I recently installed JDK 6.0.43, and after removing the old versions of Java my projects with a default JDK no longer build, with an error from maven that it can't find tools.jar.

Jenkins is running in Tomcat with the war renamed to Hudson for historical reasons, and Tomcat is running with JDK 6.0.43. JDK7 is installed on the server and configured in Jenkins, but JAVA_HOME is also set to JDK 6.0.43, so I don't know where the jre7 is getting set.
This is a problem because I have about 170 projects. Setting the specific JDK for each would be BAD, changing it for jdk7 later would be worse.

[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Fatal error compiling

Embedded error: tools.jar not found: D:\Applicazioni\Java\jre7\..\lib\tools.jar
[INFO] ------------------------------------------------------------------------
[INFO] Trace
org.apache.maven.lifecycle.LifecycleExecutionException: Fatal error compiling
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:719)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalWithLifecycle(DefaultLifecycleExecutor.java:556)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:535)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:387)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:348)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:180)
at org.apache.maven.lifecycle.LifecycleExecutorInterceptor.execute(LifecycleExecutorInterceptor.java:65)