我刚接触Gradle，正在浏览此 Spring 教程，可在此处找到：
http://spring.io/guides/gs/gradle/
我到了它告诉我添加这个任务的部分：

task wrapper(type: Wrapper) {
     gradleVersion = '2.3'
}

我运行gradle wrapper，它创建gradlew和gradlew.bat文件。
尝试运行这两个程序时，我遇到了这个异常：

Downloading https://services.gradle.org/distributions/gradle-2.3-bin.zip

Exception in thread "main" javax.net.ssl.SSLHandshakeException: sun.security.val
idator.ValidatorException: PKIX path building failed: sun.security.provider.cert
path.SunCertPathBuilderException: unable to find valid certification path to req
uested target
        at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
        at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1884)
        at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:276)
        at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:270)
        at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.
java:1341)
        at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.jav
a:153)
        at sun.security.ssl.Handshaker.processLoop(Handshaker.java:868)
        at sun.security.ssl.Handshaker.process_record(Handshaker.java:804)
        at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1016)
        at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.
java:1312)
        at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1339
)
        at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1323
)
        at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:
563)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect
(AbstractDelegateHttpsURLConnection.java:185)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLCon
nection.java:1300)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(Http
sURLConnectionImpl.java:254)
        at org.gradle.wrapper.Download.downloadInternal(Download.java:56)
        at org.gradle.wrapper.Download.download(Download.java:42)
        at org.gradle.wrapper.Install$1.call(Install.java:57)
        at org.gradle.wrapper.Install$1.call(Install.java:44)
        at org.gradle.wrapper.ExclusiveFileAccessManager.access(ExclusiveFileAcc
essManager.java:65)
        at org.gradle.wrapper.Install.createDist(Install.java:44)
        at org.gradle.wrapper.WrapperExecutor.execute(WrapperExecutor.java:126)
        at org.gradle.wrapper.GradleWrapperMain.main(GradleWrapperMain.java:56)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed:
 sun.security.provider.certpath.SunCertPathBuilderException: unable to find vali
d certification path to requested target
        at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:385)
        at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.jav
a:292)
        at sun.security.validator.Validator.validate(Validator.java:260)
        at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.j
ava:326)
        at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerIm
pl.java:231)
        at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustMan
agerImpl.java:126)
        at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.
java:1323)
        ... 19 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to
 find valid certification path to requested target
        at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCert
PathBuilder.java:196)
        at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:268)
        at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:380)
        ... 25 more

我试着在https://services.gradle.org/distributions/gradle-2.3-bin.zip打网络服务器，我没有得到任何类型的错误。我是我错过了某种配置？任何帮助将不胜感激。谢谢！