Re: Hi! Help regarding Inserting instructions in a already existing class file and updating the modified class file

i think you need to call setMethodAt, replaceMethod, or setMethods.

http://jakarta.apache.org/bcel/apidocs/org/apache/bcel/generic/ClassGen.html#setMethodAt(org.apache.bcel.classfile.Method,%20int)

btw, your printing technique will only work for a very specialized 
subset of methods:
- single return at end of method and
- no exceptions and
- no finally

you really want to add this code to method 1 (with code M1):
System.out.println("start");
try { M1 }
finally {System.out.println("end"); }

you should see how that compiles (using javap or something) and 
replicate it using bcel.

Koduru, Rajendra Kumar Reddy wrote:
> Hi,
>  
>   I just started using BCEL, I want to instrument methods in my class
> with system.out.println at start and end of methods 
> 
> Ex: 
> 
> [1]
> public class HelloBCEL { 
> 
> public static void main(String[] argv) { 
> String name = null;
> try { 
> System.out.print("Please enter your name> "); 
> name = in.readLine(); 
> } catch(IOException e) { return; } 
> System.out.println("Hello, " + name); } 
> } 
> 
> I want to instrument all the methods of above class with
> system.out.println("starting") at the start and
> system.out.println("ending") at the end, that is something which looks
> like this
> 
> [2]
> public static void main(String[] argv) { 
> System.out.println("starting");
> String name = null;
> try { 
> System.out.print("Please enter your name> "); 
> name = in.readLine(); 
> } catch(IOException e) { return; } 
> System.out.println("Hello, " + name); } 
> System.out.println("ending");
> } 
> 
> So i have used BCEL and written a clas which updates the class [1]  into
> class [2], The BCEL code written to insert statements is written as
> follows
> 
> 
> 
> import java.io.*;
> import org.apache.bcel.*;
> import org.apache.bcel.classfile.*;
> import org.apache.bcel.generic.*;
> 
> public class insertBCEL{
> 
> public static ObjectType p_stream  = null;
> 
> 	 public static void main( String args[] ) throws IOException {
> 
> 		    ClassParser cparse = new
> ClassParser("HelloBCEL.class");
> 
> 		    JavaClass clazz = cparse.parse();
> 
> 		    ClassGen cg = new ClassGen(clazz);
> 
> 		    ConstantPool cp1 = clazz.getConstantPool();
> 
> 		    ConstantPoolGen cp = new ConstantPoolGen(cp1); 
> 		
> 		    InstructionFactory factory = new
> InstructionFactory(cp);
>   
> 		    p_stream = new ObjectType("java.io.PrintStream");
> 			
> 		    Method[] meths = clazz.getMethods();
> 
> 		    for(int i = 0; i< meths.length; i++ ){
> 
> 			Code code = meths[i].getCode(); 
> 
> 			if(code != null) 
> 			System.out.println(code); 
> 
> 			System.out.println(meths[i]); 
> 
> 	 	      meths[i] =
> instrumentMeths(clazz,meths[i],cp,factory);
> 
> 			Code code1 = meths[i].getCode(); 
> 
> 			if(code1 != null) 			
> 			System.out.println(code1); 
> 		}
> 			
> 			
> 		 try {
> 		    cg.getJavaClass().dump("HelloBCEL.class");
> 		    }catch(Exception e){System.out.println(e);} 
> 	}
> 
> 
> 		public static Method instrumentMeths(JavaClass clazz,
> Method method ,ConstantPoolGen cp, InstructionFactory factory){
> 
> 			MethodGen mg = new
> MethodGen(method,clazz.getClassName(),cp);
> 
> 			InstructionList il = mg.getInstructionList();
> 		      InstructionHandle[] ihans  =
> il.getInstructionHandles(); 
> 
> 			InstructionHandle ihs = il.getStart();	
> 			InstructionHandle ihe = il.getEnd();
> 	
> 			InstructionList ils = new InstructionList();
> 			InstructionList ile = new InstructionList();
> 				
> 	
> ils.append(factory.createFieldAccess("java.lang.System","out",p_stream,C
> onstants.GETSTATIC));
> 		    	ils.append(new PUSH(cp,"starting"));
> 	
> ils.append(factory.createInvoke("java.io.PrintStream", "println",
> Type.VOID, new Type[] { Type.STRING }, Constants.INVOKEVIRTUAL)); 
> 
> 	
> ile.append(factory.createFieldAccess("java.lang.System","out",p_stream,C
> onstants.GETSTATIC));
> 		    	ile.append(new PUSH(cp,"ending"));
> 	
> ile.append(factory.createInvoke("java.io.PrintStream", "println",
> Type.VOID, new Type[] { Type.STRING }, Constants.INVOKEVIRTUAL)); 
> 			    
> 			InstructionHandle ihss = il.insert(ihs,ils);
> 			il.redirectBranches(ihs, ihss); 
> 			InstructionHandle ihee = il.insert(ihe,ile);
> 			il.redirectBranches(ihe, ihee); 
> 			mg.setMaxStack();
> 			return mg.getMethod();
> 		}
> }
> 
> Then i tried to execute the instrumented class java HelloBCEL , but it
> doesnot instrument the strings "starting" and "ending" for the class,
> pLease let me know if i am wrong somewhere in the above code.
> 
>   Hope that you can help me in this regard.
> 
> Thank you in advance,
> Reddy.
> 
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