if (element.getKind() == ElementKind.FEILD) {
        // 显示转换元素类型
        TypeElement typeElement = (TypeElement) element;
        // 输出元素名称
        System.out.println(typeElement.getSimpleName());
        // 输出注解属性值
        System.out.println(typeElement.getAnnotation(BindView.class).value());
    }
}

public JavaFile generateFinder() {

        //构建 inject 方法
        MethodSpec.Builder methodBuilder = MethodSpec.methodBuilder("inject")
                .addModifiers(Modifier.PUBLIC) 
                .addAnnotation(Override.class)
                .addParameter(TypeName.get(mClassElement.asType()), "host", Modifier.FINAL)
                .addParameter(TypeName.OBJECT, "source")
                .addParameter(Utils.FINDER, "finder");

        //inject函数内的核心逻辑,
        // host.btn1=(Button)finder.findView(source,2131427450);  ----生成代码
        // host.$N=($T)finder.findView(source,$L)                 ----原始代码
        // 对比就会发现这里执行了实际的findViewById绑定事件
        for (BindViewField field : mFiled) {
            methodBuilder.addStatement("host.$N=($T)finder.findView(source,$L)", field.getFieldName()
                    , ClassName.get(field.getFieldType()), field.getResId());
        }

        String packageName = getPackageName(mClassElement);  // com.sjq.recycletest
        String className = getClassName(mClassElement, packageName);
        ClassName bindClassName = ClassName.get(packageName, className); // bindClassName.toString()  com.sjq.recycletest.MainActivity

        //构建类对象，注意此处的 $$Injector，生成的类名是由我们自己来控制的
        TypeSpec finderClass = TypeSpec.classBuilder(bindClassName.simpleName() + "$$Injector")
                .addModifiers(Modifier.PUBLIC)
                .addSuperinterface(ParameterizedTypeName.get(Utils.INJECTOR, TypeName.get(mClassElement.asType())))   //继承接口
                .addMethod(methodBuilder.build()) // 添加方法
                .build();

        return JavaFile.builder(packageName, finderClass).build();
    }

public interface Injector<T> {
    void inject(T host, Object source, Finder finder);
}

public interface Finder {

    Context getContext(Object source);

    View findView(Object source, int id);
}

public class ActivityFinder implements Finder{

    @Override
    public Context getContext(Object source) {
        return (Activity) source;
    }

    @Override
    public View findView(Object source, int id) {
        return ((Activity) (source)).findViewById(id);
    }
}

public class ButterKnife {
　　// 
    private static final ActivityFinder finder = new ActivityFinder();
　　// 用于存储已经绑定的class，避免重复绑定
    private static Map<String, Injector> FINDER_MAP = new HashMap<>();

    public static void bind(Activity activity) {
        bind(activity, activity);
    }

    private static void bind(Object host, Object source) {
        bind(host, source, finder);
    }

    private static void bind(Object host, Object source, Finder finder) {
        String className = host.getClass().getName();
        try {
            Injector injector = FINDER_MAP.get(className);
            if (injector == null) {
　　　　　　　　　 // 此处拿到的类名就是通过注解生成的中间处理类，即 MainActivity$$Injector
                Class<?> finderClass = Class.forName(className + "$$Injector");
　　　　　　　　　 // 通过反射拿到class实例
                injector = (Injector) finderClass.newInstance();
                FINDER_MAP.put(className, injector);
            }
            injector.inject(host, source, finder);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.annotation_tv)
    public TextView tv1;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
　　　　　// tv1 的初始化过程就是在bind过程中完成的
        ButterKnife.bind(this);
        tv1.setText("annotation_demo");
    }
}

public class MainActivity$$Injector implements Injector<MainActivity> {
  @Override
  public void inject(final MainActivity host, Object source, Finder finder) {
　　// 最终还是通过 findViewById 来对 tv1 进行初始化
    host.tv1=(TextView)finder.findView(source,2131165300);
  }
}