Java test HTTPS request to https://helloworld.letsencrypt.org/

URLConnectionReader.java

// Based on java example: http://docs.oracle.com/javase/tutorial/networking/urls/readingWriting.html
// save as: URLConnectionReader.java
// compile using JDK: javac URLConnectionReader.java
// run: java URLConnectionReader
// good path: returns HTML
// bad path: throws an exception

import java.net.*;
import java.io.*;

public class URLConnectionReader {
    public static void main(String[] args) throws Exception {
        URL oracle = new URL("https://helloworld.letsencrypt.org/");
        URLConnection yc = oracle.openConnection();
        BufferedReader in = new BufferedReader(new InputStreamReader(
                                    yc.getInputStream()));
        String inputLine;
        while ((inputLine = in.readLine()) != null)
            System.out.println(inputLine);
        in.close();
    }
}

@chrisDeFouRire Letsencrypt is not in the default list of CAs in the Oracle Java JDK. Discussion here: https://community.letsencrypt.org/t/will-the-cross-root-cover-trust-by-the-default-list-in-the-jdk-jre/134

Confirmed working with Oracle JDK >= 8u101 (final release)

Also Oracle JDK >= 7u111

Error still here.
$ java -version
openjdk version "1.8.0_102"
OpenJDK Runtime Environment (build 1.8.0_102-b14)
OpenJDK 64-Bit Server VM (build 25.102-b14, mixed mode)

After copy /usr/local/linux-oracle-jdk1.8.0/jre/lib/security/cacerts to /usr/local/openjdk8/jre/lib/security/cacerts all work fine => OpenJDK have old cacerts without trust for letsencrypt.

java -version
java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

Error still there.

This SO-answer shows how to import the letsencrypt security chain, which "solves" the issue, even on a Raspberry Pi with jre 1.8.0_65:

http://stackoverflow.com/a/35454903/272180