // 設置信任證書（繞過TrustStore驗證）
            TrustManager[] trustAllCerts = new TrustManager[1];
            TrustManager trustManager = new AuthX509TrustManager();
            trustAllCerts[0] = trustManager;
            sslContext.init(keyManagerFactory.getKeyManagers(), trustAllCerts, null);
            HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());
        } else {
            //加載證書材料，構建sslContext
            sslContext = SSLContexts.custom().loadKeyMaterial(keyStore, keyPassword.toCharArray()).build();
        }

        SSLConnectionSocketFactory sslConnectionSocketFactory =
                new SSLConnectionSocketFactory(sslContext, sslProtocols.toArray(new String[sslProtocols.size()]),
                        null,
                        new HostnameVerifier() {
                            // 這里不校驗hostname
                            @Override
                            public boolean verify(String urlHostName, SSLSession session) {
                                return true;
                            }
                        });

        return sslConnectionSocketFactory;
    }
}

AuthX509TrustManager 證書信任管理器類就是實現了接口X509TrustManager的類?？梢宰约簩崿F該接口，信任我們指定的證書

public class AuthX509TrustManager implements javax.net.ssl.TrustManager, javax.net.ssl.X509TrustManager {
    public java.security.cert.X509Certificate[] getAcceptedIssuers() {
        return null;
    }
    
    public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType)
            throws java.security.cert.CertificateException {
        return;
    }

    public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType)
            throws java.security.cert.CertificateException {
        return;
    }
}