We're facing a task of conversion of a java method into a state machine. This is like to convert a SAX Parser, pushing data, into an Xml Reader, which pulls data.
The task is formalized as:
- for a given method containing split markers create a class perimitting iteration;
- each iteration performs part of a logic of a method.
We have defined rules converting all statements into a state machine except of the
statement synchronied. In fact the logic it rather linear, however
the most untrivial conversion is for try statement. Consider
an example:
public
class Test
{
void method()
throws Exception
{
try
{
A();
B();
}
catch(Exception e)
{
C(e);
}
finally
{
D();
}
E();
}
private void A()
throws Exception
{
// logic A
}
private void B()
throws Exception
{
// logic B
}
privatevoid C(Exception e)
throws Exception
{
// logic C
}
privatevoid D()
throws Exception
{
// logic D
}
privatevoid E()
throws Exception
{
// logic E
}
}
Suppose we want to see method() as a state machine in a way that split
markers are after calls to methods A(), B(), C(), D(), E().
This is how it looks as a state machine:
Callable<Boolean> methodAsStateMachine()
throws Exception
{
returnnew Callable<Boolean>()
{
public Boolean call()
throws Exception
{
do
{
try
{
switch(state)
{
case 0:
{
A();
state = 1;
returntrue;
}
case 1:
{
B();
state = 3;
returntrue;
}
case 2:
{
C(ex);
state = 3;
returntrue;
}
case 3:
{
D();
if (currentException != null)
{
throw currentException;
}
state = 4;
returntrue;
}
case 4:
{
E();
state = -1;
returnfalse;
}
}
if (currentException == null)
{
currentException = new IllegalStateException();
}
}
catch(Throwable e)
{
currentException = null;
switch(state)
{
case 0:
case 1:
{
if (e instanceof Exception)
{
ex = (Exception)e;
state = 2;
}
else
{
currentException = e;
state = 3;
}
continue;
}
case 2:
{
currentException = e;
state = 3;
continue;
}
}
currentException = e;
state = -1;
}
}
while(false);
returnthis.<Exception>error();
}
@SuppressWarnings("unchecked")
private <T extends Throwable> boolean error()
throws T
{
throw (T)currentException;
}
privateint state = 0;
private Throwable currentException = null;
private Exception ex = null;
};
}
Believe it, or not but this transformation can be done purely in xslt 2.0 with the help of the jxom (Java xml object model). We shall update jxom.zip whenever this module will be implemented and tested.
