kotlin gson反序列化默认值失效深入讲解

public <T> ObjectConstructor<T> get(TypeToken<T> typeToken) {
 final Type type = typeToken.getType();
 final Class<? super T> rawType = typeToken.getRawType();

 // first try an instance creator

 @SuppressWarnings("unchecked") // types must agree
 final InstanceCreator<T> typeCreator = (InstanceCreator<T>) instanceCreators.get(type);
 if (typeCreator != null) {
  return new ObjectConstructor<T>() {
  @Override public T construct() {
   return typeCreator.createInstance(type);
  }
  };
 }

 // Next try raw type match for instance creators
 @SuppressWarnings("unchecked") // types must agree
 final InstanceCreator<T> rawTypeCreator =
  (InstanceCreator<T>) instanceCreators.get(rawType);
 if (rawTypeCreator != null) {
  return new ObjectConstructor<T>() {
  @Override public T construct() {
   return rawTypeCreator.createInstance(type);
  }
  };
 }
 // 获取无参构造函数
 ObjectConstructor<T> defaultConstructor = newDefaultConstructor(rawType);
 if (defaultConstructor != null) {
  return defaultConstructor;
 }

 // 获取List<T>,Map<T>等构造函数，对于List,Map的情况
 ObjectConstructor<T> defaultImplementation = newDefaultImplementationConstructor(type, rawType);
 if (defaultImplementation != null) {
  return defaultImplementation;
 }

 // unSafe构造出对象，不调用任何的构造函数
 // finally try unsafe
 return newUnsafeAllocator(type, rawType);
 }

private <T> ObjectConstructor<T> newDefaultConstructor(Class<? super T> rawType) {
 try {
  // 获取无参构造函数
  final Constructor<? super T> constructor = rawType.getDeclaredConstructor();
  if (!constructor.isAccessible()) {
  accessor.makeAccessible(constructor);
  }

private <T> ObjectConstructor<T> newUnsafeAllocator(
  final Type type, final Class<? super T> rawType) {
 return new ObjectConstructor<T>() {
  private final UnsafeAllocator unsafeAllocator = UnsafeAllocator.create();
  @SuppressWarnings("unchecked")
  @Override public T construct() {
  try {
  // 
   Object newInstance = unsafeAllocator.newInstance(rawType);
   return (T) newInstance;
  } catch (Exception e) {
   throw new RuntimeException(("Unable to invoke no-args constructor for " + type + ". "
    + "Registering an InstanceCreator with Gson for this type may fix this problem."), e);
  }
  }
 };
 }

class User(val id: Int, val name: String = "sss") {
 init {
  println("init")
 }
}

public final class User {
 private final int id;
 @NotNull
 private final String name;
 
 public User(int id, @NotNull String name) {
  Intrinsics.checkParameterIsNotNull(name, "name");
  super();
  this.id = id;
  this.name = name;
  String var3 = "init";
  System.out.println(var3);
 }

 // $FF: synthetic method
 public User(int var1, String var2, int var3, DefaultConstructorMarker var4) {
  if ((var3 & 2) != 0) {
   var2 = "";
  }

  this(var1, var2);
 }
}

 @Test
 fun testJson() {
  val user = Gson().fromJson("{}", User::class.java)
  print(user.name)
 }

class User(val id: Int=1, val name: String = "sss") {
 init {
  println("init")
 }
}

public final class User {
 private final int id;
 @NotNull
 private final String name;

 public User(int id, @NotNull String name) {
  Intrinsics.checkParameterIsNotNull(name, "name");
  super();
  this.id = id;
  this.name = name;
  String var3 = "init";
  System.out.println(var3);
 }

 // $FF: synthetic method
 public User(int var1, String var2, int var3, DefaultConstructorMarker var4) {
  if ((var3 & 1) != 0) {
   var1 = 1;
  }

  if ((var3 & 2) != 0) {
   var2 = "";
  }

  this(var1, var2);
 }

 // 无参构造函数
 public User() {
  this(0, (String)null, 3, (DefaultConstructorMarker)null);
 }
}

 @Test
 fun testJson() {
  val user = Gson().fromJson("{}", User::class.java)
  print(user.name)
 }

class User(val id: Int=1 , val name: String = "sss") {
 init {
  println("init")
 }
}

class User {
 val id: Int = 1
 val name: String = "sss"

 init {
  println("init")
 }
}