Manage SoftReference time-to-live

Оказывается временем жизни SoftReference возможно управлять.
Для этого необходимо использовать опцию HotSpot JVM - -XX:SoftRefLRUPolicyMSPerMB.

"What determines when softly referenced objects are flushed?

Starting with 1.3.1, softly reachable objects will remain alive for some amount of time after the last time they were referenced. The default value is one second of lifetime per free megabyte in the heap. This value can be adjusted using the -XX:SoftRefLRUPolicyMSPerMB flag, which accepts integer values representing milliseconds. For example, to change the value from one second to 2.5 seconds, use this flag:

-XX:SoftRefLRUPolicyMSPerMB=2500

The Java HotSpot Server VM uses the maximum possible heap size (as set with the -Xmx option) to calculate free space remaining.

The Java Hotspot Client VM uses the current heap size to calculate the free space.

This means that the general tendency is for the Server VM to grow the heap rather than flush soft references, and -Xmx therefore has a significant effect on when soft references are garbage collected.

On the other hand, the Client VM will have a greater tendency to flush soft references rather than grow the heap.

The behavior described above is true for 1.3.1 through Java SE 6 versions of the Java HotSpot VMs. This behavior is not part of the VM specification, however, and is subject to change in future releases. Likewise the -XX:SoftRefLRUPolicyMSPerMB flag is not guaranteed to be present in any given release.

Prior to version 1.3.1, the Java HotSpot VMs cleared soft references whenever it found them."