That's a very terse question, but I'll take it that you're interested in whether TLS clients running on Java 7 will (out of the box) trust Let's Encrypt server certificates

The answer is that for Oracle's Java updating to 7u111 is necessary for this to work (or to 8u101 if you run Java 8) and that for other people's Java implementations it will depend upon where they get their trust store, Oracle's is the most popular in Java.