1.Class Class是Type接口的实现类 2.AtomicReference AtomicReference和AtomicInteger非常类似，不同之处就在于AtomicInteger是对整数的封装，而AtomicReference则对应普通的对象引用。也就是它可以保证你在修改对象引用时的线程安全性 3.ObjectMapper 1)用来读写JSON 2)ObjectReader,ObjectWriter的工厂 3）虽然ObjectMapper 暴露了大部分的读写方法，但是有部分读写是只在ObjectReader，ObjectWriter中 4）使用例子： 读文件中的json为对象 将对象写入json文件 json是树结构的读写，源码注释
final ObjectMapper mapper = new ObjectMapper(); // can use static singleton, inject: just make sure to reuse! MyValue value = new MyValue(); // ... and configure File newState = new File("my-stuff.json"); mapper.writeValue(newState, value); // writes JSON serialization of MyValue instance // or, read MyValue older = mapper.readValue(new File("my-older-stuff.json"), MyValue.class); // Or if you prefer JSON Tree representation: JsonNode root = mapper.readTree(newState); // and find values by, for example, using a {@link com.fasterxml.jackson.core.JsonPointer} expression: int age = root.at("/personal/age").getValueAsInt();