1. Upgrade Mac OS to Lion 10.8.1 or later as Java 7 installation only works on version 10.7.3 or later. You can do this via the App Store.
2. Download JDK 7 (I use the update 7 version) for Mac from Oracle website. Currently, it's here http://www.oracle.com/technetwork/java/javase/downloads/jdk7u7-downloads-1836413.html
3. Install JDK
4. You would probably see that some command line program (e.g. ant) doesn't work after that. You may get error message like
JAVA_HOME is not defined correctly.We cannot execute /System/Library/Frameworks/JavaVM.framework/Home/bin/java
To fix immediately, you can type (from command line)
or you can do the following:
a. sudo vi ~/.bash_profile
b. insert this line
export JAVA_HOME=`/usr/libexec/java_home -v 1.7`
You would need to restart.
5. If you try to open Eclipse, you may see this popup message "To open “Eclipse,” you need a Java SE 6 runtime. Would you like to install one now?". You could get around this by using this trick (credit go to http://apple.stackexchange.com/questions/58203/mountain-lion-with-java-7-only)
sudo mkdir /System/Library/Java/JavaVirtualMachines sudo ln -s /Library/Java/JavaVirtualMachines/jdk.1.7.0_07.jdk /System/Library/Java/JavaVirtualMachines/1.6.0.jdk
My eclipse works perfectly after this.
Hope you find this helpful.