java - 与java同学解析泛型类型

Question

尝试使用 TypeTools 惨遭失败后 Resolving generic type information with TypeTools我正在尝试使用https://github.com/cowtowncoder/java-classmate相反。

有人可以帮我修复这个代码吗？

public T fromMap(S map) {
    TypeResolver typeResolver = new TypeResolver();        
    ResolvedType type = typeResolver.resolve((new MapperImpl<T, S>() {}).getClass());
    List<ResolvedType> params = type.typeParametersFor(MapperImpl.class);
    ResolvedType typeT = params.get(0);

    ObjectMapper objectMapper = new ObjectMapper();
    T obj = objectMapper.convertValue(map, (Class<T>) typeT.getErasedType());
    return obj;

}

我收到此错误:

java.util.LinkedHashMap cannot be cast to LoginInputMapTest$Foo java.lang.ClassCastException at shouldMapToFoo(LoginInputMapTest.java:83)

使用这个最小的测试用例:

public static class Foo {
       private String a;

        public String getA() {
            return a;
        }

        public void setA(String a) {
            this.a = a;
        }

   }

   @Test
   public void shouldMapToFoo() {
       Map<String, Object> map = new HashMap<>();
       map.put("a", "aaa");

       Mapper<Foo, Map<String, Object>> mapper = new MapperImpl<>();
       Foo foo = mapper.fromMap(map);
       Assert.assertEquals(foo.getA(), map.get("a"));
   }

Answer 1

您无法在 fromMap 方法中执行任何操作来获取绑定(bind)到类型变量 T 的类型参数。

我建议您专门为 Foo 创建一个 Mapper 实现。

class FooMapperImpl<S> implements Mapper<Foo, S> {
    public Foo fromMap(S map) {
        ObjectMapper objectMapper = new ObjectMapper();
        Foo obj = objectMapper
                .convertValue(map, Foo.class);
        return obj;
    }
}

(虽然我不明白为什么你需要一个源类型 S，如果它总是一个 Map。)