Android避坑指南，Gson与Kotlin碰撞出一个不安全的操作

public class Student  {
    private Student() {
        throw new IllegalArgumentException("can not create.");
    }
    public String name;
}

data class Person(var name: String, var age: Int)

val gson = Gson()
val person = gson.fromJson<Person>("{\"age\":\"12\"}", Person::class.java)

val gson = Gson()
val person = gson.fromJson<Person>("{\"age\":\"12\"}", Person::class.java)
println(person.name )

null

data class Person(var name: String, var age: Int): People()

public class People {

    public People(){
        System.out.println("people cons");
    }

}

# 反编译之后的显示
public final class Person extends People {
   @NotNull
   private String name;
   private int age;

   @NotNull
   public final String getName() {
      return this.name;
   }

   public final void setName(@NotNull String var1) {
      Intrinsics.checkParameterIsNotNull(var1, "<set-?>");
      this.name = var1;
   }

   public final int getAge() {
      return this.age;
   }

   public final void setAge(int var1) {
      this.age = var1;
   }

   public Person(@NotNull String name, int age) {
      Intrinsics.checkParameterIsNotNull(name, "name");
      super();
      this.name = name;
      this.age = age;
   }

   // 省略了一些方法。
}

# ReflectiveTypeAdapterFactory.create
@Override 
public <T> TypeAdapter<T> create(Gson gson, final TypeToken<T> type) {
	Class<? super T> raw = type.getRawType();
	
	if (!Object.class.isAssignableFrom(raw)) {
	  return null; // it's a primitive!
	}
	
	ObjectConstructor<T> constructor = constructorConstructor.get(type);
	return new Adapter<T>(constructor, getBoundFields(gson, type, raw));
}

# ConstructorConstructor.get
public <T> ObjectConstructor<T> get(TypeToken<T> typeToken) {
    final Type type = typeToken.getType();
    final Class<? super T> rawType = typeToken.getRawType();
	
	// ...省略一些缓存容器相关代码

    ObjectConstructor<T> defaultConstructor = newDefaultConstructor(rawType);
    if (defaultConstructor != null) {
      return defaultConstructor;
    }

    ObjectConstructor<T> defaultImplementation = newDefaultImplementationConstructor(type, rawType);
    if (defaultImplementation != null) {
      return defaultImplementation;
    }

    // finally try unsafe
    return newUnsafeAllocator(type, rawType);
  }

private <T> ObjectConstructor<T> newDefaultConstructor(Class<? super T> rawType) {
    try {
      final Constructor<? super T> constructor = rawType.getDeclaredConstructor();
      if (!constructor.isAccessible()) {
        constructor.setAccessible(true);
      }
      return new ObjectConstructor<T>() {
        @SuppressWarnings("unchecked") // T is the same raw type as is requested
        @Override public T construct() {
            Object[] args = null;
            return (T) constructor.newInstance(args);
            
            // 省略了一些异常处理
      };
    } catch (NoSuchMethodException e) {
      return null;
    }
  }

public static UnsafeAllocator create() {
// try JVM
// public class Unsafe {
//   public Object allocateInstance(Class<?> type);
// }
try {
  Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
  Field f = unsafeClass.getDeclaredField("theUnsafe");
  f.setAccessible(true);
  final Object unsafe = f.get(null);
  final Method allocateInstance = unsafeClass.getMethod("allocateInstance", Class.class);
  return new UnsafeAllocator() {
    @Override
    @SuppressWarnings("unchecked")
    public <T> T newInstance(Class<T> c) throws Exception {
      assertInstantiable(c);
      return (T) allocateInstance.invoke(unsafe, c);
    }
  };
} catch (Exception ignored) {
}
  
// try dalvikvm, post-gingerbread use ObjectStreamClass
// try dalvikvm, pre-gingerbread , ObjectInputStream

}

public class Student  {
    private Student() {
        throw new IllegalArgumentException("can not create.");
    }
    public String name;
}

try {
    val unsafeClass = Class.forName("sun.misc.Unsafe")
    val f = unsafeClass.getDeclaredField("theUnsafe")
    f.isAccessible = true
    val unsafe = f.get(null)
    val allocateInstance = unsafeClass.getMethod("allocateInstance", Class::class.java)
    val student = allocateInstance.invoke(unsafe, Student::class.java)
    (student as Student).apply {
        name = "zhy"
    }
    println(student.name)
} catch (ignored: Exception) {
    ignored.printStackTrace()
}

zhy

private void testJavaPojie() {
	try {
	  Class reflectionHelperClz = Class.forName("com.example.support_p.ReflectionHelper");
	  Class classClz = Class.class;
	  Field classLoaderField = classClz.getDeclaredField("classLoader");
	  classLoaderField.setAccessible(true);
	  classLoaderField.set(reflectionHelperClz, null);
	} catch (Exception e) {
		  e.printStackTrace();
	}
}

@Keep
public class ReflectWrapper {
 
    //just for finding the java.lang.Class classLoader field's offset
    @Keep
    private Object classLoaderOffsetHelper;
 
    static {
        try {
            Class<?> VersionClass = Class.forName("android.os.Build$VERSION");
            Field sdkIntField = VersionClass.getDeclaredField("SDK_INT");
            sdkIntField.setAccessible(true);
            int sdkInt = sdkIntField.getInt(null);
            if (sdkInt >= 28) {
                Field classLoader = ReflectWrapper.class.getDeclaredField("classLoaderOffsetHelper");
                long classLoaderOffset = UnSafeWrapper.getUnSafe().objectFieldOffset(classLoader);
                if (UnSafeWrapper.getUnSafe().getObject(ReflectWrapper.class, classLoaderOffset) instanceof ClassLoader) {
                    Object originalClassLoader = UnSafeWrapper.getUnSafe().getAndSetObject(ReflectWrapper.class, classLoaderOffset, null);
                } else {
                    throw new RuntimeException("not support");
                }
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}