异常描述：
1 javax.net.ssl.SSLException: Received fatal alert: protocol_version 2 at sun.security.ssl.Alerts.getSSLException(Alerts.java:208) 3 at sun.security.ssl.Alerts.getSSLException(Alerts.java:154) 4 at sun.security.ssl.SSLSocketImpl.recvAlert(SSLSocketImpl.java:2020) 5 at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1127) 6 at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1367) 7 at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1395) 8 at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1379) 9 at org.apache.http.conn.ssl.SSLConnectionSocketFactory.createLayeredSocket(SSLConnectionSocketFactory.java:394) 10 at org.apache.http.conn.ssl.SSLConnectionSocketFactory.connectSocket(SSLConnectionSocketFactory.java:353) 11 at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:141) 12 at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:353) 13 at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:380) 14 at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:236) 15 at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184) 16 at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88) 17 at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110) 18 at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184) 19 at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82) 20 at us.codecraft.webmagic.downloader.HttpClientDownloader.download(HttpClientDownloader.java:85) 21 at us.codecraft.webmagic.Spider.processRequest(Spider.java:404) 22 at us.codecraft.webmagic.Spider.access$000(Spider.java:61) 23 at us.codecraft.webmagic.Spider$1.run(Spider.java:320) 24 at us.codecraft.webmagic.thread.CountableThreadPool$1.run(CountableThreadPool.java:74) 25 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) 26 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) 27 at java.lang.Thread.run(Thread.java:748)
原因：webmagic默认的HttpClient只会用TLSv1去请求，对于某些只支持TLS1.2的站点（例如https://juejin.im/） ，就会报错；
解决方法：https://github.com/code4craft/webmagic/issues/701