Java泛型和超类型令牌 [英] Java Generics and Super Type Tokens

问题描述

我试图将以下三个方法组合成一个通用解决方案，我尝试了一些编译但在运行时不能很好的想法。

I am trying to make the three following methods into one generic solution, I tried some ideas which compile but don't do well at runtime.

public static List<User> parseToUsers(HttpResponse response) {
  ObjectMapper mapper = new ObjectMapper();
  String results = parseToString(response);
  return mapper.readValue(results, new TypeReference<List<User>>() {});
}

public static List<Record> parseToRecords(HttpResponse response) {
  ObjectMapper mapper = new ObjectMapper();
  String results = parseToString(response);
  return mapper.readValue(results, new TypeReference<List<Record>>() {});
}

public static Record parseToRecord(HttpResponse response) {
  ObjectMapper mapper = new ObjectMapper();
  String results = parseToString(response);
  return mapper.readValue(results, new TypeReference<Record>() {});;
}

我也试过理解这个关于超级类型代币的博客文章。

编辑：

这是我到目前为止所提出的：

This is what I came up with so far:

public static <T> T parseJsonResponse(TypeReference<T> type, HttpResponse response) throws DroidException {
    ObjectMapper mapper = new ObjectMapper();
    String results = parseResponseToString(response);
    return readValue = mapper.readValue(results, type);
}

然后我这样称呼它。

parseJsonResponseToList(new TypeReference<List<Record>>() {}, response)

不太满意。有更好的解决方案吗？

Not really satisfieng.Is there a better solution?

推荐答案

那到底是什么是问题吗？你不喜欢它以什么方式？

So what exactly is the problem? In what way do you not like it?

杰克逊有其他方法来构建泛型类型;所以也许正在寻找的是：

Jackson has other ways for constructing generic types; so perhaps what are looking for is along lines of:

public List<T> listOf(String json, Class<T> elementType) {
   ObjectMapper mapper = new ObjectMapper(); // should (re)use static instance for perf!
   JavaType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, elementType);
   return mapper.readValue(json, listType);
}

TypeFactory 可以是用于以编程方式构造使用泛型的类型 - 返回类型是 JavaType ，因为基本Java Class 是类型擦除的。
TypeFactory 实际上用于将 TypeReference 转换为 JavaType 内部也是。

TypeFactory can be used to programmatically construct types that use generics -- return type is JavaType, because basic Java Class is type-erased. TypeFactory is actually used to convert TypeReference to JavaType internally as well.

编辑

关于常规，非收集/映射类型，它非常简单：

As to regular, non-Collection/Map types, it's really quite simple:

public T parseSingle(Class<T> cls, InputStream src) throws IOException {
  return mapper.readValue(src, cls);
}

（你也不想把内容读作字符串 - 不仅是它很慢，但很容易弄乱字符编码，所以如果可能的话，请输入 InputStream 或 byte [] 代替）

(you also do NOT want to read contents as String -- not only is it slow, but it's easy to mess up character encodings, so if possible, feed InputStream or byte[] instead)

这篇关于Java泛型和超类型令牌的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！