PKIX路径建设失败的URL

Question

获取数据时，我试图让数据如下（由API这样表示）：

HttpResponse<String> response = Unirest.get("https://opendata.aemet.es/opendata/api/valores/climatologicos/diarios/datos/fechaini/2017-08-16T00:00:00UTC/fechafin/2017-08-17T23:59:59UTC/estacion/2422/?api_key=eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJqb3NoZXJAY2FydGlmLmVzIiwianRpIjoiZWM3MDkxMzItNTE0ZC00OGZjLTljMjMtYTBiMzVjNTllYzdjIiwiZXhwIjoxNTEwNzMxMzU4LCJpc3MiOiJBRU1FVCIsImlhdCI6MTUwMjk1NTM1OCwidXNlcklkIjoiZWM3MDkxMzItNTE0ZC00OGZjLTljMjMtYTBiMzVjNTllYzdjIiwicm9sZSI6IiJ9.WSVaE3C9TFMMa8x1mUvHpt1-n3Cgy3p7r2DaflSm9VU") 
       .header("cache-control", "no-cache") 
       .asString(); 

然而，当我执行的代码，则抛出异常：

Exception in thread "main" com.mashape.unirest.http.exceptions.UnirestException: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target 
    at com.mashape.unirest.http.HttpClientHelper.request(HttpClientHelper.java:143) 
    at com.mashape.unirest.request.BaseRequest.asString(BaseRequest.java:56) 
    at eu.cartif.meteo.Weather_Meteo.main(Weather_Meteo.java:38) 
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target 
    at sun.security.ssl.Alerts.getSSLException(Unknown Source) 
    at sun.security.ssl.SSLSocketImpl.fatal(Unknown Source) 
    at sun.security.ssl.Handshaker.fatalSE(Unknown Source) 
    at sun.security.ssl.Handshaker.fatalSE(Unknown Source) 
    at sun.security.ssl.ClientHandshaker.serverCertificate(Unknown Source) 
    at sun.security.ssl.ClientHandshaker.processMessage(Unknown Source) 
    at sun.security.ssl.Handshaker.processLoop(Unknown Source) 
    at sun.security.ssl.Handshaker.process_record(Unknown Source) 
    at sun.security.ssl.SSLSocketImpl.readRecord(Unknown Source) 
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(Unknown Source) 
    at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source) 
    at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source) 
    at org.apache.http.conn.ssl.SSLConnectionSocketFactory.createLayeredSocket(SSLConnectionSocketFactory.java:396) 
    at org.apache.http.conn.ssl.SSLConnectionSocketFactory.connectSocket(SSLConnectionSocketFactory.java:355) 
    at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:142) 
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:359) 
    at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:381) 
    at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:237) 
    at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185) 
    at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89) 
    at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:111) 
    at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185) 
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83) 
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108) 
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56) 
    at com.mashape.unirest.http.HttpClientHelper.request(HttpClientHelper.java:138) 
... 2 more 
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target 
    at sun.security.validator.PKIXValidator.doBuild(Unknown Source) 
    at sun.security.validator.PKIXValidator.engineValidate(Unknown Source) 
    at sun.security.validator.Validator.validate(Unknown Source) 
    at sun.security.ssl.X509TrustManagerImpl.validate(Unknown Source) 
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(Unknown Source) 
    at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(Unknown Source) 
... 24 more 
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target 
    at sun.security.provider.certpath.SunCertPathBuilder.build(Unknown Source) 
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(Unknown Source) 
    at java.security.cert.CertPathBuilder.build(Unknown Source) 
... 30 more  

我也试图通过密钥工具来导入证书，但我得到一个消息说“文件密钥库不存在”。

可能有人支持我吗？在此先感谢

Answer 1

5秒钟浏览器给了我这一切的信息：

Your connection is not secure 

The owner of opendata.aemet.es has configured their web site improperly. To protect your information from being stolen, Firefox has not connected to this web site. 

Learn more… 

Report errors like this to help Mozilla identify and block malicious sites 

opendata.aemet.es uses an invalid security certificate. 

The certificate is not trusted because the issuer certificate is unknown. 
The server might not be sending the appropriate intermediate certificates. 
An additional root certificate may need to be imported. 

Error code: SEC_ERROR_UNKNOWN_ISSUER