使用浏览器从目标页面下载自签名证书，并使用默认密码将其添加到默认存储区:

keytool -import -v -trustcacerts -file selfsigned.crt -alias myserver -keystore /etc/alternatives/jre/lib/security/cacerts -storepass changeit

使用$JAVA_HOME/jre/lib/security/cacerts文件，我这里的例子来自Oracle linux 7.7。

而不是设置默认的套接字工厂(这在我看来是一件坏事)- yhis只会影响当前连接，而不是你试图打开的每一个SSL连接:

URLConnection connection = url.openConnection();
    // JMD - this is a better way to do it that doesn't override the default SSL factory.
    if (connection instanceof HttpsURLConnection)
    {
        HttpsURLConnection conHttps = (HttpsURLConnection) connection;
        // Set up a Trust all manager
        TrustManager[] trustAllCerts = new TrustManager[] { new X509TrustManager()
        {

            public java.security.cert.X509Certificate[] getAcceptedIssuers()
            {
                return null;
            }

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

            public void checkServerTrusted(
                java.security.cert.X509Certificate[] certs, String authType)
            {
            }
        } };

        // Get a new SSL context
        SSLContext sc = SSLContext.getInstance("TLSv1.2");
        sc.init(null, trustAllCerts, new java.security.SecureRandom());
        // Set our connection to use this SSL context, with the "Trust all" manager in place.
        conHttps.setSSLSocketFactory(sc.getSocketFactory());
        // Also force it to trust all hosts
        HostnameVerifier allHostsValid = new HostnameVerifier() {
            public boolean verify(String hostname, SSLSession session) {
                return true;
            }
        };
        // and set the hostname verifier.
        conHttps.setHostnameVerifier(allHostsValid);
    }
InputStream stream = connection.getInputStream();

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。

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。

我找到了一个证书提供者，该提供者不属于JDK 8u74的默认JVM受信任主机。提供者是www.identrust.com，但这不是我试图连接的域。该域已从该提供者获得其证书。请参见交叉根覆盖信任JDK/JRE中的默认列表?——读几个条目。另请参阅哪些浏览器和操作系统支持Let 's Encrypt。

因此，为了连接到我感兴趣的域名，它有一个由identrust.com颁发的证书，我执行了以下步骤。基本上，我必须获得identrust.com (DST根CA X3)证书才能被JVM信任。我可以使用Apache HttpComponents 4.5这样做:

1:从证书链下载说明中的indettrust获取证书。单击DST根CA X3链接。

2:保存到“DST Root CA X3.pem”文件中。确保在文件的开头和结尾添加行“-----BEGIN CERTIFICATE-----”和“-----END CERTIFICATE-----”。

3:创建java的keystore文件cacerts。JKS，命令如下:

keytool -import -v -trustcacerts -alias IdenTrust -keypass yourpassword -file dst_root_ca_x3.pem -keystore cacerts.jks -storepass yourpassword

4:复制生成的cacerts。将JKS密钥存储库保存到java/(maven)应用程序的资源目录中。

5:使用以下代码加载该文件，并将其附加到Apache 4.5 HttpClient。这将解决所有拥有indetrust.com颁发的证书的域的问题，util oracle将证书包含到JRE默认的密钥存储库中。

SSLContext sslcontext = SSLContexts.custom()
        .loadTrustMaterial(new File(CalRestClient.class.getResource("/cacerts.jks").getFile()), "yourpasword".toCharArray(),
                new TrustSelfSignedStrategy())
        .build();
// Allow TLSv1 protocol only
SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(
        sslcontext,
        new String[] { "TLSv1" },
        null,
        SSLConnectionSocketFactory.getDefaultHostnameVerifier());
CloseableHttpClient httpclient = HttpClients.custom()
        .setSSLSocketFactory(sslsf)
        .build();

当项目构建时，cacerts。JKS将被复制到类路径中并从那里加载。我没有，在这个时间点上，测试其他ssl站点，但如果上面的代码“链”在这个证书，那么他们也会工作，但是，我不知道。

参考:自定义SSL上下文和如何使用Java HttpsURLConnection接受自签名证书?