Android 4.x 在 https 协议下无法利用 okhttp 进行网络访问的临时解决办法

最近公司项目迁移了服务器，同样的也由 http 变成了 https 协议。不过调试的时候发现 4.x 的设备都无法进行访问网络了，5.0 及以上的设备没有遇到问题。百度许久未果，在 google 上找到了答案。
原文地址：https://github.com/square/okhttp/issues/2372

解决方法如下：

1.添加以下内容的Tls12SocketFactory.java类

import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;

/**
 * Enables TLS v1.2 when creating SSLSockets.
 * 

 * For some reason, android supports TLS v1.2 from API 16, but enables it by
 * default only from API 20.
 * @link https://developer.android.com/reference/javax/net/ssl/SSLSocket.html
 * @see SSLSocketFactory
 */
public class Tls12SocketFactory extends SSLSocketFactory {
    private static final String[] TLS_V12_ONLY = {"TLSv1.2"};

    final SSLSocketFactory delegate;

    public Tls12SocketFactory(SSLSocketFactory base) {
        this.delegate = base;
    }

    @Override
    public String[] getDefaultCipherSuites() {
        return delegate.getDefaultCipherSuites();
    }

    @Override
    public String[] getSupportedCipherSuites() {
        return delegate.getSupportedCipherSuites();
    }

    @Override
    public Socket createSocket(Socket s, String host, int port, boolean autoClose) throws IOException {
        return patch(delegate.createSocket(s, host, port, autoClose));
    }

    @Override
    public Socket createSocket(String host, int port) throws IOException, UnknownHostException {
        return patch(delegate.createSocket(host, port));
    }

    @Override
    public Socket createSocket(String host, int port, InetAddress localHost, int localPort) throws IOException, UnknownHostException {
        return patch(delegate.createSocket(host, port, localHost, localPort));
    }

    @Override
    public Socket createSocket(InetAddress host, int port) throws IOException {
        return patch(delegate.createSocket(host, port));
    }

    @Override
    public Socket createSocket(InetAddress address, int port, InetAddress localAddress, int localPort) throws IOException {
        return patch(delegate.createSocket(address, port, localAddress, localPort));
    }

    private Socket patch(Socket s) {
        if (s instanceof SSLSocket) {
            ((SSLSocket) s).setEnabledProtocols(TLS_V12_ONLY);
        }
        return s;
    }
}

2.在代码中添加下面的方法

public static OkHttpClient.Builder enableTls12OnPreLollipop(OkHttpClient.Builder client) {
    if (Build.VERSION.SDK_INT >= 16 && Build.VERSION.SDK_INT < 22) {
        try {
            SSLContext sc = SSLContext.getInstance("TLSv1.2");
            sc.init(null, null, null);
            client.sslSocketFactory(new Tls12SocketFactory(sc.getSocketFactory()));

            ConnectionSpec cs = new ConnectionSpec.Builder(ConnectionSpec.MODERN_TLS)
                    .tlsVersions(TlsVersion.TLS_1_2)
                    .build();

            List specs = new ArrayList<>();
            specs.add(cs);
            specs.add(ConnectionSpec.COMPATIBLE_TLS);
            specs.add(ConnectionSpec.CLEARTEXT);

            client.connectionSpecs(specs);
        } catch (Exception exc) {
            Log.e("OkHttpTLSCompat", "Error while setting TLS 1.2", exc);
        }
    }
    
    return client;
}

3.最后在实例化okhttp客户端的时候，作类似如下的处理

private OkHttpClient getNewHttpClient() {
    OkHttpClient.Builder client = new OkHttpClient.Builder()
            .followRedirects(true)
            .followSslRedirects(true)
            .retryOnConnectionFailure(true)
            .cache(null)
            .connectTimeout(5, TimeUnit.SECONDS)
            .writeTimeout(5, TimeUnit.SECONDS)
            .readTimeout(5, TimeUnit.SECONDS);

    return enableTls12OnPreLollipop(client).build();
}

采用了上面的方法后，4.x 的设备也可以正常的进行网络访问了，不过又遇到了新的坑。在 4.x 下，第三方的图片加载框架，无论是 glide 还是 imageloader，都无法正常加载。看来这是网站配置证书的问题，毕竟用的是免费证书，遇到问题也不足为怪了。

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