这是第一个有太多答案的古老问题，我认为我可以提供一个更有用的想法:如果服务器所有者拒绝以可信任的方式离线向我提供他们的证书，我会使用这个选项:

从服务器本身检索证书(使用命令行工具而不是浏览器) 将该证书添加到java密钥存储库以信任它。将显示证书的详细信息，以验证它。

# HOSTNAME_PORT is the host that you want to connect to - example: HOSTNAME_PORT=stackoverflow.com:443
HOSTNAME_PORT=hostname_part_of_url_without_https:port

# whatever you want to call the key within the Java key store
MY_KEY_ALIAS=the_key_I_added_with_help_from_stackoverflow

openssl s_client -showcerts -connect $HOSTNAME_PORT </dev/null 2>/dev/null|openssl x509 -outform PEM >mycertfile.pem
sudo keytool -trustcacerts -keystore $JAVA_HOME/jre/lib/security/cacerts/pki/java/cacerts -storepass changeit -importcert -alias $MY_KEY_ALIAS -file mycertfile.pem 

在出现提示时输入yes，但只有在您真正信任显示给您的证书并希望将其添加到计算机的全局java密钥存储库时才可以这样做。

通知你:$ JAVA_HOME / jre / lib /安全/除 在我的情况下(CentOS 7)指向: /etc/pki/java/cacerts

Kotlin中的变体

    @SuppressLint("CustomX509TrustManager", "TrustAllX509TrustManager")
    fun ignoreSsl() {
        val trustAllCerts: Array<TrustManager> = arrayOf(
            object : X509TrustManager {
                override fun getAcceptedIssuers(): Array<X509Certificate>? = null
                override fun checkClientTrusted(certs: Array<X509Certificate?>?, authType: String?) {}
                override fun checkServerTrusted(certs: Array<X509Certificate?>?, authType: String?) {}
            })
        val sc = SSLContext.getInstance("SSL")
        sc.init(null, trustAllCerts, SecureRandom())
        HttpsURLConnection.setDefaultSSLSocketFactory(sc.socketFactory)
    }

受下面annser的启发，我找到了一种信任自签名CA并保持信任默认CA的方法。

    File file = new File(System.getProperty("java.home"), "lib/security/cacerts");
    KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
    keyStore.load(new FileInputStream(file), "changeit".toCharArray());


    InputStream resourceAsStream = getClass().getClassLoader().getResourceAsStream("testCer.cer");
    Certificate certificate = CertificateFactory.getInstance("X.509").generateCertificate(resourceAsStream);
    keyStore.setCertificateEntry("my-server-alias", certificate);

    TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
    trustManagerFactory.init(keyStore);

    SSLContext sslContext = SSLContexts.createDefault();
    sslContext.init(null, trustManagerFactory.getTrustManagers(), null);


    // check domain
    // SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(sslContext);

    // not check domain
    SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(sslContext,
            new String[]{"TLSv1","TLSv1.1","TLSv1.2","SSLv3"},null, NoopHostnameVerifier.INSTANCE);

    CloseableHttpClient httpClient = HttpClients.custom().setSSLSocketFactory(socketFactory).build();
    factory.setHttpClient(httpClient);
    RestTemplate restTemplate = new RestTemplate(factory);

有一个更好的替代信任所有证书的方法:创建一个TrustStore，它专门信任给定的证书，并使用它来创建一个SSLContext，从中获取SSLSocketFactory在HttpsURLConnection上进行设置。以下是完整的代码:

File crtFile = new File("server.crt");
Certificate certificate = CertificateFactory.getInstance("X.509").generateCertificate(new FileInputStream(crtFile));
// Or if the crt-file is packaged into a jar file:
// CertificateFactory.getInstance("X.509").generateCertificate(this.class.getClassLoader().getResourceAsStream("server.crt"));


KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
keyStore.load(null, null);
keyStore.setCertificateEntry("server", certificate);

TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
trustManagerFactory.init(keyStore);

SSLContext sslContext = SSLContext.getInstance("TLS");
sslContext.init(null, trustManagerFactory.getTrustManagers(), null);

HttpsURLConnection connection = (HttpsURLConnection) new URL(url).openConnection();
connection.setSSLSocketFactory(sslContext.getSocketFactory());

您也可以直接从文件加载KeyStore，或者从任何受信任的来源检索X.509证书。

注意，对于这段代码，将不使用cacerts中的证书。这个特定的HttpsURLConnection将只信任这个特定的证书。

这不是解决全部问题的解决方案，但是oracle有关于如何使用这个keytool的详细文档。这解释了如何

使用keytool。 使用keytool生成证书/自签名证书。 将生成的证书导入Java客户端。

https://docs.oracle.com/cd/E54932_01/doc.705/e54936/cssg_create_ssl_cert.htm#CSVSG178

接受的答案很好，但我想添加一些东西，因为我在Mac上使用IntelliJ，无法使用JAVA_HOME路径变量让它工作。

事实证明，从IntelliJ运行应用程序时，Java Home是不同的。

要找出它的确切位置，只需执行System.getProperty("java.home")，因为可信证书就是从那里读取的。