一、生成PEM檔案

這裡以郵件傳送介面為例https://api.mailgun.net/v3/，首先執行以下命令：

openssl s_client -host api.mailgun.net -port 443 -prexit -showcerts

執行結果如下：

CONNECTED(00000003)
depth=1 C = US, O = "thawte, Inc.", CN = thawte SHA256 SSL CA
verify error:num=20:unable to get local issuer certificate
---
Certificate chain
 0 s:/C=US/ST=Texas/L=San Antonio/O=Rackspace US, Inc/OU=Mailgun/CN=*.mailgun.com
   i:
 
/C=US/O=thawte, Inc./CN=thawte SHA256 SSL CA
-----BEGIN CERTIFICATE-----
MIIGRjCCBS6gAwIBAgIQcPBE+lQWtps2UTd0ornMgjANBgkqhkiG9w0BAQsFADBD
MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMdGhhd3RlLCBJbmMuMR0wGwYDVQQDExR0
aGF3dGUgU0hBMjU2IFNTTCBDQTAeFw0xNjAyMDkwMDAwMDBaFw0xODA0MDgyMzU5
NTlaMHkxCzAJBgNVBAYTAlVTMQ4wDAYDVQQIEwVUZXhhczEUMBIGA1UEBxQLU2Fu
IEFudG9uaW8xGjAYBgNVBAoUEVJhY2tzcGFjZSBVUywgSW5jMRAwDgYDVQQLFAdN
YWlsZ3VuMRYwFAYDVQQDFA0qLm1haWxndW4uY29tMIIBIjANBgkqhkiG9w0BAQEF
AAOCAQ8AMIIBCgKCAQEAyzQJUmOuQsksJ
 
+ypj6ndmfkmFa39aXZKxIsvVSSmGSqU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 
/BAQDAgWgMB8GA1UdIwQYMBaAFCuaNa4B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-----END CERTIFICATE-----
 1 s:/C=US/O=thawte, Inc./CN=thawte SHA256 SSL CA
   i:/C=US/O=thawte, Inc./OU=Certification Services Division/OU=(c) 2008 thawte, Inc. - For authorized use only/CN=thawte Primary Root CA - G3
-----BEGIN CERTIFICATE-----
MIIEwjCCA6qgAwIBAgIQNjSeGMmcJmm2Vi5s5a1xMjANBgkqhkiG9w0BAQsFADCB
rjELMAkGA1UEBhMCVVMxFTATBgNVBAoTDHRoYXd0ZSwgSW5jLjEoMCYGA1UECxMf
Q2VydGlmaWNhdGlvbiBTZXJ2aWNlcyBEaXZpc2lvbjE4MDYGA1UECxMvKGMpIDIw
MDggdGhhd3RlLCBJbmMuIC0gRm9yIGF1dGhvcml6ZWQgdXNlIG9ubHkxJDAiBgNV
BAMTG3RoYXd0ZSBQcmltYXJ5IFJvb3QgQ0EgLSBHMzAeFw0xMzA1MjMwMDAwMDBa
Fw0yMzA1MjIyMzU5NTlaMEMxCzAJBgNVBAYTAlVTMRUwEwYDVQQKEwx0aGF3dGUs
IEluYy4xHTAbBgNVBAMTFHRoYXd0ZSBTSEEyNTYgU1NMIENBMIIBIjANBgkqhkiG
9w0BAQEFAAOCAQ8AMIIBCgKCAQEAo2Mr1LpdOK6wz7lMON8gffErR3Edi2jzVvmc
2qrlhCbepXEwvPMxI53oO4DIZld1tlcO25P1Jo5wumRSZooqiFxEGE2oony9VmEy
kBL5NYdIYLBukGdEAY3nyQ1jaHJyq2M8hrgffa2IJadqiCn7WcZ4cV8suonm04D9
V+y5UV9DMy5+JTukBNFgjLNEM5MMrSq2RKIZO6/EkG97BYeGmyxqnStsd8kAn8nP
rO0+G/fD89n4bNSgV8T7KDKqM/Dmupjf5cJOnHS/ikjC8hvwd0BBBwSyOtVMxCmp
EUA/AkbwkdXSgYOGE7Mx7UarqId2qZl9vM0xUPSltdylMrOLiwIDAQABo4IBRDCC
AUAwMgYIKwYBBQUHAQEEJjAkMCIGCCsGAQUFBzABhhZodHRwOi8vb2NzcC50aGF3
dGUuY29tMBIGA1UdEwEB/wQIMAYBAf8CAQAwQQYDVR0gBDowODA2BgpghkgBhvhF
AQc2MCgwJgYIKwYBBQUHAgEWGmh0dHBzOi8vd3d3LnRoYXd0ZS5jb20vY3BzMDcG
A1UdHwQwMC4wLKAqoCiGJmh0dHA6Ly9jcmwudGhhd3RlLmNvbS9UaGF3dGVQQ0Et
RzMuY3JsMA4GA1UdDwEB/wQEAwIBBjAqBgNVHREEIzAhpB8wHTEbMBkGA1UEAxMS
VmVyaVNpZ25NUEtJLTItNDE1MB0GA1UdDgQWBBQrmjWuARg4MOFwegXgEXajzr2Q
FDAfBgNVHSMEGDAWgBStbKqUYJzt5P/6Pgp0K2MD97ZZvzANBgkqhkiG9w0BAQsF
AAOCAQEAdKZW6K+Tlhn7JvkNsESlzel6SAN0AWwTcbfggpCZYiPj1pmv8McenqgY
Idu0lD80VhuZVS+O8EUzMrdywRNbNNP1YOUuGNFcxWrBqodQDBydZCv/G9zVLmEL
57m2kVOG2QMq0T17StorB74p8mBCqZEaDi480X2lExQC+u6LjbbIuD5WgVchJD9l
w7TJzlyNRqxT8/lVdMgr/dJ4cPX4EeX0p60g9Z3x7HD2E6zmjI3bP8byeQ6rUvLM
G3knzxaz1vPGNoBD7MWU8N2QjfjGUkZW63RHvqbzGa5xTMDh59TP7dQGKCoRPLrZ
QW4A54E3k+TaYsYdZ29jtBSG2aZi8A==
-----END CERTIFICATE-----
---
Server certificate
subject=/C=US/ST=Texas/L=San Antonio/O=Rackspace US, Inc/OU=Mailgun/CN=*.mailgun.com
issuer=/C=US/O=thawte, Inc./CN=thawte SHA256 SSL CA
---
No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 3342 bytes and written 434 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
    Session-ID: E279B2FA33421D0A68D77E6405256671A7E0438D8F61C9A85FB67ABE40B07437
    Session-ID-ctx:
    Master-Key: 9A46CDBA8230B31F0AD744A49AEB97D44346DD26687689C5BF52A1F93BC4F0EFC4A8DFCD1F38DE35FF6007E4823ED0C7
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1493541740
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)
---

 將輸出內容儲存為pem檔案，這裡我儲存為名為mailgun.pem的檔案。

二、將證書匯入truststore檔案

cp $JAVA_HOME/jre/lib/security/cacerts  trustore

本質上keyStore和strustStore檔案格式上是一回事，keyStore存的一般是私鑰，trustStore存放的是公鑰。

匯入證書（初始密碼是changeit）：

keytool -import -alias gca -file mailgun.pem -keystore truststore

 匯入成功會有提示。GOOD LUCK

三、參考

等