ass2-di/src/main/java/dst/ass2/di/agent/InjectorAgent.java

   1 package dst.ass2.di.agent;
   2
   3 import dst.ass2.di.annotation.Component;
   4 import javassist.*;
   5
   6 import java.io.ByteArrayInputStream;
   7 import java.io.IOException;
   8 import java.lang.instrument.ClassFileTransformer;
   9 import java.lang.instrument.IllegalClassFormatException;
  10 import java.lang.instrument.Instrumentation;
  11 import java.security.ProtectionDomain;
  12
  13 public class InjectorAgent implements ClassFileTransformer {
  14     public static void premain(String args, Instrumentation instrumentation) {
  15         instrumentation.addTransformer(new InjectorAgent());
  16     }
  17
  18     @Override
  19     public byte[] transform(ClassLoader loader, String className,
  20                             Class<?> classBeingRedefined, ProtectionDomain protectionDomain,
  21                             byte[] classfileBuffer) throws IllegalClassFormatException {
  22
  23         ClassPool classPool = new ClassPool();
  24         classPool.appendClassPath(new LoaderClassPath(loader));
  25         try {
  26             CtClass ctClass = classPool.makeClass(new ByteArrayInputStream(classfileBuffer));
  27
  28
  29             // only @Components may continue.
  30             if (!ctClass.hasAnnotation(Component.class)) {
  31                 return classfileBuffer;
  32             }
  33
  34             // insert our code into constructors
  35             for (CtConstructor ctor : ctClass.getConstructors()) {
  36                 try {
  37                     ctor.insertAfter("dst.ass2.di.InjectionControllerFactory.getTransparentInstance().initialize(this);");
  38                 } catch (CannotCompileException e) {
  39                     e.printStackTrace();
  40                     return classfileBuffer;
  41                 }
  42             }
  43
  44             // output new bytecode.
  45             return ctClass.toBytecode();
  46         } catch (IOException | CannotCompileException e) {
  47             e.printStackTrace();
  48             return classfileBuffer;
  49         }
  50     }
  51 }