Faketime

This native Java Agent allows you to change the time in a Java program, without affecting the system clock. It allows control over the System.currentTimeMillis() method, which is used by most other time-related functionality provided by the JVM.

How to use it

Step 1: Get the library:

Use one of these options:

Option 1: For Mac OS X: (the easy way)

Download libfaketime.jnilib into some location.

OR

Option 2: For Max OS X (the "hard" way)

Run this, on a clone of this repository:

gcc -shared -I $JAVA_HOME/include -Wall src/FakeTimeAgent.c -o libfaketime.jnilib

OR

Option 3: For Linux (64-bit)

Run this, on a clone of this repository:

gcc -fPIC -shared -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -m64 -Wall src/FakeTimeAgent.c -o libfaketime.so

OR

Option 4: For Linux (32-bit)

Run this, on a clone of this repository:

gcc -fPIC -shared -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -m32 -Wall src/FakeTimeAgent.c -o libfaketime.so

Step 2: Use it:

Run your Java program (say, org.test.Main) with these agent-specific extra arguments (see issue #3), like this:

java -agentpath:/path/to/the/library/you/got/above \
  -XX:+UnlockDiagnosticVMOptions \
  -XX:DisableIntrinsic=_currentTimeMillis \
  -XX:CompileCommand=exclude,java/lang/System.currentTimeMillis \
  org.test.Main

In your Java code, you can set the property faketime.offset.seconds to the number of seconds you want the time altered by. For example, to add a day, you can do something like this:

System.setProperty("faketime.offset.seconds", "86400");

That's it! Take a look at FakeTimeTest.java if you need to see some Java code which uses it.