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

The easy way - For the Mac

Download libfaketime.jnilib into some directory, say, /path/to/libfaketime.jnilib.
Run your Java program (say, org.test.Main) with the agent-specific extra arguments, like this:
```
  java -agentpath:/path/to/libfaketime.jnilib 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.

The "hard" way - For the Mac

Clone this repo

Run this:

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

This will create libfaketime.jnilib in the current directory. Run your Java program (say, org.test.Main) with the agent-specific extra arguments, like this:
```
  java -agentpath:/path/to/libfaketime.jnilib org.test.Main
```
or, if the current directory has libfaketime.jnilib, you can use:
```
  java -agentlib:faketime 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");
```

Just In Time-Compilation

The JavaVM may decide to recompile byte-code to assembly code (just in time-compilation) when it notices that a certain method is used often. After such a recompilation of the code the faketime magic which uses rebinding of Java native methods may stop working. If this is effect is observable depends on the actual number of invocation of System.currentTimeMillis() and whether the VM options -client and -server are set. The following JavaVM options work around this problem by excluding the method from the compilation and inline expansion process:

 -XX:CompileCommand=exclude,java/lang/System.currentTimeMillis -XX:CompileCommand=dontinline,java/lang/System.currentTimeMillis

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

aehrisch/faketime

Faketime

How to use it

The easy way - For the Mac

The "hard" way - For the Mac

Just In Time-Compilation