java中的反射

用反射你几乎可以做任何事情。Class对象的由来是将class文件读入内存，并为之创建一个Class对象。利用这个Class对象，你可以实现反射的功能。

这里要注意一件非常tricky的事情。下面的代码是无法正常运行的

                    s.getClass().getDeclaredFields()[3].setAccessible(true);
                    try {
                        String gdl = (s.getClass().getDeclaredFields()[3].get(s).toString());
                        System.out.println(field.get(s).toString());
                    }catch (Exception e){
                        e.printStackTrace();
                    }
                   System.out.println(GsonUtils.toJson(s));

要改成

                Field field = s.getClass().getDeclaredFields()[3];
                   field.setAccessible(true);
                   try {
                       String gdl = field.get(s).toString();
                       System.out.println(field.get(s).toString());
                   }catch (Exception e){
                       e.printStackTrace();
                   }
                  System.out.println(GsonUtils.toJson(s));

这是因为每次获取的field对象都是拷贝出来的不同对象。可以看下Field类copy方法的执行方式。

    Field copy() {
       // This routine enables sharing of FieldAccessor objects
       // among Field objects which refer to the same underlying
       // method in the VM. (All of this contortion is only necessary
       // because of the "accessibility" bit in AccessibleObject,
       // which implicitly requires that new java.lang.reflect
       // objects be fabricated for each reflective call on Class
       // objects.)
       if (this.root != null)
           throw new IllegalArgumentException("Can not copy a non-root Field");

       Field res = new Field(clazz, name, type, modifiers, slot, signature, annotations);
       res.root = this;
       // Might as well eagerly propagate this if already present
       res.fieldAccessor = fieldAccessor;
       res.overrideFieldAccessor = overrideFieldAccessor;

       return res;
   }