https是加密的http协议，通过不对称加密确认对称加密的密钥，之后使用对称加密进行通信。
通信流程：

http 握手
在TCP/IP协议中，TCP协议提供可靠的连接服务，采用三次握手建立一个连接。
第一次握手：建立连接时，客户端发送syn包(syn=j)到服务器，并进入SYN_SEND状态，等待服务器确认；
第二次握手：服务器收到syn包，必须确认客户的SYN（ack=j+1），同时自己也发送一个SYN包（syn=k），即SYN+ACK包，此时服务器进入SYN_RECV状态； 第三次握手：客户端收到服务器的SYN＋ACK包，向服务器发送确认包ACK(ack=k+1)，此包发送完毕，客户端和服务器进入ESTABLISHED状态，完成三次握手。 完成三次握手，客户端与服务器开始传送数据.

http端口80 https 443

tomcat 开启https

1. 生成证书 如果没有的话
   keytool -genkey -alias tomcat -keyalg RSA 在user目录下（mac）.keystore 文件
   填写一些信息就可以了
2. 今天tomcat 的配置文件进行配置 server.xml

  <Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol"
        maxThreads="150" SSLEnabled="true" scheme="https" secure="true" keystoreFile="${user.home}/.keystore" keystorePass="_密码_" clientAuth="false" sslProtocal="TLS">
    </Connector>

3. 启动tomcat ，进入https://localhost:8443 , 信任证书后，看见tomcat就配置成功了。

android UrlConnection 使用https

1. 把证书放在assets文件下

打开应该是这样的：
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

1. 官方的例子

private void googleTest() throws CertificateException, IOException, KeyStoreException, NoSuchAlgorithmException, KeyManagementException {
        // Load CAs from an InputStream
// (could be from a resource or ByteArrayInputStream or ...)
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
// From https://www.washington.edu/itconnect/security/ca/load-der.crt
        //载入证书
        InputStream caInput = new BufferedInputStream(getAssets().open("uwca.crt"));
        Certificate ca;
        try {
            ca = cf.generateCertificate(caInput);
            System.out.println("ca=" + ((X509Certificate) ca).getSubjectDN());
        } finally {
            caInput.close();
        }

        //添加我们都证书，，来认证
// Create a KeyStore containing our trusted CAs
        String keyStoreType = KeyStore.getDefaultType();
        KeyStore keyStore = KeyStore.getInstance(keyStoreType);
        keyStore.load(null, null);
        keyStore.setCertificateEntry("ca", ca);

// Create a TrustManager that trusts the CAs in our KeyStore
        String tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
        TrustManagerFactory tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
        tmf.init(keyStore);

// Create an SSLContext that uses our TrustManager
        SSLContext context = SSLContext.getInstance("TLS");
        context.init(null, tmf.getTrustManagers(), null);

// Tell the URLConnection to use a SocketFactory from our SSLContext
        URL url = new URL("https://www.baidu.com/");
        HttpsURLConnection urlConnection =
                (HttpsURLConnection) url.openConnection();
        urlConnection.setSSLSocketFactory(context.getSocketFactory());
        InputStream in = urlConnection.getInputStream();
//        copyInputStreamToOutputStream(in, System.out);
        String str = null;
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        while ((str = reader.readLine()) != null) {
            Log.i(Tag, "获取到的信息：" + str);
        }
        reader.close();
        in.close();
    }

exception

javax.net.ssl.SSLHandshakeException: java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.
证书没有通过验证,证书一定要和我们访问的链接匹配。

官方教材

1. https://developer.android.com/training/articles/security-ssl.html#UnknownCa