Dynamic Injection of code using bytecode Processing Framework Javassist

Official homepage: http://www.csg.is.titech.ac.jp /~ CHBA/Javassist/

Javassist,CglibSome code enhancement tools, such as Java bytecode enhancement at runtime. Although the speed is a little slower, it brings about concise code. Today, we use Javassist for code enhancement.

Code:

Testbean. Java

1. Package example sist. sample;
3. Public abstract class testbean {
5. Public string field;
7. Public abstract string getm ();
9. Public abstract void SETF (string F );
11. Public String getf (){
12. Return this. field;
13. }
14. }

Testbytecode. Java

1. Package example sist. sample;
3. Import Javassist. classpool;
4. Import Javassist. ctclass;
5. Import ipvsist. ctconstructor;
6. Import ipvsist. ctmethod;
8. Public class testbytecode {
10. Public static void main (string [] ARGs) throws exception {
12. Classpool pool = classpool. getdefault ();
13. Ctclass Pt = pool. makeclass ("ASDF", pool. Get ("Javassist. sample. testbean "));
15. Ctmethod Method1 = new ctmethod (pool. Get ("Java. Lang. String"), "getm", null, pt );
16. Method1.setbody ("{return/" /";}");
17. PT. addmethod (Method1 );
19. Ctconstructor cc = new ctconstructor (null, pt );
20. Cc. setbody ("This. Field =/" why? /";");
21. PT. addconstructor (CC );
23. Ctmethod method2 = new ctmethod (ctclass. voidtype, "SETF ",
24. New ctclass [] {pool. Get ("Java. Lang. String")}, pt );
25. Method2.setbody ("{This. Field = $1 ;}");
26. PT. addmethod (method2 );
28. Class <?> C = pt. toclass ();
29. Testbean bean = (testbean) C. newinstance ();
31. System. Out. println (bean. getm ());
32. System. Out. println (bean. getf ());
33. Bean. SETF ("SETF ");
34. System. Out. println (bean. getf ());
35. }
36. }

Output:

Hi!

Why?

SETF

We can see that dynamic construction is implemented and abstract functions are implemented dynamically. In code automation projects, bytecode enhancement can greatly improve the quality of code and reduce the number of code.

 

Let's look at another example:

A. Java

1. Package example sist. Demo;
3. Public Class {
5. Public void method (){
6. For (INT I = 0; I <1000000; I ++ ){
7. }
8. System. Out. println ("Method1 ");
9. }
10. }

Export sisttest. Java

1. Package example sist. Demo;
2. Import Javassist. classpool;
3. Import Javassist. ctclass;
4. Import ipvsist. ctmethod;
5. Import ipvsist. ctnewmethod;
7. Public class implements sisttest {
9. Public static void main (string [] ARGs) throws exception {
11. // Used to obtain the bytecode class. It must be in the current classpath and use the full name
12. Ctclass = classpool. getdefault (). Get ("Javassist. Demo. ");
13. // Method name to be modified
14. String mname = "method ";
15. Ctmethod mold = ctclass. getdeclaredmethod (mname );
16. // Modify the original method name
17. String nname = mname + "$ impl ";
18. Mold. setname (nname );
19. // Create a new method and copy the original method
20. Ctmethod mnew = ctnewmethod. Copy (mold, mname, ctclass, null );
21. // Main injection code
22. Stringbuffer body = new stringbuffer ();
23. Body. append ("{/nlong start = system. currenttimemillis ();/N ");
24. // Call the original code, similar to method (); ($) indicates all parameters
25. Body. append (nname + "($);/N ");
26. Body. append ("system. Out. println (/" call to method "+ mname
27. + "Took/" +/N (system. currenttimemillis ()-Start) +"
28. + "/" Ms./");/N ");
30. Body. append ("}");
31. // Replace the New Method
32. Mnew. setbody (body. tostring ());
33. // Add a new method
34. Ctclass. addmethod (mnew );
35. // The class has been changed. You cannot use a A = new A (); because the same classloader cannot load the same class twice.
36. A A = (a) ctclass. toclass (). newinstance ();
37. A. Method ();
38. }
39. }

MATERIALS:

Http://tsaijun.spaces.live.com/blog/cns! C9f557e0fd3838c1! 121. Entry

Http://www.blogjava.net/zyl/archive/2007/02/10/99171.html

Http://www.ibm.com/developerworks/cn/java/j-dyn0916/