Download JDK from the following URL, which is from official site of Oracle. Make sure that you download a JDK higher than 1.7.0_15, as Oracle BPM 12c requires JDK 1.7.0_15 and higher:

http://www.oracle.com/technetwork/java/javase/downloads/index.html.

After clicking on the preceding link, the Java SE Development Kit 7u60 window opens as shown in the following screenshot:

Install JDK, set JAVA_HOME, and update the environment variable with JAVA_HOME.