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
所有文章会优先在：
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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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