Https系列之四：https的SSL证书在Android端基于okhttp，Retrofit的使用

Https系列会在下面几篇文章中分别作介绍：

一：https的简单介绍及SSL证书的生成
二：https的SSL证书在服务器端的部署，基于tomcat,spring boot
三：让服务器同时支持http、https，基于spring boot
四：https的SSL证书在Android端基于okhttp，Retrofit的使用

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先来回顾一下

前面已分别介绍了https,SSL证书的生成，并完成了服务器端的https的部署
并提到一个重要的用于客户端的证书：公钥证书
在前面文章中，自签名SSL证书对应的公钥证书为：mycer.cer（当然这名字是自己随便定的）;在阿里云申请的CA证书中对应的公钥证书为：*.pem
如果有不清楚的，请看我之前介绍过的文章

Android自带的可信任的CA公钥证书

还要说明一下，Android系统有自带的安卓认可的证书颁发机构（如:Wosign)颁发的可信任的CA公钥证书，大概有100多个，
可自己查看，各个手机的查看方法可能不一样，在我的手机中，能在下面的位置中找到：
“设置”->”更多设置“->”系统安全“->”信任的凭据”
也就是说，如果你服务器的证书是安卓认可的证书颁发机构颁发的，那么你并不需要在Android端额外安装公钥证书，否则，你就需要安装。
注：在不同版本的Android系统上，可信任的CA证书可能是不一样的，如果你担心在别人的Android系统上可能此CA证书不被信任，那你统一都安装也是没问题的
我在阿里云上申请的免费型DV SSL证书，是属于安卓认可的证书颁发机构颁发的，不需要额外安装，当然我们的自签名证书，是必需要安装的
其实我在测试的过程中，把自签名证书和阿里云上申请的免费型DV SSL证书都用同样的方法安装了，都是OK的

我们下面就开始基于okhttp来安装公钥证书了

先看看我的okhttp和retrofit的gradle版本

compile ‘com.squareup.okhttp3:okhttp:3.8.1‘
compile ‘com.squareup.retrofit2:retrofit:2.3.0‘

增加一个OkhttpManager类

统一处理OkHttpClient的证书，完整的代码如下：

import android.content.Context;
import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.util.Arrays;
import java.util.Collection;
import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;
import okhttp3.OkHttpClient;

public class OkhttpManager {
    static private OkhttpManager mOkhttpManager=null;
    private InputStream mTrustrCertificate;
    static public OkhttpManager getInstance()
    {
        if(mOkhttpManager==null)
        {
            mOkhttpManager=new OkhttpManager();
        }
        return mOkhttpManager;
    }

    private KeyStore newEmptyKeyStore(char[] password) throws GeneralSecurityException {
        try {
            KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
            InputStream in = null; // By convention, ‘null‘ creates an empty key store.
            keyStore.load(in, password);
            return keyStore;
        } catch (IOException e) {
            throw new AssertionError(e);
        }
    }

    private X509TrustManager trustManagerForCertificates(InputStream in)
            throws GeneralSecurityException {
        CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
        Collection<? extends Certificate> certificates = certificateFactory.generateCertificates(in);
        if (certificates.isEmpty()) {
            throw new IllegalArgumentException("expected non-empty set of trusted certificates");
        }

        // Put the certificates a key store.
        char[] password = "password".toCharArray(); // Any password will work.
        KeyStore keyStore = newEmptyKeyStore(password);
        int index = 0;
        for (Certificate certificate : certificates) {
            String certificateAlias = Integer.toString(index++);
            keyStore.setCertificateEntry(certificateAlias, certificate);
        }

        // Use it to build an X509 trust manager.
        KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
        keyManagerFactory.init(keyStore, password);
        TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
        trustManagerFactory.init(keyStore);
        TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
        if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
            throw new IllegalStateException("Unexpected default trust managers:" + Arrays.toString(trustManagers));
        }
        return (X509TrustManager) trustManagers[0];
    }

    public void setTrustrCertificates(InputStream in)
    {
        mTrustrCertificate=in;
    }

    public InputStream getTrustrCertificates()
    {
        return mTrustrCertificate;
    }

    public OkHttpClient build()
    {
        OkHttpClient okHttpClient=null;
        if(getTrustrCertificates()!=null)
        {
            X509TrustManager trustManager;
            SSLSocketFactory sslSocketFactory;
            try {
                trustManager = trustManagerForCertificates(getTrustrCertificates());
                SSLContext sslContext = SSLContext.getInstance("TLS");
                sslContext.init(null, new TrustManager[] { trustManager }, null);
                sslSocketFactory = sslContext.getSocketFactory();
            } catch (GeneralSecurityException e) {
                throw new RuntimeException(e);
            }
            okHttpClient=new OkHttpClient.Builder()
                    .sslSocketFactory(sslSocketFactory, trustManager)
                    .build();
        }
        else
        {
            okHttpClient=new OkHttpClient.Builder()
                                         .build();
        }
        return okHttpClient;
    }

}

代码解释

代码不少，其实最核心的代码为：

public OkHttpClient build()
{
.......
 trustManager = trustManagerForCertificates(getTrustrCertificates());
 .......
  okHttpClient=new OkHttpClient.Builder()
                    .sslSocketFactory(sslSocketFactory, trustManager)
                    .build();
 ..........
 return okHttpClient;
}

也就是通过

void setTrustrCertificates(InputStream in)

把自己的证书对应的文件set进去

然后通过

trustManager =trustManagerForCertificates(getTrustrCertificates());

再

okHttpClient=new OkHttpClient.Builder()
                    .sslSocketFactory(sslSocketFactory, trustManager)
                    .build();

就能生成安装好了可信任证书的okHttpClient

OkhttpManager说完了，接下来，就是：

Activity中使用OkhttpManager

1：先把公钥证书文件（如：自签名的mycer.cer或CA证书的：*.pem)放到assets下，
如果使用AndroidStudio的同学，可能没有assets文件夹，自己建此文件夹，如我的为：app\src\main\assets

2：直接贴Activity主要的代码：

public class MyActivity extends AppCompatActivity {
@Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       try {
            OkhttpManager.getInstance().setTrustrCertificates(getAssets().open("mycer.cer");
            OkHttpClient mOkhttpClient= OkhttpManager.getInstance().build();
        } catch (IOException e) {
            e.printStackTrace();
        }
}

简单吧，主要代码就那两句，就生成了已安装公钥证书”mycer.cer”的mOkhttpClient
接下来的mOkhttpClient怎样使用，大家都应该清楚了吧，如果不清楚只能看OkHttpClient的基础内容了

好了，OkHttpClient搞掂了

接下来就到Retrofit了

大家应该知到Retrofit默认是以OkHttpClient来作为传输的，既然OkHttpClient搞掂了，那Retrofit就简单了
还是直接贴代码：

 Retrofit retrofit = new Retrofit.Builder()
                .client(mOkhttpClient)
                .baseUrl("your_serverl_url")
                .build();

看，只需在Retrofit中多加一句

.client(mOkhttpClient)

就把已安装了证书的mOkhttpClient作为Retrofit的传输了

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