Question

Is it possible to do method swizzling in android using java? i would like to intercept a system method and log its parameters then process it normally

Answer 1

I think that technique could not be used using Java in any environment.

Maybe you could achieve a similar result using AOP.

But what you can do with that looks limited on Android. See Aspect-oriented programming in android. In fact, since you won’t be compiling the target code (system method), compile-time weaving (which appears to be all you could use on Android) will be useless for this case. As is this answer I suppose.

One other thought… I guess you want to do this logging consistently. But if you needed this to debug a problem, you could do it using a conditional breakpoint in Eclipse.

A conditional expression can contain arbitrary Java code and may
contain more than one statement, allowing breakpoint conditions to
implement features like tracing. For example, a condition can execute
a print statement and then return a hard coded value to never suspend
(“System.out.println(…); return false;”).

I don’t know specifically whether this works with methods in the Android SDK. But it does work with methods in the Java SDK. For example, here is simple code:

    System.err.println("foo");

I made a conditional breakpoint in PrintStream.print, like this:

System.err.println("hello: " + arg0);
return false;

And the console output when debugging in the program is this:

hello: foo
foo

Note that since the JDK is not compiled with debug symbols, I can’t refer to method parameters by name, but using the arg0..argn.