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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