I have install maven in my machine. I have properly set the class-path and maven home folder. Every time I execute mvn clean install, it gives me exception. I h
The problem is probably that the JVM client doesn't trust the repo.maven.apache.org certificate. As suggested, you can try and access https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom in your browser.
If that works - this is probably the case. You will have to explicitly tell the JMV to trust maven certificate. You can refer to the answer here "PKIX path building failed" and "unable to find valid certification path to requested target"
for me on Mac OS, the certificate file is located at /Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/security and the certificate you need is the one presented to your browser when you enter the URL mentioned above