How to switch from Java 6 to Java 7 on Mac. No Java runtime present, requesting install. [updated]

An automated option is to use the script described here:
http://www.racoonlab.com/2013/08/toggle-between-java-6-and-java-7-on-mac/

How to re-enable the Apple-provided Java SE 6 applet plug-in and switch java version.

Have you installed the latest java and javaws doesn’t start?

If you have already followed the steps below once, you can perform directly points 4 and 5 this time.

After following the below steps you can switch java by declaring
for java 6

export JAVA_HOME=/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK/Home

for java 7

export JAVA_HOME=$(/usr/libexec/java_home)
export PATH=${JAVA_HOME}/bin:$PATH

How to change the plugin:

If, after installing Java for OS X 2012-006 and Java 7, you want to disable Java 7 and re-enable the Apple-provided Java SE 6 plug-in, follow these steps.

Note: You must be logged in as an administrator.

Note: If prompted for your administrator password after a command, enter it and then press the Return or Enter key.

  1. Open Terminal, located in the Utilities folder.
  2. Enter this command, then press the Return or Enter key:
    sudo mkdir -p /Library/Internet\ Plug-Ins/disabled
  3. Enter this command, then press the Return or Enter key:
    sudo mv /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin/ /Library/Internet\ Plug-Ins/disabled/
  4. Enter this command, then press the Return or Enter key:
    sudo ln -sf /System/Library/Java/Support/Deploy.bundle/Contents/Resources/JavaPlugin2_NPAPI.plugin /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin
  5. To re-enable Java SE 6 Web Start, enter this command, then press the Return or Enter key:
    sudo ln -sf /System/Library/Frameworks/JavaVM.framework/Commands/javaws /usr/bin/javaws

Additional Information

The following steps will undo the above commands and restore Java 7.

To disable Java SE 6 Web Start opening

Enter this command, then press the Return or Enter key:

sudo ln -sf /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/javaws /usr/bin