仿照https://docs.spring.io/spring-boot/docs/2.2.0.BUILD-SNAPSHOT/reference/html/getting-started.html#getting-started网址里的例子进行启动时，
执行spring run app.groovy，报错，错误信息如下
错误信息：
Caused by: org.eclipse.aether.resolution.ArtifactResolutionException: Could not transfer artifact org.springframework.boot:spring-boot-starter-web:pom:2.1.9.RELEASE from/to central (https://repo.maven.apache.org/maven2/): sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:422)
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:224)
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifact(DefaultArtifactResolver.java:201)
at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:261)
... 34 more
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(Alerts.java:192)
at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1949)
at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:302)
at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:296)
at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1506)
at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:216)
at sun.security.ssl.Handshaker.processLoop(Handshaker.java:979)
at sun.security.ssl.Handshaker.process_record(Handshaker.java:914)
at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1062)
at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1375)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1403)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1387)
at org.apache.http.conn.ssl.SSLSocketFactory.createLayeredSocket(SSLSocketFactory.java:570)
at org.apache.http.conn.ssl.SSLSocketFactory.createLayeredSocket(SSLSocketFactory.java:450)
at org.apache.http.impl.conn.DefaultClientConnectionOperator.updateSecureConnection(DefaultClientConnectionOperator.java:220)
at org.apache.http.impl.conn.ManagedClientConnectionImpl.layerProtocol(ManagedClientConnectionImpl.java:419)
at org.apache.http.impl.client.DefaultRequestDirector.establishRoute(DefaultRequestDirector.java:808)
at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:609)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:440)
at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:72)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
at org.apache.http.impl.client.DecompressingHttpClient.execute(DecompressingHttpClient.java:164)
at org.eclipse.aether.transport.http.HttpTransporter.execute(HttpTransporter.java:296)
at org.eclipse.aether.transport.http.HttpTransporter.implGet(HttpTransporter.java:252)
at org.eclipse.aether.spi.connector.transport.AbstractTransporter.get(AbstractTransporter.java:67)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$GetTaskRunner.runTask(BasicRepositoryConnector.java:453)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$TaskRunner.run(BasicRepositoryConnector.java:360)
... 42 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(PKIXValidator.java:387)
at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
at sun.security.validator.Validator.validate(Validator.java:260)
at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324)
at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229)
at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124)
at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1488)
... 65 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:146)
at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:131)
at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:382)
... 71 more
分析可得知，由于去https://repo.maven.apache.org/maven2/下载包的时候，没有证书权限。
解决办法：
1、访问该网站：https://repo.maven.apache.org/maven2/，证书下载成功后
2、到达java路径：/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/security
3、执行命令：sudo keytool -import -file ~/Documents/repo.maven.apache.org.cer-keystore cacerts -alias server
密钥库口令默认为：changeit
4、执行成功后，再次执行命令。启动成功
