Setting Diffie-Hellman keysize on Java

Issue

• How can I require Diffie-Hellman be 2048 bits or greater in Red Hat JBoss Enterprise Application Platform (EAP) 6?
• How do I set the Diffie-Hellman keysize to a defined value to avoid vulnerabilities like logjam?
• Does OpenJDK 1.7 support ephemeral key sizes larger than 1024 bits, if the -Djdk.tls.ephemeralDHKeySize=2048 parameter is set accordingly?
• Browser received a weak ephemeral Diffie-­Hellman key in SSL Server Key Exchange handshake message. (Error code: ssl_error_weak_server_ephemeral_dh_key)
• Browser is returning "Server has a weak ephemeral Diffie-Hellman public key ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY"
• Failed to access Website due to DHE key length issue, hence should we upgrade the JDK/JRE to 7 / 8 and apply this parameter " JAVA_OPTS="$JAVA_OPTS -Djdk.tls.ephemeralDHKeySize=2048"" to fix the problem?